The constraint of plasma power balance on runaway avoidance

Abstract

In a post-thermal-quench plasma, mitigated or unmitigated, the plasma power balance is mostly between collisional or Ohmic heating and plasma radiative cooling. In a plasma of atomic mixture {nα} with α labeling the atomic species, the power balance sets the plasma temperature, ion charge state distribution {ni α} with i the charge number, and through the electron temperature Te and ion charge state distribution ni α, the parallel electric field E||. Since the threshold electric field for runaway avalanche growth Eav is also set by the atomic mixture, ion charge state distribution and its derived quantity, the electron density ne, the plasma power balance between Ohmic heating and radiative cooling imposes a stringent constraint on the plasma regime for avoiding and minimizing runaways when a fusion-grade tokamak plasma is rapidly terminated.

First numerical analysis of runaway electron generation in tungsten-rich plasmas towards ITER

“…An open question is the impact of tungsten impurities on the planned mitigation system for ITER. Mitigation with shattered pellet injection requires balance between RE suppression and ohmic current preservation (to avoid a too fast CQ) [38]. This creates an operational space for the mitigation system in terms of the neon and deuterium quantities that should be injected into the plasma.…”

A mimetic finite difference based quasi-static magnetohydrodynamic solver for force-free plasmas in tokamak disruptions

“…This condition is easily satisfied in a plasma with Lundquist number much greater than unity, which applies to most cases of practical interest. It is of interest to note that during the cold VDE after the plasma thermal quench, the Ohmic heating power by a decaying plasma current, is mostly balanced by radiative cooling, so the zero-beta or force-free plasma remains a good approximation throughout the VDE [24].…”