摘要:

Static field errors in a Penning‐Malmberg trap exert a drag on confined non‐neutral plasmas, causing radial expansion and loss. We suppress this transport by applying an electrostatic wall asymmetry rotating faster than the plasma. This results in inward radial transport and plasma compression. The experiments are performed on a magnesium ion plasma in a magnetic field of 4 Tesla, within situLaser Induced Fluorescence (LIF) measurement of density and temperature profiles. Confinement of ions for up to 10 days is routinely observed. © 1995American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.47893

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

A fluid description is employed to derive the dispersion relation for modes near the cyclotron frequency &OHgr; in a nonuniform cylindrical nonneutral plasma of radiusRwith finite temperature confined by a uniform magnetic fieldB=B0ez. In contrast to the theory of Gould and LaPointe, the model includes the diamagnetic drift but omits finite‐Larmor‐radius effects. The eigenfrequencies for high‐frequency electrostatic modes with wavevectors satisfyingk ⋅ B=0 (Bernstein modes) are found in the form &ohgr;=−&OHgr;+&Dgr;&ohgr;. Solutions are obtained and compared with experiment and the theory of Gould and LaPointe. The present theory predicts that at a given temperature modes withm≳1 propagate only when the density is less than a critical value that increases withm, and that &Dgr;&ohgr; normalized by the diocotron frequency depends only on the ratio of the Debye length to the plasma radius and hence is independent ofBand the particle mass. © 1995American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.47907

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Radial transport and the damping of them=1 diocotron mode from ‘‘rotational pumping’’ has been measured on a magnetized electron column. Rotational pumping is the collisional dissipation of axial compressions caused by theE×Brotation of the column through asymmetric confining potentials. The observed transport rates are in close agreement with theory. © 1995American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.47887

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The following is a summary of a poster presentation at the Workshop. A full discussion of the matters touched on here will appear elsewhere. © 1995American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.47895

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Assembly and initial testing of the Positron Time‐of‐Flight Trap at the Lawrence Livermore National Laboratory (LLNL) Intense Pulsed Positron Facility has been completed. The goal of the project is to accumulate a high‐density positron plasma in only a few seconds, in order to facilitate study that may require destructive diagnostics. To date, densities of at least 6×106positrons per cm3have been achieved. © 1995American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.47900

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

An effect which we call rotational pumping (by analogy with magnetic pumping) causes cross‐field transport in nonneutral plasmas when the end confinement potentials are non‐axisymmetric. Because the Debye length is small the asymmetries are screened out within the plasma, but cause the surface of the plasma to distort. As a flux tube of plasma undergoesE×Bdrift rotation about the center of the column, the length of the tube oscillates about some mean value and theP∥dVwork produces a corresponding oscillation inT∥. In turn the collisional relaxation ofT∥towardT⊥produces a slow disspiation of electrostatic energy into heat and a consequent radial expansion (cross‐field transport) of the plasma. Detailed comparisons between theory and experiment have been made for the case where the asymmetry is produced by displacing the column off‐axis, that is, by creating anm=1 diocotron mode (see paper by Cluggish and Driscoll in these proceedings). The theory is generalized to include time dependent asymmetries. For the case where the asymmetry is a traveling wave that rotates faster than theE×Bdrift rotation of the plasma the particle flux is directed radially inward. © 1995American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.47902

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Magnetically confined electron columns evolve as near‐ideal 2D fluids, allowing quantitative study of instabilities, turbulence, relaxation, and self‐organization. We find that rapid global symmetrization of a distorted column can occur by a decay instability due to nonlinear beat wave damping. In the free relaxation of vortex turbulence, we find that the relaxation rate is limited by vorticity holes which persist for hundreds of rotations even in strong background shear. Finally, we observe that turbulence self‐organizes to a meta‐equilibrium state which is accurately predicted by minimization of enstrophy for a range of unstable initial conditions. © 1995American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.47903

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

An electron column in a modified Malmberg‐Penning trap is used to study the behavior of a single two‐dimensional vortex in an imposed irrotational shear flow. Phosphor screen images of the shearing process show a variety of phenomena including the fission of the original vortex, the emission, stretching, and entrainment of filamentary arms, and turbulent diffusion. The vortex lifetime is measured as a function of applied shear, with vortex strength independently adjustable. these data are compared to the predictions of a fluid theory which correctly identifies the key dimensionless parameter (shear rate/vorticity) but not its critical value. © 1995American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.47904

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Cylinders of pure electron plasma are routinely confined within cylindrically‐symmetric Penning/Malmberg traps. When azimuthal asymmetries are imposed, the plasma deforms into appropriately asymmetric shapes. Such deformed plasmas have been observed experimentally, and are long‐lived. The equilibrium and stability of these plasmas are analyzed in this paper. A very broad class of deformed plasmas are in equilibrium, but not all such plasmas are stable. Furthermore, the flux surface adiabatic invariant assures that the plasma will attain the appropriate equilibrium shape if the azimuthal boundary perturbations are applied slowly. © 1995American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.47905

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Cold positron plasmas are accumulated in a Penning trap by collisions with a nitrogen buffer gas. The trapped plasmas can be manipulated and diagnosed using nondestructive techniques, and they are being used for a range of physics experiments. One topic is the study of the physics of electron‐positron plasmas, in which the masses of both charge species are equal. Another topic is the study of the interaction of slow positrons with various forms of ordinary matter. These experiments can address important issues in atomic and molecular physics, condensed matter physics and gamma‐ray astrophysics. In this paper, we present an overview of the state of positron source and trapping technology. We then go on to describe recent progress in the accumulation and manipulation of cold positron plasmas and discuss experiments to study the electron‐beam/positron plasma system, as well as the interaction of cold positrons with a variety of molecules. © 1995American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.47906

出版商:AIP    

年代:1995

数据来源: AIP