摘要:

Guiding‐center kinetic theory has been developed for antihydrogen recombination experiments, which are conducted with magnetic fields of 3 – 5 T; temperatures of 4 – 10 K; positron densities of 107– 108cm−3; and antiproton densities of 104– 2 × 107cm−3. Collision operators provide the leading‐order correction to weak‐coupling theory as the coupling parameter increases. Six collision operators — three Landau analogs and three Balescu‐Guernsey‐Lenard analogs — are found for particles of unlike charges. One operator is the multiple‐species generalization of Dubin’s and O’Neil’s operator. A stability analysis is performed for counter‐streaming positrons and antiprotons occupying a cylindrical region coaxial with an outer conducting cylinder in a constant, axial magnetic field. The finite transverse geometry of the system is included, leading to to a three‐dimensional Penrose criterion, which is applied to drifting Maxwellian distributions to obtain the regime of stability as a function of the species’ temperature ratio, density ratio and relative mean velocity. Collisional corrections are considered. Terms resulting from collisions between particles of the same species cancel under general assumptions satisfied by both O’Neil’s operator and Dubin’s and O’Neil’s operator. The multiple‐species generalization of Dubin’s and O’Neil’s operator is used for unlike‐species collisions to find a collisionally corrected dispersion relation, which is applied to a detailed study of stability properties. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1635171

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

A ballistic method is presented for transferring positron plasmas emanating from a region with a low magnetic field and relatively high pressure into a 15 K Penning‐Malmberg trap immersed in a 3 T magnetic field with a base pressure of the order of 10−13mbar. Subsequent stacking resulted in a plasma containing 4.2 × 108positrons. Using a rotating wall electric field a plasma containing 90 million positrons was compressed to a density of 3.6 × 109cm−3. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1635172

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

A compact, two‐stage positron accumulator has been designed, constructed and tested at Swansea, as part of a larger experiment to study Rydberg states of the positronium atom. It uses the well‐understood nitrogen buffer gas technique to trap and accumulate positrons obtained from a Na‐22 radioactive source, and slowed by a solid neon moderator. The main development this system embodies over previous accumulators is reduced physical dimension, made possible by the shorter storage times required. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1635173

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

Efforts to increase the storage levels of positrons in Penning‐Malmberg and other types of traps are important for many applications. Positronics Research LLC (PRLLC) is developing a storage trap that will host several positron, electron, and mixed plasma experiments intended to maximize storage conditions for positrons with acceptable lifetimes. A warm‐bore 5 T cryomagnet with three independently controlled solenoids is used for experiment. The central solenoid is used for Penning‐Malmberg trap studies. The end coils are used for magnetic mirror and other pinch‐storage research experiments. The end potentials of the Penning‐Malmberg trap will be raised to 100 kV, creating an effective well of length 100 cm. Optimization of the radio‐frequency drive system, designed to control the plasma using Trivelpiece‐Gould modes, and assessment of diocotron instabilities of the non‐neutral plasma are being investigated using a 16‐node, distributed Linux cluster. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1635174

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

Between 104and 1069Be+ions are trapped in a Penning trap. The ions are laser‐cooled to ∼millikelvin temperatures, where they form ion crystals. This system is an example of a strongly coupled one‐component plasma. By means of Doppler laser spectroscopy we have measured the temperature and heating rate of the plasma. Initially the heating rate is low, 60 ± 40 mK/s, but after about 100 ms the plasma heats up rapidly to a few kelvin. The onset of the rapid heating coincides with the solid‐liquid phase transition. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1635175

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

The simultaneous storage of electrons and anionic clusters in a Penning trap influences the trapping conditions of the ions, e. g. it results in a shift of the motional frequencies. In addition, the overlap of the electron cloud with the stored anions leads to electron attachment to the already charged anionic clusters. The time dependence of the attachment process and the influence of the trapping potential are reviewed. These experimental results may be useful in the characterization of the stored electron ensemble. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1635176

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

The Paul Trap Simulator Experiment (PTSX) is a compact laboratory facility whose purpose is to simulate the nonlinear dynamics of intense charged particle beam propagation over large distances through an alternating‐gradient magnetic transport system. The PTSX device is a 200 cm long, 20 cm diameter cylindrical Paul trap in which a 400 V, 100 kHz signal confines cesium ions to an rms radius of 1 cm. The one‐component cesium plasmas can be confined for hundreds of milliseconds, which would correspond to an equivalent alternating‐gradient transport system many kilometers long. The normalized intensity parameters⁁ = &ohgr;p2|r=0/2&ohgr;q2, where &ohgr;qis the average transverse focusing frequency, describes whether the plasma is emittance‐dominated (s⁁≪ 1) or space‐charge‐dominated (s⁁→ 1). By increasing the amount of charge loaded into the trap, PTSX reaches values ofs⁁= 0.8. Thus, the opportunity exists to study important physics topics such as: the conditions necessary for quiescent intense beam propagation over large distances, beam mismatch and envelope instabilities, collective mode excitations, the dynamics and production of halo particles, emittance growth, compression techniques, and the effects of the distribution function on stability properties. Results are presented that demonstrate the sustainment of the radial density profile over long times, and the ability of PTSX to reach larges⁁. The results of initial three‐dimensional particle‐in‐cell simulations are also presented. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1635177

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

The experimental investigation of the formation of coherent structures in an electron beam of very low energy produced in a Malmberg‐Penning trap is presented. A rapid development of the structures is observed when, by increasing the emission current of the cathode, a sharp transition to a space charge dominated regime occurs, where a region unaccessible to beam electrons is found around the axis, and is characterized by a sharp density gradient at the edge. The transport of the structures along the beam is studied by varying the strength of the axial magnetic field. A 3D PIC simulation code is used to interpret the results. A modification of the configuration is under way, in which a pulsed electron source is used, and plasma effects in the beam transport, of relevance for X‐ray SASE‐FELs, can be investigated. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1635178

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

For the past 15 years, or so, a set of computational tools for studying non‐neutral plasmas has been developed at Brigham Young University. These codes, which include equilibrium codes (for both static plasmas and solitons), radial eigenvalue codes, 2‐d eigenvalue codes, and both 2‐d and 3‐d particle‐in‐cell simulation codes, will be discussed, along with their applications to problems of interest to the non‐neutral plasma physics community. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1635179

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

Inelastic collisions with CO2buffer gas cool a pure electron gas in a Penning‐Malmberg trap at low magnetic fields. 0.6 eV electrons are cooled by down to 30&percent; of their original temperature. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1635180

出版商:AIP    

年代:1903

数据来源: AIP