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Title: Low emittance growth in a low energy beam transport line with un-neutralized section

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Journal Article: Published Article
Journal Name:
Physical Review Accelerators and Beams
Additional Journal Information:
Journal Volume: 21; Journal Issue: 2; Related Information: CHORUS Timestamp: 2018-02-06 14:30:31; Journal ID: ISSN 2469-9888
American Physical Society
Country of Publication:
United States

Citation Formats

Prost, L., Carneiro, J. -P., and Shemyakin, A. Low emittance growth in a low energy beam transport line with un-neutralized section. United States: N. p., 2018. Web. doi:10.1103/PhysRevAccelBeams.21.020101.
Prost, L., Carneiro, J. -P., & Shemyakin, A. Low emittance growth in a low energy beam transport line with un-neutralized section. United States. doi:10.1103/PhysRevAccelBeams.21.020101.
Prost, L., Carneiro, J. -P., and Shemyakin, A. 2018. "Low emittance growth in a low energy beam transport line with un-neutralized section". United States. doi:10.1103/PhysRevAccelBeams.21.020101.
title = {Low emittance growth in a low energy beam transport line with un-neutralized section},
author = {Prost, L. and Carneiro, J. -P. and Shemyakin, A.},
abstractNote = {},
doi = {10.1103/PhysRevAccelBeams.21.020101},
journal = {Physical Review Accelerators and Beams},
number = 2,
volume = 21,
place = {United States},
year = 2018,
month = 2

Journal Article:
Free Publicly Available Full Text
Publisher's Version of Record at 10.1103/PhysRevAccelBeams.21.020101

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  • In a Low Energy Beam Transport line (LEBT), the emittance growth due to the beam’s space charge is typically suppressed by way of neutralization from either electrons or ions, which originate from ionization of the background gas. In cases where the beam is chopped, the neutralization pattern usually changes throughout the beginning of the pulse, causing the Twiss parameters to differ significantly from their steady state values, which, in turn, may result in beam losses downstream. For a modest beam perveance, there is an alternative solution, in which the beam is kept un-neutralized in the portion of the LEBT thatmore » contains the chopper. The emittance can be nearly preserved if the transition to the un-neutralized section occurs where the beam exhibits low transverse tails. This report introduces the rationale for the proposed scheme and formulates the physical arguments for it as well as its limitations. An experimental realization of the scheme was carried out at Fermilab’s PIP2IT where low beam emittance dilution was demonstrated for a 5 mA, 30 keV H- beam.« less
  • A transverse beam emittance and acceptance measurement system has been developed to visualize the relationship between the injected beam emittance and the acceptance of a cyclotron. The system is composed of a steering magnet, two pairs of slits to limit the horizontal and vertical phase-space, a beam intensity detector just behind the slits for the emittance measurement, and a beam intensity detector in the cyclotron for the acceptance measurement. The emittance is obtained by scanning the slits and measuring the beam intensity distribution. The acceptance is obtained by measuring the distribution of relative beam transmission by injecting small emittance beamsmore » at various positions in a transverse phase-space using the slits. In the acceptance measurement, the beam from an ion source is deflected to the defined region by the slits using the steering magnet so that measurable acceptance area covers a region outside the injection beam emittance. Measurement tests were carried out under the condition of accelerating a beam of {sup 16}O{sup 6+} from 50.2 keV to 160 MeV. The emittance of the injected beam and the acceptance for accelerating and transporting the beam to the entrance of the extraction deflector were successfully measured. The relationship between the emittance and acceptance is visualized by displaying the results in the same phase-plane.« less
  • The H{sup −} magnetron source provides about 100 mA H{sup −} beam to be match into the radio-frequency quadrupole accelerator. As H{sup −} beam traverses through low energy transport, it ionizes the residual gas and electrons are repelled and positive ions are trapped in the beam, due to negative potential of the beam, providing charge neutralization for the H{sup −} beam. The neutralization time for the critical density depends upon the background gas and its pressure. Critical density for xenon gas at 35 keV is about 43 times smaller than that of hydrogen and stripping cross section is only 5more » times than that of hydrogen gas. We are using xenon gas to reduce neutralization time and to improve transmission through the 200 MeV linac. We are also using pulse nitrogen gas to improve transmission and stability of polarized H{sup −} beam from optically pumped polarized ion source.« less
  • Possible mechanisms of beam emittance conservation in high current transport lines and in RF linacs are discussed. Invariance of beam emittance is treated as a problem of proper matching of the beam with focusing and accelerating channels. To obtain matching conditions for a beam with an arbitrary distribution function in transport channel, it is necessary to accept that the potential of the external focusing field is a highly nonlinear function of radius. The solution for external potential is obtained from the stationary Vlasov{close_quote}s equation for beam distribution function and Poisson{close_quote}s equation for electrostatic beam potential. Gradual change of nonlinear focusingmore » field results in adiabatic transformation of the beam with initial nonlinear distribution into the beam, matched with the linear focusing channel. Alternating-gradient focusing structure with higher order multipole component creates better matching of the beam with the channel than pure quadrupole structure. Beam emittance growth in linear accelerator is studied for a drift tube linac with solenoid focusing. It is shown that beam phase space distortion in RF linac can be eliminated by the appropriate choice of the value of focusing field with respect to acceleration gradient. An analytical approach is illustrated by results of a particle-in-cell simulation. {copyright} {ital 1996 American Institute of Physics.}« less
  • Bent solenoids can transmit charged particle beams while providing momentum dispersion. While less familiar than quadrupole and dipole systems, bent solenoids can produce superficially simple transport lines and large acceptance spectrometers for use at low energies. Design issues such as drift compensation and coupling sections between straight and bent solenoids are identified, and aberrations such as shears produced by perpendicular error fields are discussed. Examples are considered which provide the basis for the design of emittance exchange elements for the cooling system of a muon collider.