LHC. Crab Cavities from virtual reality to real reality. R. Calaga, BE-RF, LHC-PW, Chamonix On behalf of the LHC-CC collaboration

Transcription

1 LHC Crab Cavities from virtual reality to real reality R. Calaga, BE-RF, LHC-PW, Chamonix 2012 On behalf of the LHC-CC collaboration

2 Beam-Beam Team The Real Problem CERN-ATS to 16 LR encounters 2011 MD: 36 bunches 50 ns, 2 Collisions No collisions or LR Reducing crossing angle Nominal 4 IRs, 120(+) parasitic encounters Sufficiently large crossing angle inevitable (8-12 sep)

3 Consequence Piwinski angle Ineffective Overlap 2 σz Φ= σ ϕc x σ eff = σ +σ ϕ 2 x 2 z Upgrade: reduce * (by factor 2-4) Consequence approx double the crossing angle (10 sep) Note: don't forget hour-glass effect (~15% loss for */ z) 2 c

4 Some Numbers after LS1 after LS3 Energy 3.5 TeV 4 TeV 7 TeV 7 TeV * [cm] [ rad] R ( z =7.55cm) R ( z =10.1cm) Assume: 2 ϕ d. ϵ/βip N = 2.5 m, d=10 very inefficient

5 For the Upgrade 10 separation 12 separation Nominal Nb = 2 x 1011 p/b N = 2.5 m S. White, LHC-CC11 * = 15 cm Lpk < 7 x 1034 (12 sep), little margin for leveling Note: don't forget synchro-betatron resonances ~2-4 BBLRs might alleviate partially

6 To Recover - Bump RF Deflector c RF Deflector qv Δ p x=. sin (ϕ s+ωt ) E ce tan(ϕc ) 2 sin (π Q) V crab=. ω R12 cos (ϕ cc ip π Q)

7 Cavity Voltage add a cavity ~6MV/ IP-side (2 cavities)

8 Why 400 MHz LHC bunches are long RF non-linearity (longitudinal) 800 MHz Cavity, K. Ohmi 2 L Nb σ2 R Φ F ΦRF =1 Form factor ~1 ( * cm) Higher frequency (for example 800 MHz) Smaller cavities Less voltage (VT 1/ ) Not really Easier phase noise control? (see later) GUINEA-PIG simulation, Y. Sun FRF ~ 10-25%

9 Pillbox Cavity 1 f res R R beam (independent of length) R: 400 MHz ~ 610mm 800 MHz ~ 305mm Too big for IR regions Transverse Cross Section, squash TE011 TM210 TM011 TM110 TM110Y beam in/out of the plane TE111 TM010 crabbing mode (HOM) freq spectrum

10 1 SRF Deflector st Assembly into cryostat Lengler et al., NIM 164 (1979) Karlsruhe-CERN RF Separator F = GHz VT = 2 MV/m (104 cells) RF separator for GeV/c from the SPS Unknown heavy particles, baryonic states/exchange, K± & p-bar Still in use at U-70 setup at IHEP

11 1 st e Crab Cavity ± LONG R&D, but short lifetime ( ) KEK Freq: MHz Power: kw (Qext: 2x105, BW: 2.55 khz) Complex HOM Damping Scheme Feb 2007

12 THEY WORK! The real question: will the technology be efficient/transparent for the HL-LHC operation Real answer: you may have to wait a little while

13 The LHC Pillbox Conceptually simple, but practically difficult (KEKB experience) Main Constraints: Frequency 800 MHz Damping LOM/SOM/HOM remains a challenge Complexity of multiple frequencies in LHC Only vertical crossing at both IPs Surface field to kick gradient ratio is poor 2-cell version, USLARP, L. Xiao et al. 1-cell version, CERN, L. Ficcadenti et al.

14 Pillboxes TEM Cavities ~4yr of design evolution Exciting development of new concepts (BNL, CERN, CI-DL-LU, FNAL, KEK, ODU/JLAB, SLAC)

15 Short History Concentric Conducting System short for coax Leading to the telephone etc.. 80yrs later similar concepts to be applied for LHC crab cavities

16 More History /4 Freq = 100 MHz Gap Voltage = 0.5 MV Pbeam = 200 kw (1.6 MHZ, NC Cavities) Its strongly reentrant form makes the field pattern at the outer radius predominately TEM with the consequence of only moderate current flow E. Haebel

17 /4 TEM Resonator ~ /4 = mm gap a V0 b ~ /4 BNL: I. Ben-Zvi et al. Z 0=V 0 / I 0 b a I0 ~ /4 V0 Frequency resonator length and not the gap or radii of the concentric cylinders mm 194 mm 122 mm 194 mm

18 /4 Resonator, HOMs For a pure /4 resonator, next HOM is x3 the fundamental mode 1 Z 0 tan(β l )= ω C gap 56 MHz RHIC Prototype Therefore, damping is a LOT more easier (for example use a high-pass filter) 400 MHz LHC Cavity, quasi /4 Note, due to large aperture & residual Ez the LHC cavity will only a quasi /4 resonator Pedestal to cancel Ez

19 /2 TEM Resonator Two /4 resonators /2 Use HOM (TE like) for deflection 11 I0 ~ /2 V0 More elegant is to use two /2 resonators Single /2 Two /2 ~ /2 -I0 SLAC, Z. Li ODU, J. Delayen Height of the cavity is symmetric about beam pipe Only compact in dimension, LHC needs both x-y compactness

20 /2 TEM Resonator SLAC, Z. Li ODU, J. Delayen 2010 Fill these regions Full design change 2011 Symmetric Ridges Joint SLAC-ODU Effort Also, Initially proposed by F. Caspers (Crab WS 2008)

21 4R (LU-DI-JLAB) Four co-linear /4 resonators Courtesy G. Burt, B. Hall 500 MHz CEBAF Separator /4 = mm 4 eigenmodes, mode 2 is our crab mode Conical resonators for mechanical stability Downside is that the deflecting mode is NOT the lowest order mode

22 RF Geometrical Performance Chart Kick Voltage: 3 MV, 400 MHz Double Ridge (ODU-SLAC) 4-Rod (UK) ¼ Wave (BNL) Cavity Radius [mm] / /122 Cavity length [mm] Beam Pipe [mm] Peak E-Field [MV/m] < 60 MV/m Peak B-Field [mt] < 100 mt RT/Q [ ] Nearest Mode [MHz] damping more complicated 194 mm B1 B2

23 Impedance Thresholds Longitudinal Courtesy: Burov, Shaposhnikova HOM HOM HOM HOM Crab Longitudinal impedance 2.4 M total (7 TeV) Strongest monopole mode: R/Q=200 Qe<1x103 Damping Qe < Transverse Strongest dipole mode: Z < 0.6 M /m (0.58 GHz) (Qext = 500)

24 HOM Damping HOM Broadband 56 MHz Prototype Input LOM 3-5 stage Chebyshev High pass filter (placement not fixed yet) 4 Symmetric couplers on the end caps (notch/high-pass?) HOM probe 4 asymmetric couplers on cavity body

25 RF Multipoles Courtesy: A. Grudiev, R. demaria, J. Barranco ODUCAV SRHW KEKCAV UKCAV QWAVER FRSCAV Vz(x=0) [kv] i i i i Vx [MV] B(2) [mtm/m] i i i i i 250-0i i i i 266-5i i i B(3) [mtm/m2 ] B(4) [mtm/m3] i i 0 Linear tune shifts ~ Non-linear effects (b3, b4) Negligible See slide A5 for mitigation

26 Cavity Tuning Thoughts Up/down motion ± 2mm 1 khz Push/pull on cavity body SM Scissor jack type mechanism SM SM Double lever (Saclay type) Modified screw/nut (SOLEIL type) CEBAF Tuner

27 Multipacting Courtesy G. Burt, J. Delayan, Z. Li Low gradient (weak or moderate) Medium gradient (strong) beam-pipe region (similar to KEKB) High Field (weak) Not a serious worry, will require RF processing

28 RF Power RT V b Q L I b (k Δ x) Q0 R/Q = 300 Ib = 0.55 A 50 kw Margin RF Power ~8kW (VT=3 MV) For Comparison, Main RF 300kW (V=2 MV)

29 RF Power Options Courtesy E. Montesinos 50 kw/cavity, moderate power Simplified (modified) LHC coupler Common platform for 3 cavities designs Three available choices For SPS tests, reuse Tetrodes used in SPS tests Solid State Amplifiers 190 kw, 352 MHz 2.5m IOTs (TV Transmitter) Light Sources 2.5m Tetrode (SPS) 400 MHz, ~50kW Electrosys 2.0m 2.0m Single tower < 3m

30 RF Distribution Preliminary thoughts ~300m LLRF (Coupled feedback) P. Baudrenghien Crab Cryomodule Need ~20-25 m space for amplifiers on each IP-side Graphic Courtesy: S. Weisz (Space in bypass extremely limited) Waveguides/Coax

31 RF Noise Amplitude jitter ΔVT VT σ tan (θ1 / 2) σ * x z For example: c=570 rad; V/V=0.4% x*=7 m, x*=7.55cm err=1.2 rad Phase jitter θc Δ x IP = δϕ k RF For example: = , c=570 rad xip = 0.3 m (5% of x*) LHC Main RF, = at 400 MHz (Philippe) (summing noise at all betatron bands from DC 300kHz) Note: IOTs & SSAs are less noisy + betatron comb ( 0.001)

32 Planning Overview M2: Beam Tests ( ) Cavity Testing Prototype Cryomodule LS1 Final Implementation ( ?) Production of Cryomodules LS2 LS3 M2: Compact Validation & Selection ( ) Detailed planning, see E. Jensen (LHC-CC11)

33 Fabrication Options Sheet metal (deep drawing, spinning, hydro-forming) Multiple dies, electron-beam welding Solid Niobium & machining Material costs & leak tightness {Total 16 cavities (2 IPs, B1 & B2) With sheet metal (4mm thick) We need approx kg Niobium (RRR>300)}

34 4R Al-Prototype Courtesy G. Burt, B. Hall Nb Cavity from solid Ingot Ez [V/m] Al-prototype for field measurements Niobium cavity to be delivered in March E E E E E E E+00 Bead-Pull Position [cm]

35 Double Ridge Fabrication Courtesy:J. Delayan, Niowave Niowave STTR, Phase I/II Nov 2011 Jan 2012 Testing April 2012

36 Real Reality? If it is real, we believe in it The Church of Reality

37 Courtesy Beam-Beam Team A1: Leveling, X-Angle 100% CERN-ATS % 80% 70% Leveling with crossing angle Demonstrated in 2011 w/o affecting other IPs and emittance w/o crabs range is extremely limited To fully exploit leveling with x-angle, an RF cavity is ideal

38 A2: Why SC-Cavity With ~6MV/module, NC-RF is not a viable choice G Q0 = Rs Geometrical factor ~ 200 Microwave resistance Copper ~ m Niobium-SC ~ n 3 E dv G= H 2 da R s= 1 σδ Maximize aperture & minimize # of cavities (reduced impedance) A choice of 2K cryogenic system optimum for crabs (LHC-CC11)

39 A3: SPS As a Testbed Present COLDEX Long. Position: 4009 m +/- 5m Total length: m x, y: 30.3m, 76.8m Cavity validation with beam (field, ramping, RF controls, impedance) Collimation, machine protection, cavity transparency RF noise, emittance growth, non-linearities, Instrumentation & interlocks

40 A4: SPS, BA4 Setup 4 LHC Cavities in SPS (1998) RF Power Setup (~50kW, Tetrode) Courtesy E. Montesinos Y-Chamber like, similar to present COLDEX

41 with 1-T feedback P. Baudrenghien 5 dbm/div A5: RF Noise, LHC 500 khz 500 khz Selective reduction at all frev lines (V=1.5MV, QL=60k) Using a betatron comb, we can expect ~16dB reduction at selective frequencies

42 A6: RF Non-Linearity Tuning (shaping) to suppress multipoles Voltage deviation over 5mm: Horizontal: 20% 5% Vertical: x2 10% Courtesy G. Burt, J. Delayan

43 A7: Other Applications Emittance exchange x-z (P. Emma & others) x z Momentum cleaning: Qacc = (fcc/f0) (S. Fartoukh) For effective Qacc ~ 0.3 8GHz, too high freq (Y. Sun) Compensate offset collisions due to beam loading for LHeC (Zimmermann) May not be needed if phase modulation removes the phase-slip HE-LHC (16.5 TeV) σz Φ= σ ϕc x = 0.6, similar to nominal ( z = 6.5cm, x = 9 m, c = 160mrad) R = -12% wr.t. to head-on

44 A8: ProjectX Synergy 3 GeV LINAC Courtesy M. Champion, Y. Yakovlev SRF Deflector 10 MV, MHz LHC Type Concept(s) Mode l TE113 Freq 447 MHz R/Q 500 Epk 34 MV/m Bpk 74 mt Aperture 75 mm

45 A9: TEM Resonators TRIUMF INFN LNL INFN LNL-MSU A. Facco, SRF09 Argonne New Delhi INFN LNL Sputtered Saclay IPNO Right here at CERN (HIE-ISOLDE) Cavity reached (ANL 72 MHz) Ep=70 MV/m, Bp=100 mt Q0 = 1 x 109 at 4.6 K (IPAC10)