摘要:

The two‐dimensional dispersion relation for the cold‐beam, free‐electron laser is derived by applying a Lorentz transformation to the Raman decay instability of plasma. It is found that a low‐density, relativistic, free‐electron laser is actually a broad‐band amplifier; it can amplify waves throughout a frequency range of 4g2. Of these waves, the forward, high‐frequency wave has the largest temporal growth rate. However, the off‐axis, lower‐frequency waves have larger spatial growth rates. In fact, the backward waves are absolutely unstable. These low‐frequency, absolute instabilities can be very detrimental, because they have very large nonlinear saturation levels, and, hence, they can deplete the energy of the electron beam.

ISSN:0031-9171    

DOI:10.1063/1.863437

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

The collective behavior of an intense, pulsed, space‐charge‐neutral proton beam (100 kV, 3 A/cm2, 0.8 msec) incident upon a transversely oriented magnetic field of 0–6 kG has been determined experimentally. At 6 kG, a floating potential probe shows longitudinal polarization creating a positive sheath (virtual anode) within the field boundary having a peak electrostatic potential equal to the ion accelerating potential. The sheath thickness is approximatelyv/wpi, wherevis the beam velocity and wpiis the ion plasma frequency. Oscillations in the sheath potential at wpiwere observed as predicted by previous computer simulations. Ions were observed to be accelerated out of the sheath in all directions. Transverse polarization of the beam as predicted by Schmidt’s polarization drift model was not observed although the plasma dielectric constant was approximately 102.

ISSN:0031-9171    

DOI:10.1063/1.863438

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

Two‐dimensional magnetohydrodynamic numerical calculations have been performed to study the fuel behavior of a preconditioned relativistic electron beam target in which, experimentally, a portion of the beam current prepulse entered the target to provide fuel preheat and magneto‐thermoinsulation. The magnetohydrodynamic plasma model used includes radiation, thermal conduction, ionization, and resistive diffusion. The magnetohydrodynamic partial differential equations are solved by a computer code employing implicit finite‐difference methods. The fuel is shown to develop counter‐streaming vortices during the implosion phase. The computed neutron yield is in reasonable agreement with the experimental value, suggesting the origin of the neutrons to be thermonuclear. The effect of both magneto‐thermoinsulation and preheat is examined.

ISSN:0031-9171    

DOI:10.1063/1.863415

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

Glass microballoons, coated with various thicknesses of plastic ablator and filled with deuterium‐tritium gas mixtures, were irradiated with the eight‐beam Helios CO2laser. Neutron yield, fuel temperature, compressed fuel density, and implosion time were measured as functions of ablator thickness. Hydrodynamic efficiency and preheating of these targets were estimated. Transition from fuel conditions characteristic of earlier exploding pusher experiments to those characteristic of a more nearly isentropic mode of implosion is illustrated. Fuel densities above 2 g/cm3were achieved.

ISSN:0031-9171    

DOI:10.1063/1.863439

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

Laser targets, created by fast optical breakdown of shock fronts produced in an electrothermal shock tube filled with D2or H2, have been used for studies of resonance absorption of CO2laser light. In these targets, the critical‐surface density‐gradient vector always points along the shock‐tube axis, leading to reproducible hot‐electron emission by plasma wave breaking. The angular distribution and energy spectrum of this emission have been studied. For 200 psec risetime laser pulses, the measured scaling of hot‐electron temperature with laser pulse energy agrees with predictions of models of profile steepening by the ponderomotive force of the laser light. For 20 psec risetime laser pulses, the results are consistent with a model in which the detected electron emission is dominated by a ’’chirped’’ monoenergetic burst lasting only 1 to 2 psec. In this model, the electron energy spectrum is due to the integrated temporal variation of the enery of the burst, and the hot‐electron temperature is practically independent of laser pulse energy.

ISSN:0031-9171    

DOI:10.1063/1.863440

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

Previous relationships between integral properties of gravity‐capillary surface waves are shown to hold for interfacial waves, provided the definitions of the quantities involved are stated correctly.

ISSN:0031-9171    

DOI:10.1063/1.863441

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

Chappelear’s solution for short‐crested gravity waves of a permanent type is shown to be modulationally unstable for long‐crest wavelengths and stable for short‐crest wavelengths.

ISSN:0031-9171    

DOI:10.1063/1.863416

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

It is shown that the ’’forcing function’’ (the right‐hand side) of Poisson’s equation for the mean or fluctuating pressure in a turbulent flow can be divided into two parts, one related to the square of the rate of strain and the other to the square of the vorticity.

ISSN:0031-9171    

DOI:10.1063/1.863442

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

Measurements in an asymmetrically heated two‐dimensional wake show that the temperature (temporal) derivative skewness becomes slightly positive in the region between the mean velocity minimum and the mean temperature maximum, while remaining appreciably negative elsewhere.

ISSN:0031-9171    

DOI:10.1063/1.863443

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

A kinetic theory of electromagnetic flute modes in a hot electron plasma is presented. Unlike the flute‐interchange mode, the electromagnetic flute mode is destabilized by warm electrons.

ISSN:0031-9171    

DOI:10.1063/1.863412

出版商:AIP    

年代:1981

数据来源: AIP