Effects of flow collisionality on ELM replication in plasma guns

Abstract

Degradation of first wall materials due to plasma disturbances severely limit both the lifetime and longevity of fusion reactors. Among the various kinds of disturbances, type I edge localized modes (ELMs) in particular present significant design challenges due to their expected heat loading and relative frequency in next step fusion reactors. Plasma gun devices have been used extensively to replicate ELM conditions in the laboratory, however feature higher density, lower temperatures, and thus higher flow collisionality than those expected in fusion conditions. This work presents experimental visualizations that indicate strong shocks form in gun devices over spatial and temporal scales that precede ablation dynamics. These measurements are used to validate detailed magnetohydrodynamic simulations that capture the production of plasma jets and the shielding effect collisionality plays in particle transport to material surfaces. Simulations show that self-shielding effects in plasma guns reduce the free streaming heat flux by up to 90% and further reduce the incoming particle kinetic energy impinging on material surfaces. These simulations are performed over a range of operating conditions for gun devices and a discussion is provided regarding how existing experimental measurements can be interpreted when extrapolating to fusion conditions.

Dual Mode Operation of a Hydromagnetic Plasma Thruster to Achieve Tunable Thrust and Specific Impulse

“…The device, along with other pulsed Lorentz accelerators, is an extension of the original Marshall plasma gun 12 . Since their inception, Marshall guns have been used for applications ranging from simulated astrophysics 13 , plasma jet driven magneto-inertial fusion (PJMIF) 14 , z-pinch schemes 15 , material ablation 16 , and even neutron production 17 . Despite studies in the 1960's on the potential use of these hydromagnetic plasma guns in space propulsion 18 , there has been little effort since the dawn of diverse electric propulsion demonstrations (1980's) to develop them as a source of thrust for space propulsion.…”

Investigation of the plasma column evolution and dynamics in the PW-7 plasma accelerator

“…To reach the high efficiency of plasma treatment and to achieve desired effect the certain conditions of the irradiation of the target with the plasma flux generated by the accelerator must be fulfilled [10][11][12]. One condition is that the plasma flux should be completely concentrated on the surface and interact with the entire surface uniformly.…”