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Preliminary ConceptualDesign for a 5 10 MeV Electron/PositronInjector for a UCLA (I Factory

Glen Dahlbacka and Robert HartlineMaxwell Laboratories, Inc., Brobeck Division

4905 Central AvenueRichmond, California 94804

William BarlettaLawrence Livermore National Laboratory/UCLA

Claudio PellegriniUniversity of California at Los Angeles

Abstract I. DISCUSSION

UCLA is proposing a compact superconducting high lumi-nosity ( 1032-33 m-2sec-1) +e- collider for a Q factory [l]. Toachieve the required e+e- currents, full energy injection from alinac with intermediate storage n a Positron Accumulator Ring(PAR) is used. The elements of the linac are outlined with costand uture flexibility in mind. The preliminary conceptualdesignstarts with a high current gun similar in design o thosedevelopedat SLAC and at ANL (for the APS). Four 4-section linac mod-ules follow, each driven by a 60 MW klystron with a 1 petmacropulseand an average current of 8.6 A. The first 4-sectionmodule is used to create positrons in a tungsten target at 186MeV. The three remaining three modules are used o acceleratethe e+e- beam o 558 MeV (no load limit) for injection into thePAR.

Based on experience with linacs at SLAC, each 3-metercontoured S-band 3 GHz section can be expected to produceaccelerations of approximately

& = 124 Pw,where E s the particle energy in MeVand P is the klystron power in M?V.

This relationship immediately leads o a cost/benefit radeoffin the number of sections vs. the klystron power delivered toeach section.

The minimum cost for the linac occurred with one 60 MWklystron driving four 3-metersections with a 1 psec macropulse;this configuration is shown in figure 1. At 3 GHz, a total cluster

CONVERTER

COOLING WAJER

e GUN 186 MeV LINAC t i 558 MeV LINAC PAR

SOLENOIDS

COLLECTINGMAGNETS

Figure 1. Componentsf Proposednjector.

O-7803-0135-8/!XSO3.00 0IEEE 2976

1991 IEEE. Personal use of this material is permitted. However, permission to reprint/republish this materialfor advertising or promotional purposes or for creating new collective works for resale or redistribution to servers

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charge of 9 nC (three 3 nC bunches) and an average current of The positrons will then be njected in a damping ring, shown8.6 A was necessary o achieve 100 nC e+ fill at 30 Hz in less schematically n figure 3. A 30 kV, 60 kW rf systemcan drive athan 6000 cycles. The sections each store 54 oules during the four dipole, 3.8 m ring with room temperaturemagnetsof 1.3 T.1 JJSCCill time. At the highest current loading, the particles The system would accept 1.4 x lOlo e+ at 30 Hz and switchoutextract 1.7 oules from the field. This corresponds o a 3.15% 2 x 1012e+in about 55 pulses.loading.

The first 4-section module is used to drive the positron

convertor target, shown schematically in figure 2. It consists ofa 2 m radius x 7 mm tungsten rod. The converter efficiency isestimatedtobe>0.04e+/e-/GeV,sotheextract.edpositronchargewill be 0.06 nC/cluster (or 0.02 nC/bunch). The target willdissipate 300 W and will need to be conductively cooled bycopper supports and water cooling. Details of the support struc-ture will be computed with standard hermal analysis software,using the ANL design for the AIS as guidance.

e beamI--

3 nC/bunch9 nOMuster

e+L-I

0.02 nCbunch0.06 nC/cluster

Figure 2. Tungsten converter.

After the conversion, the positrons will be collected bysolenoid magnets of up to 2 meters n length. The subsequentlinac in principle can accelerateparticles to 558 MeV (no load),but because the additional capability will be degraded by rfwindow losses and loading, routine operation at 510 MeV isanticipated.

Figure3. Positron ccumulator Ring (PAR).

II. CONCLUSION

In summary, the injection and positron production systemfor a UCLA 41actory has been considered. The system equiresa high current gun that is at the state of the art. The linac andPAR are well within proven capabilities.

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