Comparison of calculated neutral beam shine-through with measured shine-through in DIII-D

Abstract

A comparison of the calculated shine-through of neutral particle beams in the DIII-D plasma to measured values inferred from the target temperature rise is reported. This provides an opportunity to verify the shine-through calculations and makes them more reliable in those cases where the shine-through cannot be measured. The DIII-D centerpost neutral beam target tiles are safeguarded against excessive beam shine-through by pyrometry and thermocouple (TC) arrays on the tiles. Shine-through beam power is calculated from the measured temperature changes reported by the target tile TC array. These measurements are performed at the beginning of each operational year at DIII-D. Theoretically, the beam energy deposited into the plasma can be expressed as a function of the change in beam density: E/sub b/spl rarr/p/=/spl epsi/[/spl int/(dt)*/spl int/(dV)*/spl int/(-dsN/sub b/(s))]. The expression for beam density propagating in a plasma is: dN/sub b/(s)/ds=-N/sub b/(s)n(s)/spl sigma/. Where N/sub b/(s) is the beam particle density, n(s) is the plasma density, /spl sigma/ is the interaction cross section, and /spl epsi/ is the energy per beam particle. The beam energy deposited onto the centerpost (shine-through) is then of the general form: E/sub cp/=/spl epsi/[/spl int/(dt)*/spl int/(dVN/sub b/(a))], where N/sub b/(a)=A[N/sub b/(0)/sub e//sup -(na/spl sigma/)/spl gamma/+/C]. Given that a, is the plasma diameter, (na) is the line density, N/sub b/(O) is the initial beam density, where A, C and g are system dependent constants. The line density and uncollided beam density are measured quantities. Values of /spl sigma/ are available in the general literature. Neutral beam energy deposition in a plasma (of known density) is inferred by comparing the results of a series of shine-through measurements for the 1997 campaign at DIII-D to the expected shine-through given by theory.