摘要:

The properties of low frequency Alfven waves in hot, magnetically confined plasmas are quite unlike those in homogeneous media. Extensive theoretical studies have uncovered the Alfven continuum along with global Alfven eigenmodes (GAE). It has been suggested that such modes may be good candidates for rf heating below the ion cyclotron frequency. We present a unified investigation on PRETEXT of the structure of the global modes. These measurements are made using two phased toroidal antennas. The GAE are predicted to appear as resonances in the antenna loading resistance and have been observed earlier on TCA. We find that in addition to antenna resistance and inductance, signals from magnetic probes at the plasma surface also exhibit this resonant behavior. The plasma parameter dependence (i.e., the amplitude and location) of these resonancces is found in good agreement with the theory. Driven plasma density fluctuations with a rich spatial structure are predicted to develop at these resonances; we have observed this structure using a CO2lser interferometer. Results from the laser and impedance measurements along with antenna phasing permit assignment of mode numbers. Since the two‐antenna configuration can simultaneously excite more than one mode in the plasma, the resulting interference effects demand careful interpretation of the spatial and temporal mode structures seen. These interference effects provide both a challenge and an opportunity for an optimum antenna design in an Alfven heating experiment.

ISSN:0094-243X    

DOI:10.1063/1.35263

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

Experiments on Alfve´n Wave Heating are being carried out on TCA at a power level up to the ohmic heating power, and with a pulse length of 30‐60 msec. The applied frequency is 2.5 MHz. There is substantial heating of both electrons and ions, and a detailed power balance suggests that the heating rate is comparable with the rf power delivered by the antennae. There is a large increase in plasma density during the rf, which can reach +300% in some conditions. This density increase is insensitive to the machine conditioning. There is an increase in the radiated power loss from the plasma centre without the lateral screens, and we show that this is independent of the number of antennae used.

ISSN:0094-243X    

DOI:10.1063/1.35240

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

Alfve´n wave experiments are being conducted on the Tokapole II tokamak, backed up by theoretical work. Several antenna designs are being tested. Earlier results with antennas carrying current in a primarily toroidal direction have shown significant loading with a strong dependence on the angle of the currents w.r.t. the equilibrium field. In such cases magnetic probes detect strong signals in the scrape‐off region, and there is little or no evidence of bulk heating despite PRF/POHMIC∼ 30−50%. A new antenna design to allow launching with any polarization and upgraded diagnostics is being installed. The experimental antenna loading is compared to a slab model in the MHD limit, with given density and current profiles and zero pressure. The antenna is modeled by a single, thin folded strap in vacuum, with variable orientation. The effects of the far wall and of eigenmodes are removed by assuming that each Fourier component of the wave damps exponentially on the far side of the Alfve´n resonant surface. The calculated radiation resistance is in the milliohm range and varies slowly with antenna orientation.

ISSN:0094-243X    

DOI:10.1063/1.35244

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

The modular and periodic antenna structure in TCA is shown to produce an extremely pure spectrum of excited waves. This purity, together with precise measurements of the antenna loading in different parts of the spectrum, has allowed us to demonstrate that it is essential to include both toroidal coupling and the Hall effect (&ohgr;/&ohgr;ci≠0) in order to explain our results. We show that toroidicity produces coupling from the directly excited ‖m‖=1 wave to ‖m‖=0,2 waves. Discrete Alfve´n Waves are also seen for ‖m‖=0,2 in addition to the directly driven ‖m‖=1. The importance of the Hall effect is most visible when a travelling wave is excited, in which case the antenna loading depends on the direction of the wave imposed. We present the antenna loading found with different excitation structures and discuss the implications on the design of AWH antenna systems.

ISSN:0094-243X    

DOI:10.1063/1.35254

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

Two quarter turn toroidal antennas are mounted in the midplane of the PRETEXT tokamak at the outer radius and located 180° apart toroidally. The currents in the antennas are run with relative phases of 0° and 180°. The tokamak is operated such that an extensive density scan is available on each shot. Magnetic probes located at the plasma edge monitor all rf field components. Global Alfve´n Eigenmodes are seen as resonances in the antenna resistance and inductance; these modes are also evident as resonances in the magnetic field components. Mode numbers suggested from these measurements and impedance values are compared with theoretical predictions1. CO2laser interferometer measurements of rf density profiles were present on shots at 2.1 Mhz and were used in mode identification.

ISSN:0094-243X    

DOI:10.1063/1.35266

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

The initial experiment to optimize an ICH system on TMX‐U is described.(AIP)

ISSN:0094-243X    

DOI:10.1063/1.35225

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

The PLT ICRF heating program is exploring the stability, confinement and heating properties of ICRF as applied to the PLT plasma. In the deuterium majority,3He minority mode aTd=5 keV, n¯e=3.7×1013cm−3, E≳100 kJ plasma has been obtained with the application of 4.25 MW of coupled ICRF power. In the deuterium majority, hydrogen minority regime direct second harmonic majority heating has been observed. Optimization studies including pellet injection are underway. Experiments with direct ion Bernstein wave (IBW) heating in both the minority heating regime and single ion regime are underway.

ISSN:0094-243X    

DOI:10.1063/1.35270

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

During the initial pulsed phase of operation of ATF, a variety of heating schemes will be undertaken, including ECH, ICRF heating, and neutral beam heating. Various ICRF heating methods will be examined, using existing rf sources. During later long‐pulse or steady‐state operation of ATF, ICRF heating may be selected for a high‐power upgrade. The design of the ATF ICRF heating launchers will utilize advances made in the national rf development program at ORNL.

ISSN:0094-243X    

DOI:10.1063/1.35226

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

New concepts for drift pumping a thermal barrier with RF in TMX device are proposed.(AIP)

ISSN:0094-243X    

DOI:10.1063/1.35227

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

The ion cyclotron heating on TEXTOR has now reached the megajoule level. Pulses of 1 MW lasting 1 s have been achieved in a predominantly mode‐conversion regime in a (H)‐D plasma yielding, after machine conditioning by means of carbonization, discharges characterized by: stationarity of all plasma parameters, lilttle if no impurity increases, and strong loop voltage decreases resulting in a total power reaching already six times the remaining ohmic input power. The global energy confinement is lower and the power deposition profile broader than in the OH phase. The heating efficiency is found to be comparable to that of neutral beam heating experiments in the so‐called L‐mode.

ISSN:0094-243X    

DOI:10.1063/1.35271

出版商:AIP    

年代:1985

数据来源: AIP