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Title: Consequences of bounds on longitudinal emittance growth for the design of recirculating linear accelerators

Abstract

Recirculating linear accelerators (RLAs) are a cost-effective method for the acceleration of muons for a muon collider in energy ranges from a couple GeV to a few 10s of GeV. Muon beams generally have longitudinal emittances that are large for the RF frequency that is used, and it is important to limit the growth of that longitudinal emittance. This has particular consequences for the arc design of the RLAs. I estimate the longitudinal emittance growth in an RLA arising from the RF nonlinearity. Given an emittance growth limitation and other design parameters, one can then compute the maximum momentum compaction in the arcs. I describe how to obtain an approximate arc design satisfying these requirements based on the deisgn in [1]. Longitudinal dynamics also determine the energy spread in the beam, and this has consequences on the transverse phase advance in the linac. This in turn has consequences for the arc design due to the need to match beta functions. I combine these considerations to discuss design parameters for the acceleration of muons for a collider in an RLA from 5 to 63 GeV.

Authors:
 [1]
  1. Brookhaven National Lab. (BNL), Upton, NY (United States). Collider-Accelerator Dept.
Publication Date:
Research Org.:
Brookhaven National Laboratory (BNL)
Sponsoring Org.:
USDOE Office of Science (SC), Nuclear Physics (NP) (SC-26)
OSTI Identifier:
1188273
Report Number(s):
BNL-107126-2015-CP
R&D Project: KBCH139; KB0202011
DOE Contract Number:
DE-SC00112704
Resource Type:
Conference
Resource Relation:
Conference: 6th International Particle Accelerator Conference (IPAC’15); Richmond, VA; 20150503 through 20150508
Country of Publication:
United States
Language:
English
Subject:
43 PARTICLE ACCELERATORS

Citation Formats

Berg, J. S.. Consequences of bounds on longitudinal emittance growth for the design of recirculating linear accelerators. United States: N. p., 2015. Web.
Berg, J. S.. Consequences of bounds on longitudinal emittance growth for the design of recirculating linear accelerators. United States.
Berg, J. S.. Sun . "Consequences of bounds on longitudinal emittance growth for the design of recirculating linear accelerators". United States. doi:. https://www.osti.gov/servlets/purl/1188273.
@article{osti_1188273,
title = {Consequences of bounds on longitudinal emittance growth for the design of recirculating linear accelerators},
author = {Berg, J. S.},
abstractNote = {Recirculating linear accelerators (RLAs) are a cost-effective method for the acceleration of muons for a muon collider in energy ranges from a couple GeV to a few 10s of GeV. Muon beams generally have longitudinal emittances that are large for the RF frequency that is used, and it is important to limit the growth of that longitudinal emittance. This has particular consequences for the arc design of the RLAs. I estimate the longitudinal emittance growth in an RLA arising from the RF nonlinearity. Given an emittance growth limitation and other design parameters, one can then compute the maximum momentum compaction in the arcs. I describe how to obtain an approximate arc design satisfying these requirements based on the deisgn in [1]. Longitudinal dynamics also determine the energy spread in the beam, and this has consequences on the transverse phase advance in the linac. This in turn has consequences for the arc design due to the need to match beta functions. I combine these considerations to discuss design parameters for the acceleration of muons for a collider in an RLA from 5 to 63 GeV.},
doi = {},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Sun May 03 00:00:00 EDT 2015},
month = {Sun May 03 00:00:00 EDT 2015}
}

Conference:
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  • Factors affecting emittance growth in linear-accelerator applications requiring high beam quality and low in-machine beam losses are explored. A generalized method is developed for matching the average properties of an arbitrary particle distribution to an accelerator structure in the presence of space-charge and other perturbations. The effects of the particle distribution and the accelerator parameters on the preservation of input emittance and other measures of beam behavior are investigated, to study optimum performance under carefully matched conditions, and to show the degradation of performance in the presence of mismatch, steering, and other errors. The concept of detailed matching invoking desirablemore » correlations is discussed briefly.« less
  • A Fixed Field Alternating Gradient (FFAG) arc can be used to reduce the cost of a recirculating accelerator. Path length variation with energy in such an arc can limit its usefulness, however, due to phase offset at the linac. This paper examines the dynamics of the reference particle in an FFAG recirculating accelerator, and describes the limitations on the design because of path length variation with energy.
  • A recirculating accelerator accelerates the beam by passing through accelerating cavities multiple times. An FFAG recirculating accelerator uses a single arc to connect the linacs together, as opposed to multiple arcs for the different energies. For most scenarios using high-frequency RF, it is impractical to change the phase of the RF on each pass, at least for lower energy accelerators. Ideally, therefore, the WAG arc will be isochronous, so that the particles come back to the same phase (on-crest) on each linac pass. However, it is not possible to make the FFAG arcs isochronous (compared to the RF period) overmore » a large energy range. This paper demonstrates that one can nonetheless make an WAG recirculating accelerator work. Given the arc's path length as a function of energy and the number of turns to accelerate for, one can find the minimum voltage (and corresponding initial conditions) required to accelerate a reference particle to the desired energy. I also briefly examine how the longitudinal acceptance varies with the number of turns that one accelerates.« less
  • In recent RLA experiments, a foil diode was utilized, followed by a 1.2-m-long 60-mTorr argon gas cell or lower pressure classical IFR transport region. In order to improve the beam capture and transport efficiency, a number of diode configurations were studied both experimentally and numerically using JASON and the latest version of MAGIC code. In particular, a conical shank diode was investigated in detail. A study of the beam current was undertaken using apertures of gradually increasing I.D. steps of 6.4 mm. An excellent agreement between experiment and simulations was observed. MAGIC predicted the exact total diode current, the currentmore » through the different radius apertures, and the beam envelope radius. An optimized diode geometry gave at the anode foil a very cold beam of 1.4 MV, 22.5 kA with an rms beam radius r = 1.5 cm and a geometric emittance epsilon = 0.04 rad.cm. The foil and gas transport region lead always to an increase of beam emittance. A similar design for a 4 MV, 10 kA diode is also presented. 8 refs., 7 figs., 1 tab.« less