| 1. |
- Ongena, J., et al.
(författare)
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Recent progress on JET towards the ITER reference mode of operation at high density
- 2001
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Ingår i: Plasma Physics and Controlled Fusion. - 0741-3335 .- 1361-6587. ; 43, s. A11-A30
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Tidskriftsartikel (refereegranskat)abstract
- Recent progress towards obtaining high density and high confinement in JET as required for the ITER reference scenario at Q = 10 is summarized. Plasmas with simultaneous confinement H-98(y.2) = 1 and densities up to n/n(Gw) similar to 1 are now routinely obtained. This has been possible (i) by using plasmas at high (delta similar to 0.5) and medium (delta similar to 0.3-0.4) triangularity with sufficient heating power to maintain Type I ELMs, (ii) with impurity seeded plasmas at high (delta similar to 0.5) and low (delta less than or equal to 0.2) triangularity, (iii) with an optimized pellet injection sequence, maintaining the energy confinement and raising the density, and (iv) by carefully tuning the gas puff rate leading to plasmas with peaked density profiles and good confinement at long time scales. These high performance discharges exhibit Type I ELMs, with a new and more favourable behaviour observed at high densities, requiring further studies. Techniques for a possible mitigation of these ELMs are discussed, and first promising results are obtained with impurity seeding in discharges at high triangularity. Scaling studies using the new data of this year show a strong dependence of confinement on upper triangularity, density and proximity to the Greenwald limit. Observed MHD instabilities and methods to avoid these in high density and high confinement plasmas are discussed.
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| 2. |
- Mantsinen, M. J., et al.
(författare)
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Localized bulk electron heating with ICRF mode conversion in the JET tokamak
- 2004
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Ingår i: Nuclear Fusion. - : IOP Publishing. - 0029-5515 .- 1741-4326. ; 44:1, s. 33-46
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Tidskriftsartikel (refereegranskat)abstract
- Ion cyclotron resonance frequencies (ICRF) mode conversion has been developed for localized on-axis and off-axis bulk electron heating on the JET tokamak. The fast magnetosonic waves launched from the low-field side ICRF antennas are mode-converted to short-wavelength waves on the high-field side of the He-3 ion cyclotron resonance layer in D and He-4 plasmas and subsequently damped on the bulk electrons. The resulting electron power deposition, measured using ICRF power modulation, is narrow with a typical full-width at half-maximum of approximate to30 cm (i.e. about 30% of the minor radius) and the total deposited power to electrons comprises at least up to 80% of the applied ICRF power. The ICRF mode conversion power deposition has been kept constant using He-3 bleed throughout the ICRF phase with a typical duration of 4-6 s, i.e. 15-40 energy confinement times. Using waves propagating in the counter-current direction minimizes competing ion damping in the presence of co-injected deuterium beam ions.
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| 3. |
- Zastrow, K. D., et al.
(författare)
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Tritium transport experiments on the JET tokamak
- 2004
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Ingår i: Plasma Physics and Controlled Fusion. - 0741-3335 .- 1361-6587. ; 46, s. B255-B265
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Tidskriftsartikel (refereegranskat)abstract
- An overview is given of the experimental method, the analysis technique and the results for trace tritium experiments conducted on the JET tokamak in 2003. Observations associated with events such as sawtooth collapses, neo-classical tearing modes and edge localized modes are described. Tritium transport is seen to approach neo-classical levels in the plasma core at high density and low q(95), and in the transport barrier region of internal transport barrier (ITB) discharges. Tritium transport remains well above neo-classical levels in all other cases. The correlation of the measured tritium diffusion coefficient and convection velocity for normalized minor radii r/a = [0.65, 0.80] with the controllable parameters q95 and plasma density are found to be consistent for all operational regimes (ELMy H-mode discharges with or without ion cyclotron frequency resonance heating, hybrid scenario and ITB discharges). Scaling with local physics parameters is best described by gyro-Bohm scaling with an additional inverse beta dependence.
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| 4. |
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| 5. |
- Gorini, Giuseppe, et al.
(författare)
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Neutron Emission from Beam-Injected Fast Tritons in JET Plasmas with Reversed or Monotonic Magnetic Shear.
- 2004
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Ingår i: 31st EPS Conference on Plasma Physics. ; , s. 4-
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The neutron emission from fast tritons in plasmas with different magnetic shearconfigurations has been investigated in a dedicated experiment on JET. Short pulses ofneutral beam injection were used to deposit fast tritons in deuterium plasmas. By comparingthe measured neutron yield with predictions based on DT reaction calculations, fast tritonlosses can be assessed. The latter are expected to be very low according to neoclassicalpredictions based on Fokker-Planck simulation [1]. Much larger “anomalous” beam-ionlosses (up to 40%) have been reported in TFTR experiments for plasma conditions withreversed magnetic shear [2]. The TFTR experiments indicated an excess DT rate in thesimulation and, to a lesser extent, in the DD rate and plasma stored energy. This wasinterpreted as anomalous beam-ion loss associated with reverse shear due to an unidentifiedloss mechanism. Evidence of a similar effect was searched for in the JET experimentsreported in this paper.
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