LHC
Crab Cavities“ from virtual reality to real reality”R. Calaga, BE-RF, LHC-PW, Chamonix 2012
On behalf of the LHC-CC collaboration
The Real “ Problem”
Nominal → 4 IRs, 120(+) parasitic encountersSufficiently large crossing angle inevitable (8-12 sep)
Beam-Beam TeamCERN-ATS-2011-217
8 to 16 LR encounters
No collisions or LR
2011 MD: 36 bunches50 ns, 2 Collisions
Reducing crossing angle
2
Consequence
Φ=σ zσ x
ϕc
σ eff=√σ x2+σ z
2ϕc2
Piwinski angle
Upgrade: reduce * (by factor 2-4)Consequence → approx double the crossing angle (10 sep)
Ineffective Overlap
Note: don't forget hour-glass effect (~15% loss for */z)
Some Numbers
2011 2012 after LS1 after LS3Energy 3.5 TeV 4 TeV 7 TeV 7 TeV
* [cm] 100 60 55 15
2 [rad] 260 313 247 473
R(z =7.55cm) 0.94 0.85 0.82 0.37
R(z =10.1cm) 0.76 0.74 0.28
2 ϕ≃d.√ϵ/βipAssume:
N = 2.5 m, d=10
very inefficient
For the Upgrade
12 separation
10 separation
Nb = 2 x 1011 p/bN = 2.5 m* = 15 cm
S. White, LHC-CC11
Lpk < 7 x 1034 (12 sep), little margin for leveling
Note: don't forget synchro-betatron resonances ~2-4BBLRs might alleviate partially
Nominal
To Recover
Δ p x=qVE. sin (ϕ s+ωt )
c
“ - Bump”
RF Deflector
RF Deflector
V crab=cE tan(ϕc)
ω R12
.2sin (πQ)
cos (ϕ cc−ip−πQ)
Cavity Voltage
~6MV/ IP-side (2 cavities)
add a cavity
Why 400 MHzLHC bunches are long
RF non-linearity (longitudinal)
Higher frequency (for example 800 MHz)“ Smaller” cavitiesLess voltage (VT 1/) → Not reallyEasier phase noise control ? (see later)
800 MHz Cavity, K. Ohmi
L∝N b
2
σ2 RΦ FRF
Φ
GUINEA-PIG simulation, Y. Sun
FRF ~ 10-25%Form factor ~1 (* 10-55 cm)
=1
Pillbox Cavity
beam
Transverse Cross Section, squash
beam in/out of the plane
TM01
0
TE11
1
TM11
0
TE01
1
freq spectrum
TM01
1
TM21
0
TM11
0Y
f res∝1R
R (independent of length)
crabbing mode (HOM)
R: 400 MHz ~ 610mm 800 MHz ~ 305mm
Too big for IR regions
Lengler et al., NIM 164 (1979)Karlsruhe-CERN RF Separator
“ 1st ” SRF Deflector
Assembly into cryostat
RF separator for 10-40 GeV/c from the SPSUnknown heavy particles, baryonic states/exchange, K± & p-bar
F = 2.865 GHzVT = 2 MV/m (104 cells)
Still in use at U-70 setup at IHEP
KEK Freq: 508.9 MHzPower: 50-120 kW (Qext: 2x105, BW: 2.55 kHz)
“ 1st” e± Crab Cavity
Feb 2007
LONG R&D, but short lifetime(2007-2010)
Complex HOM Damping Scheme
THEY WORK!
The real question: will the technology beefficient/transparent for the HL-LHC operation
Real answer: you may have to wait a little while
The LHC Pillbox
Conceptually simple, but practically difficult (KEKB experience)
Main Constraints:Frequency 800 MHzDamping LOM/SOM/HOM remains a challengeComplexity of multiple frequencies in LHCOnly vertical crossing at both IPs Surface field to kick gradient ratio is poor
1-cell version, CERN, L. Ficcadenti et al.2-cell version, USLARP, L. Xiao et al.
Pillboxes → TEM Cavities
~4yr of design evolution Exciting development of new concepts(BNL, CERN, CI-DL-LU, FNAL, KEK, ODU/JLAB, SLAC)
Short History
80yrs latersimilar concepts to be applied
for LHC crab cavities
Concentric Conducting Systemshort for coax
Leading to the telephone etc..
“ Its strongly reentrant form makes the field pattern at the outer radius predominately TEM with the consequence of only moderate current flow”
E. Haebel
Freq = 100 MHzGap Voltage = 0.5 MVPbeam = 200 kW(1.6 MW @400 MHZ, NC Cavities)
/4
More History
/4 TEM ResonatorI0
V0
ab
~/4
= 1
87.4
mm
V 0
ab
~/4
~/4
gap
Z 0=V 0/ I 0
Frequency resonator lengthand “ not” the gap or radii of the concentric cylinders
194 mm194 mm
142.5 mm122 mm
BNL: I. Ben-Zvi et al.
400 MHz LHC Cavity, quasi /4
Z 0 tan(β l)=1
ωC gap
/4 Resonator, HOMs
Note, due to large aperture & residual Ez the LHC cavity will only a quasi /4 resonator
For a pure /4 resonator, next HOM is x3 the fundamental mode
Therefore, damping is a LOT more easier (for example use a high-pass filter)
56 MHz RHIC Prototype
Pedestal to cancel Ez
V0
I0
-I0
~/2
/2 TEM Resonator
Two /4 resonators → /2➔ Use HOM (TE11 like) for deflection➔ More elegant is to use two /2 resonators
Single /2Two /2
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
~/2
Joint SLAC-ODU Effort
2010
2011
Fill these regions Full design change
SLAC, Z. LiODU, J. Delayen
/2 TEM Resonator
Symmetric Ridges
Also, Initially proposed by F. Caspers (Crab WS 2008)
/4 = 187.5 mm
Courtesy G. Burt, B. Hall4R (LU-DI-JLAB)
Four co-linear /4 resonators 500 MHz CEBAF Separator
Conical resonators for mechanical stability
Downside is that the deflecting mode is NOT the lowest order mode
4 eigenmodes, mode 2 is our crab mode
Performance Chart
Double Ridge(ODU-SLAC)
4-Rod(UK)
¼ Wave(BNL)
Cavity Radius [mm] 147.5 143/118 142/122Cavity length [mm] 597 500 380Beam Pipe [mm] 84 84 84Peak E-Field [MV/m] 33 32 47Peak B-Field [mT] 56 60.5 71RT/Q [] 287 915 318Nearest Mode [MHz] 584 371-378 575
Kick Voltage: 3 MV, 400 MHzGeo
met
rical
RF
194 mm
B1 B2
< 60 MV/m
< 100 mT
damping more complicated
Impedance Thresholds
Longitudinal impedance2.4 M total (7 TeV)
Strongest monopole mode:R/Q=200 → Qe<1x103
Damping → Qe < 100-500
Transverse
Courtesy: Burov, Shaposhnikova
HOM
HOM
HOM
HOM
Crab
Strongest dipole mode:Z < 0.6 M/m (0.58 GHz)(Qext = 500)
Longitudinal
HOM probe
Input
HOM Broadband
LOM
3-5 stage ChebyshevHigh pass filter
HOM Damping
56 MHz Prototype
(placement not fixed yet)
4 Symmetric couplers on the end caps
(notch/high-pass ?)
4 asymmetric couplers on cavity body
ODUCAV SRHW KEKCAV UKCAV QWAVER FRSCAV
Vz(x=0) [kV] 0.0 -2.1 - 2.5i -4 +1378i 0.0 0 +85.7i -0.1 -0.2i
Vx [MV] 5 5 5 5 5 5
B(2) [mTm/m] 0 0 -0.04i -32.7 - 0.1i 0.02 + 0i 25 + 0i 0 +108i
B(3) [mTm/m2 ] 1250 + 0i 229 + 0i 250 - 0i 2452 - 0.5i 464 + 0i -233 +1i
B(4) [mTm/m3] 0 0 266 - 5i 0 540 +0i -189 -14209i
RF “ Multipoles”Courtesy: A. Grudiev, R. deMaria, J. Barranco
Linear tune shifts ~ 0.0 -10-3
Non-linear effects (b3, b4) → Negligible
See slide A5 for mitigation
Cavity Tuning Thoughts
Up/down motion± 2mm → 1 kHz
Push/pull on cavity body
Scissor jack type mechanism
CEBAF TunerDouble lever(Saclay type)
SM
SM
Modified screw/nut(SOLEIL type)
SM
Low gradient (weak or moderate)
High Field (weak)
Multipacting Courtesy G. Burt, J. Delayan, Z. Li
Medium gradient (strong)beam-pipe region (similar to KEKB)
Not a serious worry, will require RF processing
RF PowerV b∝QL I b
RT
Q 0
(k Δ x)
50 kW
RF Power ~8kW (VT=3 MV)
Margin
R/Q = 300 Ib = 0.55 A
For Comparison, Main RF 300kW (V=2 MV)
RF Power Options Courtesy E. Montesinos
2.0m
2.5m
2.0m
Solid State Amplifiers190 kW, 352 MHz
Single tower < 3m
IOTs (TV Transmitter)Light Sources
Tetrode (SPS)400 MHz, ~50kW
Electrosys
2.5 m
50 kW/cavity, moderate powerSimplified (modified) LHC coupler Common platform for 3 cavities designs
Three available choicesFor SPS tests, reuse Tetrodes used in SPS tests
Crab Cryomodule
Graphic Courtesy: S. Weisz(Space in bypass extremely limited)
RF Distribution
~300m LLRF (Coupled feedback)
P. Baudrenghien
Need ~20-25 m space for amplifiers on each IP-side
Waveguides/Coax
“Preliminary thoughts”
RF Noise
Δ x IP=θck RF
δϕ
ΔV T
V T≪ 1
tan (θ/2)
σ x*
σ z
For example:c=570rad; V/V=0.4%x*=7m, x*=7.55cm
err=1.2rad
Amplitude jitter
Phase jitterFor example: = 0.0050, c=570radx
IP = 0.3m (5% of x
*)
LHC Main RF, = 0.0050 at 400 MHz (Philippe)(summing noise at all betatron bands from DC→300kHz)
Note: IOTs & SSAs are less noisy + betatron comb (0.001)
Planning Overview
M2: Compact Validation& Selection (2012-13)
M2: Beam Tests (2015-16)
Prototype Cryomodule
Final Implementation(2022-23?)
Production of Cryomodules
Detailed planning, see E. Jensen (LHC-CC11)
LS1 LS2 LS3
Cavity Testing
Sheet metal (deep drawing, spinning, hydro-forming)Multiple dies, electron-beam welding
Solid Niobium & machiningMaterial costs & leak tightness
Fabrication Options
{Total 16 cavities (2 IPs, B1 & B2)
With sheet metal (4mm thick)We need approx 500-600 kg Niobium (RRR>300)}
0 100 200 300 400 500 6000.00E+001.00E+022.00E+023.00E+024.00E+025.00E+026.00E+02
Position [cm]
Ez
[V/m
]
4R Al-Prototype Courtesy G. Burt, B. Hall
Bead-Pull
Niobium cavity to be delivered in March 2012
Nb Cavity from solid Ingot
Al-prototype for field measurements
Double Ridge FabricationCourtesy:J. Delayan, Niowave
Nov 2011 Jan 2012
NiowaveSTTR, Phase I/II
Testing April 2012
Real Reality ?
“ If it is real, we believe in it”The Church of Reality
100% 90% 80% 70%
Leveling with crossing angle
A1: Leveling, X-Angle Courtesy Beam-Beam TeamCERN-ATS-2011-217
Demonstrated in 2011 w/o affecting other IPs and emittancew/o crabs range is extremely limited
To fully exploit leveling with x-angle, an RF cavity is ideal
A2: Why SC-Cavity
Q0=GR s
Geometrical factor~ 200
Microwave resistanceCopper ~ mNiobium-SC ~ n
With ~6MV/module, NC-RF is not a viable choice
R s=1
σ δ
G=∫ E3dV
∫ H 2dA
Maximize aperture & minimize # of cavities (reduced impedance)
A choice of 2K cryogenic system optimum for crabs (LHC-CC11)
A3: SPS As a Testbed
Long. Position: 4009 m +/- 5mTotal length: 10.72 mx, 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
Present COLDEX
4 LHC Cavities in SPS (1998)
RF Power Setup (~50kW, Tetrode)
A4: SPS, BA4 Setup
Y-Chamber like, similar to present COLDEXCourtesy E. Montesinos
5 db
m/d
iv
500 kHz
500 kHz
A5: RF Noise, LHC with 1-T feedbackP. Baudrenghien
➔ Selective reduction at all frev lines (V=1.5MV, QL=60k)
➔ Using a betatron comb, we can expect ~16dB reduction at selective frequencies
Courtesy G. Burt, J. Delayan
A6: RF Non-Linearity
Voltage deviation over 5mm:Horizontal: 20% → 5%Vertical: x2 → 10%
Tuning (shaping) to suppress multipoles
A7: Other Applications
Emittance exchange x-z (P. Emma & others)
Φ=σ zσ x
ϕc
HE-LHC (16.5 TeV)= 0.6, similar to nominal(z = 6.5cm, x = 9m, c = 160mrad)
R = -12% wr.t. to head-on
Compensate offset collisions due to beam loading for LHeC (Zimmermann)May not be needed if phase modulation removes the phase-slip
Momentum cleaning: Qacc = (fcc/f0)(S. Fartoukh)For effective Qacc ~ 0.3 → 8GHz, too high freq (Y. Sun)
x
z
SRF Deflector10 MV, 366-447 MHz
3 GeV LINAC
Mode l TE113
Freq 447 MHz
R/Q 500
Epk 34 MV/m
Bpk 74 mT
Aperture 75 mm
A8: ProjectX Synergy
LHC Type Concept(s)
Courtesy M. Champion, Y. Yakovlev
A. Facco, SRF09A9: TEM Resonators
Saclay IPNO
ArgonneNew DelhiINFN LNL-MSUTRIUMF
INFN LNL
Sputtered
INFN LNL
Right here at CERN(HIE-ISOLDE) Cavity reached (ANL 72 MHz)
Ep=70 MV/m, Bp=100 mTQ0 = 1 x 109 at 4.6 K (IPAC10)