Discharge Characteristics of a Gas-Filled Capillary Plasma for Laser Wakefield Acceleration

A gas-filled capillary plasma source for potential use in conjunction with laser wakefield acceleration is developed, and its discharge characteristics are presented here. In the capillary, helium or hydrogen gas (~150 torr in pressure) is injected, and a pulsed high voltage (~25 kV) is applied for electrical discharge and plasma production. The discharge properties of the helium and hydrogen gases are compared. The plasma densities inside the capillary hole are measured with a Mach-Zehnder interferometer and are obtained separately by a simple analysis using the diffusion equation and measured current profiles.