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

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”
Beam-Beam Team
CERN-ATS-2011-217
8 to 16 LR
encounter
s
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 (8-12s sep)
Consequence
Piwinski angle
Ineffective Overlap
σz
Φ= σ ϕc
x
2
f
σ eff = √
σ +σ ϕ
2
x
2
z
Upgrade: reduce b* (by factor 2-4)
Consequence → approx double the crossing angle (10s
sep)
Note: don't forget hour-glass effect (~15% loss for b*/sz)
2
c
Some Numbers
2011
2012
after LS1
after LS3
Energy
3.5 TeV
4 TeV
7 TeV
7 TeV
b* [cm]
100
60
55
15
2f [mrad]
260
313
247
473
RF(sz =7.55cm)
0.94
0.85
0.82
0.37
0.76
0.74
0.28
RF(sz =10.1cm)
ϵ/β
Assume: 2 ϕ≃d. √
ip
eN = 2.5 mm, d=10
very inefficient
For the Upgrade
10s separation
12s separation
Nominal
Nb = 2 x 1011 p/b
eN = 2.5 mm
b* = 15 cm
S. White, LHC-CC11
Lpk < 7 x 1034 (12s sep), little margin for leveling
Note: don't forget synchro-betatron resonances F ~2-4
BBLRs might alleviate partially
To Recover
 Bump”
RF
Deflector
f
c
RF
Deflector
qV
Δ p x=
. sin (ϕ s+ ωt )
E
cE tan(ϕc )
2 sin (πQ)
V crab=
.
ωR12
cos(ϕ cc− ip− πQ)
Cavity Voltage
add a cavity
~6MV/ IP-side (2 cavities)
Why 400 MHz
LHC bunches are long
RF non-linearity (longitudinal)
L∝
N 2b
σ2
800 MHz Cavity, K. Ohmi
RΦ FΦ
RF
GUINEA-PIG simulation, Y. Sun
=1
Form factor ~1 (b* 10-55 cm)
Higher frequency (for example 800 MHz)
“Smaller” cavities
Less voltage (VT  1/w) → Not really
Easier phase noise control ? (see later)
FRF ~ 10-25%
Pillbox Cavity
1
f res ∝
R
R
beam
(independent of
length)
R: 400 MHz ~ 610mm
800 MHz ~ 305mm
Too big for
IR regions
TE011
TM210
TM011
TM110
crabbing mode
(HOM)
TM110Y
beam in/out of the plane
TE111
TM010
Transverse Cross Section, squash
freq spectrum
“1st” SRF Deflector
Assembly into cryostat
Lengler et al., NIM 164 (1979)
Karlsruhe-CERN RF Separator
F = 2.865 GHz
VT = 2 MV/m (104 cells)
RF separator for 10-40 GeV/c from the SPS
Unknown heavy particles, baryonic states/exchange, K± & p-bar
Still in use at U-70 setup at IHEP
“1st” e± Crab Cavity
LONG R&D, but short lifetime
(2007-2010)
KEK Freq: 508.9 MHz
Power: 50-120 kW
(Qext: 2x105, BW: 2.55 kHz)
Complex HOM Damping Scheme
Feb 2007
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
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.
Pillboxes → TEM Cavities
~4yr of design evolution
Exciting development of new concepts
(BNL, CERN, CI-DL-LU, FNAL, KEK, ODU/JLAB, SLAC)
Short History
Concentric Conducting System
short for coax
Leading to the telephone etc..
80yrs later
similar concepts to be applied
for LHC crab cavities
More History
l/4
Freq = 100 MHz
Gap Voltage = 0.5 MV
Pbeam = 200 kW
(1.6 MW @400 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
l/4 TEM Resonator
gap
b
a
I0
V0
b
~l/4
BNL: I. Ben-Zvi et al.
a
~l/4
Z 0= V 0 / I 0
V0
Frequency  resonator length
and “not” the gap or radii of the concentric cylinders
122 mm
142.5 mm
194 mm
194 mm
l/4 Resonator, HOMs
For a pure l/4 resonator, next HOM is
x3 the fundamental mode
1
Z 0 tan(βl)=
ωC gap
56 MHz RHIC Prototype
Therefore, damping is a LOT more easier
(for example use a high-pass filter)
400 MHz LHC Cavity, quasi l/4
Note, due to large aperture & residual Ez
the LHC cavity will only a quasi l/4
resonator
Pedestal to cancel Ez
l/2 TEM Resonator
Two l/4 resonators → l/2
 Use HOM (TE
11 like) for deflection
 More elegant is to use two l/2
resonators
I0
V0
Single l/2
Two l/2
~l/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
l/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)
4R (LU-DI-JLAB)
Four co-linear l/4
resonators
l/4
= 187.5 mm
Courtesy G. Burt, B. Hall
500 MHz CEBAF
Separator
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
Performance Chart
Kick Voltage: 3 MV, 400 MHz
Geometrical
RF
Double
Ridge
(ODUSLAC)
4-Rod
(UK)
¼ Wave
(BNL)
Cavity Radius [mm]
147.5
143/118
142/122
Cavity length [mm]
597
500
380
Beam Pipe [mm]
84
84
84
Peak E-Field
[MV/m]
33
32
47
Peak B-Field [mT]
56
60.5
71
RT/Q [W]
287
915
Nearest Mode
584
371-378
194 mm
B1
318 more
damping
complicated
575
B2
< 60 MV/m
< 100 mT
Impedance Thresholds
Longitudinal
Courtesy: Burov,
Shaposhnikova
Longitudinal impedance
2.4 MW total (7 TeV)
Strongest monopole mode:
R/Q=200W → Qe<1x103
Damping → Qe < 100-500
Transverse
Strongest dipole mode:
Z < 0.6 MW/m (0.58 GHz)
(Qext = 500)
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
RF “Multipoles”
Courtesy: A. Grudiev, R. deMaria, J. Barranco
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
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
SM
Scissor jack type
mechanism
SM
SM
Double lever
(Saclay type)
Modified screw/nut
(SOLEIL type)
CEBAF Tuner
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
RF Power
RT
V b ∝Q L I b (k Δ x)
Q0
R/Q = 300 W,
Ib = 0.55 A
50 kW
Margin
RF Power ~8kW (VT=3 MV)
For Comparison,
Main RF 300kW (V=2 MV)
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
IOTs (TV Transmitter)
Light Sources
Solid State Amplifiers
190 kW, 352 MHz
2.5
m
2.5m
Tetrode (SPS)
400 MHz, ~50kW
Electrosys
2.0m
2.0m
Single tower < 3m
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
RF Noise
Amplitude
jitter
Δ VT
VT
Phase jitter
≪
σ
1
tan (θ/ 2) σ z
θc
Δ x IP =
δϕ
k RF
*
x
For example:
qc=570mrad; DV/V=0.4%
sx*=7mm, sx*=7.55cm
qerr=1.2mrad
For example:
Df = 0.0050, qc=570mrad
DxIP = 0.3mm (5% of sx*)
LHC Main RF, Df = 0.0050 at 400 MHz (Philippe)
(summing noise at all betatron bands from DC→300kHz)
Note: IOTs & SSAs are less noisy + betatron comb (Df

0.001)
Planning Overview
M2: Beam Tests
(2015-16)
Prototype Cryomodule
Cavity
Testing
LS1
Final Implementation
(2022-23?)
Production of Cryomodules
LS2
LS3
M2: Compact Validation
& Selection (2012-13)
Detailed planning, see E. Jensen (LHC-CC11)
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 500-600 kg Niobium (RRR>300)}
4R Al-Prototype
Courtesy G. Burt, B. Hall
Nb Cavity
from solid
Ingot
Al-prototype for field measurements
Bead-Pull
Ez [V/m]
2.00E+06
1.50E+06
1.00E+06
5.00E+05
0.00E+00
0
Niobium cavity to be delivered in March 2012
100 200 300 400 500 600
Position [cm]
Double Ridge Fabrication
Courtesy:J. Delayan, Niowave
Niowave
STTR, Phase I/II
Nov 2011
Jan 2012
Testing April 2012
Real Reality ?
“If it is real, we believe in it”
The Church of Reality
Courtesy Beam-Beam Team
A1: Leveling, X-Angle
CERN-ATS-2011-217
100%
90%
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
A2: Why SC-Cavity
With ~6MV/module, NC-RF is not a viable choice
G
Q0 =
Rs
Geometrical factor
~ 200 W
∫
G=
∫
E 3 dV
H 2 dA
1
Microwave resistance
R s= σ δ
Copper ~ mW
Niobium-SC ~ nW
Maximize aperture & minimize # of cavities (reduced
impedance)
A choice of 2K cryogenic system optimum for crabs (LHC-
A3: SPS As a Testbed
Present COLDEX
Long. Position: 4009 m +/- 5m
Total length: 10.72 m
bx, by: 30.3m, 76.8m
Cavity validation with beam (field, ramping, RF controls,
impedance)
Collimation, machine protection, cavity transparency
RF noise, emittance growth, non-linearities,
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
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
A6: RF Non-Linearity
Tuning (shaping) to suppress
multipoles
Voltage deviation over 5mm:
Horizontal: 20% → 5%
Vertical: x2 → 10%
Courtesy G. Burt, J. Delayan
A7: Other Applications
Emittance exchange x-z (P. Emma & others)
ex  ez
Momentum cleaning: Qacc = (fcc/f0)hd (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
(sz = 6.5cm, sx = 9mm, fc = 160mrad)
RF = -12% wr.t. to head-on
A8: ProjectX Synergy
Courtesy M. Champion, Y. Yakovlev
3 GeV LINAC
SRF Deflector
10 MV, 366-447 MHz
LHC Type Concept(s)
Mode l
TE113
Freq
447 MHz
R/Q
500 W
Epk
34 MV/m
Bpk
74 mT
Aperture
75 mm
A9: TEM Resonators
INFN LNLMSU
TRIUM
F
INFN
LNL
A. Facco, SRF09
Argonn
e
New
Delhi
INFN
LNL
Sputtere
d
Sacla
y
IPN
O
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)