摘要:

The response of a collisionless plasma to an external perturbation does not necessarily obey the standard Debye result. In some cases, the plasma will behave in a manner opposite to the manner predicted by Debye theory; i.e. the plasma becomes morepositivein the neighborhood of a positive test charge. In general, the plasma shields out an external perturbation, but this shielding results solely from electrons dynamically trapped in the neighborhood of the test charge. A new theory of dynamic shielding is in good agreement with experiments in pure‐electron plasmas. © 1995American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.47908

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The dynamics of small ion crystals in a Paul trap has been studied by numerical solutions of deterministic equations of motion that include the time dependence of the trapping potential. For small trap voltage, the crystal shell structure agrees with earlier calculations based on a harmonic pseudopotential. Chaotic motion is also possible and, as in the 2‐ion case, increasing the trap voltage gives rise to a transition from transient to stationary chaos that is consistent with boundary crisis theroy. With increasing ion number, the critical trap voltage decreases, in accord with experiments on aluminum microspheres, but the lifetime scaling of the chaotic transients is independent of the number of ions. © 1995American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.47909

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The properties and dynamics of charged vortex structures in a nonneutral electron plasma in crossed electric and magnetic fields and their role in the processes of electron transport along and across the magnetic field lines have been considered. © 1995American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.47881

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The 2p2 3Pground state O2+ions were produced from solid iron oxide targets by laser ablation and stored in a rf ion trap. By using this technique, we measured charge transfer rate coefficients between the ground state O2+ion (at mean energy of about 2.5 eV or 2×104K) and neutrals (He, H2, N2and CO). © 1995American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.47882

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

An experiment is being constructed at Los Alamos to investigate the possibility of using a Penning trap as a fusion confinement device. The goal is to demonstrate electron densities greater than the Brillouin density at the center of the trap by filling it with particles occupying a very restricted region of phase space. The trap under construction has a containment region diameter of 6 mm, standoff lengths of 25 mm, and gaps between electrodes of 1.5 mm. High voltage tests have demonstrated standoff breakdown voltages of ≳100 kV, and established that titanium electrodes offer better performance than stainless steel or copper ones. The main diagnostic of the degree of density focusing will be transmitted beam deflection measurements. The electron source will be biased to inject a probe beam through the trap center, and this will then be imaged on a phosphor screen outside the trap. © 1995American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.47883

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The Electron Diffusion Gauge (EDG) is a Malmberg trap configuration used to investigate the application of pure electron plasmas to the measurement of background gas pressure. To form a useful gauge, the rates of different types of transport in EDG must be properly ordered and understood. The dependence of the asymmetry transport rate on plasma parameters has been determined experimentally. The relaxation of the plasma profile to a meta‐equilibrium state during asymmetry transport has also been observed. A local model of the asymmetry flux consistent with the observations is presented. Implications for pressure measurements are summarized. © 1995American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.47884

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

A particle simulation study demonstrates that an initial‐value analysis is essential in understanding the early‐time growth of diocotron modes. It is also demonstrated that the equilibrium properties of a rigid rotor (including rotation on both the high and the low frequency branches) are well described by particle simulation. © 1995American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.47910

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Space‐charge effects are a known limitation to the accuracy and precision of an entire family of mass spectrometers. We propose a new model for the study of space‐charge effects in which charged ion clouds each containing ions of a particular species interact as coupled gyrators. This model predicts a range of phenomena with implications for mass spectrometry including resonant energy exchange, synchronization, modulation, and chaotic motion. © 1995American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.47885

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The application of a rotating electric quadrupole field to a pure electron plasma confined in an elongated Penning trap of the Malmberg type operating at 1 Tesla is shown to produce an unusually long‐lived state. The observations are consistent with an assumption that the rotating field suppresses the radial expansion from transport due to alignment imperfections that normally limits the lifetime of such a plasma to a few thousand seconds. With the rotating field in operation, a lifetime of 20 hours was obtained. © 1995American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.47886

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Properties of an intense nonneutral heavy ion beam propagating through a periodic quadrupole focussing magnetic field are studied analytically and numerically including self‐field effects. For a Kapchinskj‐Vladimirski (K‐V) beam equilibrium with uniform density profile, the two nonlinear coupled envelope equations are solved for the case of amatchedbeam in the smooth‐beam approximation. Space‐charge effects are taken into account self‐consistently. The analytical solutions for the envelope and the (space‐charge‐depressed) phase advance are compared with the (exact) numerical results, and the technique can be applied to a wide range of system parameters and choices of lattice functions &kgr;q(s)=&kgr;q(s+S). Furthermore, a fully nonlinear study of the envelope equations for the case of amismatchedbeam is carried out numerically. In certain parameter regimes, the beam envelope is found to exhibit bifurcation which results in chaotic behavior of the beam envelope when the focussing field strength is increased beyond a particular threshold. The (unstable) chaotic region in the parameter space (&sgr;0, KS/&Vegr;) is determined numerically. Here, &sgr;0is a measure of the focussing strength defined by &sgr;20/S2≡⟨(∫ss0 ds&kgr;q(s))2⟩,Kis the self‐field perveance,sis the periodicity length of the focussing lattice, and &Vegr; is the unnormalized beam emittance. The relationship between chaoticity and well‐known linear instabilities is examined. In addition, for the case of a nonuniform density beam, it is found that the particle trajectory exhibits intrinsic chaoticity. The consequence of chaotic particle orbits is further investigated. © 1995American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.47880

出版商:AIP    

年代:1995

数据来源: AIP