摘要:

The spectral density functionS(k,w) associated with spontaneous turbulence in a current‐driven plasma of medium density (ne= 1019−10220m−3) is measured with the scattering of the radiation of a cw low‐power CO2‐ laser (Pi≃2 W, li= 10.6 mm). Optical homodyne detection has been used. A remarkable result is that the level of fluctuations with wave vectors k∥B is close to thermal; B is the magnetic field for plasma confinement. The level of fluctuations with k⊥B is several orders of magnitude larger than the thermal level. The phase velocity of these fluctuations is equal to the ion‐acoustic velocity. A power law spectrum of the form n¯e/ne∼w−2has been found. It is consistent with the spectrum below 1 MHz as measured by optical probes.

ISSN:0031-9171    

DOI:10.1063/1.863400

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

The Doppler shift of light reflected from a plane stratified expanding plasma is analyzed. Nonlinear effects are not considered and oblique incidence is restricted to the case ofspolarization. The frequency shift is shown to consist of two components, one due to the motion of the reflecting surface, and another due to plasma flow through that surface. The shifts have a different dependence on the angle of incidence. Typically, the two contributions are comparable in laser fusion applications, being of order dw/w∼cs/c∼10−3, wherecs= (ZTe/M)1/2is the ion sound speed in the underdense plasma. In general, the Doppler shift has a time variation which induces a bandwidth in the reflected wave.

ISSN:0031-9171    

DOI:10.1063/1.863401

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

A detailed study is presented of the 0.4–40ncplasma region created by nanosecond, 10.6 mm, 1–38 J laser pulses incident upon unfilled glass microballoon targets. Many interesting features were observed including electron density scale lengths (Lc) and step heights (Np) throughncas short as 0.3l0and as high as 38nc, respectively. An attempt has been made to explain these parameters in terms of recent theories, and a consistent picture only seems to emerge if important roles are assigned to the superthermal plasma component and the effect of inhibited energy transport during laser irradiation.

ISSN:0031-9171    

DOI:10.1063/1.863402

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

Global monotonic stability of the Burgers’ vortex is studied using the energy method, and it is shown that no finite critical viscosity exists for the problem. For bounded domains, a criterion is established which ensures that the energy of any perturbation of bounded support initially decreases.

ISSN:0031-9171    

DOI:10.1063/1.863403

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

The phase velocities of laboratory wind waves along various angles to the mean wind direction, determined from cross‐spectral densities, appear to increase with angle.

ISSN:0031-9171    

DOI:10.1063/1.863404

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

The shape of a sail and the potential flow around it are considered in two dimensions. The sail is assumed to be flexible, inextensible, and supported by a mast and a sheet. A perturbation solution is obtained for a rather tightly stretched sail at any angle of attack.

ISSN:0031-9171    

DOI:10.1063/1.863405

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

Measurements on the axis of a circular jet indicate that the autocorrelation of dissipation fluctuations exhibit a power‐law dependence in the inertial subrange with an exponent m≃0.2, and that the corresponding spectrum is consistent with this value of m.

ISSN:0031-9171    

DOI:10.1063/1.863406

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

A simple physical model for the dissipation autocorrelation function is proposed. The resulting spectrum of dissipation fluctuations has akm−1inertial range behavior. An experiment by Kholmyansky is consistent with the proposed model, and suggests that the exponent m is approximately equal to 0.25.

ISSN:0031-9171    

DOI:10.1063/1.863407

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

The Fourier interference inequality on the Hopf characteristic functional, ‖F[y,t]‖<1 for ‖curly‖≠0, is shown to imply thatf(r,t)∝ (a positive function oft) r−3asr→∞.

ISSN:0031-9171    

DOI:10.1063/1.863408

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

The statistical approach to cylindrical magnetohydrodynamic turbulence of Montgomery, Turner, and Vahala is carried somewhat further. This leads to the general result that, in statistical equilibrium, the most probable value of the turbulently fluctuating magnetic field is force free.

ISSN:0031-9171    

DOI:10.1063/1.863409

出版商:AIP    

年代:1981

数据来源: AIP