摘要:

An informal descriptive account is first given of the emittance concept and its underlying physical basis. This is followed by a discussion of the connection between emittance and entropy, and a number of questions relating to problems of current interest concerning such topics as emittance growth and equipartition between different degrees of freedom are raised. Although no new results are obtained, it is hoped that the discussion may be helpful in the search for new insights. The paper differs from that presented at the conference, and contains ideas which arose in discussion with T. P. Wangler at Los Alamos after the conference.

ISSN:0094-243X    

DOI:10.1063/1.42141

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Soon after the successful operation of the first AG proton synchrotrons an effort was made to increase their intensity and the intensity of their injectors: linear accelerators. With the help of elaborate beam dynamics codes, simulation work started, in particular at CERN, including the so‐called space charge effects. As will be described, at the same time as computations were made modeling the complex behavior of an accelerated beam, the simpler case of a pure beam transport was studied with the aim of guiding theoretical work. Such early computations, however crude they were at that time−in the late sixties or early seventies,−still remain a useful basis for the more recent elaborate developments.

ISSN:0094-243X    

DOI:10.1063/1.42154

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Space‐charge‐induced emittance growth has become a topic of much recent interest for designing the low‐velocity sections of high‐intensity, high‐brightness accelerators and beam‐transport channels. In this paper we review the properties of the space‐charge force, and discuss the concepts of matching, space‐charge and emittance‐dominated beams, and equilibrium beams and their characteristics. This is followed by a survey of some of the work over the past 25 years to identify the mechanisms of this emittance growth in both ion and electron accelerators. We summarize the overall results in terms of four distinct mechanisms whose characteristics we describe. Finally, we show numerical simulation results for the evolution of initial rms‐mismatched laminar beams. The examples show that for space‐charge dominated beams, the nonlinear space‐charge forces produce a highly chaotic filamentation pattern, which in projection to the 2‐D phase spaces results in a 2‐component beam consisting of an inner core and a diffuse outer halo. In the examples we have studied the halo contains only a few percent of the particles, but contributes about half of the emittance growth.

ISSN:0094-243X    

DOI:10.1063/1.42143

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

A brief overview will be given of recent advances in the theoretical treatment of charged particle beam transport. Topics covered will include nonlinear aberration compensation, the generalization of emittance concepts to four and six dimensional phase spaces, and the calculation and correction of aberrations arising from linear and nonlinear space charge forces.

ISSN:0094-243X    

DOI:10.1063/1.42145

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Since space charge waves on a particle beam exhibit both dispersive and nonlinear character, soliton‐behavior is possible. Some theoretical aspects of dispersive, nonlinear wave propagation in high brightness beams are discussed. Numerical examples for realizable beams are presented, and issues for future studies are noted.

ISSN:0094-243X    

DOI:10.1063/1.42146

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Experimental and numerical studies of emittance growth resulting from beam mismatch have been performed at the University of Maryland Electron Beam Transport Experiment. A 5‐beamlet distribution of energy 5 keV and total current 44 mA passes through two‐solenoid matching lenses and into a 36‐solenoid transport channel. Theory predicts substantial emittance growth due to density nonuniformity, beam mismatch, and beam misalignment. Experimentally, the 5‐beamlet configuration is mismatched and transported through the channel. Random misalignments in the channel produce a gradually growing offset in the beam. The final emittance is measured for the mismatched beam. Simulation results of the matched and mismatched beams reveal that a large halo accounts for the emittance growth in the mismatched case. This is supported by experiment. The difference between the experimental emittance data and the numerical simulation is analyzed and attributed to the fact that the density of the halo is below the detection threshold of the emittance meter. Simulation also predicts that misalignments contribute negligibly to the emittance growth. Excellent agreement is found between fluorescent screen images of beam structure and simulation results.

ISSN:0094-243X    

DOI:10.1063/1.42147

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

This paper reports the results of design studies of longitudinal beam compression and resistive‐wall instability, and the current status of the two experiments at the University of Maryland.

ISSN:0094-243X    

DOI:10.1063/1.42148

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

We describe the coordination of theory and experiment in the study of bright beam systems by the LBL Magnetic Fusion Energy group. We have developed new analytic [1] and computational [2] tools for designing practical ESQ‐focused systems, including the LBL CCVV (Constant Current Variable Voltage) prototype. This prototype has been tested both as a modular accelerator [3] and as part of a LEBT [4] for injection into an RFQ. We have also found these mathematical tools to be useful in setting up the bright‐beam measurements on our test stand [5]. Our measurements showed no emittance growth in ESQ‐focused 84 mA He+beams with emittances of 0.0075&pgr; mrad‐cm (normalized rms). We discuss analytical work on emittance growth in segmented beams [6]; these results have been used as criteria for designing accelerators with multi‐aperture sources [7]. The problem of emittance growth from beam size mismatch [8] is reviewed.

ISSN:0094-243X    

DOI:10.1063/1.42149

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Development of an efficient low‐energy beam transport section (LEBT) is an important issue in accelerator research. An experiment is undertaken to build up an electrostatic quadrupole (ESQ) lens system with an aim to transport a 30 mA, 35 kV H−beam, with normalized beam brightness of ∼8×1010A/(m‐rad)2, over a length of about 30 cm and match it into a radio‐frequency‐quadrupole. Beam parameters of a Penning‐Dudnikov type ion source at the AT‐1 test stand at Los Alamos National Laboratory are used. The LEBT section consists of six electrostatic quadrupole lenses. The apparatus is designed by detailed computer code simulation of beam dynamics. An emittance growth of about 80% is predicted in transporting the beam through the ESQ system. The ESQ lens system is fabricated. Tests of the system are planned to validate the design parameters, voltage hold‐off of the quadrupole assembly, etc. Critical issues on the design of the apparatus and its fabrication will be discussed.

ISSN:0094-243X    

DOI:10.1063/1.42150

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Magnetic transfer lines are commonly used to allow for proper formation of ion beams between ion source and first accelerator structure as well as successive rf cavities. The absence of electric fields allows plasma build‐up and the compensation of the space charge to a significant amount. The neutralization eases transverse focusing and allows for the stable transport of even very high beam currents, which under decompensated conditions would exceed the current limit of the channel. On the other hand the compensation process gives rise to internal self field nonlinearities of the beam resulting in transverse emittance degradation. Fundamental aspects of space charge neutralization of positive ion beams will be discussed and causes for field nonlinearities followed by emittance degradation at low beam energies will be outlined. Numerical results of the beam plasma analysis will be given together with an overview on the pros and cons of the use of space charge compensated transport.

ISSN:0094-243X    

DOI:10.1063/1.42151

出版商:AIP    

年代:1992

数据来源: AIP