Development of an ultrashort-pulse reflectometer for density profile measurements on GAMMA 10

An ultrashort-pulse reflectometer is under development for electron density profile and fluctuation measurements on the GAMMA 10 tandem mirror. At the heart of the system is an impulse generator which creates an 8 V, 65 ps full-width half-maximum pulse. Data was taken at the midplane of the GAMMA 10 central cell. The incident wave was launched with ordinary-mode polarization and frequency components of the reflected wave in the range 8-10 GHz were detected. The observed values of the time-of-flight are in rough agreement with those obtained from calculations using the Abel-inverted profile obtained from a 70 GHz microwave interferometer. These results suggest that the present system can be expanded to yield a reliable diagnostic for electron density profile measurements.