Physicists control the flow of electron pulses through a nanostructure
channel

Date:
September 23, 2021
Source:
Friedrich-Alexander-Universita"t Erlangen-Nu"rnberg
Summary:
Particle accelerators are essential tools in research areas such
as biology, materials science and particle physics. Researchers
are always looking for more powerful ways of accelerating
particles to improve existing equipment and increase capacities
for experiments. One such powerful technology is dielectric laser
acceleration (DLA). In this approach, particles are accelerated
in the optical near-field which is created when ultra-short laser
pulses are focused on a nanophotonic structure. Using this method,
researchers have succeeded in guiding electrons through a vacuum
channel, an essential component of particle accelerators.



FULL STORY ========================================================================== Particle accelerators are essential tools in research areas such as
biology, materials science and particle physics. Researchers are always
looking for more powerful ways of accelerating particles to improve
existing equipment and increase capacities for experiments. One such
powerful technology is dielectric laser acceleration (DLA). In this
approach, particles are accelerated in the optical near-field which is
created when ultra-short laser pulses are focused on a nanophotonic
structure. Using this method, researchers from the Chair of Laser
Physics at Friedrich-Alexander-Universita"t Erlangen-Nu"rnberg (FAU)
have succeeded in guiding electrons through a vacuum channel, an
essential component of particle accelerators. The basic design of the
photonic nanostructure channel was developed by cooperation partner TU Darmstadt. They have now published their joint findings in the journal
Nature.


========================================================================== Staying focused As charged particles tend to move further away from each
other as they spread, all accelerator technologies face the challenge of keeping the particles within the required spatial and time boundaries. As
a result, particle accelerators can be up to ten kilometres long, and
entail years of preparation and construction before they are ready for
use, not to mention the major investments involved. Dielectric laser acceleration, or DLA, uses ultra-fast laser technology and advances in semi-conductor production to potentially minimise these accelerators to
merely a few millimetres or centimetres in size.

A promising approach: Experiments have already demonstrated that DLA
exceeds currently used technologies by at least 35 times. This means
that the length of a potential accelerator could be reduced by the same
factor. Until now, however, it was unclear whether these figures could
be scaled up for longer and longer structures.

A team of physicists led by Prof. Dr. Peter Hommelhoff from the Chair
of Laser Physics at FAU has taken a major step forward towards adapting
DLA for use in fully-functional accelerators. Their work is the first
to set out a scheme which can be used to guide electron pulses over
long distances.

Technology is key The scheme, known as 'alternating phase focusing'
(APF) is a method taken from the early days of accelerator theory. A fundamental law of physics means that focusing charged particles
in all three dimensions at once -- width, height and depth -- is
impossible. However, this can be avoided by alternately focusing the
electrons in different dimensions. First of all, electrons are focused
using a modulated laser beam, then they 'drift' through another short
passage where no forces act on them, before they are finally accelerated,
which allows them to be guided forward.

In their experiment, the scientists from FAU and TU Darmstadt incorporated
a colonnade of oval pillars with short gaps at regular intervals,
resulting in repeating macro cells. Each macro cell either has a focusing
or defocusing effect on the particles, depending on the delay between
the incident laser, the electron, and the gap which creates the drifting section. This setup allows precise electron phase space control at the
optical or femto-second ultra- timescale (a femto-second corresponds
to a millionth of a billionth of a second). In the experiment, shining
a laser on the structure shows an increase in the beam current through
the structure. If a laser is not used, the electrons are not guided and gradually crash into the walls of the channel.

'It's very exciting,' says FAU physicist Johannes Illmer, co-author of
the publication. 'By way of comparison, the large Hadron collider at CERN
uses 23 of these cells in a 2450 metre long curve. Our nanostructure uses
five similar- acting cells in just 80 micrometres.' When can we expect to
see the first DLA accelerator? 'The results are extremely significant,
but for us it is really just an interim step,' explains Dr. Roy Shiloh,
'and our final goal is clear: we want to create a fully-functional
accelerator -- on a microchip.' Work in this area is being driven
by the international 'accelerator on a chip' (ACHIP) collaboration,
of which the authors are members. The collaboration has already proven
that, in theory, APF can be adjusted to achieve acceleration of electron
beams. Complex, three-dimensional APF setups could therefore form the
basis for the particle accelerator technology of the future. 'We have
to capture the electrons in all three dimensions if we are to be able
to accelerate them over longer distances without any losses,' explains
Dr. Uwe Niedermayer from TU Darmstadt, and co-author of the publication.

========================================================================== Story Source: Materials provided by Friedrich-Alexander-Universita"t_Erlangen-Nu"rnberg.

Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. R. Shiloh, J. Illmer, T. Chlouba, P. Yousefi, N. Scho"nenberger, U.

Niedermayer, A. Mittelbach, P. Hommelhoff. Electron phase-space
control in photonic chip-based particle acceleration. Nature,
2021; 597 (7877): 498 DOI: 10.1038/s41586-021-03812-9 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/09/210923115651.htm

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