摘要:

Radio frequency ( f=350 kHz) inductive breakdown has been studied in a toroidal stellarator. The time delay between the application of the radio frequency pulse and the buildup of detectable plasma density is measured as a function of the discharge parameters. It is shown that the confinement time of energetic electrons (∼100 eV), produced during the breakdown, may be deduced from the breakdown characteristics. The experimentally determined confinement times are compared with predictions of neoclassical transport theory and are found to have functional dependence on the discharge parameters approximately consistent with plateau scaling, but to be shorter than predicted by the neoclassical diffusion model.

ISSN:0031-9171    

DOI:10.1063/1.865625

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

Increases in average density have been observed during lower‐hybrid current‐drive experiments (LHCD) on the Versator II tokamak [Phys. Rev. Lett.48, 152 (1982)], and on other LHCD experiments where inductive‐Ohmic and lower‐hybrid current drive are combined. In the present experiment it is found that this density increase is the result of an improvement in global particle confinement time &tgr;pin comparison to purely Ohmic discharges with similar plasma parameters. Furthermore, it is found that the improved confinement deteriorates when the anomalous Doppler relaxation instability of the anisotropic high‐energy electron tail becomes unstable during LHCD, and the loss rate of tail electrons increases. However, energetic electron losses alone are at least an order of magnitude too small to explain this deterioration in particle confinement.

ISSN:0031-9171    

DOI:10.1063/1.865626

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

Experimental measurements of the equilibrium in the S‐1 spheromak [M. Yamada, J. Sinnis, H. P. Furth, M. Okabayashi, G. Sheffield, T. H. Stix, and A. M. M. Todd, inProceedingsoftheUS‐JapanSymposiumonCompactTorusesandEnergeticParticleInjection(Princeton Plasma Physics Laboratory, Princeton, NJ, 1979), p. 171] by use of magnetic probes inside the plasma show that the final magnetic equilibrium is one that has relaxed close to the Taylor (minimum‐energy) state, even though the plasma is far from that state during formation. The comparison is made by calculating the two‐dimensional &mgr; profile of the plasma from the probe data, where &mgr; is defined as &mgr;0 j∥/B. Measurements using a triple Langmuir probe proved evidence to support the conclusion that the pressure gradients in the relaxed state are confined to the edge region of the plasma.

ISSN:0031-9171    

DOI:10.1063/1.865627

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

An experimental study of the confinement properties of a low‐(average) beta discharge plasma in a spindle cusp magnetic field is described. Electron and ion densities, space potentials, and plasma flow velocities were measured in the ring and point cusps. The leak width of the escaping plasma was measured over a large range of magnetic field strengths and neutral pressures. Leak widths varying between the hybrid gyrodiameter and the ion gyrodiameter were observed. The dependence of the leak width on neutral pressure and magnetic field is accounted for by a simple model in which plasma diffuses across the magnetic field as a result of neutral particle collisions while streaming out of the cusps along the magnetic field lines. At the lowest neutral pressures investigated, the scaling of the leak width with magnetic field strength suggests that noncollisional mechanisms (e.g., Bohm diffusion) determine the leak width.

ISSN:0031-9171    

DOI:10.1063/1.865628

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

The evolution of a magnetic bubble resulting from the expansion of Nd‐laser‐generated plasma into a photoionized magnetized background plasma is examined experimentally and is compared with theory and computer simulations. The initial laser‐produced plasma speed is greater than the plasma sound and Alfve´n speeds and is energetic enough to be unmagnetized; the background plasma is effectively magnetized and its density is varied from the collisionless to the collisional regimes. The data support theoretical predictions that the initial expansion of the magnetic bubble is dominated by the uncoupled laser‐produced plasma.

ISSN:0031-9171    

DOI:10.1063/1.865578

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

The trend of energy decay of three‐dimensional isotropic turbulence with a particular initial condition for various Reynolds numbers is investigated by comparing the data obtained using different methods. The question is then raised whether the curves of energy decay for different Reynolds numbers can cross each other.

ISSN:0031-9171    

DOI:10.1063/1.865579

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

A new pure electron‐plasma containment apparatus exhibits radial losses approximately 20 times smaller than the prior apparatus. However, the new containment times show the same (L/B)−2scaling with plasma column length and magnetic field as obtained previously. The radial transport is apparently induced by small irregularities that break the cylindrical symmetry of the magnetic and electric containment fields. The fact that the two devices show the same (L/B)−2scaling suggests the dominance of a single generic process, although this process has not yet been identified.

ISSN:0031-9171    

DOI:10.1063/1.865580

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

Time‐resolvedK&agr;emission from targets struck by relativistic electrons is used as a diagnostic of the electron flow in pinch relativistic electron beam diodes. Pinch dynamics in thin foil anode diodes are studied. A transition from a regime of reflexing pinch to a regime of flow dominated by ion emission from the anode is observed. Current fluctuations in the pinch region are also detected.

ISSN:0031-9171    

DOI:10.1063/1.865581

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

The validity of a stability argument in which only the ambipolar potential is perturbed to select a suitable solution when multiple ambipolar roots occur is questioned.

ISSN:0031-9171    

DOI:10.1063/1.865582

出版商:AIP    

年代:1986

数据来源: AIP

ISSN:0031-9171    

DOI:10.1063/1.866024

出版商:AIP    

年代:1986

数据来源: AIP