FAST SCANNING PROBE FOR TOKAMAK PLASMAS

We describe a fast reciprocating probe drive, which has three main new features: (1) a detachable and modular probe head for easy maintenanc e, (2) a combination of high heat flux capability, high bandwidth, and low-Z materials construction, and (3) low weight, compact, inexpensiv e construction. The probe is mounted in a fast pneumatic drive in orde r to reach plasma regions of interest and remain inserted long enough to obtain good statistics while minimizing the heat flux to the tips a nd head. The drive is pneumatic and has been designed to be compact an d reliable to comply with space and maintenance requirements of tokama ks. The probe described here has five tips which obtain a full spectru m of plasma parameters: electron temperature profile T-e(r), electron density profile n(e)(r), floating potential profile V-f(r), poloidal e lectric field profile E-theta(r), saturation current profile I-sat(r), and their fluctuations up to 3 MHz. We describe the probe show radial profiles of various parameters. We compare the density and temperatur e data to that obtained with a helium beam. We also discuss the techni ques to process the data optimally, particularly double probe data and profile fits. (C) 1998 American Institute of Physics. [S0034-6748(98) 00307-4]