From “Physics” : “Controlling Instabilities in a Plasma Particle Accelerator”

About Physics

From “Physics”

July 6, 2022
Allison Gasparini

Researchers demonstrate that the self-modulation of a proton bunch can be controlled if the protons are preceded by a bunch of relativistic electrons.

L. Verra et al. (AWAKE Collaboration) [1].

CERN AWAKE schematic.

CERN AWAKE.

CERN AWAKE.

In conventional particle accelerators, particles are propelled using radio-frequency cavities, typically completing multiple laps of a circuit before reaching their target energy. An alternative technique that can get particles up to speed much more quickly is proton-driven plasma wakefield acceleration, but this method is prone to the self-modulation instability (SMI), which breaks the particle bunch into a train of microbunches. Now, researchers at the Advanced Proton Driven Plasma Wakefield Acceleration Experiment (AWAKE) at CERN have found a way to control how the SMI develops, suggesting the possibility of exploiting the effect in future particle accelerators [1].

When a proton bunch is injected into a plasma at relativistic speeds, it generates a sequence of electron-density waves called wakefields. “Surfing” these waves is how subsequently injected charged particles can be accelerated at rates beyond conventional accelerators. But the wakefields can also affect the proton bunch itself, amplifying initial proton-density variations in an unpredictable, self-reinforcing process that makes it difficult to synchronize the injection of the particles to be accelerated.

The AWAKE team took control of this process by injecting a relativistic electron bunch into the plasma less than a nanosecond before the protons. These electrons drive wakefields that are strong enough to overwhelm density fluctuations in the plasma and in the proton bunch, which would usually make the outcome of the SMI uncertain. Crucially, the researchers found that the amplitude of the wakefields and the growth of the SMI could be regulated by varying the total charge in the electron bunch. The researchers hope that this new ability to control and reproduce the SMI can be applied to accelerate electron beams in particle-physics experiments in the next decade.

References:

L. Verra et al. (AWAKE Collaboration), “Controlled growth of the self-modulation of a relativistic proton bunch in plasma,” Phys. Rev. Lett. 129, 024802 (2022).

See the full article here .

five-ways-keep-your-child-safe-school-shootings

Please help promote STEM in your local schools.

Stem Education Coalition

Physicists are drowning in a flood of research papers in their own fields and coping with an even larger deluge in other areas of physics. How can an active researcher stay informed about the most important developments in physics? Physics highlights a selection of papers from the Physical Review journals. In consultation with expert scientists, the editors choose these papers for their importance and/or intrinsic interest. To highlight these papers, Physics features three kinds of articles: Viewpoints are commentaries written by active researchers, who are asked to explain the results to physicists in other subfields. Focus stories are written by professional science writers in a journalistic style and are intended to be accessible to students and non-experts. Synopses are brief editor-written summaries. Physics provides a much-needed guide to the best in physics, and we welcome your comments.

From CERN: “AWAKE: More plasma = more acceleration”

From CERN

26 November, 2019
Anaïs Schaeffer

The helicon plasma cell was commissioned in Building 169, where plasma generation tests are ongoing (Image: CERN)

In May 2018, the AWAKE experiment [below] carried out the first ever acceleration of electrons using a wakefield created by protons flowing through plasma. AWAKE demonstrated that it is not only possible but also efficient to use plasma wakefields generated by proton beams to accelerate charged particles, thereby fulfilling the objective of the AWAKE Run 1 phase. The experiment was carried out over a distance of 10 metres, with a rubidium plasma cell.

The next phase, AWAKE Run 2, will start after the LS2 and involves maintaining the quality of an electron beam when it is accelerated and demonstrating the feasibility of the technology over several hundred metres. “The AWAKE plasma is currently produced by sending a laser pulse which transforms rubidium gas into plasma by ionisation. This works well as the AWAKE cell is 10 metres long, but this ionisation method is not appropriate for a larger scale”, explains Alban Sublet, an applied physicist in the Vacuum, Surfaces and Coatings group within the Technology Department.

This is where the helicon plasma cell comes in. A helicon wave is a low frequency electromagnetic wave capable of generating very high-density plasmas, like those needed for AWAKE. “We are currently working with a 1-metre prototype helicon plasma cell developed by the Institute for Plasma Physics in Greifswald (Germany). In this set-up, helicon waves are generated by radiofrequency antennas, which surround a quartz tube filled with argon at low pressure”, explains Alban Sublet. In theory, this set-up should enable very long cells to be created as the tube can be extended and antennas added to spread the plasma over long distances.

Ensuring that the generated plasma remains homogeneous throughout the cell remains a challenge. How can we be sure that the density required for AWAKE is uniformly reached throughout the cell? “For the time being we only have a diagnostic tool that enables us to measure the density profile of the plasma locally”, points out Alban Sublet. “So far, we have deduced the density of the rubidium plasma cell indirectly by measuring the density of the rubidium gas before it is ionised”, adds Edda Gschwendtner, technical coordinator and leader of the AWAKE project at CERN.

To resolve this problem, the team responsible for the tests is currently working in collaboration with the University of Wisconsin (UW), Madison (United States) and the Swiss Plasma Center (SPC) at the EPFL in Lausanne. Two plasma diagnostic techniques are currently being studied and will be tested at CERN in 2020. “Developing a diagnostic tool capable of measuring the uniformity of the plasma with the precision required by AWAKE throughout the length of the cell is a significant challenge”, explains Alban Sublet. “Once we have developed a reliable diagnostic method, we will be able to optimise the helicon plasma cell and then design a longer helicon cell for use in AWAKE in a few years.” Synergies exist with the field of coatings and surface treatments, where this type of plasma might be used in the future, as is the case for certain industrial applications.

See the full article here.

five-ways-keep-your-child-safe-school-shootings
Please help promote STEM in your local schools.

Stem Education Coalition

Meet CERN in a variety of places:

Quantum Diaries

Cern Courier

CERN AWAKE

CERN AWAKE

THE FOUR MAJOR PROJECT COLLABORATIONS

ATLAS

CERN ATLAS Image Claudia Marcelloni CERN/ATLAS

ALICE

CERN/ALICE Detector

CMS

LHCb

LHC

CERN map

CERN LHC Tunnel

From ESOblog: “From giant telescopes to mini particle accelerators”

From ESOblog

How ESO helped CERN’s AWAKE experiment catch a wave

How can knowledge about building ESO’s world-class telescopes help accelerate tiny particles at CERN? Surprisingly, it can be vital! Organisations that are part of the EIROforum often share resources and knowledge, and two ESO engineers were recently involved in designing CERN’s newest particle acceleration experiment, contributing expertise that was essential in the successful start of the experiment earlier this year. In this week’s blog post those two scientists, Marco Quattri and Paolo La Penna, describe their role in the project.

Paolo La Penna

Marco Quattri

The Advanced Wakefield (AWAKE) experiment investigates how charged particles can be accelerated using strong electric fields called plasma wakefields. A wakefield is an electromagnetic field that oscillates in a plasma. Charged particles “surf” the positive and negative zones of the wave, becoming accelerated to very high velocities meaning they have a lot of energy. Plasma wakefields can achieve energies hundreds of times greater than fields in traditional accelerators, making them a promising technique to use in future particle physics research.

Particles being accelerated in a plasma wakefield. Credit: CERN-AWAKE group.

While previous wakefield accelerators used either intense laser pulses or electrons to create an electric field, AWAKE is the first experiment to instead use high-intensity protons beams sent through plasma cells to generate these fields. Using protons to create a wakefield means that particles — in this case, electrons — can be accelerated to high velocities in just one step, whereas typically several stages are required to reach such high energies. The acceleration obtained over a given distance in a plasma wakefield is also much higher than in existing technologies; slow-moving electrons enter AWAKE and are accelerated by a factor larger than a hundred over a distance of just ten metres. CERN’s Large Hadron Collider, in comparison, was designed to be almost 27 kilometres long to enable sufficient acceleration.

Once electrons have been accelerated in the wakefield, a magnet deflects them, directing them to a screen that emits light when hit by high-energy electrons. Mirrors reflect the light emitted by the screen towards a camera, in what we call an optical line. This is where we came in, because CERN has no specific expertise in mounting and qualifying large mirrors. The camera is located in an adjacent tunnel to protect it from the large amount of radiation coming from the screen, so the entire line is about 16 metres long and includes three folding mirrors to direct the light. We used a simulation to help calculate the best size and dimensions of these mirrors, based on the properties of the camera lens and the screen dimensions. The simulation also helped specify the surface quality of the mirrors. Optimising the dimensions and surface helps balance quality against cost!

Having defined the properties of the mirrors, we also assisted with designing their mounts. It is very important that the mounts don’t deform the mirrors at all, as this would blur the resulting image, so we designed them to support the mirrors at three points. We also had to ensure that the mounts protect the mirrors from vibrations propagating through the floor.

ESO has a long and unique history of designing, mounting and testing large mirrors. Those on our telescopes, for example, must be optimised and supported to direct light in the most effective way possible. The instruments installed on the telescopes also host some complicated optics. So we were able to use the expertise and experience we’ve gained here at ESO and apply it to this new experiment.

The mirrors that Paolo and Marco helped design. Credit: CERN-AWAKE group.

Overall, we provided CERN with support in computing the optical and mechanical performances of the mirrors, designing the mounts, defining the mirror specifications, alignment and calibration procedures and procuring the whole line. Although the installation of AWAKE began in 2011, ESO only started collaborating on the project in mid-2016. In May 2018 the team successfully demonstrated the acceleration of electrons and their detection on the screen. This marked the first-ever demonstration of accelerating electrons using a wakefield in a plasma.

It was really great to support CERN, an ESO partner institution, in this way. It was particularly interesting to see how our expertise in designing telescopes to observe objects in the distant Universe can also be helpful for much smaller-scale, Earth-based projects. We would like to thank our line managers for supporting us in carrying out this project and would encourage other ESO employees to take opportunities to work with other partner institutions.

See the full article here .

five-ways-keep-your-child-safe-school-shootings

Please help promote STEM in your local schools.

Stem Education Coalition

Visit ESO in Social Media-

Facebook

Twitter

YouTube

ESO is the foremost intergovernmental astronomy organisation in Europe and the world’s most productive ground-based astronomical observatory by far. It is supported by 16 countries: Austria, Belgium, Brazil, the Czech Republic, Denmark, France, Finland, Germany, Italy, the Netherlands, Poland, Portugal, Spain, Sweden, Switzerland and the United Kingdom, along with the host state of Chile. ESO carries out an ambitious programme focused on the design, construction and operation of powerful ground-based observing facilities enabling astronomers to make important scientific discoveries. ESO also plays a leading role in promoting and organising cooperation in astronomical research. ESO operates three unique world-class observing sites in Chile: La Silla, Paranal and Chajnantor. At Paranal, ESO operates the Very Large Telescope, the world’s most advanced visible-light astronomical observatory and two survey telescopes. VISTA works in the infrared and is the world’s largest survey telescope and the VLT Survey Telescope is the largest telescope designed to exclusively survey the skies in visible light. ESO is a major partner in ALMA, the largest astronomical project in existence. And on Cerro Armazones, close to Paranal, ESO is building the 39-metre European Extremely Large Telescope, the E-ELT, which will become “the world’s biggest eye on the sky”.

ESO/Cerro LaSilla 600 km north of Santiago de Chile at an altitude of 2400 metres.

ESO VLT 4 lasers on Yepun

ESO/Vista Telescope at Cerro Paranal, with an elevation of 2,635 metres (8,645 ft) above sea level.

ESO/NTT at Cerro LaSilla 600 km north of Santiago de Chile at an altitude of 2400 metres.

VLT Survey Telescope at Cerro Paranal with an elevation of 2,635 metres (8,645 ft) above sea level.

ALMA on the Chajnantor plateau at 5,000 metres.

ESO/E-ELT,to be on top of Cerro Armazones in the Atacama Desert of northern Chile. located at the summit of the mountain at an altitude of 3,060 metres (10,040 ft).

APEX Atacama Pathfinder 5,100 meters above sea level, at the Llano de Chajnantor Observatory in the Atacama desert.

Leiden MASCARA instrument, La Silla, located in the southern Atacama Desert 600 kilometres (370 mi) north of Santiago de Chile at an altitude of 2,400 metres (7,900 ft)

Leiden MASCARA cabinet at ESO Cerro la Silla located in the southern Atacama Desert 600 kilometres (370 mi) north of Santiago de Chile at an altitude of 2,400 metres (7,900 ft)

ESO Next Generation Transit Survey at Cerro Paranel, 2,635 metres (8,645 ft) above sea level

SPECULOOS four 1m-diameter robotic telescopes 2016 in the ESO Paranal Observatory, 2,635 metres (8,645 ft) above sea level

ESO TAROT telescope at Paranal, 2,635 metres (8,645 ft) above sea level

ESO ExTrA telescopes at Cerro LaSilla at an altitude of 2400 metres

From Sanford Underground Research Facility via SingularityHub: “This Breakthrough New Particle Accelerator Is Small But Mighty”

From Sanford Underground Research Facility

via

SingularityHub

Sep 04, 2018
Edd Gent

CERN AWAKE

Particle accelerators have become crucial tools for understanding the fundamental nature of our universe, but they are incredibly big and expensive. That could change, though, after scientists validated a new approach that could usher in a generation of smaller, more powerful accelerators.

The discovery of the Higgs Boson in 2012 was a scientific triumph that helped validate decades of theoretical research. But finding it required us to build the 17-mile–long Large Hadron Collider (LHC) beneath Switzerland and France, which cost about $13.25 billion.

LHC

CERN map

CERN LHC Tunnel

CERN LHC particles

CERN CMS Higgs Event

CERN ATLAS Higgs Event

Now scientists at CERN, the organization that runs the LHC, have published results of the first successful test of a proton-driven plasma wakefield accelerator in Nature. The machine is the first successful demonstration of an idea only dreamt up in 2009, which could achieve considerably higher energies over shorter distances than older approaches.

The idea of using wakefields to accelerate particles has been around since the 1970s. By firing a high–energy beam into a plasma—the fourth state of matter that is essentially a gas whose electrons have come loose from their atoms or molecules—it’s possible to get its soup of electrons to oscillate.

This creates something akin to the wake formed as a ship passes through water, and by shooting another beam of electrons into the plasma at a specific angle, you can get the electrons to effectively ride this plasma wave, accelerating them to much higher speeds.

Previous approaches have relied on lasers or electron beams to create these wakefields, but their energy dissipates quickly, so they can only accelerate particles over short distances. That means reaching higher energies would likely require multiple stages [Nature]. Protons, on the other hand, are easy to accelerate and can maintain high energies over very long distances, so a wakefield accelerator driven by them is able to accelerate particles to much higher speeds in a single stage.

In its first demonstration, the AWAKE experiment boosted electrons to 2 GeV, or 2 billion electronvolts (a measure of energy also commonly used as a unit of momentum in particle physics) over 10 meters. In theory, the same approach could achieve 1 TeV (1,000 GeV) if scaled up to 1 kilometer long (0.6 miles).

CERN AWAKE schematic

CERN AWAKE

That pales in significance compared to the energies reached by the LHC, which smashes protons together to reach peak energies of 13TeV. But proton collisions are messy, because they are made up of lots of smaller fundamental particles, so analyzing the results is a time-consuming and tricky task.

That’s why most designs for future accelerators plan to use lighter particles like electrons, which will create cleaner collisions [PhysicsWorld]. Current theories also consider electrons to be fundamental particles (i.e., they don’t break into smaller parts), but smashing them into other particles at higher speeds may prove that wrong [New Scientist].

These particles lose energy far quicker than protons in circular accelerators like the LHC, so most proposals are for linear accelerators. That means that unlike the LHC, where particles can be boosted repeatedly as they circulate around the ring multiple times, all the acceleration has to be done in a single go. The proposed International Linear Collider (ILC) is expected to cost $7 billion [Science] and will require a 20– to 40–kilometer-long tunnel to reach 0.25 TeV.

ILC schematic, being planned for the Kitakami highland, in the Iwate prefecture of northern Japan

That’s because, like the LHC, it will rely on radio frequency cavities, which bounce high-intensity radio waves around inside a metallic chamber to create an electric field that accelerates the particles. Reaching higher energies requires many such RF cavities and therefore long and costly tunnels. That makes the promise of reaching TeVs over just a few kilometers with proton-driven wakefield accelerators very promising.

But it’s probably a bit early to rip up the ILC’s designs quite yet. Building devices that can generate useful experimental results will require substantial improvements in the beam quality, which is currently somewhat lacking. The current approach also requires a powerful proton source—in this case, CERN’s Super Proton Synchrotron—so it’s more complicated than just building the accelerator.

The Super Proton Synchrotron (SPS), CERN’s second-largest accelerator.

Nonetheless, AWAKE deputy spokesperson Matthew Wing told Science that they could be doing practical experiments within five years, and within 20 years the technology could be used to convert the LHC into an electron-proton collider at roughly a 10th of the cost of a more conventional radio frequency cavity design.

Last year, physicists working on the Advanced Wakefield collaboration at CERN added an electron source and beamline (pictured) to their plasma wakefield accelerator. Maximilien Brice, Julien Ordan/CERN

That could make it possible to determine whether electrons truly are fundamental particles, potentially opening up entirely new frontiers in physics and rewriting our understanding of the universe.

See the full article here .

five-ways-keep-your-child-safe-school-shootings
Please help promote STEM in your local schools.

Stem Education Coalition

About us.
The Sanford Underground Research Facility in Lead, South Dakota, advances our understanding of the universe by providing laboratory space deep underground, where sensitive physics experiments can be shielded from cosmic radiation. Researchers at the Sanford Lab explore some of the most challenging questions facing 21st century physics, such as the origin of matter, the nature of dark matter and the properties of neutrinos. The facility also hosts experiments in other disciplines—including geology, biology and engineering.

The Sanford Lab is located at the former Homestake gold mine, which was a physics landmark long before being converted into a dedicated science facility. Nuclear chemist Ray Davis earned a share of the Nobel Prize for Physics in 2002 for a solar neutrino experiment he installed 4,850 feet underground in the mine.

Homestake closed in 2003, but the company donated the property to South Dakota in 2006 for use as an underground laboratory. That same year, philanthropist T. Denny Sanford donated $70 million to the project. The South Dakota Legislature also created the South Dakota Science and Technology Authority to operate the lab. The state Legislature has committed more than $40 million in state funds to the project, and South Dakota also obtained a $10 million Community Development Block Grant to help rehabilitate the facility.

In 2007, after the National Science Foundation named Homestake as the preferred site for a proposed national Deep Underground Science and Engineering Laboratory (DUSEL), the South Dakota Science and Technology Authority (SDSTA) began reopening the former gold mine.

In December 2010, the National Science Board decided not to fund further design of DUSEL. However, in 2011 the Department of Energy, through the Lawrence Berkeley National Laboratory, agreed to support ongoing science operations at Sanford Lab, while investigating how to use the underground research facility for other longer-term experiments. The SDSTA, which owns Sanford Lab, continues to operate the facility under that agreement with Berkeley Lab.

The first two major physics experiments at the Sanford Lab are 4,850 feet underground in an area called the Davis Campus, named for the late Ray Davis. The Large Underground Xenon (LUX) experiment is housed in the same cavern excavated for Ray Davis’s experiment in the 1960s.
LUX/Dark matter experiment at SURF

In October 2013, after an initial run of 80 days, LUX was determined to be the most sensitive detector yet to search for dark matter—a mysterious, yet-to-be-detected substance thought to be the most prevalent matter in the universe. The Majorana Demonstrator experiment, also on the 4850 Level, is searching for a rare phenomenon called “neutrinoless double-beta decay” that could reveal whether subatomic particles called neutrinos can be their own antiparticle. Detection of neutrinoless double-beta decay could help determine why matter prevailed over antimatter. The Majorana Demonstrator experiment is adjacent to the original Davis cavern.

Another major experiment, the Long Baseline Neutrino Experiment (LBNE)—a collaboration with Fermi National Accelerator Laboratory (Fermilab) and Sanford Lab, is in the preliminary design stages. The project got a major boost last year when Congress approved and the president signed an Omnibus Appropriations bill that will fund LBNE operations through FY 2014. Called the “next frontier of particle physics,” LBNE will follow neutrinos as they travel 800 miles through the earth, from FermiLab in Batavia, Ill., to Sanford Lab.

LBNE

From CERN via Interactions.org: “AWAKE achieves first ever acceleration of electrons in a proton-driven plasma wave”

From CERN

via

Interactions.org

AWAKE

AWAKE explores the use of plasma to accelerate particles to high energies over short distances

29 August 2018. In a paper published today in the journal Nature, the AWAKE collaboration at CERN reports the first ever successful acceleration of electrons using a wave generated by protons zipping through a plasma. The acceleration obtained over a given distance is already several times higher than that of conventional technologies currently available for particle accelerators. First proposed in the 1970s, the use of plasma waves (or so-called wakefields) has the potential to drastically reduce the size of accelerators in the next several decades.

The Advanced Proton Driven Plasma Wakefield Acceleration Experiment (AWAKE) is an accelerator R&D project based at CERN. It is a proof-of-principle experiment investigating the use of plasma wakefields driven by a proton bunch to accelerate charged particles.

A plasma wakefield is a type of wave generated by particles travelling through a plasma. AWAKE sends proton beams through plasma cells to generate these fields. By harnessing wakefields, physicists may be able to produce accelerator gradients hundreds of times higher than those achieved in current radiofrequency cavities. This would allow future colliders to achieve higher energies over shorter distances than is possible today.

AWAKE uses proton beams from the Super Proton Synchrotron (SPS)

The Super Proton Synchrotron (SPS), CERN’s second-largest accelerator. (Image: Julien Ordan/CERN

AWAKE is the world’s first proton-driven plasma wakefield acceleration experiment. Besides demonstrating how protons can be used to generate wakefields, AWAKE will also develop the necessary technologies for long-term, proton-driven plasma acceleration projects.

AWAKE is an international scientific collaboration made up of 16 institutes and involving over 80 engineers and physicists (November 2017).

These protons are injected into a 10-metre plasma cell to initiate strong wakefields. A second beam – the “witness” electron beam – would then be accelerated by the wakefields, gaining up to several gigavolts of energy. Following AWAKE’s approval in autumn 2013, the first proton beams were sent to the plasma cell at the end of 2016. During the 2016–2017 run, strong wakefields generated by the proton beams in plasma were observed for the first time and studied in detail. In 2018, electrons will be generated in these plasma wakefields.

five-ways-keep-your-child-safe-school-shootings
Please help promote STEM in your local schools.

Stem Education Coalition

From Horizon The EU Research and Innovation Magazine: “Plasma accelerators could overcome size limitations of Large Hadron Collider”

From Horizon The EU Research and Innovation Magazine

09 July 2018
Jon Cartwright

A plasma cell can help sustain stronger acceleration fields than in conventional accelerators, at only a fraction of their size. Image credit – © DESY, Heiner Müller-Elsner

Plasma particle accelerators more powerful than existing machines could help probe some of the outstanding mysteries of our universe, as well as make leaps forward in cancer treatment and security scanning – all in a package that’s around a thousandth of the size of current accelerators. All that’s left is for scientists to build one.

If you know what a particle accelerator is, you probably think first of the Large Hadron Collider (LHC) – that gargantuan ring on the Franco-Swiss border that smashes protons and ions together, exposing the secrets of the subatomic world.

LHC

CERN map

CERN LHC Tunnel

CERN LHC particles

Built by the European lab CERN, the LHC accelerates particles to the kinds of speeds found during the eruption of the early universe. To do so, it needs a very, very big circumference – 27 kilometres.

Yet the LHC is already finding limits to what it can explore. Physicists want even more powerful accelerators – but building one much bigger than the LHC is hard to contemplate.

Dr Ralph Assmann, a leading scientist at the German particle physics lab DESY, believes a completely different approach is needed. He thinks accelerators can be powerful, yet up to 1,000 times smaller, if they are based on a strange type of matter known as a plasma – a cloud of negative electrons and positive ions.

‘Plasma accelerators provide a path to energies beyond the LHC,’ he said. ‘Particle physicists must take this opportunity very seriously.’

Swing

Conventional accelerators work by sending charged particles through oscillating electromagnetic fields. By switching back and forth, these fields kick the particles to an incrementally higher energy with every cycle – a bit like pushing a child on a swing.

The trouble with this approach is that the individual kicks – which are generated by electrical components – can only be so powerful, or the field itself will break down. High energies therefore demand lots and lots of soft kicks, which is why conventional accelerators get so big.

Plasmas, however, can sustain much bigger fields. Nearly 40 years ago, physicists discovered that if a laser pulse or a particle beam is sent into a plasma, it is possible to momentarily separate the negative and positive charges, generating a field of some 100 billion volts per metre.

Any electrons stranded in the wake of this separation are propelled forwards. The effect, like a surfer riding a wave, is known as plasma wakefield acceleration.

In recent years, the energies accessible with plasma wakefield accelerators have risen sharply. Scientists like Dr Assmann want to increase these energies, but also to improve the stability and quality of the electron beams coming out of the accelerator.

Host of applications

That would make plasma accelerators suitable for particle physics but also a host of other applications, including cancer treatment, medical diagnostics, security scanners and the study of advanced materials. Conventional accelerators already help with these applications, but their size and cost means that demand currently far outstrips supply.

Dr Assmann is coordinating a project, EuPRAXIA, to come up with a design for the world’s first plasma wakefield accelerator with an energy of five giga-electronvolts (GeV) that can actually be used for research. That is less than one-thousandth the energy of the LHC but, as Dr Assmann points out, you have to walk before you can run.

‘Clearly, high-field accelerators, like plasma accelerators, (are) the logical long-term solution for advancing the energy frontier in particle physics,’ he said. ‘But it will require a realistic and sustained approach.’

A two-storey design limits the length of the 5 GeV EuPRAXIA plasma accelerator facility, although it could extend to 35-250m depending on what applications are added downstream. Diagram not to scale. Image credit – Horizon

With 40 labs and universities on board, EuPRAXIA will have to answer key questions, such as whether all the accelerated electrons should come from the plasma, or whether additional electrons should be fed into the machine. The design is expected to be completed towards the end of next year.

EuPRAXIA is not the only plasma accelerator project in town, however. At CERN, a powerful wakefield accelerator called AWAKE has already been built, but with a twist – it uses a proton beam to drive it.

CERN AWAKE schematic

CERN AWAKE

Bigger impact

Protons are more than 1,800 times more massive than electrons, which means they have a much bigger impact when it comes to dividing the charges in a plasma. According to Dr Edda Gschwendtner, the CERN project leader of the AWAKE experiment, that means a proton-driven plasma accelerator could accelerate electrons to high energies in just a single stage, rather than multiple stages, as is often proposed.

AWAKE takes the proton beam from one of CERN’s existing accelerators, and in the last two years has successfully created strong plasma wakefields. This year, the goal is to actually accelerate electrons in that wakefield to energies exceeding 1 GeV.

The AWAKE experiment uses a proton beam to create a strong plasma wakefield. Image credit – CERN

In years to come, Dr Gschwendtner wants to boost AWAKE’s output to several tens of GeV. That would be enough to probe certain theoretical proposals of today’s particle physics – dark photons, for instance, which some physicists believe could constitute the dark matter that predominates in the universe.

Plasma accelerators still have a long way to go before they can out-perform the likes of the LHC. But when conventional accelerators are so big and costly, Dr Gschwendtner believes they could be the only way forward.

‘New technologies must be developed,’ she said. ‘Plasma wakefield acceleration is a very promising novel accelerator technique.’

The research in this article has received EU funding.

See the full article here .

five-ways-keep-your-child-safe-school-shootings
Please help promote STEM in your local schools.

Stem Education Coalition

From DESY: “Electron beams that chop themselves”

DESY

2018/04/06

First experimental proof of self-modulation of particle bunches.

View through the plasma cell along the flight path of the electron beam. Visible in the middle is the pink glow of the plasma. Credit: DESY, Johannes Engel.

In a multi-national effort a team of researchers from DESY, the Lawrence Berkeley National Laboratory (LBNL) and other institutes have demonstrated a remarkable feature of self-organisation in a particle beam that can be of great use for a future generation of compact accelerators: Using the high quality electron beam at DESY’s PITZ facility, the scientists could show that long electron bunches can chop themselves into a row of shorter bunches when they fly through a cloud of electrically charged gas, called a plasma.

At the same time the electrons’ energies were seen to be modulated along each bunch. These results are the experimental proof of a novel plasma acceleration concept pursued by the AWAKE (Advanced Wakefield Experiment) collaboration at the European particle physics lab CERN in Geneva. The team led by DESY scientist Matthias Groß presents its findings in the journal Physical Review Letters.

Particle accelerators at the energy frontier like the Large Hadron Collider (LHC) at CERN are extremely costly to build and operate.

LHC

CERN/LHC Map

CERN LHC Tunnel

CERN LHC particles

Nevertheless there is strong interest to increase available beam energies even further to refine the standard model of particle physics and discover physics beyond. Plasma wakefield accelerators could be the answer to this problem. Today’s bulky structures could be replaced with millimetre-sized plasmas enabling several orders of magnitude stronger acceleration.

To accelerate an electron bunch in this way the plasma electrons are separated from the plasma molecules, forming a so-called plasma wakefield that creates an immense accelerating field. The separation of electrons and molecules in the plasma can be achieved through a high-energy bunch of charged particles. Using proton bunches is very attractive since sufficient energy can be stored in a proton beam to drive a plasma accelerator and generate electron bunches with energies in the LHC regime of tera-electronvolts (TeV) in a single stage. The AWAKE experiment is hosted by CERN to investigate this promising scheme. However, proton bunches as they are generated in today’s accelerators are much too long to be useful in plasma accelerators. Therefore, the generation of suitable proton bunches from a conventional accelerator is a key issue for the AWAKE setup.

CERN AWAKE

CERN AWAKE

A self-modulated electron bunch. Credit: DESY

This task can be accomplished by utilising the so-called self-modulation instability. In this case a plasma wave is initiated at or near the front of the bunch and the resulting electric fields lead to the desired re-organisation of the particle bunches in the beam. This self-modulation effect was described in theory and simulation, but so far only indirect indications were observed in experiment. This is where the unique capabilities of the PITZ facility comes into play, explains group leader Frank Stephan: “The combination of a flexible photocathode laser, high electron beam quality and excellent diagnostics made it possible to demonstrate this effect unambiguously for the first time.” The measurements showed that an incident long electron bunch split itself into three smaller bunches.

DESY PITZ

”The breakthrough results described in our manuscript can be scaled directly to the proton regime and thus open the path to validate the self-modulation scheme towards the next-generation of high-energy physics accelerators at CERN,” emphasises main author Matthias Groß. “Our positive results show that the self-modulation can be practically used in experiments and that unwanted effects like beam hosing, which tend to destroy particle bunches, can be kept under control. This experimental data has been eagerly anticipated in the plasma wakefield accelerator community, especially by the AWAKE collaboration, for several years. The presented achievement is a further example where a plasma wakefield theory based prediction is directly validated in experiment. And looking ahead, our special cross shaped plasma cell which was utilized to gain these results may be of great interest to other groups working on beam-driven plasma wakefield acceleration as well.”

See the full article here .

Please help promote STEM in your local schools.

Stem Education Coalition

DESY is one of the world’s leading accelerator centres. Researchers use the large-scale facilities at DESY to explore the microcosm in all its variety – from the interactions of tiny elementary particles and the behaviour of new types of nanomaterials to biomolecular processes that are essential to life. The accelerators and detectors that DESY develops and builds are unique research tools. The facilities generate the world’s most intense X-ray light, accelerate particles to record energies and open completely new windows onto the universe. 
That makes DESY not only a magnet for more than 3000 guest researchers from over 40 countries every year, but also a coveted partner for national and international cooperations. Committed young researchers find an exciting interdisciplinary setting at DESY. The research centre offers specialized training for a large number of professions. DESY cooperates with industry and business to promote new technologies that will benefit society and encourage innovations. This also benefits the metropolitan regions of the two DESY locations, Hamburg and Zeuthen near Berlin.

From CERN: “AWAKE: Closer to a breakthrough acceleration technology”

CERN

24 Nov 2017
Iva Raynova

The electron source and electron beam line of AWAKE have just been installed. (Image: Maximilien Brice, Julien Ordan/CERN)

CERN AWAKE schematic

We are one step closer to testing a breakthrough technology for particle acceleration. The final three key parts of AWAKE have just been put in place: its electron source, electron beam line and electron spectrometer. This marks the end of the installation phase of the Proton Driven Plasma Wakefield Acceleration Experiment (AWAKE), a proof-of-principle experiment at CERN that is developing a new technique for accelerating particles.

The accelerators currently in use rely on electric fields generated by radiofrequency (RF) cavities to accelerate charged particles by giving them a “kick”. In AWAKE, a beam of electrons will “surf” waves of electric charges, or wakefields. These waves are created when a beam of protons is injected into the heart of AWAKE, a 10-metre plasma cell full of ionised gas. When the protons travel through the plasma, they attract free electrons, which generate wakefields. A second particle beam, this time of electrons, is injected into the right phase behind the proton beam. As a result, it feels the wakefield and is accelerated, just like a surfer riding a wave.

After exiting the plasma cell, the electrons will pass through a dipole magnet, which will curve their path. More energetic particles will get a smaller curvature. As well as the electron beam line, another new component is the scintillator that awaits the electrons at the end of the dipole, showing whether or not they have been accelerated. Essentially, this is a screen that lights up whenever a charged particle passes through it. Successfully accelerated electrons will be bent to a lesser degree by the magnetic field and will appear on one side of the scintillator.

Ans Pardons, integration and installation coordinator of AWAKE, beside the one-metre-wide scintillator. (Image: Maximilien Brice, Julien Ordan/CERN)

From now until the end of 2017, the whole AWAKE experiment, including the electron source and the electron beam line, will be being commissioned and prepared for a very important year ahead. “It is very important to first create a high-quality electron beam with the correct energy and intensity, and then to successfully send it through the electron beam line and the plasma cell,” explains Ans Pardons, integration and installation coordinator of AWAKE.

The first milestone was reached in December 2016, when the first data showed that the wakefields had been successfully generated. After a very successful 2017 run, it is now time for AWAKE’s next big step. Next year will be fully dedicated to proving that the acceleration of electrons in the wake of proton bunches is possible.

See the full article here.

Please help promote STEM in your local schools.

Stem Education Coalition

Meet CERN in a variety of places:

Quantum Diaries

Cern Courier

THE FOUR MAJOR PROJECT COLLABORATIONS

ATLAS

ALICE

CMS

LHCb

LHC

Quantum Diaries

From CERN Courier: “AWAKE makes waves”

CERN Courier

Jan 13, 2017
No writer credit

Proton-bunch comparison

In early December, the AWAKE collaboration made an important step towards a pioneering accelerator technology that would reduce the size and cost of particle accelerators.

CERN AWAKE schematic

Having commissioned the facility with first beam in November, the team has now installed a plasma cell and observed a strong modulation of high-energy proton bunches as they pass through it. This signals the generation of very strong electric fields that could be used to accelerate electrons to high energies over short distances.

AWAKE (Advanced Proton Driven Plasma Wakefield Acceleration Experiment) is the first facility to investigate the use of plasma wakefields driven by proton beams. The experiment involves injecting a “drive” bunch of protons from CERN’s Super Proton Synchrotron (SPS) into a 10 m-long tube containing a plasma. The bunch then splits into a series of smaller bunches via a process called self-modulation, generating a strong wakefield as they move through the plasma.

CERN Super Proton Synchrotron

“Although plasma-wakefield technology has been explored for many years, AWAKE is the first experiment to use protons as a driver – which, given the high energy of the SPS, can drive wakefields over much longer distances compared with electron- or laser-based schemes,” says AWAKE spokesperson Allen Caldwell of the Max Planck Institute for Physics in Munich.

While it has long been known that plasmas may provide an alternative to traditional accelerating methods based on RF cavities, turning this concept into a practical device is a major challenge. The next step for the AWAKE collaboration is to inject a second beam of electrons, the “witness” beam, which is accelerated by the wakefield just as a surfer accelerates by riding a wave. “To have observed indications for the first time of proton-bunch self-modulation, after just a few days of tests, is an excellent achievement. It’s down to a very motivated and dedicated team,” says Edda Gschwendtner, CERN AWAKE project leader.

See the full article here .

Please help promote STEM in your local schools.

Stem Education Coalition
THE FOUR MAJOR PROJECT COLLABORATIONS

ATLAS

ALICE

CMS

LHCb

LHC

From LBNL: “Laser R&D Focuses on Next-Gen Particle Collider”

Berkeley Lab

December 13, 2016
Glenn Roberts Jr.
geroberts@lbl.gov
510-486-5582

‘Road map’ provides a vision for upgrades, new lasers at Berkeley Lab

Wim Leemans, director of Berkeley Lab’s Accelerator Technology & Applied Physics Division, speaks with graduate students Joost Daniels, left, and Kelly Swanson in the BELLA laser control room. Berkeley Lab’s BELLA Center is the site of a laser plasma wakefield acceleration R&D effort and other laser experiments that could help set the stage for a next-generation particle collider. (Credit: Paul Mueller)

BELLA Center

A set of new laser systems and proposed upgrades at the Department of Energy’s (DOE) Lawrence Berkeley National Laboratory (Berkeley Lab) will propel long-term plans for a more compact and affordable ultrahigh-energy particle collider.

Progress on these laser systems and laser-driven accelerators could also provide many spinoffs, such as a new tool to hunt for radioactive materials, and a miniaturized and highly tunable free-electron laser system enabling a range of science experiments.

These efforts are outlined in a DOE-sponsored workshop report that focuses on a set of 10-year road maps designed to kick-start R&D driving a next-generation particle collider for high-energy physics. The ultimate goal is a machine capable of exploring physics beyond the reach of CERN’s Large Hadron Collider (LHC). Today’s most powerful collider, the LHC enabled the discovery of the Higgs boson that resulted in the 2013 Nobel Prize in physics.

The LHC, with a main ring 17 miles in circumference, collides protons—subatomic particles liberated from the center of atoms—at collision energies of up to 13 trillion electronvolts (13 TeV).

LHC at CERN

Meanwhile, proposals for next-generation linear colliders would collide electrons and their antiparticles, positrons, at lower energies—from a few hundred billion electronvolts (GeV) up to a few TeV. And while the collision energies of these machines would be lower than those of the LHC, the physics of their electron-positron collisions would be complementary, enabling more specific, detailed measurements for some particle properties and phenomena.

Building a TeV-level electron-positron collider with today’s accelerator technology is possible but would be expensive due to its great size (its footprint would likely measure more than 20 miles).

In an effort to reduce the scope and associated cost of a next-generation collider, the Office of High Energy Physics within DOE’s Office of Science brought together more than two dozen experts from DOE and across the country to prepare an Advanced Accelerator Development Strategy Report that sets goals for three potentially game-changing accelerator technologies over the next 10 years.

Among other recommendations, the report highlights the need for R&D at BELLA, the Berkeley Lab Laser Accelerator, which is based on one of those three technologies: a laser-driven plasma wakefield accelerator (LWFA). This form of acceleration uses a laser or lasers to accelerate electrons to high energies.

Two other wakefield acceleration concepts being developed elsewhere—one for a particle-beam-driven accelerator, the other for a dielectric wakefield accelerator—are also included in the road map.

Other acceleration techniques are in development that are outside the scope of the report, including an R&D effort based at CERN called AWAKE that is exploring proton-driven plasma wakefield
acceleration.

CERN Awake schematic

Scheme of the AWAKE experiment within CERN’s structure (Image courtesy CERN)

The new approaches to particle acceleration endorsed in the report all offer potential ways to shrink high-energy particle accelerators by creating compact, dense waves of plasmas—formed in hot, highly charged gases—that rapidly accelerate bunches of precisely placed electrons like a surfer riding on an ocean wave.

BELLA researchers have already demonstrated a modular LWFA setup for reaching high energies, and are now working to improve upon this. The near-term goal outlined in the report is to achieve electron-beam energies of 10 GeV, up from BELLA’s current world record of 4.3 GeV.

“Once we have 10 GeV beams it will open up a whole new host of things. It will be a major step forward,” said Wim Leemans, director of the Lab’s Accelerator Technology & Applied Physics Division. The 10 GeV goal is significant because it represents an energy threshold for generating high charge positron beams, which would be required for a next-generation collider.

The LWFA road map, Leemans said, “gives us an anchor in the whole accelerator program” outlined for the DOE national laboratory complex.

The BELLA team will pursue two different approaches for achieving this 10 GeV goal: a single-accelerator-stage setup using a single laser, and a two-stage approach with two separate lasers.

The first stage will raise the electron beam energy to 5 GeV, and the second stage will accelerate the beam an additional 5 GeV, to 10 GeV. The second BELLA beamline for the two-beam setup could be constructed by the end of 2018, as outlined in the road map report, provided funding is available.

The report notes that in addition to advances in accelerator technology, there must also be new developments in laser technology, and supporting equipment such as mirrors, to realize this new type of collider.

BELLA now uses sapphire crystals doped with titanium to produce its laser light. To achieve far higher energies, and average beam power, the DOE report recommends pursuing other types of lasers, such as optical fiber, solid state, or carbon dioxide lasers, among other approaches.

A key technology challenge for BELLA is to make its pulses more rapid-fire, increasing from a current rate of about 1 pulse per second to a rate of about 1,000 per second, or 1 kilohertz (in a future development dubbed “K-BELLA”).

Ultimately, a pulse rate of 10,000 or 100,000 per second would be ideal for a next-generation collider, said Carl Schroeder, a Berkeley Lab senior scientist who leads theoretical and modeling efforts for BELLA experiments and has been working on conceptual designs and modeling for this LWFA collider.

If its R&D effort is successful, BELLA’s maximum energy should be sufficient to reach the 10 GeV acceleration milestone, said Anthony Gonsalves, a Berkeley Lab staff scientist who works on BELLA. “We’ve got plenty of room in the ‘tank’—there is a lot of headroom in energy that we haven’t even explored yet.”

Besides work to develop one-beam and two-beam approaches to a 10 GeV LWFA, the Lab’s development of a new, compact type of free-electron laser (FEL) and a separate portable gamma-ray source—to begin testing next year—may be the first important applications of the LWFA technology if the efforts prove successful.

FELs are highly tunable sources of light that can help explore matter down to the atomic and molecular scales with ultrabright pulses measured in femtoseconds, or quadrillionths of a second. The FEL project seeks to miniaturize X-ray FELs by replacing a kilometer-long conventional accelerating structure with a wakefield accelerator less than 10 meters long.

The plasma-based gamma-ray source, meanwhile, could prove to be a useful and portable tool for detecting nuclear materials.

Schroeder said, “The FEL and gamma-ray source are recognized as early applications of this technology. The laser systems for these experiments will be commissioned this winter.

“The roadmap lays out a rich program for the next decade,” added Leemans. “Key concepts are being developed towards future plasma based colliders, and BELLA, with upgrades, will enable the testing and development of many of these concepts.”

The BELLA Center is supported principally by the DOE Office of Science.

See the full article here .

Please help promote STEM in your local schools.

Stem Education Coalition

A U.S. Department of Energy National Laboratory Operated by the University of California