摘要:

Results are summarized of a diagnostic study of underdense plasma targets, leading to the first observation of stimulated Brillouin scattering arising from thermal‐level fluctuations. Included are; (1) a detailed analysis of spectroscopic measurements of the plasma before and during laser heating, (2) computer calculations of plasma evolution during the laser pulse, (3) observations and anlaysis of Brillouin scatter, and (4) spectroscopic observations of forbidden satellite line emission during Brillouin scatter.

ISSN:0031-9171    

DOI:10.1063/1.863502

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

Under the cap‐cyclide coordinate system, the marginal stability of a sharp boundary toroidal plasma whose cross section is D shaped is examined using the energy principle. The analytical results are valid for arbitrary &bgr;, arbitrary aspect ratio, and arbitrary elongation of the plasma. There exists a maximum elongation for a given aspect ratio. The critical beta &bgr;cis computed for several aspect ratios and elongations. For given aspect ratio, &bgr;cincreases as long as the elongation increases.

ISSN:0031-9171    

DOI:10.1063/1.863503

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

Using reduced nonlinear magnetohydrodynamic equations, finite beta, resistivel= 2 stellarator equilibria with no net current are found. Stability to low mode number internal magnetohydrodynamic modes is investigated, and beta limits comparable to tokamaks are found. Low shear equilibria appear to be substantially more stable than high shear.

ISSN:0031-9171    

DOI:10.1063/1.863504

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

Several interesting characteristics of the PS‐1 spheromak plasma have been inferred from one‐dimensional simulations of the implosion phase of the experiment. The calculations demonstrate that metallic impurities in the pre‐imploded plasma, which come from the electrodes, strongly affect the dynamics of the implosion. The simulations also indicate that the resistivity and Joule heating are much larger than their classical values, suggesting that microinstabilities are a principal source of ion heating. Finally, the calculations suggest the existence of a hot, low‐density plasma between the plasma column and the wall, which carries a non‐negligible fraction of the poloidal current.

ISSN:0031-9171    

DOI:10.1063/1.863505

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

An important difference between the classical collision operator,C(f), and Kaufman’s quasi‐linear diffusion operator in action space,D(f), is that only the former conserves particles, momentum, and energy at each spatial point. The nonlocal character of action‐space diffusion allows all transport fluxes to be expressed directly in terms of appropriate moments ofD. Thus, a general description of quasi‐linear diffusion and convection across flux surfaces in any collisionless, axisymmetric toroidal system is obtained, in terms of scale factors relating the invariant surfaces to the flux surfaces. Several analogues to the neoclassical problem are apparent, including the collisionless version of the Ware–Galeev pinch effect, whose derivation in action space is especially straightforward. Toroidicity modifies not only particle orbits but also the spatial structure of the fluctuations, and both modifications affect the resulting transport in an important way. The use of appropriate action‐angle variables automatically includes the orbital effects; crucial features of the toroidal eignmode structure are incorporated by use of the ballooning representation. This makes the fastest radial variation explicit, in terms of a single parameter describing the degree to which submodes localized on different rational surfaces overlap. The variation on slower length scales, and the overall spectral amplitude, are not determined. The radial particle flux corresponding to a Maxwellian distribution function is displayed and its dependence on properties of the spectrum is analyzed.

ISSN:0031-9171    

DOI:10.1063/1.863506

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

The parallel energy loss and parallel energy diffusion of a nearly monoenergetic, well collimated, and tenuous test particle beam in a plasma has been measured. Parallel refers to the initial beam direction. Test particles of H1 +, H2 +, H3 +, and Ar+at energies of 1, 2, and 3 keV were utilized. The parameterXranged from 0.28 to 3.03, whereX= (test particle speed)/(plasma electron thermal speed). The near equilibrium, field‐free, and highly homogeneous plasma consisted of electrons and singly ionized Cs both at a temperature of 2100 °K and a density of 1×1011cm−3. The energy loss data are compared both to classical theories with phenomenological cutoffs and to fully convergent theories. The best agreement is obtained with the work of Itikawa and Aono. The energy diffusion results are compared to the theory of Spitzer, and to the Spitzer theory with nondominant terms added. The agreement is satisfactory except forX≳1.5.

ISSN:0031-9171    

DOI:10.1063/1.863507

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

A collisionless electric sheath model between a metal surface and a magnetized plasma is given. The magnetic field is assumed to be uniform and has a small angle of incidence with respect to the surface. It is shown that the ambipolar wall potential is essentially independent of the angle of incidence. The finite Larmor radius and secondary electron effects on the wall potential are derived. The sheath thickness is shown to depend strongly on the surface absorption characteristics.

ISSN:0031-9171    

DOI:10.1063/1.863508

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

Zero‐frequency cyclotron waves, which can be excited by a variety of static perturbations, produce large‐scale disruption of relativistic electron beam equilibria. A study of their basic nonlinear properties and an examination of methods with which to achieve their effective suppression are presented. A simple set of envelope equations based on the signal‐particle equations of motion is derived. Both analytic and numerical solutions are obtained for the case of a uniform magnetic guide field. The envelope equations are then used to investigate methods of suppression. It is found that although a spatially steeply rising magnetic field is a key component in achieving such suppression, initial beam momentum flaring plays a crucial role. Relativistic, fully electromagnetic particle‐in‐cell simulations designed to examine methods of suppression are presented.

ISSN:0031-9171    

DOI:10.1063/1.863482

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

Simulations demonstrating effective growth of slow cyclotron waves on a beam exhibiting a scattered distribution of particle velocities are described. No dramatic changes from the cold beam results for the dispersive properties are observed, but significant modifications of radial eigenmode structure appear.

ISSN:0031-9171    

DOI:10.1063/1.863509

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

It is shown how the phenomenon of osmosis may be treated using the phenomenological theory of Brownian motion in a flowing fluid. The theory is also generalized to include viscous stresses in the particle and mixture momentum equations.

ISSN:0031-9171    

DOI:10.1063/1.863479

出版商:AIP    

年代:1981

数据来源: AIP