| 1. |
- Ongena, J., et al.
(författare)
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Overview of recent results on Heating and Current Drive in JET
- 2007
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Ingår i: RADIO FREQUENCY POWER IN PLASMAS. - : AIP. ; , s. 249-256
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Konferensbidrag (refereegranskat)abstract
- Recent progress on heating and current drive on JET is reported. Topics discussed are: high power coupling of ICRF/LH at ITER relevant antenna/launcher-separatrix distances, succesfull demonstration of 3 dB couplers for ELM tolerance of the ICRF system, influence of ICRF on LH operation, rotation studies in plasma without external momentum with standard and enhanced JET toriodal field ripple, studies of different ICRF heating schemes and of NTM avoidance schemes using Ion Cyclotron Current Drive. A brief outlook on future plans for experiments at JET is given.
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| 2. |
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| 3. |
- Mantsinen, M. J., et al.
(författare)
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Modification of sawtooth oscillations with ICRF waves in the JET tokamak
- 2007
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Ingår i: RADIO FREQUENCY POWER IN PLASMAS. - : AIP. - 9780735404441 ; , s. 35-42
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Konferensbidrag (refereegranskat)abstract
- Methods of modifying sawtooth oscillations using waves in the ion cyclotron range of frequencies (ICRF) in the JET tokamak are presented. Examples of sawtooth stabilization by ICRF-accelerated high-energy ions are shown, including experiments with ICRF-acceleration of 4He-beam ions to simulate the effects of fusion born alpha particles. With high power ICRF heating in low-density plasmas, fast ion stabilization of sawteeth is lost and a new type of small-period and small-amplitude sawteeth appears. ICRF-induced radial pinch with toroidally asymmetric waves is found to be useful in affecting the radial profile of the ICRF-driven fast ion populations and thereby their influence on sawteeth. Ion cyclotron current drive (ICCD) applied close to the sawtooth inversion radius is effective in modifying the sawtooth period. The latest achievements include the successful application of ICCD to shorten the fast-ion-induced long-period sawteeth and thereby avoid triggering of neoclassical tearing modes (NTMs).
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| 4. |
- Chapman, I. T., et al.
(författare)
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The physics of sawtooth stabilization
- 2007
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Ingår i: Plasma Physics and Controlled Fusion. - 0741-3335 .- 1361-6587. ; 49:12B, s. B385-B394
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Tidskriftsartikel (refereegranskat)abstract
- Long period sawteeth have been observed to result in low-beta triggering of neo-classical tearing modes, which can significantly degrade plasma confinement. Consequently, a detailed physical understanding of sawtooth behaviour is critical, especially for ITER where fusion-born a particles are likely to lead to very long sawtooth periods. Many techniques have been developed to control, and in particular to destabilize the sawteeth. The application of counter-current neutral beam injection (NBI) in JET has resulted in shorter sawtooth periods than in Ohmic plasmas. This result has been explained because, firstly, the counter-passing fast ions give a destabilizing contribution to the n=1 internal kink mode-which is accepted to be related to sawtooth oscillations-and secondly, the flow shear strongly influences the stabilizing trapped particles. A similar experimental result has been observed in counter-NBI heated plasmas in MAST. However, the strong toroidal flows in spherical tokamaks mean that the sawtooth behaviour is determined by the gyroscopic flow stabilization of the kink mode rather than kinetic effects. In NBI heated plasmas in smaller conventional aspect-ratio tokamaks, such as TEXTOR, the flow and kinetic effects compete to give different sawtooth behaviour. Other techniques applied to destabilize sawteeth are the application of electron cyclotron current drive (ECCD) or ion cyclotron resonance heating (ICRH). In JET, it has been observed that localized ICRH is able to destabilize sawteeth which were otherwise stabilized by a co-existing population of energetic trapped ions in the core. This is explained through the dual role of the ICRH in reducing the critical magnetic shear required to trigger a sawtooth crash, and the increase in the local magnetic shear which results from driving current near the q=1 rational surface. Sawtooth control in ITER could be provided by a combination of ECCD and co-passing off-axis negative-NBI fast ions.
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| 5. |
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| 6. |
- Krusa, M., et al.
(författare)
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Oxidative cellulose degradation by cellobiose dehydrogenase from Phanerochaete chrysosporium : A model compound study
- 2005
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Ingår i: Holzforschung. - 0018-3830 .- 1437-434X. ; 59:3, s. 263-268
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Tidskriftsartikel (refereegranskat)abstract
- Cellobiose dehydrogenase (CDH) is an extracellular enzyme produced by various wood-degrading fungi. It oxidizes cellobiose to cellobionolactone under reduction of molecular oxygen to hydrogen peroxide, and Fe3+ to Fe2+. These activated agents can thereafter form highly reactive hydroxyl radicals, which depolymerize wood polymers. In this work, cellulose depolymerization by CDH was studied using a model compound, methyl beta-D-glucopyranoside. The formation of glucose, arabinose, gluconic acid, erythrulose and formaldehyde were detected and a mechanism for the reaction is proposed. The biological importance of this enzyme-initiated reaction is discussed.
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