Transparent Injection into Electron and Positron Accelerator Rings
Date
2023-09-01
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
ORCID
0009-0008-9481-1045
Type
Thesis
Degree Level
Masters
Abstract
Particle accelerator rings utilize high energy particles for a broad range of scientific purposes. Synchrotron
light source facilities such as the Canadian Light Source (CLS) utilize radiation emitted by the acceleration
of electrons in an electromagnetic trap called a storage ring to investigate many topics including agricultural,
biomedical, and materials science problems. Particle colliders like the planned Future Circular Collider
electron-positron machine (FCC-ee) also store a beam of accelerated particles in a collider ring. The difference
is that the FCC-ee will also have a second beam traveling in the opposite direction. The two beams collide
at interaction points (IPs) which are observed using very precise detectors. Colliders study the fundamental
particles’ structure and test the standard model, one goal of FCC-ee is to intensely study the Higg’s boson[1].
In both machines the particle beams travel in very high vacuum to minimize scattering off gas particles.
However, the beams travel near the speed of light and traverse the nearly 100 km FCC-ee ring many thousands
of times, and the much smaller 171 m CLS ring millions of times, per second. Thus, particle losses are
non-negligible and beam current decays over time. In a light source the intensity of radiation provided to
experiments is important for the quality of their measurements. In a collider the key value is luminosity, a
measure of the rate of interactions between particles. Both these values depend on the beam current stored in
the rings and each machine benefits greatly from maintaining consistently high beam current. Thus, particles
are regularly injected into the rings to prevent the beam current from decaying, called top-up injection.
In order to store new particles in an accelerator ring, pulsed magnets are used to steer the additional
particles into the machine. These magnets disturb the beam stored in the ring resulting in oscillation of the
beam after each injection. The intensity of light CLS provides modulates as the electron beam moves relative
to experimental optics, affecting researcher’s data. Similarly, misalignment of the beams in a collider will
reduce the luminosity. Ideally, injection would be transparent to the experiments, not disturbing the stored
beam. In practice transparent injection does not completely remove the disturbance but minimizes it.
This thesis presents my work on transparent top-up injection for CLS and FCC-ee. For the CLS I had the
objective of finding alternative injection schemes which could be implemented into the current CLS machine,
and minimizing the post-injection transient oscillation of the stored beam. Simulation of several approaches
achieved a reduction of the magnitude of post-injection stored beam oscillation by a factor of 50. However,
the large size of the injected beam at the CLS meant that the injection efficiency was insufficient for the
alternative injection approach to be used in normal operations.
For FCC-ee my objectives were to develop magnet settings to allow for each of four proposed injection
approaches. Further, I studied injection with the novel multipole kicker magnet design proposed for FCC-ee.
Simulation of effects of the multipole kicker on the stored beam, and its sensitivity to misalignments and
other errors showed that there is risk for instabilities of the beam potentially resulting in significant losses.
These studies led to a recommendation for the baseline injection scheme as the FCC-ee project continues.
Description
Keywords
Accelerator, Synchrotron, Collider, Electron, Positron, Injection
Citation
Degree
Master of Science (M.Sc.)
Department
Physics and Engineering Physics
Program
Physics