Aag-lBrg8 12:41pm From-APT/TPO

T m :

5 0 566 77443

Dtvelopmenr of a Racer Electronics System for Expanding the APT Proton Beam

. - Appmed brpublic mlease:

drsrnDulron IS unlimmd. co NF-488937-

Aurhorls): S. Chapclle, GA E.L. Hubbard, GA T.L. Smith, GA

R.E. Shafer, APTRPO-GA M.E. S C ~ U ~ Z ~ , APTTTPO-GA

Los Alamos N AT I 0 N A L LAB 0 R AT0 R Y Las A l m s Nabanal Lammtory. an affirmanva acricweqd oppanuntly empioyer. IS operarsd oy me Unwarsib of Calitornta lor me U.S. Oeparuneflr of Energy u w r coflrraEf W-7405-ENG-36. By accepwnce ot th~s arwle. the WMisher recognizer mar ma US Government r m n s a nmsxclutrive. rwdty-frae license to puaisjn or reproduce me pu~itsnetl mnn a? rnts cmtrrbaion. or io a w w omas io do so. for US. Government purp0ses-L~~ ~ l a m o s NaIional Lawtarory requests mar me pu~~isttar idenw~ m ~ s W e as Work pertormea mderme auspices of me US. Depmenl of Energy Los Alamos Nabanal Laeoramry strongly supports acaaemtc treedorn an4 a researwrs ngnr TO puMtsh, as an instttuken. nowever, Ihe Laboratory does nor endorse me v i e ~ p n r of a publicailon or grrarantee 116 rechnw correcmess.

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DEVELOPMENT OB A RGSTER ELECTRONICS SYSTEM FOR EXPANRING THE APT PROTON BEAM *

S. Chapelle, E. L. Hubbad, T. L. Srnid~ General Atomics, San Diego, California 92121 USA

M. E. Schuhe, R. E. Shatkr General Atomics, Los Alamos, New Mexico 87544 USA

A brrruc r A 1700 MeV, 1 0 mA proton bnear acccehmr is king

designed for Acccleramr Producaon of %Iiurn (APT). A bm expansion s y s ~ m IS ritqcnre4 to uniformly irradiau n 19 x 190 CUJ uiriun production target Ths p p c r drscriks a k a m expansion system cornsring of eight territc d~polc magncrs to wEer rhe beam in the x- and y- planes ana dso Qescnbes Ihc salient fearwes of h e dcsign of rbe electronics chat WC uniquc to rhs e r p d r . fight lmuIaw$ Gate Bipolar Trarstor (IGS’ij-based modulators dnre thc rasvzr magnets with uiangulnr current wavcfomis that arc synchrowd using p h - lacked loops (PLZS) rtpd rolrage conaolled crystal oscil\ators (VCXOs). Faulr Qctecrion circuiuy shuw down Lhe beam before rhe wger can be Wnagcd by a falure ol the raster sysran. Test data are pnrsenced for the protorypc system.

1 BACKGROUND In rhr propsea wrer-rype beam exponder. &ere will

be four horiwnrd wd fory ven-ilicd raster rnqgcrs. They will be modulated SO rhar rhe usget i s ‘paurrcd” by rhe 1 I 2 cm proton h a m in B parrcrn somewhat like the ones sh;hQwn ia Fig. 1. Thc panern is achieved by modularing the vemcd- and haizouwl-axis rnagacu with wiagcltar current wavcfoms at s1agh:hJy ckfferem fiequcncies m the 500 IO 6OOHz range [l]. The cnnre wger IS rbcn m4alrd in a period of appraimazely 20 ms.

figure 1: Sample parrtms rhat ure available by changing lfic rauo of [be s- arid y-plwc rastenng frequencies.

Work supparred by h e DOE rrnder cuntraa DE-ACW- W S 9 6 Q 7 .

An obvious problenr of uung a rasiercd approach LO beam expansion is rhw the bcam ran oat be qilowed to dwell on one spot of the target for Very long (on the order of 0.5 ms) or else Jamagc to rhc target could psylr. The prevandon of conirnon rude anJ singlc poiyr Failuscs has becn a ma- design drivcr. Tbe 4ght rnagncr sysymn a ~ c pwposely designmi IO op~rate synchronously and in~icpendcncly. SI char i i failure of one system will 401 affect Ihc operation of any orkcr sysrcm, and therefore rhc beam will always bc moved acmsr rtrr =get Fs. 2 shows che mrxr magnets w they tit iuco the bgh erwrgy bewn tmn~pon ( W T ) pofiion of rht APT Linac.

DoubJcr,m,= rvl~ht-~s 8Rwerrtugr~b Fmalqu.ul 6- quads 4 & 4 Y rkuolcr couu.yct

b- Figure 3: Raster magners in HEBT

2 SYSTEM PESC-ION The blcck QliigisrYn of rhe Rasrzr Magncc Systcm is

show m Fig. 3. The Logical blocks of tbe syyszecrc ttre mc 1) Master Clock 2) PLUIGBT Gare Dnver, 3) IGBT Modrrlaror, 4) Rwcr Wgner and 5 ) Fault Derection CirCUlUy

Figwc 3: Rrtster systcm concept

3.1 Masrrr Clock The Master Clock produccr zwo drffererir frequencies,

one for h e four x-plwc rnagners an4 a second for rhe four y-plane rnagrc~. Tbc choice of frequencies IS c m f u l l ~ mule 10 avoid bear parrerns Impartant desi9 issucs of the Muster Clock are rclared to accurazely splining out a

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I 024-MHe CryStd-CoRKOJlcd muter oscillaror to two different -‘&vide by N’ circuits to drivc the horizoriId and vcmcal planes with ;I rmnimum amounr of skew bcrwecn the channels The Master Clock incluQcs on-card fault check circuitry that monitors rhc clorlo 10 notify sht user OF a fault. The clock fault ourpurs UC sent u, four ndtpcndear &visions in rbe Beam EnabIc circuitq ro lum off h e &nac b e m before a raster systcm failure causes damage LO the Larger.

2.2 PLUICBT Gatr Driver Each magnet gels irs rirmng signal from th t Maswr

Clwk descnbed above. Each of the rnagwki has I

PLUICBT Garc Driver rhar will, using a phae-tockcd Imp, synchronize irself LO the Master Clock, or else if the Master Clock ftuls, is able to prOducc ics own clock so that the kam conunues to be rasxercd onto rhe target. This design approach is uscd to prcclu& a common mode failure that might cause damage to thc rargec blank[

For Lhis applicatron u sequcnrial type of phase dccector, rather than lm analog muliipher type, is used in each PLL to gcnenir emor signals for dic VCXOs m Each IGBT gak dnvcr, Thc sequcnrial phase dctecror resulp in modularor-to d u l a r o r phase crrofs Ice rban about SO ns w the rastemg fnqucncies. The phase dctecror then outputs &e w c s~gniil to tt VCXO rhw varics the frequency ;~ccordingly. If thc Masw Clock signal fails, rhe VCXOs of each modulator will m;unuirj u clock slgnd, akhough the rnortdarars, will no longer bc synchronad However, Ihc drift i s slow, allowing ample time for the f a t detecuon circwuy to d e r e a the problem and U&C action. The PLUIGBT Gate Drrver, ftri the name implies,

gemares properly tine4 signals at suillcienr p w e r IO directly d n v c the gates of the lGBTs of the modulator. Currece riraing &o requires that Zhe signals sen1 IO the ZGBTs mcluck some dcadumc to ensure ws two iGBTs m series are never turned on 31 the same rim, rhus avoidmg shoot-&rough failures.

2-3 lGBT Modrciuror “bc lCBT modulator consisrs of an w/dc convertcr, a

capacitor bag, w\d 3~ IGBT H-briJge (Fig. 4)- Each modulwx will be powered by unintcrrupuble p w c r 10 prevenr a common mode failure duc to rhe loss ot’ uc inplrr volmgc. Tbc ac/dc converrcr will chargc up and mainram a consrant voltage on the capacciror bwk. Charge is d r a w Into and out of the cappciw banb by rhc H-bridge. Tbc value of rhc dc outpur voltage of rhr poser supply IS dictated by s y s m Levcl t-eqwremcnts in that rhe dc volrage represmrs the rare of changc of the current in the rasm magncr rnductance (V = L*dUdr).

Thc dc volrage values are &fferent for the x-mis magnets trnd y-uxis magnets bccaust che rcquired peak detkctions (Le. peal; B-field) ctiffer. Final beam expansion and sizing is ac~ually controlled by TWO

quaaupole magnets locured downstream of rhc r;ts[rr magnets in the HEBT bcamlinc as shown in Fig. 2. Thc 3r capacitor bank crchanges reactive power with the magna on a loo0 Hz rirncscale (twicc per cycle). The IGBT H-Bndge circuit drives the rqstcr magnets with 01 voliagc sqwe wave, rcsulring in 4 uiangcllar cweni waveform. The urnins of the lGBT gate ciwuic is c o n ~ l k d by rhe PUlZGBT Gate Driver alrcudy mnriomd.

- - Figure 4: IGBT Modularor

The choice of IGBTs e rhe swilthc:, for rhc &bridge was mu& on h e basis of lfir opcmring frequency of SDOHz and thc low losses rhtli rhek deviccs edubir, in conrrast to rhe choice of MOSFET swirches ia &e system descrikd in 121- Freewheeling diodes are inclu~ed across each switch LO return rhe stwed energy in the inducuve load LO rhe capacitor bank each half cycle, which i s whenever the voltage applied M rhe load c h a p poltrriry. Because of rkis exchange of stored energy or rciicrivt power bccween the capacitors and thc magact, the applieu dc real power to mainmin charge OR the 36 mF capairor bank JS only 4% of the p%k reicuve power in h? 1084, mahag rhis 8 very cFficienc syszern.

2.4 Fault Derecnon CircltiF The bean can nor be ullowd to STOF sweeping across

rhc target. The Faulr Detection Circuit is b e wa~hdog circuirry consisung of m a p e w field and current scnsors and rhc assocrated processing cimms that will check to bc sure no serious falure modes east in cbc Rasrcr S y s m . If a failure is derec1c4 the Fauir Dereruon Ckuir rcmovcs the beam enable from rhe Linac, rhus sbunirg down rhr beam until repairs can be made.

That are two &Jut pickup coils waund in each magna rhar will have a volrage mduced tn them when &ere is a change in rbc magnetic field (dS/Jt) Since the field is a uianguhr waveform, rhis induced volwgc is esscndally a square wave rhar can be used to detecr a fault in either the magricL or ~hc magnet drive. There arc also two Rogo~sJa current loops per rrragner chac wiU be used 10 mewm rhc derivative of rhe miangular current. Each of lhese four =mors rrmovcs rhe km enable signal from one of the four divimm of che F4dr Qercssaon Circuitcy if ir clekcts a fa&. The b c ~ is shut off if LWO or more of rhz four beltrn enable signals are missmg.

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t 2.5 R w r r Magner

The raster magnets arc ferritc, 30-cm long wirh an 8-cm quare uperrurc. A magner crass-scccion is shown in Fig. 5. A prototype maper has bccn buik and mted Wuch uses Cer3uuc Magncucs ChOSOOS Hi-mu, low loss fen‘irr rsrher than rhe a.u cole of 121. T h i s i s I nickel- zm* mami31 with a permeability of 4500+ pLUH/m uc lSOOGauss. Thc inductance with two 20-rw coils is 1 1 mH which produrcs peak fielas of WI Gauss ar 1 0 0 ~ . From a raharion Iwdness mmdpoinr. rhcre i s cxpaiencc with ferrite cores as kickcr magnets kt B r o o k v e n Nw-onal Laboratory rhar show IbaL the fcmte maread will outlasr rhc coils

FERRITE CORE

Figure 5; Rasps magna CCOSS section

3 TESTRESULTS A raw maulator and magact have been successfully

rcsred t l ~ LANL. A phoro of rhe rnodulaior ana rhe rcsulring triangular cumnr is shown in Fig. 6. The moclulator is Jcsigncd IO operate at volmgcs up w 300 V arid lQOOkkr. For &is magnet with an inductance of approximately 1.1 rnH. when the voimge is scc to 243 V, peak Opcmiug currenl i s ti- 100 A (59 A ms).

Figwt 6: MoJubror md wsc wavcform (+/-lo0 A, 500 Hz)

The ourpur power capabiliry of rhe power supply IS based on rhc predicrcd losscs in [bc load, which i s rhe sum of rhcr losscs in rhc IGBT H-bridge, me cable. and losscs in lhc magna whch include rhe maper cable misrancc and lhc rnalplcr eddy cucrm losscs. Ar 243 V and 100A peak current. rkc ciuipqr powcr i s essmually rcsc-rivc and cqwl

IO 14,200 VARs. The mcasure4 inpur power (mal) i s only 925 Wars With approximarely 9oojoules smred in rhz 36mF capacitor bank, the l/e discharge ume is abour 2 seconds (loo0 cyclcs?r) if rhr dc charging cwcuir IS turncd off Fig. 7 shows thc ras~cr waveforms as measured on an oPcllloscopc.

i - 1

The spikes visible in she nwdularor uohagc ure cdused by rhc stray mducranccs being switched by &e lGBTs in rhr moduhlor. Tbc peaking char is stcn on rhc 6-doc wcl~cform, on chc orherhand. has two disringuishable features:

AII overall UR droop &e u) chs resistsrnce of rhe circuit, and A rhon overshoat of abow 10% at rkc b e g w g . wirh a nme consLant of abut 100 mmsec. T h i s is due to rddy currenls III the coil r h c essentially shield pan of the volume of thc Ferrite maper. Tbc volragc wershooi i s thereby caused because rhr initial mductmce is ady 90% of its dc valuc

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4 CONCLUSIONS A raswr rnagwt sysrem rhar b capable of safely md

reliably cxpandmg a pmton bm onta rhe wgcr has k e n developed and cesreQ. Test clam @.en on a prototype mdicatc bar Che efficicncy is berm than 9046. The full- scale design is robust due ro rhr appbcauon of re&inJancy as wcll as rhe use of independent f4dr dewlion cucuiuy that monirors rhe operation of the rwer system. B w d OII I ~ C posidvc resulu of b e prototype rest. a cornpicrc sysrem of eight magnets, maduhors and faub drcect cirtwb is currently being fabricxcd for full sprem evaluurion and resrirrg.

5 REFERENCES [l] CR-Rosc and R.E. Shafer, “ A WQ-A, 500-Rz,

Triangular Current Wave MoJul-~ and Magnet Used for Pmcle Bcm Rastcring,” Roc. 1997 Pddt Accel. cod., #7P089 (Vacouvcr, 5/97).

[2] C. Yw, et d.. ‘Targcr Raslrr Sysrem at CEBAF.” Nucl. Imr. and Mcth., Vol. A365, pp 46-48 (1!395).