摘要:

A systematic study of the electromagnetic effects on the toroidal ion temperature gradient mode is presented using the local and nonlocal theories with the full kinetic terms. For the nonlocal study, a numerical code is developed to solve the electromagnetic gyrokinetic equation in the ballooning space. The electromagnetic coupling to the shear Alfve´n mode is shown to give a stabilization of the toroidal temperature gradient mode at almost the same plasma pressure as that at which the kinetically modified magnetohydrodynamic (MHD) ballooning mode becomes destabilized. The transitional &bgr; value is shown to be lower in the full kinetic description than in the fluid theory. Possible correlations of these stability results with experimental observations are discussed.

ISSN:0899-8221    

DOI:10.1063/1.860623

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

The stability of toroidicity‐induced Alfve´n eigenmodes (TAE) is investigated in general tokamak equilibria with finite aspect ratio and finite plasma beta. The finite orbit width of the hot particles and the collisional damping of the trapped electrons are included. For the trapped hot particles, the finite orbit width is found to be stabilizing. For the circulating hot particles, the finite orbit width effect is stabilizing for larger values ofvh/vA(≳1) and destabilizing for smaller values ofvh/vA(<1), wherevhis the hot particle speed andvAis the Alfve´n speed. The collisional damping of the trapped electrons is found to have a much weaker dependence on the collision frequency than the previous analytic results. The contribution of the curvature term to the trapped electron collisional damping is negligible compared to that of the parallel electric field term for typical parameters. The calculated critical hot particle beta values for the TAE instability are consistent with the experimental measurements.

ISSN:0899-8221    

DOI:10.1063/1.860572

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

The correlation between edge radiation, electron temperature, and density fluctuations has been studied in the vicinity of the upper poloidal limiter of the TJ‐I tokamak [Phys. Fluids B4, 4007 (1992)]. When edge impurity radiation is strongly peaked in the proximity of the limiter radius, electron temperature fluctuations are notably higher than density fluctuations. Results suggest that edge turbulence may be driven by radiative instabilities.

ISSN:0899-8221    

DOI:10.1063/1.860962

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

The magnetohydrodynamic stability of a low‐pressure plasma confined along the magnetic field by the end walls that are perfectly reflecting the impinging particles is considered. It is shown that, if the magnetic field lines do not intersect the walls along the normal, a fast instability can develop. An explicit expression for the growth rate has been derived, and an analogy with the usual flute instability has been traced. The instability can play some role in the scrape‐off layers of tokamaks with poloidal limiter.

ISSN:0899-8221    

DOI:10.1063/1.860573

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Probe measurements over the two‐dimensional plasma cross section of the average and fluctuating density, electron temperature, and potential, as well as the Reynolds stress, have been made in the Interchangeable Module Stellarator (IMS) [D. T. Anderson, J. A. Derr, and J. L. Shohet, IEEE Trans. Plasma Sci.PS‐9, 212 (1981)]. These measurements were performed at two magnetic field strengths, and also when a positively biased electrode induces a poloidal plasma flow. The data shows the fluctuation‐induced transport to be poloidally asymmetric and dependent upon the location of the electron cyclotron resonance position, and upon the electrode biasing. The induced poloidal plasma flow changes the nominally outward fluctuation‐induced particle transport to be inward (negative radial transport) by changing the phase relationship of the density and potential oscillations. The amplitude of the density and potential fluctuations are, in general, not reduced by the sheared poloidal flow. Calculations are presented comparing the computed Reynolds stress induced poloidal plasma flows with the flow calculated from momentum balance.

ISSN:0899-8221    

DOI:10.1063/1.860574

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Previous numerical and analytic kinetic studies have investigated the influence of velocity shear on the ion temperature gradient (ITG) mode. These studies relied on a differential approximation to study mode structures withk⊥&rgr;i≪1. A recently developed gyrokinetic integral code is here used to explore the effects of sheared flows on the ITG mode for arbitrary values ofk⊥&rgr;iin sheared slab geometry. It is found that both the mode structure and eigenfrequencies predicted by the integral code can differ from the results obtained by the differential approach, even in theky&rgr;i≪1 limit. Although some trends predicted by the differential approximation are recovered by the integral approach, there are some significant differences. For example, the slight destabilizing effect observed for small values of the perpendicular velocity shear atk⊥&rgr;i≪1 is amplified when the integral approach is applied. In dealing with the higher radial eigenmodes, which can often exhibit the largest growth rates, it is emphasized that their finer radial structure usually dictates that the integral equation analysis is required. Results from the integral code are presented together with comparisons with results from the differential approach.  

ISSN:0899-8221    

DOI:10.1063/1.860575

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

An analysis of the radial structure of the ion‐temperature‐gradient‐driven mode is presented and the dependence of the radial correlation lengthLron parameters such as magnetic shear is discussed. It is found thatLrdecreases algebraically with increasing shear for moderate to large shear values, and it decreases exponentially with decreasing shear for low shear values. These results seem in qualitative agreement with several experiments which observe strong reduction of the transport coefficients close to the magnetic axis.

ISSN:0899-8221    

DOI:10.1063/1.860576

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

The effects of thermal trapped particles on then=1 internal kink mode are studied using drift kinetic theory. Strong modifications of the magnetohydrodynamic (MHD) results are found, and marginal stability generally occurs at nonzero rotation frequency. For equal electron and ion temperatures, the trapped particles increase the marginal poloidal beta atq=1 substantially above the MHD value. For unequal electron and ion temperatures, the drift resonance with the hotter species becomes increasingly destabilizing and for sufficiently unequal temperatures, this leads to instability below the ideal‐MHD threshold. Treatment of trapped thermal particles requires consideration of the effects of an electrostatic potential. The potential is weakly stabilizing for the internal kink mode. Furthermore, finite beta couples unstable, nearly electrostatic, trapped particle modes to the internal kink mode. At high beta, thermal fluctuations of the trapped particle modes can lead to significant internal kink displacements.

ISSN:0899-8221    

DOI:10.1063/1.860577

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Measurements of the radiative power loss are performed on the Extrap‐T1 reversed‐field pinch [Phys. Scr.44, 358 (1991)] using an absolutely calibrated vacuum ultraviolet spectrometer in the wavelength range between 100 and 1700 A˚. The contributions to the radiative power loss from deuterium, carbon, nitrogen, oxygen, and chlorine are measured. These partial radiative power losses are further divided into contributions from different ionization stages of these impurities. The additional contribution to the cooling rate due to ionization processes is estimated. Impurities are found to be a main contributor to the power loss in the initial phase of the discharge. Toward the end of the discharge, radiative power loss amounts to less than 10% of the input power, due to the decrease of the electron density. Because of the short particle confinement time and high recycling of impurities, specifically oxygen, the rate coefficient for radiative power loss per ion is only slightly reduced by the increase of the temperature beyond the temperature of maximum radiative power loss per ion.

ISSN:0899-8221    

DOI:10.1063/1.860578

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

The modulational instability development of Langmuir waves is investigated in highly collisional plasmas where the characteristic frequency &OHgr; of the modulated perturbations is much less than &ngr;eff, the effective electron collision frequency. It is demonstrated that the modulational instability for the situation considered is mostly determined by collisional effects (differential Joule heating nonlinearity), in contrast to the well‐known modulational instability in collisionless plasmas (where ponderomotive force nonlinearity dominates). Rates and thresholds of the instability are found in various limits. The modulational instability is most effective when the angles between a pump wave vector and wave vectors of the modulational perturbations are of order unity.

ISSN:0899-8221    

DOI:10.1063/1.860579

出版商:AIP    

年代:1993

数据来源: AIP