Experimental Measurement of Electron Heat Diffusivity in a Tokamak

Abstract

The electron temperature perturbation produced by internal disruptions in the center of the Oak Ridge Tokamak (ORMAK) is followed with a multi-chord soft x-ray detector array. The space-time evolution is found to be diffusive in •character, wi ~h a .conduction coefficient larger by a factor of 2.5 -15 than that implied by the energy containment time, apparently because it is a measurement for the small group of electrons whose energies exceed the cut-off energy of the detectors.A useful model for understanding the energy transport governing the behavior of tokamak discharges is a three-region plasma model. The central core region (r < aD, the disruption radius) suffers internal d ..

Double transport barrier experiments on Alcator C-Mod

“…27,28,29,30 Transient transport experiments using ITB formation to deduce the χ hp have been reported. 31 This paper is the first report of using sawtooth-induced heat pulse to investigate ITB thermal transport characteristics.…”

Perturbative studies of turbulent transport in fusion plasmas

“…The first technique employed for heat pulse propagation studies made use of the heat and particle pulses expelled from the plasma core following an MHD crash, typically the one associated with sawtooth activity [22]. More recently, cold pulses generated at the edge by ELMs and propagating to the centre have also been used [23].…”

Measuring the electron heat diffusion coefficient in a tokamak from Sawtooth oscillation observations

“…Fortunately the naturally occurring internal disruptions in tokamaks [1,2] cause small, cyclic temperature perturbations with little effect on other plasma parameters and thus provide an incisive probe for measuring the radial electron heat conduction coefficient x in a tokamak [3]. In the first attempt [3] to measure x by following the space-time Q evolution of the temperature perturbations induced by internal disruptions, the evolution was found to be diffusive but apparently governed by a coefficient about an order of magnitude larger than that governing the background plasma. This discrepancy was later resolved [2j through a better understanding of the internal disruption process which resulted in more correct initial conditions and "near-field" response considerations.…”

“…It was concluded that the electron heat conduction coefficient is the same (within experimental error) as that governing the background plasma, and that this method represents a unique and very precise method of microscopically measuring the radial electron heat conduction coefficient. c In the process of a detailed reexamination of the heat pulse propagation problem [3] we have developed a wide variety of techniques for determining x from the space-time evolution of the internal-disruptione induced temperature perturbations. In this work several methods are proposed for taking and analyzing the data to obtain both spatially averaged and local estimates of x • The various methods are illustrated e with ORMAK data of the same type and in many cases the same as that used in Refs [2] and [3].…”

“…c In the process of a detailed reexamination of the heat pulse propagation problem [3] we have developed a wide variety of techniques for determining x from the space-time evolution of the internal-disruptione induced temperature perturbations. In this work several methods are proposed for taking and analyzing the data to obtain both spatially averaged and local estimates of x • The various methods are illustrated e with ORMAK data of the same type and in many cases the same as that used in Refs [2] and [3]. With this set of albeit crude experimental data from ORMAK, determination of x (r) from r = 0 to r = 12 em is shown to e be possible and entirely consistent with power balance inferences of X (r) in ORMAK [4].…”