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Abstract

The propagation of heat pulses originating from sawtooth activity in JET has been investigated in a series of limiter discharges with the parameters I-"rm p"simeq 3 MA, B-"rm T"simeq 3T, kappa =1.45. The auxiliary power was varied, so that the total power ranged from 2 to 13.5 MW. Electron temperature perturbations in a 20 cm region around a minor radius r="2over 3"a were recorded with high time resolution, using a 12-channel electron cyclotron emission (ECE) polychromator. From these measurements the electron heat diffusivity chi"rm HP"-"rm e" was derived. Over the whole range of powers considered, chi"rm HP"-"rm e" was found to be independent of power and to lie in the range 2.5 pm 0.5 m2/s. We compare chi"rm HP"-"rm e" to chi"rm GLO"-"rm e" derived from global power balance analysis. For ohmic heating the latter is lower than chi"rm HP"-"rm e" by a factor 2.5. For increasing auxiliary power, chi"rm GLO"-"rm e" approaches chi"rm HP"-"rm e". A model for the dependence of the local chi-"rm e" on the temperature gradient is presented, which permits a unified description of the heat pulse behaviour, the deterioration of confinement and a certain degree of profile consistency. The model does not invoke non-local parameters like the total power input. It is shown that the present heat pulse data contradicts tau-"rm E"-scaling laws of the typical form tau-"rm E" div "rm P""-0.5".

Additional information

Authors: TUBBING B J D, JET JOINT UNDERTAKING, ABINGDON, UK;LOPES CARDOZO N, JET JOINT UNDERTAKING, ABINGDON, UK;VAN DER WIEL M J JET JOINT UNDERTAKING, ABINGDON, UK, JET JOINT UNDERTAKING, ABINGDON, UK
Bibliographic Reference: REPORT JET-P(87)12, 1987, AVAILABILITY: JET, ABINGDON, UK
Record Number: 1989126081200 / Last updated on: 1989-05-01
Category: PUBLICATION
Available languages: en