A preliminary analysis of measurements on ..beta.. = 0.6 and 1.0 disk-and-washer linac cavities has indicated some limitations on washer support methods; in particular, that the use of radial supports should be avoided until further testing is completed

Potter, J. M.

Schriber, S. O.

UNT Digital Library

LA-VR-79-3373TITLE: LIMITATIONS OF THE DISK-AND-WASHER STRUCTUREAUTHOR(S):Stan O. Schriber and James M. PotterSUBMITTED TO:1979 Linear Accelerator Conference, Montauk, NY, Sept. 9-14,.,.- .. I, . ,--- —. ......... ,. .,,. .-.. l,,,,..,...,..,-,, ~,’, II.,.,B} srcepIantw= of tik article for public~tion. thrPublltilw ramgnh lb ~mait’u (Ikrnw) rltihtoin uny copyrixht ~nd the Covernnwnt and IIS ●uthorlzdn,pmntutiv~ have ml-trlctArlKht toreprodwlnwhok or in pnrt add srtklc under ●ny copyrightKU* by the publlsti./(D1 :10s alamossel-ntih laboratoryof tho !Mvorshy of CaliforniaLOS ALAMOS, NEW MEXICO c7546a ,An Allirmotivo Attion/Equol OppoJIum}y [mploy~lMllsmf1979 LINEAR ACCELERATOR CONFWENCELIMITATIONS OF THE DISK-AND-WASHZR STRUCTURE*S. O. Schriber+ nna J. U. PotterLos Alarnos Scientific Labor@torvL08 Alms, new Mexico 875~~SumsaryA preliminary enalycis of measure-to on# - 0.6 ●sd 1.0 disk-snd+asher Iinac cavitieshas indicated some limlt~tionnon washer supportmethods; in particular, that the use of -#dialsupports should be woided until furt~’er tecti ISis completed.IntroductionThe digk-and-washer cevi’y geometry 1 for●n sccele:ating structure offers many ●dvantsgeaincluding high rf conversion ●fficiency ●nd highcoupling factor, so we initioted a detailedstudy that included computer calculations ●ndexperimental measurements to determine limita-tion, if ●ny, that uould have to be consideredin ●n operational system.Other than Geometrical choices that havebeen discussed ●lsewhere, 2*3 the method usedto support ●nd COCI the waaher must be consideredcarefully because of the implication it haa oncompensation procedures required to give●cceptable, on-axis, ● lectric field distribu-tions3●nd on structure tuning. An earlierstudy of support methods with ●luminumcavities shows the importance of s~etricalwasher support schemes becauae they ●ither●liminate or reduce the complexity of themecompensating procedures. Figure 1 ohovs thesupport methods studied (L, TO ●nd radial). Theradial support appeared to offer the ❑oat●dvantages, but the ●ffects this echeme uouldhave uo quality factor, Q, ●nd ctructureimpedance, Z, ~ere unknown. For this reaaon,computer studies -re initiated and 6 = 0.6●nd 1.0, copper etructurea were fabricated toinvestigate the ●ffects of ●~etrical ouppoxttechniques on Q ●nd Z..— —L TO RADIALFig. 1.Waaher oupport ●ethods.●work Parforged under the auapicee of the U.S.Department of Energy.~iaitor frow Chalk River NuclearLaboratories, Chalk River, Ontario, Can#da.CalculstionaComputer cslculationa for the differentcavity geometries have been done using the codeSUPtZRFISh.6 Geometrical parameter for thisstudy tre shown in Fig. 2.Radial Support EffectsTlse ●ffect. that radial support diameter andlength have on cavitv quality fzctor ●reillustrated in Fig. 3. The ratio of qualitvfactor (Q) with stems, to the qualitv factor(Qo) without ●terns is shown ●a ● function ofstem length ●nd diameter in dimensionless unitsbaaed on the resonance wave length, meB = 0.6 disk-and-washer cavity geometry withradial support stems was simulated bv.a coaxia!cavity with its ●xis of rotation centered on thestem and washer, because SUPERPISH does nothandle three-dimensional geometries. fseeFig. 4.) Size ●nd volume of the wcsher, disk.outer cylinder, ●nd stem were scaled to give a1370-MHz coaxial mode that had ● field dis-tribution equivalent to the ●ccelerating modefield distribution of the real cavity. Stem●ffects tere determined % comparing calculatedhL+Fig. 2.Geometrical paraaetera ofdisk-and-waaher structure.1100.88 OS [7OISK LENGTH; FIxED041 1 , Io 0,2 04 06STEM LENGTH / A● . Q/QO wc ●:- length for fixed disk length.100.8:~\WASHER LENGTH; 06FIXED0“4t---0 02 04 06STEM LENGTH/A1 I Io 01 0.2 0.39TEMDIAWETER /hc. Q/Q {o ●tam dirntar for stem length =80.2 1.ri~. 3.Stdy of 8 ■ 0.6 cavity qualityfactcr uOlnB ● coaxial mdal.I#I.STEM “HASHER” %?it. 4.SOPERYISR nimlatiom tiel with coaxitlgmtry uoed to study tho R _ 0.6 cmvity.reoulto vith md without ● ●t-. Variation ofst- langth wao ●ccapliched in two wayc, bothwith ●imilar reoulto. The firot method,Fig. 3a, was to change tha wnoher langth keepingthr dimk lcntth or coaxial cavity lenBth fixed.Pigura ?b ●houo rocults of cslculationc for thewashar length fixad ●nd diok length or coaxialcavity langth chan~in~. Both -thodc ahou thatthe langth of the radial support ●tn ohould beC1OBC to ● qusrtcr wavalan8th to ●chiavaapproximstaly 96% Q/Qo. Reoults ❑ot ah= inthe figure demonstrated that the r~dial stemohould h an ald mltipla of 1/4 in langth,the nallor the wltiplc the lwer the looses.Figure 3C ●hms the ratio O/QO ●m a functionof rtrm di=~eter for ● 0.28 h l.nsth #t@m. Anopt{- ●tcm diwtar of ●pproximately 0.09 iis indicatad for thim gomtry. For four●upport ot- this -uld bo ●quivalmt to●pproximately 0.045 1.~cao raoulto indicstc that thsre ohould bea raoonanca botwcon the ●ten and the rett of thecavity ●uch that the raoonant fraqucncy of t~.e●tructurc w{th ● ctcm should cross through thereoonant fraqu~ncy of s •tcmlaa~ ●tructurc ●sthe otum langth i- vsriad frm, ●av, ~/B to31/8. It -t thus propooed to look for this●ffGet ~crimontally.Optiw # for A/b ladial SupportoCaputationn wre ●loo done to {nveatigac*the conacqucnccs to ●ffactiw ●hunt impedance,ZT2, wh~n radial oupport ●t- wat ba●pproxim.stely A/4 long. An opt- gapbotwon notts no lontar can ba colccted touaimire ZT2, bcauoa the sap mat ba ●djustedto ●chiovc tho required w/7 ●ccaloratin8 modrfrsqueney, *12A. Va held tho fraquency ●t1150 WIE, ●nd tho ~aoher radiuo, ~, ●qua] tothe cavity r diua, B.c, ●inuc A/A. ?iture 53shows hw ZT vari,tn ●o ● function of theouter cylinder rad]~: ~, for particlt bats-tAsLz IDISR MD MSmR ?~ns(1350 MC, tu - tn = 10.3%, O ● 30°, ~ ■ 1.1 a, ~- 0.2$ m)mm.hrface z Pmr homi tcd inField I$cttl”wallaZT2 M1/m) (ull/a) Outar Cyl. Di ●k—— —0.40.40.413.5716. S717. @8.5711.7613.120.0700.3150.s420.350.350.3s1465719319211650.ss10.s490.7!$016.3233.5618.7015.95.32.4co. ]<0.1~o.11.7I.C1.198.899.008.906.796.195.891. n@aol86.3~1,774.364.60.60.60.6]4.4516.6517.1810.2912.6013.180.2290.525o.@050.90.90.92610931607346470.9090.82?0.73543.963~.5135.34t.s3.81.93.33.04.20.80.80.816. s015.5016.3811.1712.2313.160.3870.5560.921106s1.6s1.680.ss7o.a220.72065.9971.735!.07&.g3.91.60.20.40.51.01.01.012.8414.4515.3410.5712.1713.110.3310.5800.9372.6<2.652.65360@50789660660.9180.8100.70856.5582.0565.215.93.91.80.91.31.817.624.433.6For ● cli~ht werall lona in ZT2, ● c~on~ cm be oelected for ●ll beta. The choiceobviouoly depend- m the pzrticle accelerated●d the fiml ●nergy. ?or ●lectron-, m radiuowould be umed thst ia hewily weithted in fworof higheot ZT29 where P - 1.0. For the PionOmermtor for Hedical Irradiation, PICMI,5that requires structure with beta from 0.5 to0.8, ● c-on outer mdius of 15.75 cm could beuted because this dimnsim not aly matcheswailable pips oi. : but make. ● reasonablecmpromite for ZT2. Acoam ~ for ●llbeta otructureo lead- to the sew ~ for ●lltha washer-. Pabricstim and wterial procure-ment shou!d be cimplifiod bacauee of the c-onradii. Externally, the ●ccelerator =uld hweth~ sme diaeter for ●ll beta, which couldsimplify ●li~ent ●d installation fixtures.In thim otudy, wamhera ~re supported bvradiml support stem of difftrent diawtero ●?wteria]o fcoppm, ●ltminum, ●d ttainlecacteel). UC detemined ●ff~ctn of metal ●upportebv cmparioon to meamiranta mde with thewaaher supported bv ● low-lona, dielectric=terial such ●s Teflon. The higheot oual~tymo -00 ‘00 .70 .- co ,E2s0.gw+ 40.Nw.to.10.lfomourments on Radial SUDPOrte?lesmureunts of Z ●d Q havo been done onB - 0.6 ●d B = 1.0, OPHC coppar, ditk-md-wamher cwitim that -r hilt at 1320 HHz fortest- of PI~I gemetry. ! onl~ c prelidnaryMal:aic of tham measutw-ts will be m-entedImra. The cwity QtmB mmmred usins lightlyempled 100PC to d~temine the ohape of theresonmce cum for thp m/2A mods. The O andw+e Q@ ●lso ~re checked for reference,b-auoe radial wpport~ hwe very Iittla ●ffectm thaoe ales. In all imtmeoo, proper caremm takan to itmurs -d contact aid clcm●urfamo. Mmouremento wmre re~mtad -y time~to imura there wre no m~oteutic wroro orinconcictencies in thz data. Mcamrewnto ofZ/Q -ra dono usins otrndard baadpwll techniques.I?it. 5.Shunt bpedmce varmm cwityouter radium ●t 1390 Wz.3?f~tor ma obtaiwd uo{rIs the mllaot diatmwpporto coneistmt with cons? ralnto of r{~iditymd mrpplyin~ eoolin~. A- ●pactmd, the Imotretittivity (copPar) ●upporto yicldw! the hotrmnulto. Ma ●chicvcd 912 of thsorotical Z of ●csr(ty witbut ampporto with # 9 - O.k PI~I#-try that hmo ● radial oupport btmm lrgthof ~rozkately 0.20 i. W obtsimd a ●lightiDpmwwn: in Q dwn the st- umre eoldared inpltie, We mda zn mdditimal uatu~t intiich orm of the far radial wpporta uzccomvartad into ● otmb tuner ●tondi~ MycmJ theomtor cavity -11. fir rmault -a ●imilsr tottmt dmvn in Pig. 3s0Wasou-ntc with the ~ = I.O PIGIIcatry ~ve Qa laas than BOX of theoretical Qfor # Se-try that hao ● otem ltngth of ●bout0.35 A. A opacial, copperplatcd-aluminumcavity W- built for the @ _ 1.0 PICHI waoherto make the otm length 1/4, kwt sEmin, Iotathan 802 of thooretica! Q uao mmaurad for theVla tie. Me then ran ● mriao ofmammrmentt to leak for ●ffects ● s predicted inFig, 3, by uoin~ m ●lminm pillboa cavity mndcopper waohers of different diame?ers, thusrequiring different stem Imgthc. We di4 notobserve the pred!ctad trends, and there was noindicatim of a atam ramnance ●ffect.ConcluoionrProblm with ●greement between theoreticaland ●~erimentml reaulta m rmdial wsher●upporcs in the diok-md%asher otructureindicate that rsdisl stem ohould not be usedunless further masuramanta and calculations●hcw better renulto. ~are ●ppmrs to be come●greement for the B - 0,6 cavity, but not iorthe B= !. O otructure. ~e reduction in Q andZ preoently obsrrved for the 0 = 1.0structure, ● t least, ●ppear- co preclude the useof radial ●teu. ?or Im-beta cavities, it●pposro that radial ●terns .FLuld hc ●bout A/Llong and have the mallant diamter conmiotentwith other deoign cmotrsints.Ack~lod~ ncafig athorc -Id lfke te thankR, A. Jmmeaon nd D, A. Bwnoon for theirParticipation in diocuationo related to th{cmrk.1.2.3.4.5.ReforenccoV. G. Andraev, V. M. Balugin, V. C. P.ulman,l!. A. Hirochnih, and B. M. Pirozhanko,‘Study of Righ-l!ncrgy Proton LinauStructure,” in “Procccdingm of the Iq??Proton Linear Accelerator Conference,October 10-13, 1972,” LOO Almmoa ScientificLaboratory report LA-5115, 114 {1Q77)S. O. Schriber, “Roum-Tmperature Cavitiesfor Bigh-Beta Accelerating Structures,”Proc. of Cnnf. on Future Poss. for ElectronAccel,, Ch@rlotteoville, VA, January 197Q.p. L-1.J. H. Pott@r, S. 0, Schriber ●ndF. J. Etmphry, mxperimentml and Calcul#te?~ Propertiao of thr Di@k-and-WasherStructure,” ICEE Trann. RUC1. Sci, ~,#3, 3763 ~1979).E. A. Knapp and O. A. Swnoon, “The PIGHIProErnm ● t US1,” Proc. of 1976 Proton LinacConf., Atomic Energy of Canada Ltd. ReportHO, AECL-M77, 230 f1976).K, Ilslbnch, R. F, Iiolainger, W. 1!. Jule andD. A. Swenson, “Propcrtias of theCylindrical RJ C4vity Ev~luation CodeSUPI!RFISR,” Proc. of !976 Proton LinacConf., Atmic Enern of Canada Ltd. ReportNO. AECL-5677, 338 (1976),4

Limitations of the disk-and-washer structure

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Limitations of the disk-and-washer structure

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