A metre-scale plasma discharge for plasma wakefield acceleration

Abstract The construction, diagnosis, and analysis of a 1 m discharge argon plasma cell is presented for the application to plasma wakefield accelerator experiments. The specifications of the plasma cell were tailored towards the requirements of the advanced wakefield experiment at CERN. A high voltage (9 kV) switch was designed that produced square current pulses with 350 A peak current, variable pulse length between 5 µ s and 30 µ s and ( 54 ± 19 ) ns jitter. The switch was used to produce discharges for gas pressures in the 0.02–1 mbar range. The plasma was diagnosed using interferometry and spectroscopy. An argon plasma with equilibrium temperature of 0.75 eV for pulses longer than 10 µ s was produced when balancing the injection and evacuation of argon through the cell. Hydrogen contamination was identified when closing the gas injection and evacuation valves. This suppressed argon ionisation and produced plasmas with 28% total ionisation at 0.1 mbar measured using Stark broadening. 19% argon ionisation at 0.1 mbar was measured via interferometry in the absence of hydrogen contamination.