| 1. |
|
|
| 2. |
|
|
| 3. |
|
|
| 4. |
- Ongena, J., et al.
(författare)
-
Recent progress on JET towards the ITER reference mode of operation at high density
- 2001
-
Ingår i: Plasma Physics and Controlled Fusion. - 0741-3335 .- 1361-6587. ; 43, s. A11-A30
-
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.
|
|
| 5. |
- Monier-Garbet, P, et al.
(författare)
-
Impurity-seeded ELMy H-modes in JET, with high density and reduced heat load
- 2005
-
Ingår i: Nuclear Fusion. - : IOP Publishing. - 0029-5515 .- 1741-4326. ; 45:11, s. 1404-1410
-
Tidskriftsartikel (refereegranskat)abstract
- Experiments performed at JET during the past two years show that, in high triangularity H-mode plasmas with I-p = 2.5 MA, n(e)/n(Gr) approximate to 1.0, it is possible to radiate separately up to approximate to 40% of the total injected power on closed flux surfaces in the pedestal region (argon seeding) and up to approximate to 50% of the injected power in the divertor region (nitrogen seeding), while maintaining the confinement improvement factor at the value required for ITER, H98(y, 2) 1.0. The total radiated power fraction achieved in both cases (65-70%) is close to that required for ITER. However, Type I ELMS observed with impurity seeding have the same characteristics as that observed in reference pulses without seeding: decreasing plasma energy loss per ELM with increasing pedestal collisionality. One has to reach the Type III ELM regime to decrease the transient heat load to the divertor to acceptable values for ITER, although at the expense of confinement. The feasibility of an integrated scenario with Type-III ELMS, and q(95) = 2.6 to compensate for the low H factor, has been demonstrated on JET. This scenario would meet ITER requirements at 17 MA provided that the IPB98 scaling for energy content is accurate enough, and provided that a lower dilution is obtained when operating at higher absolute electron density.
|
|
| 6. |
- Strachan, J. D., et al.
(författare)
-
Modelling of carbon migration during JET C-13 injection experiments
- 2008
-
Ingår i: Nuclear Fusion. - : IOP Publishing. - 0029-5515 .- 1741-4326. ; 48:10
-
Tidskriftsartikel (refereegranskat)abstract
- JET has performed two dedicated carbon migration experiments on the final run day of separate campaigns ( 2001 and 2004) using (CH4)-C-13 methane injected into repeated discharges. The EDGE2D/NIMBUS code modelled the carbon migration in both experiments. This paper describes this modelling and identifies a number of important migration pathways: ( 1) deposition and erosion near the injection location, ( 2) migration through the main chamber SOL, (3) migration through the private flux region (PFR) aided by E x B drifts and ( 4) neutral migration originating near the strike points. In H-Mode, type I ELMs are calculated to influence the migration by enhancing erosion during the ELM peak and increasing the long-range migration immediately following the ELM. The erosion/re-deposition cycle along the outer target leads to a multistep migration of C-13 towards the separatrix which is called 'walking'. This walking created carbon neutrals at the outer strike point and led to 13C deposition in the PFR. Although several migration pathways have been identified, quantitative analyses are hindered by experimental uncertainty in divertor leakage, and the lack of measurements at locations such as gaps and shadowed regions.
|
|
| 7. |
- Hellsten, Torbjörn, et al.
(författare)
-
Fast wave current drive in JET ITB-plasma
- 2005
-
Ingår i: AIP Conference Proceedings. - : AIP. - 0094-243X. ; , s. 273-278
-
Konferensbidrag (refereegranskat)abstract
- Fast wave current drive has been performed in JET plasmas with internal transport barriers, ITBs, and strongly reversed magnetic shear. Although the current drive efficiency of the power absorbed on the electrons is fairly high, only small effects are seen in the central current density. The main reasons are the parasitic absorption of RF power, the strongly inductive nature of the plasma and the interplay between the fast wave driven current and bootstrap current. The direct electron heating in the FWCD experiments is found to be strongly degraded compared to that with the dipole phasing.
|
|
| 8. |
- Coad, J. P., et al.
(författare)
-
Erosion/deposition in JET during the period 1999-2001
- 2003
-
Ingår i: Journal of Nuclear Materials. - 0022-3115 .- 1873-4820. ; 313, s. 419-423
-
Tidskriftsartikel (refereegranskat)abstract
- Coated divertor and wall tiles exposed in JET for the 1999-2001 operations have been used to assess erosion/deposition. Deposited films of up to 90 mum thickness at the inner wall of the divertor tiles are, for the most part, enriched in beryllium and other metals, whilst carbon is probably chemically sputtered from these tiles and transported to shadowed regions of the inner divertor. However, from the composition at the surface of the tiles, it appears that the chemical erosion was 'switched off' by reducing the JET vessel wall temperature for the last part of the operations to 200 degreesC. Thick powdery deposits localised at the ion transport limit at each corner of the divertor may be due to physical sputtering. Erosion of the coatings is seen at the outer divertor wall, and on all the inner wall and outer limiter tiles.
|
|
| 9. |
|
|
| 10. |
- Andrew, P, et al.
(författare)
-
Outer divertor target deposited layers during reversed magnetic field operation in JET
- 2005
-
Ingår i: Journal of Nuclear Materials. - : Elsevier BV. - 0022-3115 .- 1873-4820. ; 337:1-3, s. 99-103
-
Tidskriftsartikel (refereegranskat)abstract
- Divertor surface temperatures are significantly affected by the presence of deposited surface layers. This phenomenon can be used to monitor deposited layer evolution on a shot-by-shot basis. It was found that during an experimental campaign where the B x del B direction was reversed that the outer target, normally an erosion zone, became a deposition zone.
|
|
