Speaker
Description
It is known that the addition of a static magnetic field has a degrading effect on the performance of RF cavities, a situation presenting particular problems for the cooling channel of a muon collider. Within this environment, a strong external magnetic field (2–5 T) is superimposed upon the RF field in order to provide beam focusing. The RF field for such systems is required to be in the range of ~10’s MV/m at frequencies in the UHF range (~100’s MHz). It is important to understand the mechanisms whereby the breakdown process is initiated in order to mitigate the onset and establish if these field levels are sustainable. Simulations of particle evolution offer a route to understand these dynamics.
At the energy levels typical in an RF accelerator, it might normally be considered that secondary yield is unlikely to result in growth of electron population in a cavity across the main gap. Yet some electrons in such a system may result in yields exceeding unity. Examples include particles in or near to the main gap field with a phase which results in them being heavily decelerated before arriving on the target surface (which may be the emitting surface) in the main gap, and particles emitted in relatively low field regions of the cavity. Simulations can potentially understand whether these particle trajectories, modulated by the external field, can result in problematic loading of the cavity with excess charge.
To allow reasonably physical simulation of these dynamics requires a secondary yield model that can address the full range of electron energies observed. Conventional SEY models (Furman-Pivi, Vaughan) are modelled for low-energy collisions reaching ~10 keV, whereas electrons within these environments can reach tens of MeV. It is important to extrapolate these models in a reasonably physical manner to ensure the overall dynamic are well modelled.
This poster presents a high-energy SEY Furman-Pivi like model extending up to 10MeV implemented within CST and applied to a model of the 201MHz Copper Cavities planned for the MICE experiment as a test device. Compared with the default models this showed a significant (~50%) reduction in predicted secondary electron populations generated by field-emission sources.
| What category does your poster fit in? | Muon Cooling |
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