Determination Of Plasma Parameters In The PUPR Mirror and Cusp Plasma Machine Via Electrostatic Probe Methods

Electrostatic probes are constructed for the PUPR Mirror and Cusp Plasma Machine and preliminary measurements of the plasma parameters are obtained. The machine is cylindrical in shape with two copper coils wound around the machine to provide the necessary mirror or cusp field configuration. The plasma is heated using the electron cyclotron heating method at a frequency of 2.45 GHz. I-V characteristics are obtained using single, double, and emissive Langmuir probes in Argon plasma at approximately 1*10-4 Torr and with approximate field strength of ~ 0.1T at the point cusp. The single and double Langmuir probes consist of 3.5 mm radius stainless steel disks. Characteristics are obtained for the single and double Langmuir probes using a source meter and programming a voltage sweep while recording the current from the digital readout. The emissive probe is constructed by using a tungsten filament and characteristics are obtained in a manner similar to that described for the single and double Langmuir probes. An emission current is superposed on top of the sweeping signal using a DC power source. An electron temperature of approximately 7.5eV is observed in the plasma at a density of ~4.0*1014m-3 using the single Langmuir probe. In addition, with the distribution function obtained from the single probe, the plasma potential is observed to be approximately 25-30V. The measurement of 25-30V for the plasma potential is supported by measurements obtained from the emissive probe.