Impurity induced neutralization of megaelectronvolt energy protons in JET plasmas

Korotkov, A.; Gondhalekar, A.; Stuart, A.J.

doi:10.1088/0029-5515/37/1/i05

Cited by 85 publications

(157 citation statements)

References 16 publications

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“…As the power level is raised the tail temperature shows a modest increase but the fast ion density increases substantially due to influx of particles from the limiter. Also shown in figure 6 are results from the JET fast neutral particle analyser [12] which show a similar triton tail energy. The best performance achieved with 2ω CT in JET is shown in figure 7 for an RF power of 8 MW and a D:T ratio of 40:60.…”

Section: Heating At the Second-harmonic Tritium Resonancementioning

confidence: 82%

ICRF results in D-T plasmas in JET and TFTR and implications for ITER

JET

Teams

Start

1998

Plasma Phys. Control. Fusion

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Abstract.Recent experiments in D-T plasmas on the JET and TFTR tokamaks have evaluated a wide range of ITER relevant ion cyclotron heating scenarios. Absorption of fast waves at the second-harmonic tritium resonance has provided bulk ion heating in TFTR supershots and electron heating in JET H-mode discharges. In JET, deuterium minority heating has generated 1.7 MW of fusion power with 6 MW of radio frequency power giving a record steady-state Qvalue of 0.22. Strong bulk ion heating has been achieved with He 3 minority heating with central ion temperatures up to 13 keV being produced in H-modes with a density of 3.6 × 10 19 m −3 . Hydrogen, deuterium and He 3 minority heating methods have produced plasmas with normalized confinement times greater than or equal to that required by ITER for ignition. These H-modes are characterized by small-amplitude, high-frequency ELMs, each of which transports less than 1.5% of the plasma energy content to the limiters. The heavy minority scheme of tritium in a deuterium plasma has been demonstrated both as a heating scheme and a generator of suprathermal neutrons. On TFTR mode conversion to an ion Bernstein wave has achieved central bulk ion heating in supershots with target ion temperatures greater than 20 keV.

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Section: Heating At the Second-harmonic Tritium Resonancementioning

confidence: 82%

ICRF results in D-T plasmas in JET and TFTR and implications for ITER

JET

Teams

Start

1998

Plasma Phys. Control. Fusion

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“…Finally, information on the presence of fast ICRF-accelerated ions was obtained with gammaray (γ-ray) spectrometry analysis [24] and both low-and high-energy neutral particle analysis (NPA) [25].…”

Section: Experimental Set-upmentioning

confidence: 99%

Hydrogen plasmas with ICRF inverted minority and mode conversion heating regimes in the JET tokamak

Mayoral

Lamalle²,

Eester³

et al. 2006

Nucl. Fusion

131

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Abstract:During the initial operation of the International Thermonuclear Experimental Reactor (ITER), it is envisaged that activation will be minimised by using hydrogen (H) plasmas where the reference ion cyclotron resonance frequency (ICRF) heating scenarios rely on minority species such as helium ( 3 He) or deuterium (D). This paper firstly describes experiments dedicated to the study of 3 He heating in H plasmas with a sequence of discharges in which 5 MW of ICRF power was reliably coupled and the 3 He concentration, controlled in real-time, was varied from below 1 % up to 10 %. The minority heating regime was observed at low concentrations (up to 2 %). Energetic tails in the 3 He ion distributions were observed with effective temperatures up to 300 keV and bulk electron temperatures up to 6 keV. At around 2 %, a sudden transition was reproducibly observed to the mode conversion regime, in which the ICRF fast wave couples to short wavelength modes, leading to efficient direct electron heating and bulk electron temperatures up to 8 keV. Secondly, experiments performed to study D minority ion heating in H plasmas are presented. This minority heating scheme proved much more difficult since modest quantities of carbon (C) impurity ions, which have the same charge to mass ratio as the D ions, led directly to the mode conversion regime.Finally, numerical simulations to interpret these two sets of experiments are under way and preliminary results are shown.

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“…Presence of a fast 3 He ion population was detected by (i) its contribution to the neutron rate through the nuclear reaction 9 Be( 3 He,n) 11 C; (ii) gamma-ray spectrometry [6 ] based on nuclear reactions between energetic 3 He, 9 Be and 12 C impurities, and (iii) low-and high-energy neutral particle analysis (NPA) [7]. Fig.…”

Section: Icrf Heating In Hydrogen Plasmasmentioning

confidence: 99%

“…This absorption-free region acts as a barrier preventing particles from reaching higher energies. At fixed magnetic field, E* measured with a high-energy neutral particle analyzer (NPA) [26], which detects protons with energies between 0.28 and 1.1MeV. Note that the JET tokamak is ideally suited to perform this type of experiment which requires confining and diagnosing protons in the MeV range (In the low magnetic field discharges of the experiment the Larmor radius of 1MeV protons was up to ~0.09m, about 10% of the discharge horizontal minor radius.)…”

Section: Finite Larmor Radius (Flr) Effects On the Icrh Minority Ion mentioning

confidence: 99%

Expanding the operating space of ICRF on JET with a view to ITER

et al. 2006

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This paper reports on ITER-relevant ICRF physics investigated on JET in 2003 and early 2004.Minority heating of helium three in hydrogen plasmas -( 3 He)H -was systematically explored by varying the 3 He concentration and the toroidal phasing of the antenna arrays. The best heating performance (a maximum electron temperature of 6.2keV with 5MW of ICRF power) was obtained with a preferential wave launch in the direction of the plasma current. A clear experimental demonstration was made of the sharp and reproducible transition to the mode conversion heating regime when the 3 He concentration increases above ~2%. In the latter regime the best heating performance (a maximum electron temperature of 8keV with 5MW of ICRF power) was achieved with dipole array phasing, i.e. a symmetric antenna power spectrum. Minority heating of deuterium in hydrogen plasmas -(D)H -was also investigated but was found inaccessible, because this scenario is too sensitive to impurity ions with Z/A=1/2 such as C 6+ , small amounts of which directly lead into the mode conversion regime. Minority heating of up to 3% of tritium in deuterium plasmas was systematically investigated during the JET Trace Tritium experimental campaign (TTE). This required operating JET at its highest possible magnetic field (3.9 to 4T) and the ICRF system at its lowest frequency (23MHz). The interest of this scenario for ICRF heating at these low concentrations and its efficiency at boosting the suprathermal neutron yield were confirmed, and the measured neutron and gammay ray spectra permit interesting comparisons with advanced ICRF code simulations.Investigations of finite Larmor radius effects on the RF-induced high-energy tails during second harmonic (ω=2 ω c ) heating of a hydrogen minority in D plasmas clearly demonstrated a strong decrease of the RF diffusion coefficient at proton energies ~1MeV, in agreement with theoretical 4 expectations. Fast wave heating and current drive experiments in deuterium plasmas showed effective direct electron heating with dipole phasing of the antennas, but only small changes of the central plasma current density were observed with the directive phasings, in particular at low single pass damping. New investigations of the heating efficiency of ICRF antennas confirmed its strong dependence on the parallel wavenumber spectrum. Advances i n topics of a more technological nature are also summarized: ELM studies using fast RF measurements, the successful experimental demonstration of a new ELM-tolerant antenna matching scheme, and technical enhancements planned on the JET ICRF system for 2006, themselves equally strongly driven by the preparation for ITER.5

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Impurity induced neutralization of megaelectronvolt energy protons in JET plasmas

Cited by 85 publications

References 16 publications

ICRF results in D-T plasmas in JET and TFTR and implications for ITER

ICRF results in D-T plasmas in JET and TFTR and implications for ITER

Hydrogen plasmas with ICRF inverted minority and mode conversion heating regimes in the JET tokamak

Expanding the operating space of ICRF on JET with a view to ITER

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