Design and fabrication of Langmuir probe system for determination of glow discharge parameters for vacuum vessel conditioning of Damavand tokamak

In this paper, the plasma parameters of hydrogen glow discharge were measured using Langmuir probe system. To measure these parameters in Damavand tokamak, different parts of the Langmuir probe were designed and fabricated. The electrode used in this system is a tungsten wire with diameter and length of 0.1 and 6 mm, respectively. The electrical circuit constructed for this system is capable of supplying voltage and current in the order of 400 V and 1 A, and can produce triangular pulses in the frequency range of 10 Hz to 10 kHz, respectively. Glow discharge hydrogen plasma, which is used for vacuum vessel cleaning and conditioning, is produced by two electrodes located in the lower part of the Damavand tokamak with the voltage of 450 V, current of 1.5 A and pressure of 10-3 Torr. By applying voltage to the electrode of probe, in the range of 200 to 350 V, the current drawn from the probe was measured. By interpreting the current-voltage characteristic, the plasma parameters were determined. The electron temperature, plasma density, plasma potential, and Debye length of the hydrogen glow discharge measured using this system are 5.8e V, 1.17×1015 m-3, 236 V and 523 μm, respectively.