Filamentation During Final Transport in a High Pressure Gas

摘要

The filamentation instability has been identified as a possible pathology afflicting final transport even when gas pressure is high enough to eliminate the two-stream mode. This phenomenon is characterized by the spontaneous appearance of many narrow magnetic pinches within the pulse, with a corresponding increase in transverse temperature and emittance. If the time of flight of an ion exceeds one magnetic plasma period of the beam, then there is a danger of filamentation. However, large electrical conductivity (generated by the passage of the beam through the gas) inhibits mode growth for a pulse of finite duration. In addition, transverse thermal velocity damps perturbations of small transverse dimension, and therefore also acts to suppress mode growth. These ideas are developed here in a brief analytical treatment. (ERA citation 04:024956)