摘要:

Single integral expressions for the particle loss rate from an electrostatic trap withZe&Fgr;0/T≫1 are derived that span all possible mirror ratiosR, where &Fgr;0,Z, andTare the potential well depth, charge number, and species temperature. The two expressions are shown to be identical for a range of intermediateRso that one expression is valid for small to intermediateR(R≲1), while the other is appropriate from intermediate to largeR(R≫T/Ze&Fgr;0). Three particularly simple analytic limits are found to exist: (i)R≪T/Ze&Fgr;0, (ii)T/Ze&Fgr;0≪R≲1, and (iii)R≫1.

ISSN:0031-9171    

DOI:10.1063/1.865155

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

In this paper, an account is presented of an investigation into the propagation of large amplitude space‐charge waves in an inhomogeneous waveguide. The study is motivated by the possibility of using these waves for the collective acceleration of ions. Measurements are reported that show an increase in the wave phase velocity as the guide diameter, and hence the effective plasma frequency is decreased. Results are also presented which show that the wave phase velocity is a function of its amplitude, and that large amplitude, nonlinear waves propagate more slowly than those described by linear theory. The results demonstrate that it is possible to control the wave propagation characteristics, and therefore indicate the electron‐beam‐supported slow space‐charge waves provide a suitable medium for collective ion acceleration. Finally, a summary is given of possible advantages of an electron beam‐wave accelerator over those using externally generated rf fields.

ISSN:0031-9171    

DOI:10.1063/1.865156

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

Intense relativistic electron beams fired into air at varying pressures display a wide range of microwave signatures. These experiments held beam current, energy, and pulse length constant while varying gas pressure. Our observing window is 10 to 40 GHz. At low pressures (<10 mTorr) exponential spectra result, consistent with beam reflexing or virtual cathode oscillations. Above 20 mTorr the spectrum flattens and suggests collective emission at the beam‐generated plasma frequencies. Power falls linearly with pressure above 20 mTorr, until electron‐Neutral collisions damp the emission at a few Torr. However, weak 10 GHz emission appears at full atmospheric pressure.

ISSN:0031-9171    

DOI:10.1063/1.865157

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

An expression of the light pressure &Pgr; is derived for the case of a nearly monochromatic electromagnetic wave with arbitrarily time‐dependent amplitude. Thereby &Pgr; is defined as the time‐averaged force density exerted on a plasma by the wave. The resulting equations are valid for both transverse and longitudinal waves. The light pressure turns out to consist of two components: the well‐known gradient‐type term and a new nonstationary solenoidal term. This is true for warm as well as cold plasmas. The importance of the new term for the generation of static magnetic fields is shown, and a model in which shear forces may result is given. Formulas for the nonstationary light pressure developed previously are discussed.

ISSN:0031-9171    

DOI:10.1063/1.865158

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

A kinetic stability theorem is developed for relativistic non‐neutral electron flow in a planar high‐voltage diode with applied magnetic field. The effects of strong inhomogeneities and intense self‐electric and self‐magnetic fields are retained in the analysis in a fully self‐consistent manner. Use is made of global (spatially averaged) conservation constraints satisfied by the fully nonlinear Vlasov–Maxwell equations, assuming electromagnetic perturbations with extraordinary‐mode polarization, and space‐charge‐limited flow withE0x(x=0)=0 at the cathode. It is also assumed that they‐averaged,x‐directed net flux of particles,ymomentum, and energy, vanish identically at the cathode (x=0) and at the anode (x=d). It is shown that the class of self‐consistent Vlasov equilibriaf0b(H,Py) is stable for small‐amplitude perturbations, providedf0bis a monotonic decreasing function ofH−VbPy, i.e., provided ∂f0b/∂(H−VbPy)≤0. Here,His the energy andPyis the canonicalymomentum. The generality of thissufficientconditionforstabilityshould be emphasized. First, the derivation of the stability theorem has not been restricted to a specific choice off0b(H−VbPy). Moreover, the fully non‐neutral electron equilibria are generally characterized by strong spatial inhomogeneities and intense self‐electric and self‐magnetic fields. For the class of equilibria with ∂f0b/∂(H−VbPy)≤0, it is also shown that the density profilen0b(x)=∫ d3p f0bandx–xpressure profileP0b(x) =∫ d3p vxpxf0bdecrease monotonically from the cathode (x=0) to the anode (x=d) provided the applied magnetic field at the anode (Ba) is sufficiently strong that (Vb/c)Ba≥4&pgr;e ∫d0 dx’ n0b(x’).

ISSN:0031-9171    

DOI:10.1063/1.865159

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

It is shown here that the Rayleigh–Taylor instability in a device like a theta pinch has two different stages. The first stage is during the implosion phase of the theta pinch, and the second stage initiates after the formation of the plasma column. Termination of the first stage and evolution of the second stage from growth to a highly nonlinear stage and eventual wave breaking is presented by holographic interferometry. Though the instability in the first stage has been investigated before, here by employing microscopic theory it is shown that the magnetic field gradient is the driving mechanism of the instability in the latter stage.

ISSN:0031-9171    

DOI:10.1063/1.865161

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

Ballooning instabilities are studied in the Berkeley multiple mirror experiment. Counterstreaming theta pinch and Marshall gun source hydrogen plasmas are used to achieve a high beta ( &bgr;>25%), where &bgr; is the ratio of plasma to magnetic pressure at temperaturesTe=Ti≊15 eV. Four magnetic field configurations are investigated, each at varying mirror ratios, to explore a range of drive and connection length parameters. In two of these the magnetic field is pulsed from a stable to a locally unstable configuration for initiation of ballooning activity. The other two (static) configurations are a weakly unstable local field region, and the standard linked quadrupole multiple‐mirror configuration. Depending on the configuration, critical &bgr;’s are found for the onset of ballooning that vary from 5% for the most unstable configuration to greater than 25% for the standard multiple‐mirror configuration. Them=1 azimuthal mode is predominant, with some admixture ofm=2. The experimental results are compared with predictions from a magnetohydrodynamic theory. In the model the pressure is taken to be isotropic and constant along the axis, except in the diverging field regions at the device ends where the pressure falls to maintain beta constant, consistent with experimental observations. The theoretical results generally predict somewhat higher critical betas for them=1 mode than those observed. Estimates of the effect of finite Larmor radii, nearby conducting walls, axially nonuniform pressure profiles and resistivity, are also given.

ISSN:0031-9171    

DOI:10.1063/1.865162

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

The polarization of electron‐cyclotron emission at the second harmonic (&ohgr;=2&ohgr;ce) has been measured both without and with a microwave absorber installed within view of the receiver to reduce wall reflection. Whereas without the absorber the radiation is dominantly unpolarized, with the absorber installed the radiation is significantly polarized, and the extraordinary mode intensity is typically three times the ordinary mode intensity. This indicates that wall reflections significantly depolarize the received radiation. Right‐hand‐cutoff effects are also observed and electron temperature is inferred from the emission from optically thin plasmas.

ISSN:0031-9171    

DOI:10.1063/1.865163

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

Some aspects of multiple‐wavelength interaction on solid targets have been experimentally studied at CO2‐laser wavelengths with 1‐nsec pulses. Contrary to predictions, the use of a two‐line (10.6‐ and 9.6‐&mgr;m) source does not reduce the back reflection. This result could be explained by a very short Brillouin interaction length or/and a very low saturation level. The hot‐electron production is also not significantly modified by multiline illumination. A signal at the frequency sum indicates that, even atI&lgr;2as low as 5×1013W cm−2 &mgr;m2, the critical surface is not well defined and that both the 9.6‐ and 10.6‐&mgr;m light interact in the same resonant zone. Finally, significant sidebands were measured at 8.7 and 12 &mgr;m. Some 1 (1)/(2) ‐dimensional simulations with mobile ions indicate that those sidebands probably originate from the beat frequency resonant density at 0.0123nc.

ISSN:0031-9171    

DOI:10.1063/1.865164

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

A time‐dependent analysis is made of the inviscid, incompressible Taylor column generated by the uniform motion of a thin disk of radiusarising slowly along the vertical axis of rotation of a tall, vertical, rotating, liquid‐filled right circular cylinder of radiusb. It is shown analytically that the effect of the sidewalls of the cylinder on the Taylor column drag on the disk may be neglected ifa/b<0.1. Even ifa/b∼0.4, the increase in drag above unbounded Taylor column value is less than 10%.

ISSN:0031-9171    

DOI:10.1063/1.865165

出版商:AIP    

年代:1985

数据来源: AIP