Low Velocity Boron Micro-pellet Injector for Edge and Core Impurity Transport Measurements
Authors: H.W. Kugel, J. Gorman, R. Kaita, T. Munsat, and D. Stutman
A simple Low Velocity Boron Micro-Pellet Injector has been under development for the Current Drive Experiment-Upgrade (CDX-U) Spherical Torus edge and core impurity transport measurements and wall conditioning. The injector consists of 16 barrels on a rotatable turret. Each barrel can be loaded with boron powder particles of diameters ranging from 1 to 40 micron diameter in amounts ranging from less than 0.25 mg to more than 2 mg. A selected barrel is manually rotated into firing position using a vacuum precision rotary/linear motion feedthrough. A piezoelectric valve gas feed system triggered by CDX-U discharge timing is used to control H2 or D2 propellant gas at a cylinder pressure of 5.8 x 10-3 Pa (40 psi) or less. The injector barrel-to-CDX-U plasma edge distance is 0.47 m. Initial low mass injections of neutral boron beams were performed into CDX-U plasmas at a velocity of 23 m/s. Measurements were obtained with a filtered gated CCD TV camera, bolometry, visible spectroscopy, and ultra soft x-ray diagnostics. This work is in support of the present CDX-U research program and possible applications on the National Spherical Torus Experiment (NSTX).