  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.
