Progress with the SNS front-end systems

Keller, R.; Abraham, W.; Ayers, J.J.; Cheng, D.; Cull, Paul; DiGennaro, R.; Doolittle, Lawrence; Gough, Richard; Greer, J.; Hoff, M.; Leung, K. N.; Lewis, S. A.; Lionberger, C.; MacGill, R.A.; Minamihara, Y.; Monroy, M.; Oshatz, D.; Pruyn, J.; Ratti, A.; Reijonen, J.; Schenkel, T.; Staples, J.; Syversrud, D.; Thomae, R.; Virostek, S.; Yourd, R.

doi:10.1109/pac.2001.987434

Cited by 9 publications

(8 citation statements)

References 2 publications

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“…Berkeley Lab is engaged in the construction of the front-end systems (FES) of the Spallation Neutron Source (SNS) presently being built at Oak Ridge National Laboratory [1,2]. Two subsystems of the front end are the ion source and the Low Energy Beam Transport (LEBT) section.…”

Section: Introductionmentioning

confidence: 99%

Beam measurements on the H− source and low energy beam transport system for the Spallation Neutron Source

Thomae

Gough

Keller

et al. 2002

Review of Scientific Instruments

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The ion source and Low Energy Beam Transport section of the front-end systems presently being built by Berkeley Lab are required to provide 50 mA of H -beam current at 6% duty factor (1 ms pulses at 60 Hz) with a normalized rms emittance of less than 0.20 π-mm-mrad. Experimental results, including emittance, chopping, and steering measurements, on the performance of the ion source and LEBT system operated at the demanded beam parameters will be discussed. LBNL-481692

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Section: Introductionmentioning

confidence: 99%

Beam measurements on the H− source and low energy beam transport system for the Spallation Neutron Source

Thomae

Gough

Keller

et al. 2002

Review of Scientific Instruments

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“…The Spallation Neutron Source (SNS) comprises a 1-GeV H , linac injecting a storage ring with a 1 ms injection time and single-turn extraction, operating at 60 Hz [1]. During the 1 ms injection into the ring, approximately 1200 turns are accumulated.…”

Section: Beam Requirementsmentioning

confidence: 99%

The SNS four-phase LEBT chopper

Staples

Ayers²,

Cheng³

et al.

Proceedings of the 1999 Particle Accelerator Conference (Cat. No.99CH36366)

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The Spallation Neutron Source front end incorporates a beam chopper in the LEBT that will remove a 295 ns section of beam at a 1.118 MHz rate (65% transmission) with less than 50 ns rise/falltime. The H , beam pulse length is one ms at a 60-Hz rate (6% duty factor). The LEBT is all-electrostatic, and the chopper incorporates four 3-kV solid-state switches driving an einzel lens, split into quadrants, with a 4-phase chopping waveform. The suppressed beam is targeted on a four-segment Faraday cup which provides on-line intensity and steering diagnostics. Results of proton beam tests will be reported. BEAM REQUIREMENTSThe Spallation Neutron Source (SNS) comprises a 1-GeV H , linac injecting a storage ring with a 1 ms injection time and single-turn extraction, operating at 60 Hz [1]. During the 1 ms injection into the ring, approximately 1200 turns are accumulated. To reduce the activation of the extraction Lambertson septum magnet, a 295 ns notch is introduced in the injected beam by two sets of choppers, operating at the ring revolution frequency of 1.188 MHz. waveform on the four segments deflects the beam sequentially in four directions, shown in Figure 1, creating the 295 ns gaps in the 1 ms beam pulse. The four electrode segments are each independently pulsed to ं 3 kV by solidstate switches, deflecting the beam sequentially along each of the 45 degree diagonals. The solid-state switches have active pull-up and pull-down, providing a less-than 50 ns chopping transitions. Figure 2 shows an early version of the split einzel electrode. IMPLEMENTATION Figure 2: Split Chopper ElectrodeThe beam is targeted onto a diagnostic plate, split along the diagonals similar to the chopping electrode itself, in the wall common to the end of the LEBT and the start of the RFQ. The four segments of the target electrode are electrically isolated and water cooled, serving as a beam current diagnostic and a beam steering diagnostic. For a 65 keV, 35 mA H , beam with a 65% duty factor and with 35% of the current removed by the 1.188 MHz chopper, the total average power dissipated on the target is 48 watts.Angular beam steering is provided by a symmetric d-c bias on each segment of up to ं1 kV. Beam position steering is provided by physically moving the entire ion source and LEBT relative to the RFQ and the diagnostic plate on a sliding vacuum seal. ELECTRONICSThe key electronic component of the LEBT chopper system is the solid-state ं3 kV bipolar switch. This switch is

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Section: Physics Requirementsmentioning

confidence: 99%

“…LBNL has designed and is fabricating the Front-End Systems (FES) comprising an ion source, lowenergy beam transport (LEBT) with a pre-chopper, 402.5 MHz RFQ, and MEBT. The FES will accelerate a 38 mA, 6% duty factor, H -ion beam to 2.5 MeV for injection into the 1 GeV linac [1].The MEBT lattice matches the beam from the RFQ through two fast traveling wave choppers into the first tank of the DTL. The 35-cm long choppers perform the final beam chopping that prevents beam from intercepting the septum of the extraction kicker magnet in the accumulator ring during its rise time.…”

mentioning

confidence: 99%

Mechanical design of the SNS MEBT

Oshatz

DeMello

Doolittle

et al.

PACS2001. Proceedings of the 2001 Particle Accelerator Conference (Cat. No.01CH37268)

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The Lawrence Berkeley National Laboratory (LBNL) is presently designing and building the 2.5 MeV front end for the Spallation Neutron Source (SNS). The front end includes a medium-energy beam transport (MEBT) that carries the 2.5 MeV, 38 mA peak current, H -beam from the radio frequency quadrupole (RFQ) to the drift tube linac (DTL) through a series of 14 electromagnetic quadrupoles, four rebuncher cavities, and a fast traveling wave chopping system. The beamline contains numerous diagnostic devices, including stripline beam position and phase monitors (BPM), toroid beam current monitors (BCM), and beam profile monitors. Components are mounted on three rafts that are separately supported and aligned. The large number of beam transport and diagnostic components in the 3.6 meter-long beamline necessitates an unusually compact mechanical design. PHYSICS REQUIREMENTSThe SNS is an accelerator-based user facility that will produce pulsed beams of neutrons for use in scattering experiments. LBNL has designed and is fabricating the Front-End Systems (FES) comprising an ion source, lowenergy beam transport (LEBT) with a pre-chopper, 402.5 MHz RFQ, and MEBT. The FES will accelerate a 38 mA, 6% duty factor, H -ion beam to 2.5 MeV for injection into the 1 GeV linac [1].The MEBT lattice matches the beam from the RFQ through two fast traveling wave choppers into the first tank of the DTL. The 35-cm long choppers perform the final beam chopping that prevents beam from intercepting the septum of the extraction kicker magnet in the accumulator ring during its rise time. A closely spaced lattice with strong focusing is required to minimize emittance growth, due to the nonlinear charge distribution of the beam and the 62-cm drifts required for insertion of the choppers [2]. The layout of the beamline has been optimized to minimize emittance growth while taking into consideration the mechanical implications of closely spaced transport components and diagnostic devices.The MEBT lattice consists of fourteen quadrupole magnets, four rebuncher cavities, two traveling-wave choppers, and a chopper target that intercepts the deflected beam (see Figure 1). Four quadrupoles, one rebuncher, and one chopper are mounted on the first and third rafts, with the remainder of the components arranged symmetrically on the second raft. Six quadrupoles, the first and last magnets on each raft, incorporate dipole steering to correct for misalignments between rafts. Diagnostic devices located between transport components monitor beam quality during operation and enable tuning of the MEBT itself. TRANSPORT COMPONENTSPhysically compact devices have been devised, with careful consideration for mounting and alignment features in order to accomplish the positional accuracy and tight longitudinal spacing necessitated by the goal of minimal emittance growth. Quadrupole MagnetsThe physical envelope of the quadrupoles was tightly constrained by the available longitudinal space and the fit with the beam position monitors (BPM) and beampipes that it surrou...

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Progress with the SNS front-end systems

Cited by 9 publications

References 2 publications

Beam measurements on the H− source and low energy beam transport system for the Spallation Neutron Source

Beam measurements on the H− source and low energy beam transport system for the Spallation Neutron Source

The SNS four-phase LEBT chopper

Mechanical design of the SNS MEBT

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