Plasma accelerators recover in a FLASH

Date:
March 2, 2022
Source:
Deutsches Elektronen-Synchrotron DESY
Summary:
Scientists have demonstrated at the FLASHForward experiment that
in principle it is possible to operate plasma accelerators at
the repetition rates desired by particle physicists and photon
scientists. This opens the opportunity to utilize such high-gradient
accelerators as booster stages in existing high-repetition-rate
facilities, such as the large- scale X-ray free-electron lasers
FLASH and European XFEL, in order to significantly increase the
energy of long trains of particles in short distances.



FULL STORY ==========================================================================
An international team of researchers led by DESY scientists has
demonstrated for the first time at the FLASHForward experiment that in principle it is possible to operate plasma accelerators at the repetition
rates desired by particle physicists and photon scientists. This
opens the opportunity to utilise such high-gradient accelerators as
booster stages in existing high- repetition-rate facilities, such as
the large-scale X-ray free-electron lasers FLASH and European XFEL, in
order to significantly increase the energy of long trains of particles
in short distances. The team presents the results of their studies in
the journal Naturetoday.


========================================================================== Plasma acceleration is an innovative technology for application to the
next generation of particle accelerators due to both its compactness and versatility, with the aim being to utilise the accelerated electrons for various fields of application in science, industry, and medicine. The acceleration takes place in an extremely thin channel -- typically
only a few centimetres long -- which is filled with an ionised gas,
the plasma. A high- energy laser or particle beam fired through the
plasma can excite a strong electromagnetic field -- a kind of 'wake' --
which can be used to accelerate charged particles. In this way, plasma accelerators can achieve acceleration gradients up to a thousand times
higher than the most powerful accelerators in use today. They could
thus drastically reduce the size of kilometre-scale facilities such as
particle colliders or free-electron lasers.

Modern accelerators for cutting-edge science must also meet high
requirements in terms of efficiency, beam quality, and number of
bunches accelerated per second. In order to generate a particularly
large number of light flashes or particle collisions in the shortest
possible time, thousands or even millions of densely packed particle
bunches must be propelled through accelerators in a single second. Plasma accelerators would, therefore, have to achieve a similar repetition rate
in order to be competitive with state-of-the-art particle- accelerator technology. Current test facilities for plasma acceleration are usually operated at much slower repetition rates in the range of one to ten accelerations per second. The team led by DESY researcher Jens Osterhoff
has now proven that much higher rates are possible. "At FLASHForward
we were able to show for the first time that, in principle, repetition
rates in the megahertz range are supported by the plasma acceleration processes," says Osterhoff.

At FLASHForward the accelerating wave -- the so-called wakefield in the
plasma -- is generated by an electron bunch from the FLASH accelerator
that ploughs through the plasma at almost the speed of light. The
electrons of this 'drive beam' cause the freely moving electrons of the
plasma to oscillate in its wake and thus generate very strong electric
fields. These fields accelerate the electrons of a particle packet flying directly behind the driver bunch. "Unlike in conventional accelerators,
where long-living electromagnetic waves stored in a resonating cavity
can accelerate several particle bunches in quick succession, the electromagnetic fields generated in plasma decay very quickly after
each acceleration process," explains Richard D'Arcy, first author of the
study. "To start a new similar acceleration process, the plasma electrons
and ions must then have 'recovered' to approximately their initial state
such that the acceleration of the next pair of particle bunches is not
modified by that of the previous one."In their experiments, the scientists
took advantage of the highly flexible superconducting FLASH accelerator
to generate particle bunches with extremely short temporal spacings.

The first bunch generated ploughed through the plasma, driving a
high-strength wakefield and thus perturbing the plasma in its wake. At
variable intervals thereafter, pairs of particle bunches were sent
through the plasma cell; the first driving a second wakefield and the
second being accelerated by the resulting fields. The properties of
these subsequent bunches were precisely measured by the experimenters and compared with those of bunches that had experienced this process in an undisturbed plasma. The result: after about 70 billionths of a second
(70 nanoseconds), it was no longer possible to distinguish whether
the second acceleration had taken place in a previously disturbed or undisturbed plasma. "We were able to precisely observe the decay of the perturbation, which reached completion within the first 70 nanoseconds,
and to explain it exactly in simulations," says D'Arcy. "In subsequent measurements, we want to check how different framework conditions in
the setup influence the recovery time of the plasma wave." For example,
the heating of the plasma medium due to high-frequency operation may
have an influence on how quickly the plasma takes to replenish.

========================================================================== Story Source: Materials provided by
Deutsches_Elektronen-Synchrotron_DESY. Note: Content may be edited for
style and length.


========================================================================== Related Multimedia:
* FLASHForward_plasma_cells ========================================================================== Journal Reference:
1. R. D'Arcy, J. Chappell, J. Beinortaite, S. Diederichs, G. Boyle, B.

Foster, M. J. Garland, P. Gonzalez Caminal, C. A. Lindstro/m,
G. Loisch, S. Schreiber, S. Schro"der, R. J. Shalloo, M. The'venet,
S. Wesch, M.

Wing, J. Osterhoff. Recovery time of a plasma-wakefield accelerator.

Nature, 2022; 603 (7899): 58 DOI: 10.1038/s41586-021-04348-8 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2022/03/220302110550.htm

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