The sag of the potential in low pressure reflex discharge

Summary form only given. In this work Penning discharge was studied in order to investigate how cathode potential penetrates into magnetized plasma along magnetic field. If negative voltage was applied on end electrodes and there was a magnetic field while cylindrical vacuum chamber was grounded then reflex discharge initiated. The distinctive feature of this discharge was geometry factor. Cathode was greatly ranged from anode (cathode radius r=20 mm, anode radius R=400 mm), but dielectric plates were on the chamber ends.The length of vacuum chamber made of stainless steel was 2000 mm. There was uniform magnetic field in the range of 0-2 kG along the axis. The Penning discharge was studied with the usage of different cathodes: solid disk (r=20 mm) and ring (r1=235 mm, r2=295 mm). The gas was helium by pressure in range from 1 to 35 mTorr, maximum voltage was 1.2 kV. Two mode of discharge operating was found in the case of 35 mTorr. Current-voltage characteristic (CVC) of discharge and radial potential profile was measured. The electron temperature and plasma density was obtained using double probe CVC.