Ion Temperature and Hydrodynamic-Energy Measurements in aZ-Pinch Plasma at Stagnation

Abstract

The time history of the local ion kinetic energy in a stagnating plasma was determined from Doppler-dominated line shapes. Using independent determination of the plasma properties for the same plasma region, the data allowed for inferring the time-dependent ion temperature, and for discriminating the temperature from the total ion kinetic energy. It is found that throughout most of the stagnation period the ion thermal energy constitutes a small fraction of the total ion kinetic energy; the latter is dominated by hydrodynamic motion. Both the ion hydrodynamic and thermal energies are observed to decrease to the electron thermal energy by the end of the stagnation period. It is confirmed that the total ion kinetic energy available at the stagnating plasma and the total radiation emitted are in balance, as obtained in our previous experiment. The dissipation time of the hydrodynamic energy thus appears to determine the duration (and power) of the K emission.

Compressing turbulence and sudden viscous dissipation with compression-dependent ionization state

“…The plasma in magnetically driven [2,[4][5][6] or laser driven [7,8] compressions can be turbulent. There can be substantial reduction in viscosity growth due to increasing ionization state for a gas-puff Z-pinch.…”

“…Consider, for example, a neon gas-puff Z-pinch [2] that starts with T ∼ 13 eV and Z ∼ 3, and finishes with T ∼ 200 eV and Z ∼ 9. The temperature increase causes a growth in the viscosity by a factor of ∼ 900, while the (mean) ionization state growth reduces the viscosity by a factor of ∼ 80, drastically cutting the overall viscosity increase.…”

“…[1], we consider a plasma temperature that increases due to the 3D adiabatic compression of an ideal gas in a box of side length L, going as T = T 0 (L 0 /L) 2 . The (mean) ionization state, Z, is treated as having some dependence on L (i.e., the amount of compression) as well.…”

Experimental investigations of ablation stream interaction dynamics in tungsten wire arrays: Interpenetration, magnetic field advection, and ion deflection

“…A good example of this is seen in the exaggerated stagnation temperatures of Z-pinch plasmas measured through spectroscopic measurements of the Doppler broadening of emission lines. 23,24 In this case, without careful consideration, the meso-scale hydro-motion of the plasma at stagnation would lead to an overestimation of the microscopic ion temperature. In the case of the present experiments, we are concerned over the effects of non-Maxwellian ion distribution functions.…”

Diagnostic constraints on the amount of cold mass in imploded argon pinches on Z

“…To account for the observed width of 14 eV also requires a Doppler width of 10.6 eV (from a 50 ± 10 keV effective ion temperature) added in quadrature to the other components. It is important to note that the "effective" ion temperature inferred is not necessarily thermal, and may include turbulence as well as bulk motion [9].…”