Runaway discharges in TCABR

Abstract

It is found in experiments carried out in Tokamak Chauffage Alfvén Brésilien (TCABR) that two regimes of runaway discharges (RADs) with very different characteristics are possible. The RAD-I regime, which is similar to that observed in other tokamaks, can be obtained by a gradual transfer from a normal resistive to a RAD by decreasing the plasma density. This regime can be well understood using the Dreicer theory of runaway generation. The total toroidal current contains a substantial resistive component and the discharge retains some features of standard tokamak discharges. The second runaway regime, RAD-II, was recently discovered in the TCABR tokamak (Galvão R.M.O. et al 2001 Plasma Phys. Control. Fusion 43 1181). The RAD-II regime starts just from the beginning of the discharge, provided that certain initial conditions are fulfilled and, in this case, the runaway tail carries almost the full toroidal current. The background plasma is cold and detached from the limiter due to the recombination process. The primary Dreicer process is suppressed in the RAD-II and the secondary avalanche process dominates, even at the start-up phase, in the generation of the toroidal current. It is possible to trigger a transition from the RAD-I to the RAD-II regime using plasma cooling by gas puffing. The experimental results are shown to be in reasonable agreement with theoretical predictions based on the runaway avalanche process.

Runaway electron energy measurement using hard x-ray spectroscopy in “Damavand” tokamak

“…11,12 So far in different tokamaks, many experiments have been done to deduce energy of runaway electrons from the energy spectrum of hard x-ray photons. 13,14 Damavand tokamak is a small size machine, which could provide convenient conditions to investigate the mechanisms of production, behavior, prevention, and shutdown of runaway currents in fusion plasmas.…”

Post-disruptive runaway electron beams in the COMPASS tokamak

“…One of the promising/potential methods to evaluate is to calculate the Shafranov by adding and from EFIT and then evaluate the value of the effective for the relativistic particles, as explained in Kuznetsov et al. (2004): , where is the relativistic Lorentz factor, is the Alfvén current ( ) and is the current carried by the RE. As one can see, an estimate of the average runaway electron energy is required (for calculation of ).…”

Comparative study of runaway electron diffusion in the rise phase of low q a and normal q a discharges in the SINP tokamak

“…They are useful diagnostics for magnetic turbulence. Hence, there are efforts to study these electrons by various techniques and under various conditions [5][6][7][8][9][10][11].…”