Higher order mode damping considerations for the SPL cavities at CERN

Transcription

1 Highr ordr mod damping considrations for th SPL cavitis at CERN W. Wingartn

2 Outlin Th SPL study at CERN HOM damping rquirmnts for SPL study Optimisation of cavity gomtry rlatd to HOM damping Conclusion on gomtry damping HOMs Outlook Spar slids On longitudinal HOM xcitation for pulsd bams 2

3 Th SPL study at CERN Intrnational cross rlations of intrst with ESS, Projct X, SNS, Myrrha, JPARC An intrnational collaboration was stablishd for th SPL study Goal: dvlop multi-mgawatt sc proton linac cryomodul as a drivr for non-lhc physics programs such as nutrino and Radioactiv Ion Bam (RIB) physics. Dlivrabl: dvloping, in collaboration with xtrnal labs, bulk niobium 5-cll 704 MHz lliptical cavitis, to b tstd at 2 K, around th bginning of 203, in a ½ lngth cryo-modul with 4 cavitis. Th Suprconducting Proton Linac (SPL) study is now part of CERN s Mid Trm Plan. 3

4 HOM damping rquirmnts for SPL study Bam bunch lngth.2 mm bunch charg b 4 pc avrag puls currnt 40 ma (0.4 ms puls lngth with 50 Hz rptition rat) nrgy 5 GV bam powr 4 MW no. of cavitis 200 Cavity frquncy MHz numbr of clls 5 long. loss factor dsign bunch lngth s = 2 mm V/pC 4

5 Pmax W HOM damping rquirmnts for SPL study 2 HOM singl bunch HOM powr spctrum av. HOM powr pr cavity (k b I) 22 W worst cas HOM powr pr cavity (rsonant xcitation of mod for xt = 0 4 ) rquird damping xt, monopol mods 0 5 ditto, dipol mods 0 7 ~ 00 W Int. Workshop on HOM Damping in SRF Cavitis Cornll.0 Univrsity Octobr f Hz

6 HOM damping rquirmnts for SPL study 3 Rquird wrt bam brak up for whol linac x limits basd on bam dynamic simulations Simulatd cass: nominal, RF rrors, choppd bams, fundamntal pass-band mods Exampl: nominal Ovrall conclusion: Courtsy: Marcl Schuh / CERN-BE-RF 6

7 P W P[W] Pmax W P max [W] HOM damping rquirmnts for SPL study 4 Rquird wrt powr dposition pr cavity I = 40 ma; puls lngth ms, R/ = 00 W ; Rp. rat 50 Hz; f HOM = 2. GHz; 0 = 0 0 Powr built-up/dcay during puls of ms Maximum powr vs. frquncy showing principal Fourir componnts of bam t s t[sc] f f[hz]

8 P rad [W] Prad W Pc W P c [W] HOM damping rquirmnts for SPL study 5 Rquird wrt powr dposition pr cavity I = 40 ma; puls lngth ms, R/ = 00 W ; Rp. rat 50 Hz; f HOM = 2. GHz; 0 = 0 0 f (HOM) prcisly on bam spctral lin thrshold x xt x xt 8

9 P rad [W] Prad W P c [W] Pc W P rad [W] Prad W P c [W] Pc W HOM damping rquirmnts for SPL study 6 Rquird wrt powr dposition pr cavity Df= 0.0 MHz xt x I = 40 ma; puls lngth ms, R/ = 00 W ; 0 8 Rp. rat 50 Hz; f HOM = 2. GHz; 0 = Df= 0.0 MHz xt x Df= 0. MHz 0 7 Df= 0. MHz xt x xt x

10 HOM damping rquirmnts for SPL study 7 Rquird wrt powr dposition pr cavity Validation of rcursiv analytical calculations Courtsy: Marcl Schuh / CERN-BE-RF 0

11 HOM damping rquirmnts for SPL study 8 Conclusion I = 40 ma; puls lngth ms, R/ = 00 W ; Rp. rat 50 Hz; f HOM = 2. GHz; 0 = 0 0 Th main bam Fourir componnts (n 352 MHz) contribut significantly to th HOM powr, th 50 Hz Fourir componnt, howvr, only marginally; to rduc th HOM powr blow 00 W, th -valu of th HOM must b < 0 4 Avoiding th main bam Fourir componnts by th HOM frquncis within 0 khz rducs th HOM powr significantly, with a tndncy to bcom vn smallr for largr -valus (P < > 0 7 ) Th HOM powr could possibly b rducd by inlastic dtuning or an appropriat dsign of th cavity (though without changing th fundamntal mod frquncy) with th aim to kp sufficintly off ALL HOM frquncis from th main Fourir componnts

12 Optimisation of cavity gomtry rlatd to HOM damping Diffrnt bam tub diamtrs invstigatd Rfrnc dsign (Saclay): Ø 8 cm tapr Bam tub Ø 2 cm Bam tub Ø 4 cm Bam tub Ø 6 cm 2

13 Optimisation of cavity gomtry rlatd to HOM damping 2 Longitudinal Loss Factors Sourc: R. Calaga 3

14 Optimisation of cavity gomtry rlatd to HOM damping 3 L vs. f damping via normal conducting bam tub (plus normal conducting tapr) Most significant longitudinal monopol HOM for 5-cll 704 MHz cavity with 8 cm (rfrnc gomtry), 2 cm, 4 cm & 6 cm bam tub diamtr and.00e+ tapr ithr sc or nc.00e+0.00e E+08 tapr sc tapr nc high Al iron.00e+07.00e+06.00e+05.00e frquncy [MHz] 4

15 Optimisation of cavity gomtry rlatd to HOM damping 4 HOM / fundamntal mod vs. f damping via bam tub mad of stainlss stl by Karol Krizka/Univrsity of Toronto and summr studnt at CERN: Tchnical Not, SPL cavity: Powr dissipatd at bllows, 9 July 200 5

16 Optimisation of cavity gomtry rlatd to HOM damping 5 L vs. f damping via two 50 Ω antnnas in bam tub Ø = 3.6 cm L P I j ant 0 j positions of HOM couplr ports 5-cll 704 MHz cavity (rfrnc gomtry) with 8 cm bam tub diamtr with 2 HOM antnnas P P 2 0 r 2 i E ant c Z 0 I E+.00E+0.00E+09.00E+08.00E+07.00E+06.00E+05 antnna cntroid 3 cm away from transition to tapr P ant 2 2 W 2862 f GHz port 6.00E E MV m for 3.6 cm dia frquncy [MHz]

17 Optimisation of cavity gomtry rlatd to HOM damping 6 L vs. f damping via coaxial antnna shown at 4th SPL Collaboration Mting - jointly with ESS at LUND (Swdn) Courtsy Hans-Waltr Glock/Uni Rostock Targt valu 7

18 Optimisation of cavity gomtry rlatd to HOM damping 7 L vs. f damping with fundamntal powr couplr 0.00E+07.00E+06.00E+05.00E+04.00E+03.00E+02.00E+0 Targt valu.00e E E-02.00E-03 frquncy [MHz] powr couplr cntroid 8.5 cm away from first cll for 50 Ω powr couplr in bam tub Ø = 0 cm P I j ant L j r E P P 2 i Z 0 ant c I 2 Ths numbrs ar only stimations! 8

19 Optimisation of cavity gomtry rlatd to HOM damping 8 L vs. f damping with fundamntal powr couplr (FPC) HFSS: 80 modl with lump circuit lmnt at FPC window MicroWav Studio: full cavity (360 ) with port at FPC window Calculat loadd valu of systm (damping) Courtsy: Marcl Schuh / CERN-BE-RF 9

20 Optimisation of cavity gomtry rlatd to HOM damping 9 Hat is dissipatd in ss bllows P rad t P HOM t xt 0 P c t t PHOM 0 Fundamntal mod: Hat dissipation in 704 MHz, 25 MV/m, 0 = 0 0 : P c = 23 W CW => 5 6 W pulsd Hat dissipation in SS 704 MHz, 25 MV/m, quivalnt 0 = 3 0 : P c = 4 W CW => W pulsd HOM: Hat dissipation in SS 22 MHz, 0 = ; construct HOM dampr with xt < 0 5 or/and count on damping by powr couplr: xt < 0 4 (to b chckd!) Undr ths assumptions th hat dissipatd in th SS bllows for th HOM at 2.2 GHz is lss than 3 W (worst cas). xt 20

21 Conclusion on gomtry Prsnt cavity/tunr/couplr/h tank/bam tub layout 704 MHz 5 cll cavity bulk Nb 2K fundamntal powr couplr MW pulsd antnna prob 2 HOM couplr ports Intr-cavity bllows stainlss stl, no activ cooling.06 m activ lngth (without bam tubs).395 m ovr all 2

22 Conclusion on gomtry 2 Prsnt cavity/tunr/couplr/h tank/bam tub layout Pumping port HOM port Tunr Cool-down lin port H vssl (Ti) Cavity (Nb) Magntic shilding (cryoprm ) Includs spcific faturs for cryo-modul intgration (intr-cavity supports, cryognic fds, magntic shilding ) RF couplr port Courtsy: Th.Rnaglia, V. Parma; CERN 22

23 Conclusion on damping HOMs In th frquncy rang f = MHz, damping of HOMs is not sufficint, nithr by dissipation in bam tub (largly irrspctiv of absorbr matrial) or 50 Ω antnna placd in bam tub For f > 800 MHz, damping of HOMs is strongr, in particular for largr bam tub diamtr than our rfrnc dsign, but still insufficint for our nds ( < 0 4 ) Antnna HOM absorbrs ar ndd that ar trimmd for 300 and 500 MHz and rjct th fundamntal mod [Corollary: Thr may b a chanc to damp th HOMs via th fundamntal powr couplr (to b confirmd by simulations and masurmnts of th impdanc of th powr couplr as sn by th cavity)] 23

24 Outlook Thr is a first dsign dvlopd at Rostock Univrsity, basd on th HOM couplrs for LEP and LHC LHC HOM couplr Th nxt stps ar th Elctrical validation and th Mchanical/cryognic validation of modl Tuning to 704 MHz OK but cooling and construction to b chckd Prototyp manufactur of HOM couplr and warm RF tsts on Cu cavity modl 24

25 Thank you for your attntion! Acknowldgmnts to my collagus in CERN/BE-RF as wll as th mmbrs of th SPL-cavity working group 25

26 Spar slids 26

27 Insrtion (on rcursiv analytical calculations) On longitudinal HOM xcitation for pulsd bams CW bam: V ' n ptb Vq ' n 0 V q pt b 2 m- m M N n N T b T g V m-,n V mn V m,n V MN T ib T i t 27

28 Insrtion (on rcursiv analytical calculations) On longitudinal HOM xcitation for pulsd bams 2 n t mt (truncatd ) t* t m( t) Ti T i p 2 f i t T d t (truncatd) if t* N- T or N othrwis T d T b L f L 0 T x g b i ib i N Tb T T T V q R f q 28

29 Insrtion (on rcursiv analytical calculations) On longitudinal HOM xcitation for pulsd bams 3 29 q pt n q pt n q pt n N pt N m q pt n q pt n q pt n pt N m mn V V V V V V V V V b b b i b b b g , 2, b b b i b b i i pt npt T n N T p pt NpT pt pt m q mn V V b i mn t t p mn mn T t n T m t t V t V mn ; L mn mn HOM R t V t V t P * 0 t P t P xt HOM rad xt HOM c t P t P 0

30 Sourc: J. Plouin t al., 3rd SPL Collaboration Mting-3 Novmbr, CERN #frq r/ bta_opt o Rs_nOhm Oprating frquncy mod () : f 0 = MHz No monopol HOM at 2f 0 Mod at 2.64 MHz vry nar 3f 0 Cut-off frquncis for th mod TM00 Ø 80 mm : 2865 MHz Ø 30 mm : 763 MHz Ø 40 mm : 637 MHz List of monopol HOM calculatd with Suprfish btwn 0 and 3000 khz Axisymtric calculations Int. Workshop on HOM Damping in SRF Cavitis Cornll Univrsity