Measuring Pellet Ablation Parameters in Particle Beam Experiments*

Cryogenic pellet ablation by plasma is described by the neutral-gas-plasma shielding model. Data used to scale the effects of ablation mechanisms is sourced primarily in-situ from tokamak experiments. This data suffers from poor precision due to limited means of diagnosis in large plasma devices and additional complexity arising from the plasma dynamics. An ablation test stand under development at Columbia University will provide more direct ablation measurements. The test stand linearly propels pellets, ablating them through particle (electron or ion) beams. Pellet volume is measured along the path before and after ablation to determine the mass lost. With precise control of the amount of gas frozen into the pellet, fractional ablation is obtained. The ablation rate is proportional to photon production which is measured via photodiodes. The measurement of emitted light yields time-dependent ablation data. Ejected mass deflects the pellet from the original path, providing an additional direct ablation diagnostic. Ablation in plasma is a function of electron temperature, electron density, and plasma velocity. The relationship between electron temperature to beam energy, electron density to beam current, and plasma velocity to beam energy is explored to better inform ablation models.