Go Forth and Build a Versatile Plasma Source – Words of Wisdom from Noah Hershkowitz

In this talk I will describe the origins of the West Virginia University helicon source program. The focus will be on the key results from the program over the past two decades and the collaborative role played by Professor Noah Hershkowitz throughout that time. The West Virginia University Hot hELIcon eXperiment (HELIX) provided variable density and ion temperature plasmas, with controllable levels of thermal anisotropy, for space relevant laboratory experiments as well as fundamental studies of helicon source physics. Through auxiliary ion heating, the ion temperature anisotropy (T_⊥/T_||) was variable from 1 to 20 for parallel plasma beta (β=8πnkT_i||/B²) values that spanned the range 0.0001 to 0.01. Through measurements of sub-mm wave fluctuations localized to the plasma edge; enhancements in plasma density, electron temperature, and ion temperature at specific antenna frequencies and magnetic field strengths; measurements of energetic electrons; ion thermal anisotropy measurements; and electric field measurements; the key role of slow waves in helicon sources was identified. Neutral pumping, another topic championed by Professor Hershkowitz, was also studied extensively using single photon and two-photon measurements of neutral species in helicon sources.