Spectroscopic Diagnostics Of The PBFA II Ion Source

High-power ion diodes are being considered as a driver for inertial confinement fusion. The anode plasma which serves as a source for the ion beam must be understood in order to optimize the available ion beam power. We are using visible spectroscopy to study the properties of this source on the PBFA II accelerator. The challenge is to perform sophisticated measurements in the harsh PBFA II environment, which includes 8 MeV endpoint bremsstrahlung, severe EMP, and mechanical shock associated with delivery of 30 TW of electrical power to the 15 cm radius diode. The diagnostic uses collecting optics to couple light from the anode plasma into a 40 m long fiber optic link. This link transports the light to a remote screen room where it is injected into a 1 m Czerny-Turner spectrograph. A streak camera located at the exit of the spectrograph records a time-resolved spectrum. Calibrations of this system include collection efficiency into the fiber optic, the effects of background radiation on the fibers, the fiber transmission and refractive index as a function of wavelength, and the absolute streaked spectrograph sensitivity as a function of wavelength.