Ultrashort Pulse Reflectometry (USPR) Diagnostic for HIT-SIU

Ultrashort Pulse Reflectometry (USPR) is a plasma diagnostic technique involving the propagation of ultrashort duration (~few nsec) chirps which contain frequency components spanning large portions of the plasma density profile. Upon reflection, each frequency component reflects from a distinct density layer. The reflected wave packet is down-converted and passed through a multi-channel filter bank, with time-of-flight (TOF) measurements made on each of the filtered wave packets. Window and other spurious reflections are gated out using high-speed microwave switches. A highly portable version of this diagnostic is being fabricated for electron density profile measurements on compact, short duration devices such as spheromaks and FRCs. At the heart of the 44 channel system spanning 26.5 to 75 GHz is a field programmable gate array (FPGA) that acquires and processes data collected on each pulsed discharge. Details about the USPR diagnostic, including plasma data collected on the HIT-SIU device, will be presented.