摘要:

The requirements for transporting high‐current, negative‐ion beams are presented with particular emphasis on applications involving negative‐hydrogen‐ion beams. In addition to the usual matching and steering problems, particular attention must be paid to beam emittance growth in the transport system. Depending on the application, a number of approaches have been developed using both magnetic and electric lenses. I discuss the design considerations for transporting and matching these beams to radio‐frequency quadrupole accelerators, and present a survey of the various types of beamlines now used for negative‐ion beams.

ISSN:0094-243X    

DOI:10.1063/1.44810

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

A method and a computer program are developed for computing the dynamics of precision beams. The numerical method used for integrating differential equations is conservative. Within a paraxial approximation, the method ensures strict conservation of the phase volume at every step of calculations. Geometrical aberrations up to the third order are included and the space charge is taken into consideration within the paraxial approximation. The method is valid for relativistic beams. Controlling fields can have arbitrary longitudinal distributions. An accompanying frame of reference with a moving base is used where a trajectory of one of the particles is chosen to be a curvilinear axis. If a beam axis does not coincide with that of the device through which the beam travels, or if the angle of the beam axis deviation from that of the device (e.g. a scanner) considerably exceeds the angular divergence, within the given accuracy the method allows to be restricted with calculations of aberrations of lower order than in the case of a fixed frame of reference with a rectilinear axis. The method ensures simultaneous calculations of dynamics of any number of particles. For the case when a set consists of a large number of particles, a gain in the calculation time is obtained in comparison with times for calculation of the dynamics of all the individual particles. Dynamics of a broad H−beam having a small angular divergence at the inlet is studied in the scanner field. In order to keep the angular divergence at a small level at the outlet either distortion of the angular divergence of the beam should not be allowed or appearing angular distortions should be incessantly suppressed. Distributions of fields acting upon the beam while scanning are found when a small angular divergence at the outlet is provided.

ISSN:0094-243X    

DOI:10.1063/1.44811

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

A compact 6‐lens electrostatic quadrupole lens system in conjunction with a short, single einzel lens section has been developed with the aim of transporting a 30 mA, 35 kV H−beam [normalized beam brightness of about 1011A/(m‐rad)2] over a length of about 30 cm and focusing it into an RFQ. The effect of a neutral background gas on the measurements of the beam from the ion source is studied in order to evaluate reliably the input beam parameters for the lens design. The beam dynamics calculations have been made using simulation codes for typical H−beam parameters from two different ion sources; a magnetron type and a volume source type. The simulation results show a relatively modest emittance growth, that is within about 50–60% even in the case of an input beam with very small beam radius (1.1 mm) and very large divergence (72 mrad).

ISSN:0094-243X    

DOI:10.1063/1.44813

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

H−beam space‐charge neutralization is measured for 65‐mA, 35‐keV beams extracted from a circular‐aperture Penning surface‐plasma source, the small‐angle source. The H−beam is transported to a RFQ matchpoint by a two‐solenoid magnet system. Beam noise is typically ±4%. A four‐grid analyzer is located in a magnetic‐field‐free region between the two solenoid magnets. H−beam potentials are deduced from kinetic energy measurements of particles (electrons and positive ions) ejected radially from the beam channel by using a gridded energy analyzer. Background neutral gas density is increased by the introduction of additional Xe and Ar gases, enabling the H−beam to become overneutralized.

ISSN:0094-243X    

DOI:10.1063/1.44814

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

The acceleration of D−and H−beams has been studied at energies of up to 105 keV, with currents of the order of 2 A, in multi‐second pulses. The optimum extraction voltage has been studied as a function of the beam energy and current. The perveance of the negative ion accelerator has been measured over a wide range of operating conditions with H−and D−beams. The experimental results have been compared to beam optics calculations performed with the SLACAD negative ion code developed at Cadarache: a good agreement has been found. Strong perturbations of negative ion beamlet trajectories have been evidenced in the case of large gap, large aspect ratio accelerators. A comparison between merged beamlets and multi‐hole accelerators has been performed. The observed linear increase of the stray accelerated electron current with the extraction voltage has been explained by simulation with a Monte‐Carlo code developed at Cadarache.

ISSN:0094-243X    

DOI:10.1063/1.44815

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

High energy acceleration of the hydrogen negative ions has been investigated using a 350 keV negative ion source. The source consists of a cesium seeded multicusp plasma generator, an extractor and a two‐stage electrostatic accelerator. Beams of 350 keV, 130 mA, 1 s were obtained stably with a current density of 9.4 mA/cm2. The heat loadings of the accelerator grids caused by the electrons leaking from the extraction gap to the acceleration gaps were negligible. The heat loadings by the direct interception of the negative ions were reduced to a few percent of the acceleration power by optimizing beam optics. The heat loadings by the stripped electrons from the negative ions were dominant and proportional to the source operating pressure. Therefore, it is important to operate the source at as low a pressure as possible.

ISSN:0094-243X    

DOI:10.1063/1.44816

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

A simple model of the optics of an ion source has been developed and compared with the exact Poisson solution calculated by the computer code SNOW. The model replaces the exact Poisson potential by a Laplacian potential that is calculated by substituting a planar plate for the plasma and plasma sheath. The Laplacian potential is then used with and without a linear space‐charge correction to calculate particle trajectories. In this model the only free parameter is the distance between the planar plate and the plasma electrode. In general, there is good agreement between emittance curves calculated by the model and the SNOW results even when no space‐charge correction is used. For the geometry we studied, this implies that the effects of the plasma sheath and non‐linear space‐charge forces are small compared to aberrations introduced by the plasma aperture.

ISSN:0094-243X    

DOI:10.1063/1.44817

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

The focussing of an H−beam by a gridded Einzel lens has been studied at beam currents of 20–40 mA at 25 kV and 30 kV, with and without adding argon to the vacuum vessel as a neutralizing gas. The lens consisted of a central cylinder (6 cm long × 6 cm ID) sandwiched between two ground rings, each filled with a 92% transparent tungsten mesh. A negative high voltage was applied to the central cylinder to focus the beam. The beam diameter and divergence at the input to the lens were varied by changing the beam perveance in two ways: by varying the discharge power, and by varying the bias voltage on the plasma electrode of the source. Emittance and spot size were measured about 9.3 cm from the center of the lens. Emittance growth through the lens with and without the argon will be discussed. Introducing the argon produced a parallel beam core whose extent depended on the lens voltage.

ISSN:0094-243X    

DOI:10.1063/1.44818

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

The simulation of negative ion source physics should treat several charged species interacting with applied electric and magnetic fields, and also self fields resulting from ionic and electronic space charge, with complex boundary conditions imposed. Standard numerical codes exist to model these effects in positive ion source design problems. However in negative ions sources additional effects are important: ion, electron and neutral species can interact through collisions, charge exchange, stripping, and viscous effects, among others. A new multispecies hybrid fluid/orbit integration/Poisson‐Boltzmann algorithm is described, and applied to the LBL high brightness charge exchange (CXS) concept.

ISSN:0094-243X    

DOI:10.1063/1.44819

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

The energy distribution of H−produced at a low work function surface in a cesiated hydrogen discharge were measured with a magnetic momentum analyzer. The converter bias was changed from 0 to 150 V to see the difference in energy spectrum of H−ions. In addition to the peak corresponding to the energy of the converter, the peak at the energy equivalent to the potential of the plama electrode was found in the spectrum. The amount of the H−current of this energy group was larger than the H−current produced at the converter surface, when the bias to the plasma electrode was properly adjusted.

ISSN:0094-243X    

DOI:10.1063/1.44820

出版商:AIP    

年代:1992

数据来源: AIP