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  • richardmitnick 4:37 pm on April 6, 2018 Permalink | Reply
    Tags: , , , , , , , , Plasma wakefield accelerator   

    From DESY: “Electron beams that chop themselves” 



    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.


    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.



    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.


    ”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 .

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    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.

  • richardmitnick 10:01 am on January 26, 2017 Permalink | Reply
    Tags: Accelerating mirror, , Black hole paradox, , , Plasma wakefield accelerator, , Shooting electron waves through plasma could reveal if black holes permanently destroy information,   

    From Science Alert: “Shooting electron waves through plasma could reveal if black holes permanently destroy information” 


    Science Alert

    25 JAN 2017

    Interstellar/Paramount Pictures

    Without having to enter a black hole ourselves…

    One of the greatest dilemmas in astrophysics is the black hole paradox – if black holes really do destroy every scrap of information that enters them.

    Now, physicists might have finally come up with a way to test the paradox once and for all, by accelerating a wave of negatively charged electrons through a cloud of plasma.

    As far as objects in space go, black holes need little introduction. Get too close, and their concentrated mass will swallow you, never to return.

    But in the 1970s, physicists including Stephen Hawking proposed that black holes weren’t necessarily forever.

    Thanks to the peculiarities of quantum mechanics, particles did indeed radiate away from black holes, Hawking hypothesised, which means, theoretically, black holes could slowly evaporate away over time.

    This poses the paradox. Information – the fundamental coding of stuff in the Universe – can’t just disappear. That’s a big rule. But when a black hole evaporates away, where does its bellyful of information go?

    A clue might be found in the nature of the radiation Hawking described. This form of radiation arises when a pair of virtual particles pops into existence right up against a black hole’s line of no return – the ‘event horizon’.

    Usually, such paired particles cancel each other out, and the Universe is none the wiser. But in the case of Hawking radiation, one of these particles falls across the horizon into the gravitational grip of the black hole. The other barely escapes off into the Universe as a bona fide particle.

    Physicists have theorised that this escaped particle preserves the information of its twin thanks to the quirks of quantum dynamics. In this case, the phenomenon of entanglement would allow the particles to continue share a connection, even separated by time and space, leaving a lasting legacy of whatever was devoured by the black hole.

    To demonstrate this, physicists could catch a particle that has escaped a black hole’s event horizon, and then wait for the black hole to spill its guts in many, many years, to test if there’s indeed a correlation between one of the photons and its entangled twin. Which, let’s face it, isn’t exactly practical.

    Now, Pisin Chen from the National Taiwan University and Gerard Mourou from École Polytechnique in France have described a slightly easier method.

    They suggest that a high-tech ‘accelerating mirror’ should provide the same opportunity of separating entangled particles.

    That sounds strange, but as a pair of particles zips into existence in this hypothetical experiment, one would reflect from the accelerating mirror as the other became trapped at the boundary. Just as it might happen in a black hole.

    Once the mirror stopped moving, the ‘trapped’ photon would be freed, just as the energy would be released from a dying black hole.

    Chen’s and Mourou’s mirror would be made by pulsing an X-ray laser through a cloud of ionised gas in a plasma wakefield accelerator. The pulse would leave a trail of negatively charged electrons, which would serve nicely as a mirror.

    By altering the density of the plasma on a small enough scale, the ‘mirror’ would accelerate away from the laser pulse.

    As clever as the concept is, the experiment is still in its ‘thought bubble ‘stage. Even with established methods and trusted equipment, entanglement is tricky business to measure.

    And Hawking radiation itself has yet to be observed as an actual thing.

    Yet Chen’s and Mourou’s model could feasibly be built using existing technology, and as the researchers point out in their paper, could also serve to test other hypotheses on the physics of black holes.

    It sounds far more appealing than waiting until the end of time in front of a black hole, at least.

    This research was published in Physical Review Letters.

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

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