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  • richardmitnick 9:02 pm on May 22, 2015 Permalink | Reply
    Tags: , Fusion technology,   

    From PPPL: “A little drop will do it: Tiny grains of lithium can dramatically improve the performance of fusion plasmas” 


    PPPL

    May 22, 2015
    Raphael Rosen

    1
    Left: DIII-D tokamak. Right: Cross-section of plasma in which lithium has turned the emitted light green. (Credits: Left, General Atomics / Right, Steve Allen, Lawrence Berkeley National Laboratory)

    Scientists from General Atomics and the U.S. Department of Energy’s (DOE) Princeton Plasma Physics Laboratory (PPPL) have discovered a phenomenon that helps them to improve fusion plasmas, a finding that may quicken the development of fusion energy. Together with a team of researchers from across the United States, the scientists found that when they injected tiny grains of lithium into a plasma undergoing a particular kind of turbulence then, under the right conditions, the temperature and pressure rose dramatically. High heat and pressure are crucial to fusion, a process in which atomic nuclei – or ions – smash together and release energy — making even a brief rise in pressure of great importance for the development of fusion energy.

    “These findings might be a step towards creating our ultimate goal of steady-state fusion, which would last not just for milliseconds, but indefinitely,” said Tom Osborne, a physicist at General Atomics and lead author of the paper. This work was supported by the DOE Office of Science.

    The scientists used a device developed at PPPL to inject grains of lithium measuring some 45 millionths of a meter in diameter into a plasma in the DIII-D National Fusion Facility – or tokamak – that General Atomics operates for DOE in San Diego.

    DOE DIII-D Tokamak
    DIII-D National Fusion Facility

    When the lithium was injected while the plasma was relatively calm, the plasma remained basically unaltered. Yet as reported this month in a paper in Nuclear Fusion, when the plasma was undergoing a kind of turbulence known as a “bursty chirping mode,” the injection of lithium doubled the pressure at the outer edge of the plasma. In addition, the length of time that the plasma remained at high pressure rose by more than a factor of 10.

    Experiments have sustained this enhanced state for up to one-third of a second. A key scientific objective will be to extend this enhanced performance for the full duration of a plasma discharge.

    Physicists have long known that adding lithium to a fusion plasma increases its performance. The new findings surprised researchers, however, since the small amount of lithium raised the plasma’s temperature and pressure more than had been expected.

    These results “could represent the birth of a new tool for influencing or perhaps controlling tokamak edge physics,” said Dennis Mansfield, a physicist at PPPL and a coauthor of the paper who helped develop the injection device called a “lithium dropper.” Also working on the experiments were researchers from Lawrence Livermore National Laboratory, Oak Ridge National Laboratory, the University of Wisconsin-Madison and the University of California-San Diego.

    Conditions at the edge of the plasma have a profound effect on the superhot core of the plasma where fusion reactions take place. Increasing pressure at the edge region raises the pressure of the plasma as a whole. And the greater the plasma pressure, the more suitable conditions are for fusion reactions. “Making small changes at the plasma’s edge lets us increase the pressure further within the plasma,” said Rajesh Maingi, manager of edge physics and plasma-facing components at PPPL and a coauthor of the paper.

    Further experiments will test whether the lithium’s interaction with the bursty chirping modes — so-called because the turbulence occurs in pulses and involves sudden changes in pitch — caused the unexpectedly strong overall effect.

    See the full article here.

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    Princeton Plasma Physics Laboratory is a U.S. Department of Energy national laboratory managed by Princeton University. PPPL, on Princeton University’s Forrestal Campus in Plainsboro, N.J., is devoted to creating new knowledge about the physics of plasmas — ultra-hot, charged gases — and to developing practical solutions for the creation of fusion energy. Results of PPPL research have ranged from a portable nuclear materials detector for anti-terrorist use to universally employed computer codes for analyzing and predicting the outcome of fusion experiments. The Laboratory is managed by the University for the U.S. Department of Energy’s Office of Science, which is the largest single supporter of basic research in the physical sciences in the United States, and is working to address some of the most pressing challenges of our time. For more information, please visit science.energy.gov.

     
  • richardmitnick 7:53 am on May 22, 2015 Permalink | Reply
    Tags: , , Fusion technology   

    From AAAS: “The new shape of fusion” 

    AAAS

    AAAS

    21 May 2015
    Daniel Clery

    1
    A plasma glows inside MAST, a spherical tokamak.

    ITER, the international fusion reactor being built in France, will stand 10 stories tall, weigh three times as much as the Eiffel Tower, and cost its seven international partners $18 billion or more. The result of decades of planning, ITER will not produce fusion energy until 2027 at the earliest. And it will be decades before an ITER-like plant pumps electricity into the grid. Surely there is a quicker and cheaper route to fusion energy.

    Fusion enthusiasts have a slew of schemes for achieving the starlike temperatures or crushing pressures needed to get hydrogen nuclei to come together in an energy-spawning union. Some are mainstream, such as lasers, some unorthodox. Yet the doughnut-shaped vessels called tokamaks, designed to cage a superheated plasma using magnetic fields, remain the leading fusion strategy and are the basis of ITER. Even among tokamaks, however, a nimbler alternative has emerged: a spherical tokamak.

    Imagine the doughnut shape of a conventional tokamak plumped up into a shape more like a cored apple. That simple change, say the idea’s advocates, could open the way to a fusion power plant that would match ITER’s promise, without the massive scale. “The aim is to make tokamaks smaller, cheaper, and faster—to reduce the eventual cost of electricity,” says Ian Chapman, head of tokamak science at the Culham Centre for Fusion Energy in Abingdon, U.K.


    Download mp4 here.

    Culham is one of two labs about to give these portly tokamaks a major test. The world’s two front-rank machines—the National Spherical Torus Experiment (NSTX) at the Princeton Plasma Physics Laboratory in New Jersey and the Mega Amp Spherical Tokamak (MAST) in Culham—are both being upgraded with stronger magnets and more powerful heating systems. Soon they will switch on and heat hydrogen to temperatures much closer to those needed for generating fusion energy. If they perform well, then the next major tokamak to be built—a machine that would run in parallel with ITER and test technology for commercial reactors—will likely be a spherical tokamak.

    PPPL NSTX
    NSTX

    Mega Amp Spherical Tokamak
    MAST

    A small company spun off from Culham is even making a long-shot bet that it can have a spherical tokamak reactor capable of generating more energy than it consumes—one of ITER’s goals—up and running within the decade. If it succeeds, spherical tokamaks could change the shape of fusion’s future. “It’s going to be exciting,” says Howard Wilson, director of the York Plasma Institute at the University of York in the United Kingdom. “Spherical tokamaks are the new kids on the block. But there are still important questions we’re trying to get to the bottom of.”

    TOKAMAKS ARE AN INGENIOUS WAY to cage one of the most unruly substances humans have ever grappled with: plasma hot enough to sustain fusion. To get nuclei to slam together and fuse, fusion reactors must reach temperatures 10 times hotter than the core of the sun, about 150 million degrees Celsius. The result is a tenuous ionized gas that would vaporize any material it touches—and yet must be held in place long enough for fusion to generate useful amounts of energy.

    Tokamaks attempt this seemingly impossible task using magnets, which can hold and manipulate plasma because it is made of charged particles. A complex set of electromagnets encircle the doughnut-shaped vessel, some horizontal and some vertical, while one tightly wound coil of wire, called a solenoid, runs down the doughnut hole. Their combined magnetic field squeezes the plasma toward the center of the tube and drives it around the ring while also twisting in a slow corkscrew motion.

    But plasma is not easy to master. Confining it is like trying to squeeze a balloon with your hands: It likes to bulge out between your fingers. The hotter a plasma gets, the more the magnetically confined gas bulges and wriggles and tries to escape. Much of the past 60 years of fusion research has focused on how to control plasma.

    Generating and maintaining enough heat for fusion has been another challenge. Friction generated as the plasma surges around the tokamak supplies some of the heat, but modern tokamaks also beam in microwaves and high-energy particles. As fast as the heat is supplied, it bleeds away, as the hottest, fastest moving particles in the turbulent plasma swirl away from the hot core toward the cooler edge. “Any confinement system is going to be slightly leaky and will lose particles,” Wilson says.

    Studies of tokamaks of different sizes and configurations have always pointed to the same message: To contain a plasma and keep it hot, bigger is better. In a bigger volume, hot particles have to travel farther to escape. Today’s biggest tokamak, the 8-meter-wide Joint European Torus (JET) at Culham, set a record for fusion energy in 1997, generating 16 megawatts for a few seconds.

    Joint European Torus
    JET

    (That was still slightly less than the heating power pumped into the plasma.) For most of the fusion community, ITER is the logical next step. It is expected to be the first machine to achieve energy gain—more fusion energy out than heating power in.

    In the 1980s, a team at Oak Ridge National Laboratory in Tennessee explored how a simple shape change could affect tokamak performance. They focused on the aspect ratio—the radius of the whole tokamak compared to the radius of the vacuum tube. (A Hula-Hoop has a very high aspect ratio, a bagel a lower one.) Their calculations suggested that making the aspect ratio very low, so that the tokamak was essentially a sphere with narrow hole through the middle, could have many advantages.

    Near a spherical tokamak’s central hole, the Oak Ridge researchers predicted, particles would enjoy unusual stability. Instead of corkscrewing lazily around the tube as in a conventional tokamak, the magnetic field lines wind tightly around the central column, holding particles there for extended periods before they return to the outside surface. The D-shaped cross section of the plasma would also help suppress turbulence, improving energy confinement. And they reckoned that the new shape would use magnetic fields more efficiently—achieving more plasma pressure for a given magnetic pressure, a ratio known as beta. Higher beta means more bang for your magnetic buck. “The general idea of spherical tokamaks was to produce electricity on a smaller scale, and more cheaply,” Culham’s Chapman says.

    But such a design posed a practical problem. The narrow central hole in a spherical tokamak didn’t leave enough room for the equipment that needs to fit there: part of each vertical magnet plus the central solenoid. In 1984, Martin Peng of Oak Ridge came up with an elegant, space-saving solution: replace the multitude of vertical ring magnets with C-shaped rings that share a single conductor down the center of the reactor (see graphic, below).

    3
    JAMES PROVOST

    U.S. fusion funding was in short supply at that time, so Oak Ridge could not build a spherical machine to test Peng’s design. A few labs overseas converted some small devices designed for other purposes into spherical tokamaks, but the first true example was built at the Culham lab in 1990. “It was put together on a shoestring with parts from other machines,” Chapman says. Known as the Small Tight Aspect Ratio Tokamak (START), the device soon achieved a beta of 40%, more than three times that of any conventional tokamak.

    It also bested traditional machines in terms of stability. “It smashed the world record at the time,” Chapman says. “People got more interested.” Other labs rushed to build small spherical tokamaks, some in countries not known for their fusion research, including Australia, Brazil, Egypt, Kazakhstan, Pakistan, and Turkey.

    The next question, Chapman says, was “can we build a bigger machine and get similar performance?” Princeton and Culham’s machines were meant to answer that question. Completed in 1999, NSTX and MAST both hold plasmas about 3 meters across, roughly three times bigger than START’s but a third the size of JET’s. The performance of the pair showed that START wasn’t a one-off: again they achieved a beta of about 40%, reduced instabilities, and good confinement.

    Now, both machines are moving to the next stage: more heating power to make a hotter plasma and stronger magnets to hold it in place. MAST is now in pieces, the empty vacuum vessel looking like a giant tin can adorned with portholes, while its €30 million worth of new magnets, pumps, power supplies, and heating systems are prepared. At Princeton, technicians are putting the finishing touches to a similar $94 million upgrade of NSTX’s magnets and neutral beam heating. Like most experimental tokamaks, the two machines are not aiming to produce lots of energy, just learning how to control and confine plasma under fusionlike conditions. “It’s a big step,” Chapman says. “NSTX-U will have really high injected power in a small plasma volume. Can you control that plasma? This is a necessary step before you could make a spherical tokamak power plant.”

    4
    Engineers lift out MAST’s vacuum vessel for modifications during the €30 million upgrade. © CCFE

    The upgraded machines will each have a different emphasis. NSTX-U, with the greater heating power, will focus on controlling instabilities and improving confinement when it restarts this summer.

    PPPL NSTX-U
    NSTX-U

    “If we can get reasonable beta values, [NSTXU] will reach plasma [properties] similar to conventional tokamaks,” says NSTX chief Masayuki Ono. MAST-Upgrade, due to fire up in 2017, will address a different problem: capturing the fusion energy that would build up in a full-scale plant.

    Fusion reactions generate most of their energy in the form of high-energy neutrons, which, being neutral, are immune to magnetic fields and can shoot straight out of the reactor. In a future power plant, a neutron-absorbing material will capture them, converting their energy to heat that will drive a steam turbine and generate electricity. But 20% of the reaction energy heats the plasma directly and must somehow be tapped. Modern tokamaks remove heat by shaping the magnetic field into a kind of exhaust pipe, called a divertor, which siphons off some of the outermost layer of plasma and pipes it away. But fusion heat will build up even faster in a spherical tokamak because of its compact size. MAST-Upgrade has a flexible magnet system so that researchers can try out various divertor designs, looking for one that can cope with the heat.

    Researchers know from experience that when a tokamak steps up in size or power, plasma can start misbehaving in new ways. “We need MAST and NSTX to make sure there are no surprises at low aspect ratio,” says Dennis Whyte, director of the Plasma Science and Fusion Center at the Massachusetts Institute of Technology in Cambridge. Once NSTX and MAST have shown what they are capable of, Wilson says, “we can pin down what a [power-producing] spherical tokamak will look like. If confinement is good, we can make a very compact machine, around MAST size.”

    BUT GENERATING ELECTRICITY isn’t the only potential goal. The fusion community will soon have to build a reactor to test how components for a future power plant would hold up under years of bombardment by high-energy neutrons. That’s the goal of a proposed machine known in Europe as the Component Test Facility (CTF), which could run stably around the clock, generating as much heat from fusion as it consumes. A CTF is “absolutely necessary,” Chapman says. “It’s very important to test materials to make reactors out of.” The design of CTF hasn’t been settled, but spherical tokamak proponents argue their design offers an efficient route to such a testbed—one that “would be relatively compact and cheap to build and run,” Ono says.

    With ITER construction consuming much of the world’s fusion budget, that promise won’t be tested anytime soon. But one company hopes to go from a standing start to a small power-producing spherical tokamak in a decade. In 2009, a couple of researchers from Culham created a spinoff company—Tokamak Solutions—to build small spherical tokamaks as neutron sources for research. Later, one of the company’s suppliers showed them a new multilayered conducting tape, made with the high-temperature superconductor yttrium-barium-copper-oxide, that promised a major performance boost.

    Lacking electrical resistance, superconductors can be wound into electromagnets that produce much stronger fields than conventional copper magnets. ITER will use low-temperature superconductors for its magnets, but they require massive and expensive cooling. High-temperature materials are cheaper to use but were thought to be unable to withstand the strong magnetic fields around a tokamak—until the new superconducting tape came along. The company changed direction, was renamed Tokamak Energy, and is now testing a first-generation superconducting spherical tokamak no taller than a person.

    Superconductors allow a tokamak to confine a plasma for longer. Whereas NSTX and MAST can run for only a few seconds, the team at Tokamak Energy this year ran their machine—albeit at low temperature and pressure—for more than 15 minutes. In the coming months, they will attempt a 24-hour pulse—smashing the tokamak record of slightly over 5 hours.

    Next year, the company will put together a slightly larger machine able to produce twice the magnetic field of NSTX-U. The next step—investors permitting—will be a machine slightly smaller than Princeton’s but with three times the magnetic field. Company CEO David Kingham thinks that will be enough to beat ITER to the prize: a net gain of energy. “We want to get fusion gain in 5 years. That’s the challenge,” he says.

    “It’s a high-risk approach,” Wilson says. “They’re buying their lottery ticket. If they win, it’ll be great. If they don’t, they’ll likely disappear. Even if it doesn’t work, we’ll learn from it; it will accelerate the fusion program.”

    It’s a spirit familiar to everyone trying to reshape the future of fusion.

    See the full article here.

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  • richardmitnick 1:18 pm on April 28, 2015 Permalink | Reply
    Tags: , Fusion technology, ,   

    From PPPL at Princeton: “An improvement to the global software standard for analyzing fusion plasmas (Nuclear Fusion)” 

    Princeton University
    Princeton University

    PPPL Large
    PPPL

    April 28, 2015
    Raphael Rosen, Princeton Plasma Physics Laboratory

    The gold standard for analyzing the behavior of fusion plasmas may have just gotten better. Mario Podestà, a staff physicist at the U.S. Department of Energy’s Princeton Plasma Physics Laboratory (PPPL), has updated the worldwide computer program known as TRANSP to better simulate the interaction between energetic particles and instabilities – disturbances in plasma that can halt fusion reactions. The program’s updates, reported in the journal Nuclear Fusion, could lead to improved capability for predicting the effects of some types of instabilities in future facilities such as ITER, the international experiment under construction in France to demonstrate the feasibility of fusion power.

    ITER Tokamak
    ITER Tokamak

    Podestà and co-authors saw a need for better modeling techniques when they noticed that while TRANSP could accurately simulate an entire plasma discharge, the code wasn’t able to represent properly the interaction between energetic particles and instabilities. The reason was that TRANSP, which PPPL developed and has regularly updated, treated all fast-moving particles within the plasma the same way. Those instabilities, however, can affect different parts of the plasma in different ways through so-called “resonant processes.”

    The authors first figured out how to condense information from other codes that do model the interaction accurately – albeit over short time periods – so that TRANSP could incorporate that information into its simulations. Podestà then teamed up with TRANSP developer Marina Gorelenkova at PPPL to update a TRANSP module called NUBEAM to enable it to make sense of this condensed data. “Once validated, the updated module will provide a better and more accurate way to compute the transport of energetic particles,” said Podestà. “Having a more accurate description of the particle interactions with instabilities can improve the fidelity of the program’s simulations.”

    1
    Schematic of NSTX tokamak at PPPL with a cross-section showing perturbations of the plasma profiles caused by instabilities. Without instabilities, energetic particles would follow closed trajectories and stay confined inside the plasma (blue orbit). With instabilities, trajectories can be modified and some particles may eventually be pushed out of the plasma boundary and lost (red orbit). Credit: Mario Podestà

    Fast-moving particles, which result from neutral beam injection into tokamak plasmas, cause the instabilities that the updated code models. These particles begin their lives with a neutral charge but turn into negatively charged electrons and positively charged ions – or atomic nuclei – inside the plasma. This scheme is used to heat the plasma and to drive part of the electric current that completes the magnetic field confining the plasma.

    PPPL Tokamak
    PPPL Tokamak

    The improved simulation tool may have applications for ITER, which will use fusion end-products called alpha particles to sustain high plasma temperatures. But just like the neutral beam particles in current-day-tokamaks, alpha particles could cause instabilities that degrade the yield of fusion reactions. “In present research devices, only very few, if any, alpha particles are generated,” said Podestà. “So we have to study and understand the effects of energetic ions from neutral beam injectors as a proxy for what will happen in future fusion reactors.”

    PPPL, on Princeton University’s Forrestal Campus in Plainsboro, N.J., is devoted to creating new knowledge about the physics of plasmas — ultra-hot, charged gases — and to developing practical solutions for the creation of fusion energy. Results of PPPL research have ranged from a portable nuclear materials detector for anti-terrorist use to universally employed computer codes for analyzing and predicting the outcome of fusion experiments. The Laboratory is managed by the University for the U.S. Department of Energy’s Office of Science, which is the largest single supporter of basic research in the physical sciences in the United States, and is working to address some of the most pressing challenges of our time. For more information, visit science.energy.gov.

    See the full article here.

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  • richardmitnick 4:07 pm on March 13, 2015 Permalink | Reply
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    From PPPL: “PPPL and General Atomics scientists make breakthrough in understanding how to control intense heat bursts in fusion experiments” 


    PPPL

    March 13, 2015
    Raphael Rosen

    1
    Computer simulation of a cross-section of a DIII-D plasma responding to tiny magnetic fields. The left image models the response that suppressed the ELMs while the right image shows a response that was ineffective.

    2

    Researchers from General Atomics and the U.S. Department of Energy’s Princeton Plasma Physics Laboratory (PPPL) have made a major breakthrough in understanding how potentially damaging heat bursts inside a fusion reactor can be controlled. Scientists performed the experiments on the DIII-D National Fusion Facility, a tokamak operated by General Atomics in San Diego. The findings represent a key step in predicting how to control heat bursts in future fusion facilities including ITER, an international experiment under construction in France to demonstrate the feasibility of fusion energy. This work is supported by the DOE Office of Science (Fusion Energy Sciences).

    The studies build upon previous work pioneered on DIII-D showing that these intense heat bursts – called “ELMs” for short – could be suppressed with tiny magnetic fields. These tiny fields cause the edge of the plasma to smoothly release heat, thereby avoiding the damaging heat bursts. But until now, scientists did not understand how these fields worked. “Many mysteries surrounded how the plasma distorts to suppress these heat bursts,” said Carlos Paz-Soldan, a General Atomics scientist and lead author of the first of the two papers that report the seminal findings back-to-back in the same issue of Physical Review Letters this week.

    Paz-Soldan and a multi-institutional team of researchers found that tiny magnetic fields applied to the device can create two distinct kinds of response, rather than just one response as previously thought. The new response produces a ripple in the magnetic field near the plasma edge, allowing more heat to leak out at just the right rate to avert the intense heat bursts. Researchers applied the magnetic fields by running electrical current through coils around the plasma. Pickup coils then detected the plasma response, much as the microphone on a guitar picks up string vibrations.

    The second result, led by PPPL scientist Raffi Nazikian, who heads the PPPL research team at DIII-D, identified the changes in the plasma that lead to the suppression of the large edge heat bursts or ELMs. The team found clear evidence that the plasma was deforming in just the way needed to allow the heat to slowly leak out. The measured magnetic distortions of the plasma edge indicated that the magnetic field was gently tearing in a narrow layer, a key prediction for how heat bursts can be prevented. “The configuration changes suddenly when the plasma is tapped in a certain way,” Nazikian said, “and it is this response that suppresses the ELMs.”

    The work involved a multi-institutional team of researchers who for years have been working toward an understanding of this process. These researchers included people from General Atomics, PPPL, Oak Ridge National Laboratory, Columbia University, Australian National University, the University of California-San Diego, the University of Wisconsin-Madison, and several others.

    The new results suggest further possibilities for tuning the magnetic fields to make ELM-control easier. These findings point the way to overcoming a persistent barrier to sustained fusion reactions. “The identification of the physical processes that lead to ELM suppression when applying a small 3D magnetic field to the inherently 2D tokamak field provides new confidence that such a technique can be optimized in eliminating ELMs in ITER and future fusion devices,” said Mickey Wade, the DIII-D program director.

    The results further highlight the value of the long-term multi-institutional collaboration between General Atomics, PPPL and other institutions in DIII-D research. This collaboration, said Wade, “was instrumental in developing the best experiment possible, realizing the significance of the results, and carrying out the analysis that led to publication of these important findings.”

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  • richardmitnick 7:24 am on February 17, 2015 Permalink | Reply
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    From physicsworld: “Smaller fusion reactors could deliver big gains” 

    physicsworld
    physicsworld.com

    Feb 16, 2015
    Michael Banks

    1
    Hot topic: size may not be everything in tokamak design

    Researchers from the UK firm Tokamak Energy say that future fusion reactors could be made much smaller than previously envisaged – yet still deliver the same energy output. That claim is based on calculations showing that the fusion power gain – a measure of the ratio of the power from a fusion reactor to the power required to maintain the plasma in steady state – does not depend strongly on the size of the reactor. The company’s finding goes against conventional thinking, which says that a large power output is only possible by building bigger fusion reactors.

    The largest fusion reactor currently under construction is the €16bn ITER facility in Cadarache, France.

    ITER Tokamak

    This will weigh about 23,000 tonnes when completed in the coming decade and consist of a deuterium–tritium plasma held in a 60 m-tall, doughnut-shaped “tokamak”. ITER aims to produce a fusion power gain (Q) of 10, meaning that, in theory, the reactor will emit 10 times the power it expends by producing 500 MW from 50 MW of input power. While ITER has a “major” plasma radius of 6.21 m, it is thought that an actual future fusion power plant delivering power to the grid would need a 9 m radius to generate 1 GW.

    Low power brings high performance

    The new study, led by Alan Costley from Tokamak Energy, which builds compact tokamaks, shows that smaller, lower-power, and therefore lower-cost reactors could still deliver a value of Q similar to ITER. The work focused on a key parameter in determining plasma performance called the plasma “beta”, which is the ratio of the plasma pressure to the magnetic pressure. By using scaling expressions consistent with existing experiments, the researchers show that the power needed for high fusion performance can be three or four times lower than previously thought.

    Combined with the finding on the size-dependence of Q, these results imply the possibility of building lower-power, smaller and cheaper pilot plants and reactors. “The consequence of beta-independent scaling is that tokamaks could be much smaller, but still have a high power gain,” David Kingham, Tokamak Energy chief executive, told Physics World.

    The researchers propose that a reactor with a radius of just 1.35 m would be able to generate 180 MW, with a Q of 5. This would result in a reactor just 1/20th of the size of ITER. “Although there are still engineering challenges to overcome, this result is underpinned by good science,” says Kingham. “We hope that this work will attract further investment in fusion energy.”

    Many challenges remain

    Howard Wilson, director of the York Plasma Institute at the University of York in the UK, points out, however, that the result relies on being able to achieve a very high magnetic field. “We have long been aware that a high magnetic field enables compact fusion devices – the breakthrough would be in discovering how to create such high magnetic fields in the tokamak,” he says. “A compact fusion device may indeed be possible, provided one can achieve high confinement of the fuel, demonstrate efficient current drive in the plasma, exhaust the heat and particles effectively without damaging material surfaces, and create the necessary high magnetic fields.”

    The work by Tokamak Energy follows an announcement late last year that the US firm Lockheed Martin plans to build a “truck-sized” compact fusion reactor by 2019 that would be capable of delivering 100 MW. However, the latest results from Tokamak Energy might not be such bad news for ITER. Kingham adds that his firm’s work means that, in principle, ITER is actually being built much larger than necessary – and so should outperform its Q target of 10.

    The research is published in Nuclear Fusion.

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  • richardmitnick 8:36 pm on December 8, 2014 Permalink | Reply
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    From PPPL: “Monumental effort: How a dedicated team completed a massive beam-box relocation for the NSTX upgrade” 


    PPPL

    December 8, 2014
    By John Greenwald

    Your task: Take apart, decontaminate, refurbish, relocate, reassemble, realign and reinstall a 75-ton neutral beam box that will add a second beam box to the National Spherical Torus Experiment-Upgrade (NSTX-U) and double the experiment’s heating power. Oh, and while you’re at it, hoist the two-story tall box over a 22-foot wall.

    Members of the “Beam Team” faced those challenges when moving the huge box from the Tokamak Fusion Test Reactor (TFTR) cell to the NSTX-U cell. The task required all the savvy of the PPPL engineers and technicians who make up the veteran team. “They’re a tight-knit group that really knows what they’re doing,” said Mike Williams, director of engineering and infrastructure and associate director of PPPL and a former member of the team himself.

    The second box is one of the two major components of the upgrade that will make NSTX-U the most powerful spherical tokamak fusion facility in the world when construction is completed early next year. The new center stack that serves as the other component will double the strength and duration of the magnetic field that controls the plasma that fuels fusion reactions.

    The two new components will work together hand-in-glove. The stronger magnetic field will increase the confinement time for the plasma while the second beam box performs double-duty. Its beams will raise the temperature of the plasma and will help to maintain a current in the plasma to demonstrate that future tokamaks can operate in a continuous condition known as a “steady state.” The second box is “an absolutely crucial part of the upgrade,” said Masayuki Ono, project director for the NSTX-U.

    PPPL Tokamak
    PPPL Tokamak

    Work began in 2009

    Work on the second beam box began in 2009 when technicians clad in protective clothing dismantled and decontaminated the box as it sat in the TFTR test cell. While the box had used radioactive tritium to heat the plasma in TFTR, no tritium will be used in NSTX-U experiments.

    The decontamination took huge effort, said Tim Stevenson, who led the beam box project. Workers wearing protective garb used cloths, Windex and sprayers with deionized water to clean every part of the box by hand, and went over each part as many as 50 separate times. The cloths were then packaged and shipped to a Utah radiation-waste disposal site.

    Next came the task of moving the beam box and its cleaned and refurbished components out of the TFTR area and into the NSTX-U test cell next door. But how do you get something so massive to budge?

    The Beam Team solved the problem with air casters, said Ron Strykowsky, who heads the NSTX-U upgrade program. Using a ceiling crane, workers lifted the box onto the casters, which floated the load on a cushion of air just above the floor, enabling forklifts to tow it. Technicians then removed some hardware from the large doorway between the two test cells so the beam box could get through.

    The doorway led to a section of the NSTX-U area that is separated from the vacuum vessel by a 22-foot shield wall — a barrier too high for the box and its lid to clear when suspended by sling from a crane. Workers surmounted the problem by first lifting the box and then the lid, which had been removed during the decontamination process. The parts cleared the wall and sailed over the vacuum vessel before coming to rest on the test cell floor. The vessel itself was wrapped in plastic to prevent contamination from any tritium that might still be in the box and the lid as they swung by overhead.

    “Like rebuilding a ship in a bottle”

    The beam box was now ready to be reassembled and reinstalled. But carving out room for all the parts and equipment, including power supplies, cables, and cooling water pipes, proved difficult. “There were so many conflicting demands for space that it was like rebuilding a ship in a bottle,” Stevenson said, citing a remark originally made by engineer Larry Dudek, who heads the center stack upgrade project. “There was no existing footprint,” Stevenson said. “We had to make our own footprint.”

    Technicians needed to cut a port into the vacuum vessel for the beam to pass through. But the supplier-built unit that connected the box to the vessel left too much space between the unit and this new port, requiring the Welding Shop to fill in the gap. “The Welding Shop saved the port,” Stevenson said.

    Still another challenge called for ensuring that the beam would enter the plasma at precisely the angle that NSTX-U specifications required. Complicating this task was the test cell’s uneven floor, which meant that the position of the box also had to be adjusted. To align the beam, engineers used measurements to derive a bull’s-eye on the inside of the vessel; technicians then used laser technology to zero in on the target. The joint effort aligned the beam to within 80 thousands of an inch of the target.

    Installing power supplies

    Left to complete was installation of power supplies, a task accomplished earlier this year. The job called for bringing three orange high-voltage enclosures — the source of the power — up from a basement area and into the test cell through a hatch in the floor. Taken together, the two NSTX-U beam boxes will have the capacity to put up to 18 megawatts of power into the plasma, enough to briefly light some 20,000 homes.

    When asked to name the greatest challenge the project encountered, Stevenson replied, “The whole thing was fraught with challenges and difficulties. It was a monumental team effort that took a great deal of preparation. And when it was show-time, everyone showed up.”

    See the full article here.

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  • richardmitnick 8:24 pm on November 17, 2014 Permalink | Reply
    Tags: , Fusion technology, LPPFusion   

    From LPP: “Physics of Plasmas Publishes LPPFusion’s Runaway Electron Theory” 

    lpp
    LPPFusion

    November 17, 2014
    No Writer Credit

    aip

    Physics of Plasmas, the leading journal in the field of plasma physics, has published LPPFusion’s new paper on Runaway electrons as a source of impurity and reduced fusion yield in the dense plasma focus. The paper, by Chief Scientist Eric J. Lerner and Chief Research Officer Hamid R. Yousefi, was published online October 22, 2014 less than a month after it was submitted for peer-review. Physics of Plasmas had published a previous LPPFusion paper on record-breaking ion energies in 2012.

    The new paper describes the evidence that runaway electrons are a key cause of vaporization of electrodes in the dense plasma focus device, an idea first reported on LPPFusion’s website in April of this year. Runaway electrons occur when very strong electric fields, such as in lightning bolts, accelerate electrons moving through a mainly neutral gas. If the field is strong enough the electrons gain more energy between each collision with an atom than they lose in the collision, thus speeding up to high energy.

    In FF-1, when the current pulse is just starting and the gas in the device is mostly neutral, very large fields build up as the electrons try to push their way through the resisting gas. With very few electrons able to move, the ones that do have to travel fast to carry a given current. The fast-moving runaway electrons gain as much as 3 keV of energy, slamming into the anode and depositing enough heat energy to vaporize some of the metal. This vaporized metal becomes a major impurity in the plasma, disrupting the formation of plasma filaments and leading to lower density in the plasmoid that the current generates. Lower density in turn leads to much lower fusion yield.

    This runaway mechanism is a second main source of impurities, the first being arcing between different pieces of the electrodes. While one-piece, monolithic electrodes will eliminate all arcing, more steps need to be taken to eliminate the runaway electrons. The most important is pre-ionization. In this technique a small current breaks down the plasma resistance before the main pulse passes through—smoothing the way, as it were. The small pulse has too little energy to cause runaway electrons, and by the time the main pulse comes through, there are lots of free electrons ready to move. With many electrons, the current can be carried with each electron moving slowly and thus having little energy. Thus runaway electrons don’t occur in the main pulse either. High pressure in the gas, which make collisions of electrons with atoms more common, can help to prevent runaways as well.

    Pre-ionization is a bit like deliberately creating a traffic jam. Runaway electrons are like cars on a highway at mid-day. There are fewer cars passing a given point but at a higher speed. These faster- moving cars, like the runaway electrons, are carrying more energy. At rush hour, there are far more cars passing a given point per minute, but they all move at a slower speed. Pre-ionization, by creating lots of free electrons, an electron ”rush hour”, allows a higher current with slower moving electrons, eliminating the fast runaways.

    The paper will be available for free download from Physics of Plasmas’ only until Nov.21, 2014.

    See this full article here.

    LPP and PPRC collaborate on pre-ionization experiments

    ero

    The FF-1 anode, which is plated with 0.001 inches of silver, shows a ring of erosion near the end of the insulator (which has been removed along with the cathode). On the right side, where deposits have been cleaned away, the copper color shows clearly where a ring of silver has been vaporized and measurements show about 0.12 grams eroded in 125 shots. On the left side, not cleaned, the copper is deposited lower on the anode, covering up silver below.

    LPP’s research team, having identified impurities vaporized from the electrodes as the main obstacle to higher yields, has been attempting to account theoretically for all sources of vaporization, so as to eliminate them. In January, the team looked more closely at the material eroded from around the anode near the insulator (see photo). Two things seemed surprising: the amount of material—about 1 mg per shot, or half of all the impurities in the plasma; and the fact that the vaporization occurred right at the start of the pulse, when the current flow is the weakest. No possible mechanism seemed to account for so much erosion so fast.

    However, a literature search turned up the answer: runaway electrons. Runaway electrons occur when very strong electric fields, such as in lightning bolts, accelerate electrons moving through a mainly neutral gas. If the field is strong enough the electrons gain more energy between each collision with an atom than they lose in the collision, thus speeding up to high energy. In FF-1, electrons gains as much as 3 keV of energy, slamming into the anode and depositing enough heat energy to vaporize the silver plating and some of the copper underneath. Once the plasma is fully ionized and its resistance drops, the high accelerating fields no longer exist, so the runaway electrons stop—But by then, the plasma has already been contaminated.

    There are two solutions to this problem. One is simply increasing the initial pressure of the gas, so more collisions occur. This will happen with FF-1 as it approaches peak current. But for now, an additional solution is needed: pre-ionization. In this technique a small current breaks down the plasma resistance before the main pulse passes through—smoothing the way, as it were. The small pulse has too little energy to cause runaway electrons, and by the time the main pulse comes through, the resistance that can sustain the large electric field is gone. Experiments by plasma focus groups in Pakistan and elsewhere had good results with pre-ionization.

    To directly test if pre-ionization can eliminate the “ring around the anode” erosion, LPP’s collaborators at the Plasma Physics Research Center (PPRC) in Tehran, Iran are conducting experiments using this technique on their 2-kJ DPF device. At the same time, LPP is doing preliminary tests of pre-ionization techniques on FF-1. Together, the experiments should be able to show how to eliminate this source of erosion prior to FF-1’s next round of experiments with tungsten electrodes.

    See this full article here.

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  • richardmitnick 2:29 pm on November 11, 2014 Permalink | Reply
    Tags: , , , Fusion technology,   

    From PPPL: “PPPL researchers present cutting edge results at APS Plasma Physics Conference” 


    PPPL

    November 10, 2014
    Kitta MacPherson
    Email: kittamac@pppl.gov
    Phone: 609-243-2755

    Some 135 researchers, graduate students, and staff members from PPPL joined 1,500 research scientists from around the world at the 56th annual meeting of the American Physical Society Division of Plasma Physics Conference from Oct. 27 to Oct. 31 in New Orleans. Topics in the sessions ranged from waves in plasma to the physics of ITER, the international physics experiment in Cadarache, France; to women in plasma physics. Dozens of PPPL scientists presented the results of their cutting-edge research into magnetic fusion and plasma science. There were about 100 invited speakers at the conference, more than a dozen of whom were from PPPL.

    sw
    Conceptual image of the solar wind from the sun encountering the Earth’s magnetosphere. No image credit

    The press releases in this issue are condensed versions of press releases that were prepared by the APS with the assistance of the scientists quoted and with background material written by John Greenwald and Jeanne Jackson DeVoe. The full text is available at the APS Virtual Pressroom 2014: http://www.aps.org/units/dpp/meetings/vpr/2014/index.cfm.

    How magnetic reconnection goes “Boom!”

    MRX research reveals how magnetic energy turns into explosive particle energy

    Paper by: M. Yamada, J. Yoo

    Magnetic reconnection, in which the magnetic field lines in plasma snap apart and violently reconnect, creates massive eruptions of plasma from the sun. But how reconnection transforms magnetic energy into explosive particle energy has been a major mystery.

    Now research conducted on the Magnetic Reconnection Experiment (MRX) at PPPL has taken a key step toward identifying how the transformation takes place, and measuring experimentally the amount of magnetic energy that turns into particle energy. The investigation showed that reconnection in a prototypical reconnection layer converts about 50 percent of the magnetic energy, with one-third of the conversion heating the electrons and two-thirds accelerating the ion in the plasma.

    “This is a major milestone for our research,” said Masaaki Yamada, the principal investigator for the MRX. “We can now see the entire picture of how much of the energy goes to the electrons and how much to the ions in a prototypical reconnection layer.”

    What a Difference a Magnetic Field Makes

    Experiments on MRX confirm the lack of symmetry in converging space plasmas

    Paper by: J. Yoo

    Spacecraft observing magnetic reconnection have noted a fundamental gap between most theoretical studies of the phenomenon and what happens in space. While the studies assume that the converging plasmas share symmetrical characteristics such as temperature, density and magnetic strength, observations have shown that this is hardly the case.

    PPPL researchers have now found the disparity in plasma density in experiments conducted on the MRX. The work, done in collaboration with the Space Science Center at the University of New Hampshire, marks the first laboratory confirmation of the disparity and deepens understanding of the mechanisms involved.

    Data from the MRX findings could help to inform a four-satellite mission—the Magnetospheric Multiscale Mission, or MMS—that NASA plans to launch next year to study reconnection in the magnetosphere. The probes could produce a better understanding of geomagnetic storms and lead to advanced warning of the disturbances and an improved ability to cope with them.

    Using radio waves to control density in fusion plasma

    Experiments show how heating electrons in the center of hot fusion plasma can increase turbulence, reducing the density in the inner core

    Paper by: D. Ernst, K. Burrell, W. Guttenfelder, T. Rhodes, A. Dimits

    Recent fusion experiments on the DIII-D tokamak at General Atomics in San Diego and the Alcator C-Mod tokamak at MIT show that beaming microwaves into the center of the plasma can be used to control the density in the center of the plasma. The experiments and analysis were conducted by a team of researchers as part of a National Fusion Science Campaign.

    The new experiments reveal that turbulent density fluctuations in the inner core intensify when most of the heat goes to electrons instead of plasma ions, as would happen in the center of a self-sustaining fusion reaction. Supercomputer simulations closely reproduce the experiments, showing that the electrons become more turbulent as they are more strongly heated, and this transports both particles and heat out of the plasma.

    “As we approached conditions where mainly the electrons are heated, pure trapped electrons begin to dominate,” said Walter Guttenfelder, who did the supercomputer simulations for the DIII-D experiments along with Andris Dimits of Lawrence Livermore National Laboratory. Guttenfelder was a co-leader of the experiments and simulations with Keith Burrell of General Atomics and Terry Rhoades of UCLA. Darin Ernst of MIT led the overall research.

    Calming the Plasma Edge: The Tail that Wags the Dog

    Lithium injections show promise for optimizing the performance of fusion plasmas

    Paper by: G.L. Jackson, R. Maingi, T. Osborne, Z. Yan, D. Mansfield, S.L. Allen

    Experiments on the DIII-D tokamak fusion reactor that General Atomics operates for the U.S. Department of Energy have demonstrated the ability of lithium injections to transiently double the temperature and pressure at the edge of the plasma and delay the onset of instabilities and other transients. Researchers conducted the experiments using a lithium-injection device developed at PPPL.

    Lithium can play an important role in controlling the edge region and hence the evolution of the entire plasma. In the present work, lithium diminished the frequency of instabilities known as “edge localized modes” (ELMs), which have associated heat pulses that can damage the section of the vessel wall used to exhaust heat in fusion devices.

    The tailored injections produced ELM-free periods of up to 0.35 seconds, while reference discharges without lithium showed no ELM-free periods above 0.03 sec. The lithium rapidly increased the width of the pedestal region—the edge of the plasma where temperature drops off sharply—by up to 100 percent and raised the electron pressure and total pressure in the edge by up to 100 percent and 60 percent respectively. These dramatic effects produced a 60 percent increase in total energy-confinement time.

    Scratching the surface of a material mystery

    Scientists shed new light on how lithium conditions the volatile edge of fusion plasmas

    Paper by: Angela Capece

    For fusion energy to fuel future power plants, scientists must find ways to control the interactions that take place between the volatile edge of fusion plasma and the physical walls that surround it in fusion facilities. Such interactions can profoundly affect conditions at the superhot core of the plasma in ways that include kicking up impurities that cool down the core and halt fusion reactions. Among the puzzles is how temperature affects the ability of lithium to absorb and retain the deuterium particles that stray from the fuel that creates fusion reactions.

    Answers are now emerging from a new surface-science laboratory at PPPL that can probe lithium coatings that are just three atoms thick. The experiments showed that the ability of ultrathin lithium films to retain deuterium drops as the temperature of the molybdenum substrate rises—a result that provides insight into how lithium affects the performance of tokamaks

    Experiments further showed that exposing the lithium to oxygen improved deuterium retention at temperatures below about 400 degrees Kelvin. But without exposure to oxygen, lithium films could retain deuterium at higher temperatures as a result of lithium-deuterium bonding during a PPPL experiment.

    Putting Plasma to Work Upgrading the U.S. Power Grid

    PPPL lends GE a hand in developing an advanced power-conversion switch

    Paper by: Johan Carlsson, Alex Khrabrov, Igor Kaganovich, Timothy Summerer

    When researchers at General Electric sought help in designing a plasma-based power switch, they turned to PPPL. The proposed switch, which GE is developing under contract with the DOE’s Advanced Research Projects Agency-Energy, could contribute to a more advanced and reliable electric grid and help lower utility bills.

    The switch would consist of a plasma-filled tube that turns current on and off in systems that convert the direct current coming from long-distance power lines to the alternating current that lights homes and businesses; such systems are used to reverse the process as well.

    To assist GE, PPPL used a pair of computer codes to model the properties of plasma under different magnetic configurations and gas pressures. GE also studied PPPL’s use of liquid lithium, which the laboratory employs to prevent damage to the divertor that exhausts heat in a fusion facility. The information could help GE develop a method for protecting the liquid-metal cathode—the negative terminal inside the tube—from damage from the ions carrying the current flowing through the plasma.

    Laser experiments mimic cosmic explosions

    Scientists bring plasma tsunamis into the lab

    Researchers are finding ways to understand some of the mysteries of space without leaving earth. Using high-intensity lasers at the University of Rochester’s OMEGA EP Facility focused on targets smaller than a pencil’s eraser, they conducted experiments to create colliding jets of plasma knotted by plasma filaments and self-generated magnetic fields.

    In two related experiments, researchers used powerful lasers to recreate a tiny laboratory version of what happens at the beginning of solar flares and stellar explosions, creating something like a gigantic plasma tsunami in space. Much of what happens in those situations is related to magnetic reconnection, which can accelerate particles to high energy and is the force driving solar flares towards earth.

    Laboratory experiment aims to identify how tsunamis of plasma called “shock waves” form in space

    By W. Fox, G. Fisksel (LLE), A. Bhattacharjee

    William Fox, a researcher at the U.S. Department of Energy’s Princeton Plasma Physics Laboratory, and his colleague Gennady Fiksel, of the University of Rochester, got an unexpected result when they used lasers in the Laboratory to recreate a tiny version of a gigantic plasma tsunami called a “shock wave.” The shock wave is a thin area found at the boundary between a supernova and the colder material around it that has a turbulent magnetic field that sweeps up plasma into a steep tsunami-like wave of plasma.

    Fox and Fiksel used two very powerful lasers to zap two tiny pieces of plastic in a vacuum chamber to 10 million degrees and create two colliding plumes of extremely hot plasma. The researchers found something they had not anticipated that had not previously been seen in the laboratory: When the two plasmas merged they broke into clumps of long thin filaments due to a process called the “Weibel instability.” This instability could be causing the turbulent magnetic fields that form the shock waves in space. Their research could shed light on the origin of primordial magnetic fields that formed when galaxies were created and could help researchers understand how cosmic rays are accelerated to high energies.

    Magnetic reconnection in the laboratory

    By: G. Fiksel (LLE), W. Fox, A. Bhattacharjee

    Many plasmas in space already contain a strong magnetic field, so colliding plasmas there behave somewhat differently. Gennady Fiksel, of the University of Rochester, and William Fox continued their previous research by adding a magnetic field by pulsing current through very small wires. They then created the two colliding plumes of plasma as they did in an earlier experiment. When the two plasmas collided it compressed and stretched the magnetic field and a tremendous amount of energy accumulated in the field like a stretched rubber band. As the magnetic field lines pushed close together, the long lines broke apart and reformed like a single stretched rubber band, forming a slingshot that propels the plasma and releases the energy into the plasma, accelerating the plasma and heating it.

    The experiment showed that the reconnection process happens faster than theorists had previously predicted. This could help shed light on solar flares and coronal mass ejections, which also happen extremely quickly. Coronal mass ejections can trigger geomagnetic storms that can interfere with satellites and wreak havoc with cellphone service.

    The laser technique the scientists are using is new in the area of high energy density plasma and allows scientists to control the magnetic field to manipulate it in various ways.

    See the full article here.

    Princeton Plasma Physics Laboratory is a U.S. Department of Energy national laboratory managed by Princeton University.

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  • richardmitnick 7:10 am on November 11, 2014 Permalink | Reply
    Tags: , , , Fusion technology,   

    From PPPL: “Hole in one: Technicians smoothly install the center stack in the NSTX-U vacuum vessel” 


    PPPL

    November 10, 2014
    John Greenwald

    With near-surgical precision, PPPL technicians hoisted the 29,000-pound center stack for the National Spherical Torus Experiment-Upgrade (NSTX-U) over a 20-foot wall and lowered it into the vacuum vessel of the fusion facility. The smooth operation on Oct. 24 capped more than two years of construction of the center stack, which houses the bundle of magnetic coils that form the heart of the $94 million upgrade.

    lift
    Closeup of the center stack being lowered into position by an overhead crane. (Photo by Elle Starkman/PPPL Office of Communications)

    “This was really a watershed moment,” said Mike Williams, the head of engineering and infrastructure at PPPL and associate director of the Laboratory. “The critical path [or key sequence of steps for the upgrade] was fabrication of the magnets, and that has now been done.”

    The lift team conducted the final steps largely in silence, attaching the bundled coils in their casing to an overhead crane and guiding the 21 foot-long center stack into place. The clearances were tiny: The bottom of the casing passed just inches over the shielding wall and the top of the vacuum vessel. Inserting the center stack into the vessel was like threading a needle, since the clearance at the opening was only about an inch. Guidance came chiefly from hand signals, with some radio communication at the end.

    more

    Key features

    The installation merged three key features of the upgrade that had been developed separately. These included the casing, the bundled coils and the work to ready the vacuum vessel for the center stack. Slipping the casing over the bundle was a highly precise task, with the space between them less than an inch. “The key word is ‘fit-up,’” said Ron Strykowsky, who heads the upgrade project. “We had a robust-enough design to handle all the very fine tolerances.”

    Installation of the center stack completed a key portion of the upgrade and opened another chapter. “For me, the burden is off our shoulders,” said Jim Chrzanowski, who led the coil project and retired on Oct. 31 after 39 years at PPPL. “We’ve delivered the center stack and are happy,” added Steve Raftopoulos, who worked alongside Chrzanowski and succeeds him as head of coil building. “This is my baby now,” said Raftopoulos, noting that he will be called on to resolve any problems that occur once the center stack is in operation.

    Praise for technicians

    The two leaders praised the many technicians who made the center stack possible. They ranged from a core of roughly a dozen workers who had been with the project from the beginning to technicians throughout the Laboratory who were called on to pitch in. “We drafted everyone,” Chrzanowski said.

    Their tasks included sanding, welding and applying insulation tape to each of the 36 copper conductors that went into the center stack, and sealing them all together through multiple applications of vacuum pressure impregnation — a potentially volatile process. Next came fabrication and winding of the ohmic heating coil that wraps around the conductors to put current into the hot, charged plasma that fuels fusion reactions.

    “Everyone who worked on this feels a lot of pride and ownership,” Raftopoulos said. “Steve and I were the conductors, but the technicians were the orchestra,” Chrzanowski said. “We’ve got to give credit to the guys who actually build the machines. They take our problems and make them go away.”

    Completion of the upgrade now rests with technicians working under engineer Erik Perry. Their jobs include connecting the center stack to the facility’s outer coils to complete a donut-shape magnetic field that will be used to confine the plasma. The work calls for installation of layers of custom-made electrical equipment plus hoses for water to cool the coils, all of which must fit around diagnostic and other equipment. Also ahead lies the task of connecting a second neutral beam injector for heating the plasma to the vacuum vessel. “It’s like a big puzzle,” said Perry. “Everything must fit together, and that’s what we excel at.”

    See the full article here.

    Princeton Plasma Physics Laboratory is a U.S. Department of Energy national laboratory managed by Princeton University.

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  • richardmitnick 6:52 pm on October 28, 2014 Permalink | Reply
    Tags: , Fusion technology,   

    From PPPL: “Bob Ellis designs a PPPL first: A 3D printed mirror for microwave launchers” 


    PPPL

    October 28, 2014
    John Greenwald

    When scientists at the Korea Supercomputing Tokamak Advanced Research (KSTAR) facility needed a crucial new component, they turned to PPPL engineer Bob Ellis. His task: Design a water-cooled fixed mirror that can withstand high heat loads for up to 300 seconds while directing microwaves beamed from launchers to heat the plasma that fuels fusion reactions.

    be
    Bob Ellis with a 3D-printed plastic prototype for a non-mirror part of the launcher. (Photo by Elle Starkman/PPPL Office of Communications)

    kstar
    KSTAR Tokamak

    Ellis, who had designed mirrors without coolant for shorter experiments, decided to try out a novel manufacturing process called 3D printing that produces components as unified wholes with minimal need for further processing. 3D printing would enable the mirror to be built for less cost than a non-water-cooled mirror produced by conventional manufacturing, Ellis said, “and that was a very nice thing to find out about.”

    The project marked a first for PPPL, which had previously used 3D printers to build plastic models but had not employed the process for creating metal parts. “Metal came into 3D printing about five years ago and was sort of exotic then,” said Phil Heitzenroeder, who heads the Mechanical Engineering Division at PPPL. “Now 3D is beginning to drift down into real-world metal products.”

    Ellis created a CAD-CAM model of the shoebox-size mirror system and delivered it to Imperial Machine & Tool Co. to produce the stainless steel and copper component through metal 3D printing. The process puts down hair-thin layers of stainless steel powder and fuses the powder in each layer with lasers. The parts are thus built from the bottom up layer by layer — another name for 3D printing is “additive manufacturing” — and follow every twist and turn of the CAD-CAM design.

    The stainless steel granules have the consistency of talcum powder before they are fused, said Christian M. Joest, president of the 70-year-old Columbia, N.J., machining and fabricating company. The 3D process took about 20 hours to complete, Joest said.

    The process proved ideal for the water-cooled mirror, which PPPL shipped to KSTAR in early October. The part consists of a thin sheet of polished copper mounted atop a stainless steel base, with serpentine channels for water winding through the base’s center. Conventional construction could have required the base to be built in multiple pieces so that the channels could be drilled, with the pieces then welded back together. “3D printing allows you to produce components in a single piece,” Ellis said, “and that’s a huge advantage.”

    Ellis now is designing a steerable mirror for KSTAR that can be controlled by computer to direct microwaves into different parts of the plasma. Ellis dubs this mirror, to be delivered next year, “Generation 2.0,” since it will have flat cooling channels rather than the round ones on the fixed mirror. The flat channels will increase the efficiency of the coolant, he said, which will be important for shedding heat from the constantly moving steerable mirror.

    See the full article here.

    Princeton Plasma Physics Laboratory is a U.S. Department of Energy national laboratory managed by Princeton University.

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