Low velocity boron micro-pellet injector for edge and core impurity transport measurements

A simple low velocity boron micro-pellet injector has been under developmen t for Current Drive Experiment Upgrade (CDX-U) spherical torus edge and cor e impurity transport measurements, and wall conditioning. The injector cons ists of 16 barrels on a rotatable turret. Each barrel can be loaded with bo ron powder particles of diameters ranging from 1 to 40 mu m diameter in amo unts 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/line ar motion feedthrough. A piezoelectric valve gas feed system triggered by C DX-U discharge timing is used to control H-2 or D-2 propellant gas at a cyl inder 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 neutra l boron beams were performed into CDX-U plasmas at a velocity of 23 m/s. Me asurements were obtained with a filtered gated charge coupled device TV cam era, bolometry, visible spectroscopy, and ultrasoft x-ray diagnostics. This work is in support of the present CDX-U research program and possible appl ications on National Spherical Torus Experiment. (C) 1999 American Institut e of Physics. [S0034-6748(99)52501-X].