摘要:

It is shown that elongated field‐reversed configurations based on the Maschke–Hernegger solution of the Grad–Shafranov equation are unstable to internal tilting. The particle transport properties across the flux surfaces of such a model are also considered in the limit of large elongation of the separatrix. An estimation of the time of confinement of particles in terms of classical conductivity, which is lower than previous estimates, is given.

ISSN:0031-9171    

DOI:10.1063/1.864673

出版商:AIP    

年代:1984

数据来源: AIP

摘要:

Wave absorption near the electron cyclotron gyrofrequency by the current‐carrying energetic tail in tokamak plasmas is investigated. It is shown that by the proper choice of the angle of propagation, strong wave damping occurs for wave frequencies much less than the central electron cyclotron frequency and that the extraordinary mode can be launched from the low magnetic field side of the torus. It is also found that wave absorption is weakly dependent on the perpendicular temperature of the resonant particles.

ISSN:0031-9171    

DOI:10.1063/1.864674

出版商:AIP    

年代:1984

数据来源: AIP

摘要:

The average force acting on a current‐carrying plasma column is calculated when a straight multipolar helical winding is displaced laterally with respect to the plasma, whose average position is kept fixed by a uniform external transverse magnetic fieldBx. This nonsymmetric equilibrium problem is solved for force‐freej/B=const plasmas by Fourier‐analyzing plasma and vacuum fields into helical harmonics and numerically solving the free boundary interface for their amplitudes. In the stellarator limit the average helical force is as predicted from stellarator expansion theory. In the new OHTE limit, bothl=2 andl=3 reversed pitch pinches are repelled from the helix. A simple explanation is offered in terms of plasma diamagnetism to the helical field.

ISSN:0031-9171    

DOI:10.1063/1.864675

出版商:AIP    

年代:1984

数据来源: AIP

摘要:

It is shown that the Vlasov equation based on the Lorentz force equation does not describe inverse bremsstrahlung since the force by inverse bremsstrahlung is not included in the Lorentz force equation. It is also shown that quasilinear theory based on the classical Vlasov equation can adequately explain inverse bremsstrahlung.

ISSN:0031-9171    

DOI:10.1063/1.864651

出版商:AIP    

年代:1984

数据来源: AIP

摘要:

The theory of total heat transfer to cylindrical collectors in collisionless plasma flow with no magnetic field is presented. The treatment has been done for orbit‐motion‐limited conditions (Debye length sufficiently large), for the speed ratioS=U/(2kT/m)1/2of the flow velocity to the most probable ion thermal velocity from 0 to 10, and for various values of the nondimensional collector potential &khgr;p=qVp/kT.

ISSN:0031-9171    

DOI:10.1063/1.864676

出版商:AIP    

年代:1984

数据来源: AIP

摘要:

Simple analytic relations are derived for the floating potential of a solid object in contact with a magnetized plasma as a function of the electron/ion mass ratio, the electron/ion temperature ratio, and the secondary electron emission coefficient. Simple analytic relations are also obtained for the sheath transmission factors, i.e., the particle and energy fluxes to floating and nonfloating surfaces. These analytic formulations, derived from a fluid model treatment of ion flow, are found to give results in close agreement with results derived from more complex analysis based on kinetic theory and numerical models. Tokamak scrape‐off plasmas are often characterized by ion distributions which have finite drift velocities at the point where the ions enter the scrape‐off plasma from the main plasma (via cross‐field diffusion). The Bohm criterion governing the drift velocity of ions as they enter the electrostatic sheath in front of a limiter, divertor plate, or probe is generalized for this case.

ISSN:0031-9171    

DOI:10.1063/1.864677

出版商:AIP    

年代:1984

数据来源: AIP

摘要:

An experiment is described in which plasma flow to a tokamak limiter is controlled through the use of a local toroidal divertor coil mounted inside the limiter itself. This coil produces a local perturbed fieldBCapproximately equal to the local unperturbed toroidal fieldBT&bartil;3 kG, such that whenBCadds toBTthe field lines move into the limiter and the local plasma flow to it increases by a factor as great as 1.6, and whenBCsubtracts fromBTthe field lines move away from the limiter and the local plasma flow to it decreases by as much as a factor of 4. A simple theoretical model is used to interpret these results. Since these changes occur without significantly affecting global plasma confinement, such a control scheme may be useful for optimizing the performance of pumped limiters.

ISSN:0031-9171    

DOI:10.1063/1.864678

出版商:AIP    

年代:1984

数据来源: AIP

摘要:

Using a launching structure consisting of four large diameter hemispherical grids located at the corners of a square, it is observed that the amplitude of a resonantly produced soliton is greater than ten times the value of an individual soliton. This observation extends to three dimensions Kaup’s conjecture that the two‐dimensional resonance‐soliton creation requires a finite interaction tune.

ISSN:0031-9171    

DOI:10.1063/1.864679

出版商:AIP    

年代:1984

数据来源: AIP

摘要:

Reduction of stimulated Brillouin scattering by the generation of higher ion wave harmonics is investigated. A theory model is derived which includes all harmonics. A simplified model based on the truncation to second harmonic ion waves reveals several interesting features. When damping and detuning are neglected the reflectivity is drastically reduced in a low‐density plasma (ne<0.25ncr), but the solution turns phase unstable at low reflectivity levels. Finite damping of ion waves extends the range of validity of the model. Still nonlinear damping of the primary decay may considerably exceed the linear damping, rendering the generation of the second harmonic an important mechanism. A large detuning of the second harmonic is required before it can be considered decoupled. The strong interaction between the ion waves introduces a power shift which is able to dynamically reduce the Brillouin reflectivity. Undersone parameter conditions the reflectivity approaches an oscillatory steady state. The accuracy of the second harmonic model rapidly improves as damping and detuning of the ion waves increase, suggesting that harmonic generation is important in a medium‐length (L/Lg<10), slightly damped plasma.

ISSN:0031-9171    

DOI:10.1063/1.864652

出版商:AIP    

年代:1984

数据来源: AIP

摘要:

Hot electron emission from a uv laser produced plasma with incident intensities 8×1013–2×1015W/cm2was measured by means of an electron spectrometer. Because of the small hot electron population, the self‐consistent target potential due to escaped electrons may be considered for the first time in the data reduction. The total energy in hot electrons of temperature 50 keV is shown to be ≲10−3of the incident laser energy. The target potential ≲80 kV. The hot electron temperature is essentially independent of intensity, the angular distribution of electron emission shows a weak polarization asymmetry, and the intensity threshold of hot electron production is 5×1013W/cm2, all consistent with the two‐plasmon decay instability being responsible for heating the electrons. The predicted spectrum of plasma waves is such that the accelerated electrons should be directed into the plasma almost parallel to the laser axis. Because only a small fraction of these electrons are reflected backwards to the detector, the x‐ray yield is a factor of 20 higher than the escaped electrons would indicate.

ISSN:0031-9171    

DOI:10.1063/1.864647

出版商:AIP    

年代:1984

数据来源: AIP