Transparent Injection into Electron and Positron Accelerator Rings

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.

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