Singletip Langmuir Measurements of UW-RWM Plasma

The rotating wall machine is a linear screw-pinch built to study the role of different wall boundary conditions on the resistive wall mode (RWM). Its plasma is created by a hexagonal array of electrostatic guns. The central seven guns can be biased to discharge up to 1 kA of current each. The 20 cm diameter, 1.2 m long plasma column is held in place by a 600 G (max) axial guide field. A singletip Langmuir probe inserted from the opposite end of the chamber yields measurements of $T_e, n_e$ and $V_p$ in $r$ and $z$. Several multivariable fitting routines are employed on the I-V curve to derive the standard measurements. I will present 2D Langmuir profiles of the unbiased plasma column in several density and field configurations; biased plasma current measurements are an ongoing concern.