摘要:

The use of ICRF heating in plasmas containing a mixture of deuterium and tritium has been explored on the TFTR tokamak. A detailed exploration of heating at the second harmonic tritium cyclotron resonance has been carried out. Effective central heating has been demonstrated even in competition with additional edge absorption mechanisms. A new regime of effective heating via enhanced mode conversion to an ion Bernstein wave (IBW) has been demonstrated. This regime allows both on and off axis electron heating and current drive. The interaction of ICRF waves with alpha particles has been investigated. The threshold for toroidal Alfven eigenmode (TAE) instabilities was investigated in DT plasmas with H minority ICRF heating. The enhanced expulsion of fusion products by interaction with the fast wave or the mode‐converted IBW has been observed under certain conditions. ©1996 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.49556

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

During ICRF heating experiments, the new four‐strap A2 antennas on JET have coupled 16.5 MW of power into single null divertor plasmas (Fig. 1). In combined heating experiments a maximum of 32 MW has been achieved by adding 15 MW of hydrogen minority ICRH to 17 MW of neutral beam injection (NBI). This combined heating power is a record for the present campaign and was achieved in a high density, strongly radiating, reactor‐like scenario with ‘grassy’ ELMs. Central electron temperatures close to 15 keV have been obtained with both RF—only and combined heating in ELM—free plasmas which were created with high flux expansion in the divertor region and which were substantially triangular (&dgr;&bartil;0.3). Similar discharges were used to obtain the highest D‐D reactivity in JET with NBI. The addition of hydrogen minority ICRH to these plasmas increases both the reactivity and the H‐factor obtained by comparing the thermal energy content to the ITERH93‐P scaling. RF‐only H‐modes have been produced in plasmas with currents (Ip) up to 4.7 MA and the power thresholds are similar those with NBI. AtIp=4.7 MA and a toroidal field (Bt) of 3.2 T, a plasma energy content of 7 MJ was achieved with 8 MW of 51.3 MHz ICRH in 0&pgr;0&pgr; phasing. The heating efficiency, as determined from power modulation experiments, is close to 100% with 0&pgr;0&pgr; and 0&pgr;&pgr;0 phasing. The efficiency decreases for phasings such as 00&pgr;&pgr; and monopole which produce average values of the parallel wavevector less than 3.5 m−1. However, the recent introduction of a separator limiter at the center of one antenna has improved its heating efficiency for perpendicularly launched waves and such separators will be fitted to all antennas in the near future. ©1996 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.49521

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

ICRF has been applied at power levels up to of 4 MW for plasma heating with good results in the L‐ and H‐modes, alone and in combination with NI. Mainly minority heating has been applied so far, in some cases combined with second harmonic. Modulation experiments allowed to determine the power absorption efficiency, deposition profiles and the local heat conduction. The ICRF was also shown to have further interesting and beneficial effects on the plasma: the central impurity concentration of tungsten injected by Laser Blow Off was reduced, and a transiently improved energy confinement at the beginning of the NBI pulse was stabilized. The influence of plasma variations on the RF system and methods allowing stable operation, e.g. during the ELMy H‐mode, were studied. Coupling measurements were also used to examine SOL characteristics. Experiments comparing antennas with and without Faraday screen show only minor differences of their electrical properties and heating characteristics. ©1996 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.49561

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

ICRF heating experiments have been carried out in the Alcator C‐Mod tokamak at power levels up to 3.5 MW. Features of Alcator C‐Mod include high density operation, molybdenum plasma facing components, and a closed divertor configuration. The heating is accomplished with two two‐strap antennas each run with dipole phasing at 80 MHz in deuterium plasmas with a hydrogen minority resonant at 5.3 T. Plasmas withTi=4 keV andTe=5 keV atn¯e=1×1020m−3have been produced with 3.5 MW of heating power. The heating has been shown to be strongest with a low minority concentration (1–5%) and the resonance on axis. Forn¯e≳2×1020m−3, the centralZeffremains below 1.5 with more than 2.5 MW of applied rf power. L‐mode confinement scaling is observed both for ohmic and ICRF‐heated plasmas with some deterioration at higher densities. H‐mode transitions have been produced with the threshold for ELM‐free H‐modes at or below the ASDEX/DIII‐D scaling. Enhanced confinement with strongly peaked density profiles has been achieved by lithium pellet injection. Applying 3 MW of rf power shortly after pellet penetration producesTi0=4 keV and a factor of five increase in fusion neutron rate (up to 9×1013s−1), and an H‐mode transition. ©1996 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.49586

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

The first experiments to heat neutral‐beam‐fueled D‐T plasmas with ICRF were conducted during the past year on TFTR. These experiments were performed with full‐bore (R∼2.62 m) plasmas in the low recycling, ‘‘supershot’’ regime with confinement times exceeding two times the empirical L‐mode value. Up to 6 MW of RF were coupled into plasmas fueled by up to 24 MW of D‐T beam injection. Some discharges utilized all T beam fueling to maximize the effect of the second harmonic tritium absorption. Extensive Li‐pellet injection was employed in this regime in an attempt to reduce wall recycling and improve plasma confinement. Although significant second harmonic tritium heating was seen in some plasmas, many discharges were characterized by a degradation in performance and reactivity early in the neutral beam pulse as a result of enhanced recycling of impurities and deuterium from the carbon tile limiter. The proximity of the outboard limiter appears to have exacerbated attempts to limit this enhanced influx. ©1996 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.49538

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

High power ICRF heating and current drive experiments have been performed in a variety of plasma conditions during TFTR’s deuterium‐tritium phase. Second harmonic tritium heating was observed in D‐T Supershots, current drive was observed in He‐3/He‐4 mode conversion studies, current drive was observed in fast wave studies, the influence of H‐minority energetic tail ions on TAE modes and alpha particle induced TAE modes was studied, and the influence of ICRF on alpha particle and other energetic fusion product losses was observed. In each case, coupling of high rf power presented a unique set of operating conditions and challenges. The ICRF generators have undergone evolutionary upgrades, auxiliary circuit modifications have been added, and antenna conditioning scenarios have been refined. We assess the effect of these improvements on operating performance and describe our present limits under the different plasma conditions. ©1996 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.49546

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

ICH‐induced toroidal plasma rotation was initially observed from Doppler shift measurements of the FeXXV K&agr; line using the TFTR horizontal crystal spectrometer for discharges with ion cyclotron heating of 2 MW RF power and without any neutral beam power in a D(H) plasma. The magnitude of plasma rotation depended on the IC resonance location. The observed rotations were in the counter‐plasma‐current direction and of the order of 5×104m/s. Simple estimates relate the induced rotation to loss of ions from the plasma core. Later experimental results, as recorded by the charge exchange recombination spectrometer during beam blips at the end of the ICH pulse, with up to 6 MW of RF power in a4He(H) plasma provided the radial profile of rotation. ©1996 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.49555

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Direct electron heating obtained with a four‐element array phased at (0,&pgr;/2,&pgr;,3&pgr;/2) without a Faraday shield is compared with that obtained with a Faraday shield on the same antenna. ©1996 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.49502

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

The removal of the Faraday screen from one of the four ICRF antennas in ASDEX Upgrade and the achievement of the H‐mode with that antenna alone allowed for the first time H‐mode specific effects of screenless antenna operation to be analyzed in a divertor tokamak. Only in particular cases could small but consistent differences be seen as compared to an antenna with screen. The threshold power is marginally (<10%) higher for a screenless antenna. In the power range that has been reached with only one ICRF antenna (up to 1.3 MW, ELMy and ELM‐free conditions, but still near the threshold), there is a slight difference in quality of the H‐mode, reflected in a lower edge electron temperature and a lower total plasma energy for the antenna without screen (−10%). The screenless antenna was also operated in combination with neutral beam injection (type I ELMs) and under CDH conditions (small type III ELMs, detached divertor) with no significant differences to an antenna with screen. Only modulation experiments allowed to detect a minimal difference (<5%) in plasma stored energy under reversed field conditions, i.e. when the Faraday screen is misaligned to the magnetic field by about 30°, in favour of the antenna with screen. ©1996 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.49511

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Experimentation with TEXTOP tokamak using the ICR plasma heating together with an auxiliary heating system involving the neutral beam injection have allowed to extend the improved confinement mode to the high density regime. The third harmonic D heating and a new reactor coating with edge radiative cooling have given a strong increase of the neutron yield. ©1996 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.49514

出版商:AIP    

年代:1996

数据来源: AIP