First Ion Velocity Distribution Function Measurements In A Room Temperature Calcium Plasma With Laser Induced Fluorescence

Measurements with laser-induced fluorescence (LIF) techniques on metastable states are not always indicative of the bulk ion dynamics and signal-to-noise ratio (SNR) is limited by photon counting proportional to metastable state density. Calcium ions provide access to ground state, single-photon LIF transitions with affordable diode lasers which are favorable to typically employed argon ion metastable states. Ground state LIF provides a large increase in SNR due to the larger state density and is more indicative of bulk ion behavior. A novel plasma source has been developed for production of room temperature calcium plasma. The mass of calcium (40.078 au) is very similar to that of argon (39.95 au) and the ground state transition of Ca-II (396.96 nm) is very close to a metastable transition in Ar-II (394.95 nm). The Ar-II transition shares an upper state with the commonly employed 668 nm LIF scheme, allowing calcium to act as a convenient test particle in argon plasmas with similar dynamics and diagnostic access. Calcium plasma is produced by first vaporizing solid calcium, then passing a collimated neutral beam of calcium through an ionization source developed at the University of Iowa. The ionized beam of calcium is then interrogated with LIF and provides demonstration of the increased SNR LIF technique. Also presented are axially and radially scanned LIF measurements obtained through a confocal telescope focused into the plasma production region to characterize the source.