Simulation of RF Cavity Dark Current in Presence of Helical Magnetic Field

TL;DR

This paper simulates the behavior of RF cavity dark current in a helical magnetic field, revealing how the combined magnetic components affect electron motion and cavity performance, crucial for muon cooling in collider applications.

Contribution

It provides the first detailed simulation of dark current dynamics in a helical magnetic field within an RF cavity, highlighting effects of dipole components on electron trajectories.

Findings

Magnetic field configuration significantly influences dark current distribution.

Dipole components cause less focused electron emission at field sites.

Simulation results aid in optimizing RF cavity design for muon cooling.

Abstract

In order to produce muon beam of high enough quality to be used for a Muon Collider, its large phase space must be cooled several orders of magnitude. This task can be accomplished by ionization cooling. Ionization cooling consists of passing a high-emittance muon beam alternately through regions of low Z material, such as liquid hydrogen, and very high accelerating RF cavities within a multi-Tesla solenoidal focusing channel. But first high power tests of RF cavity with beryllium windows in solenoidal magnetic field showed a dramatic drop in accelerating gradient due to RF breakdowns. It has been concluded that external magnetic fields parallel to RF electric field significantly modifies the performance of RF cavities. However, magnetic field in Helical Cooling Channel has a strong dipole component in addition to solenoidal one. The dipole component essentially changes electron motion in a cavity compare to pure solenoidal case, making dark current less focused at field emission sites. The simulation of dark current dynamic in HCC performed with CST Studio Suit is presented in this paper.