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Title: Lower hybrid current drive favoured by electron cyclotron radiofrequency heating

The important goal of adding to the bootstrap a fraction of non-inductive plasma current, which would be controlled for obtaining and optimizing steady-state profiles, can be reached by using the Current Drive produced by Lower Hybrid waves (LHCD). FTU (Frascati Tokamak Upgrade) experiments demonstrated, indeed, that LHCD is effective at reactor-graded high plasma density, and the LH spectral broadening is reduced, operating with higher electron temperature in the outer region of plasma column (T{sub e-periphery}). This method was obtained following the guidelines of theoretical predictions indicating that the broadening of launched spectrum produced by parametric instability (PI) should be reduced, and the LHCD effect at high density consequently enabled, under higher (T{sub e-periphery}). In FTU, the temperature increase in the outer plasma region was obtained by operating with reduced particle recycling, lithized walls and deep gas fuelling by means of fast pellet. Heating plasma periphery with electron cyclotron resonant waves (ECRH) will provide a further tool for achieving steady-state operations. New FTU experimental results are presented here, demonstrating that temperature effect at the plasma periphery, affecting LH penetration, occurs in a range of plasma parameters broader than in previous work. New information is also shown on the modelling assessing frequenciesmore » and growth rates of the PI coupled modes responsible of spectral broadening. Finally, we present the design of an experiment scheduled on FTU next campaign, where ECRH power is used to slightly increase the electron temperature in the outer plasma region of a high-density discharge aiming at restoring LHCD. Consequent to model results, by operating with a toroidal magnetic field of 6.3 T, useful for locating the electron cyclotron resonant layer at the periphery of the plasma column (r/a∼0.8, f{sub 0}=144 GHz), an increase of T{sub e} in the outer plasma (from 40 eV to 80 eV at r/a∼0.8) is expected by the JETTO code, sufficient for recovering LHCD. An ECRH power of 0.8 MW, and the standard FTU regime at high plasma density (n{sub eav}∼1.3×10{sup 20}m{sup −3} and plasma current of 0.5 MA) have been considered. The code has been set with transport modelling to reproduce the evolution of FTU kinetic profiles.« less
Authors:
; ; ; ;  [1] ; ;  [2] ;  [3] ; ;  [4]
  1. Associazione EURATOM/ENEA sulla Fusione, Centro Ricerche Frascati, 00044, Frascati (Italy)
  2. Università di Roma Sapienza, Dipartimento Ingegneria Elettronica, Rome (Italy)
  3. CEA, IRFM, F-13108 Saint-Paul-lez-Durance (France)
  4. Università di Roma Tre, Dipartimento Ingegneria Elettronica, Rome (Italy)
Publication Date:
OSTI Identifier:
22263854
Resource Type:
Journal Article
Resource Relation:
Journal Name: AIP Conference Proceedings; Journal Volume: 1580; Journal Issue: 1; Conference: 20. topical conference on radiofrequency power in plasmas, Sorrento (Italy), 25-28 Jun 2013; Other Information: (c) 2014 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; CYCLOTRONS; DENSITY; ECR HEATING; ELECTRIC CURRENTS; ELECTRON TEMPERATURE; ELECTRONS; FT TOKAMAK; GHZ RANGE; LINE BROADENING; LOWER HYBRID CURRENT DRIVE; LOWER HYBRID HEATING; MAGNETIC FIELDS; PARAMETRIC INSTABILITIES; PLASMA DENSITY; RF SYSTEMS; SIMULATION