LLRF for EUCARD Crab Cavities Graeme Burt (on behalf of Amos Dexter) Paris May 2011.
-
Upload
garey-mason -
Category
Documents
-
view
220 -
download
1
Transcript of LLRF for EUCARD Crab Cavities Graeme Burt (on behalf of Amos Dexter) Paris May 2011.
![Page 1: LLRF for EUCARD Crab Cavities Graeme Burt (on behalf of Amos Dexter) Paris May 2011.](https://reader031.fdocuments.us/reader031/viewer/2022013012/56649f435503460f94c631ae/html5/thumbnails/1.jpg)
LLRF for EUCARD Crab Cavities
Graeme Burt (on behalf of Amos Dexter)
Paris
May 2011
![Page 2: LLRF for EUCARD Crab Cavities Graeme Burt (on behalf of Amos Dexter) Paris May 2011.](https://reader031.fdocuments.us/reader031/viewer/2022013012/56649f435503460f94c631ae/html5/thumbnails/2.jpg)
Crab Parameters
Beam Energy
BunchCharge
BunchRepitition
Crab peakPower
BunchLength
ILC 0.5 TeV 3.2 nC 3 MHz 1.24 kW 300 m
CLIC 1.5 TeV 0.6 nC 2 GHz 288 kW 100 m
LHC 7 TeV 18.4 nC 40 MHz 12.7 kW 7.55 cm
Stiff beam, needs a large voltage and/or small crossing angle
Long bunch = low frequency to avoid non-linear kick
Huge beam loading and wakes
Simpler design required
Short timescales, high current
![Page 3: LLRF for EUCARD Crab Cavities Graeme Burt (on behalf of Amos Dexter) Paris May 2011.](https://reader031.fdocuments.us/reader031/viewer/2022013012/56649f435503460f94c631ae/html5/thumbnails/3.jpg)
Tolerance for Gaussian Amplitude Errors
2
crab
21
x
cz
2crab
2crab2
2crab
2crab1
crab
2
crab
12
crab
crab
V
VV
41
VV2
VVexp
VV2
VVexp
V
dV
V
dV
V
V2
1
V
VS
sz = 44000 nm
sx = 45 nm
qc = 0.02 rad
Luminosity Reduction Factor S
0.88
0.90
0.92
0.94
0.96
0.98
1.00
0% 1% 2% 3% 4% 5% 6% 7%
Cavity Amplitude Error ( V / Vcrab)
S gaussian
S simple
![Page 4: LLRF for EUCARD Crab Cavities Graeme Burt (on behalf of Amos Dexter) Paris May 2011.](https://reader031.fdocuments.us/reader031/viewer/2022013012/56649f435503460f94c631ae/html5/thumbnails/4.jpg)
Kick and tolerance for 3 TeV CM
MV4.210122252
103105.1102
R2
cEV
12
8122
12
occrab
amplitude error on each cavity 1.0% 1.5% 2.0% 2.5% 3.0%
luminosity reduction 0.9953 0.9914 0.9814 0.9714 0.9596
To minimise required cavity kick R12 needs to be large (25 metres suggested)Vertical kicks from unwanted cavity modes are bad one needs R34 to be small.For 20 mrad crossing and using as 12 GHz structure
Error in kick tilts effective collision from head on.
2
crab
21
x
cz
V
VV
41
1S
Luminosity Reduction Factor gives
![Page 5: LLRF for EUCARD Crab Cavities Graeme Burt (on behalf of Amos Dexter) Paris May 2011.](https://reader031.fdocuments.us/reader031/viewer/2022013012/56649f435503460f94c631ae/html5/thumbnails/5.jpg)
Waveguide routing?
klystron bunker
crab cavitylength ~ 0.1 m
crab cavity
detector
23.4 m
20 m
detector hall
![Page 6: LLRF for EUCARD Crab Cavities Graeme Burt (on behalf of Amos Dexter) Paris May 2011.](https://reader031.fdocuments.us/reader031/viewer/2022013012/56649f435503460f94c631ae/html5/thumbnails/6.jpg)
CLIC SolutionWakefields Large irises
Small number of cellsStrong damping
Phase and amplitude control Passive during 156 ns bunch train
Beamloading compensation High energy flow through cavity * small number of cells * high group velocity * low efficiency
Phase synchronisation (4.4 fs) Same klystron drives both cavitiesTemperature stabilized waveguide
Phase reference Optical interferometer
Phase measurementcalibration
DBM andDown conversion to ~ 1 GHz,Digital phase detectionStaggered sample and hold
Phase stability Thick irisesStrong cavity cooling
![Page 7: LLRF for EUCARD Crab Cavities Graeme Burt (on behalf of Amos Dexter) Paris May 2011.](https://reader031.fdocuments.us/reader031/viewer/2022013012/56649f435503460f94c631ae/html5/thumbnails/7.jpg)
Fill Time and Beamloading
16 cell crab cavity with 0.4 mm offset beam at 40 ns
1.5
1.6
1.7
1.8
1.9
2.0
2.1
2.2
2.3
2.4
2.5
0 50 100 150 200
time (ns)
Tra
nsv
erse
kic
k (M
V)
)1n(U
Q
R
cxfq
QUv
L
UU
dt
dUnrepng
cell
n1nn
For each cell solve energy equation
convection - dissipation - beamloading
Input = 6.45 MW
Initial kick = 2.40 MV
Plateau = 2.37 MV
vg = group velocity
Lcell = cell length
Un = energy in cell n
frep = bunch frequency
q = bunch charge
dx = bunch offset
![Page 8: LLRF for EUCARD Crab Cavities Graeme Burt (on behalf of Amos Dexter) Paris May 2011.](https://reader031.fdocuments.us/reader031/viewer/2022013012/56649f435503460f94c631ae/html5/thumbnails/8.jpg)
Beamloading in 16 Cell Cavity
Beam offset (mm) -0.4 0.0 0.4
Power entering cell 1 (MW) 6.388 6.388 6.388
Power leaving cell 16 (MW) 5.619 5.341 5.063
Ohmic power loss (MW) 1.071 1.047 1.023
Beamload power loss (MW) -0.302 0.000 0.302
E max for cell 1 (MV/m) 51.1 51.1 51.1
Efficiency 12.04% 16.39% 20.74%
Kick (MV) 2.428 2.400 2.372
Cavity Parameters as on last slide and Q = 6381
A short inefficient cavity with a high power flow achieves adequate amplitude stability
Can we make the gradient?
Is pulse heating OK (consider low temperature operation)?
![Page 9: LLRF for EUCARD Crab Cavities Graeme Burt (on behalf of Amos Dexter) Paris May 2011.](https://reader031.fdocuments.us/reader031/viewer/2022013012/56649f435503460f94c631ae/html5/thumbnails/9.jpg)
Cavity variables
Cell lengthsets phase
advance
iris thickness
iris radius
Equator radius sets frequency
beam
-4
-2
0
2
4
6
8
10
12
0 1 2 3 4 5 6 7 8
Gro
up v
eloc
ity
as %
of s
peed
of
lig
ht
iris radius (mm)
simulation
fit
0
10
20
30
40
50
60
70
4 5 6 7 8
Iris radius (mm)
R/Q
Oh
ms p
er
cell
Surface field/ Transverse gradient
0
1
2
3
4
5
6
7
8
4 5 6 7 8
iris radius (mm)
Es/E
t
5700
5800
5900
6000
6100
6200
6300
6400
6500
4 5 6 7 8
Iris radius (mm)
Q f
acto
r
Given the maximum surface fields and the available power one must chose number of cells and iris parameters to maximise luminosity
![Page 10: LLRF for EUCARD Crab Cavities Graeme Burt (on behalf of Amos Dexter) Paris May 2011.](https://reader031.fdocuments.us/reader031/viewer/2022013012/56649f435503460f94c631ae/html5/thumbnails/10.jpg)
Cell number for fixed surface field
0
5
10
15
20
25
30
2 3 4 5 6 7 8
Num
ber o
f cel
ls
Iris radius (mm)
Number of cells for 2.4 MV transverse kick not exceeding surface field 110 MV m-1.
![Page 11: LLRF for EUCARD Crab Cavities Graeme Burt (on behalf of Amos Dexter) Paris May 2011.](https://reader031.fdocuments.us/reader031/viewer/2022013012/56649f435503460f94c631ae/html5/thumbnails/11.jpg)
Cell Number Optimisation
Cell number mapped to power requirement for 115 MV m-1
0
5
10
15
20
25
30
3.5 4 4.5 5 5.5 6 6.5 7
Iris radius (mm)
Po
wer
Req
uir
emen
t (M
W)
10 cells
11cells 15
cells
9 cells
8 cells
16 cells
12cells
Cavity power requirement for a beam offset of 0.375 mm
![Page 12: LLRF for EUCARD Crab Cavities Graeme Burt (on behalf of Amos Dexter) Paris May 2011.](https://reader031.fdocuments.us/reader031/viewer/2022013012/56649f435503460f94c631ae/html5/thumbnails/12.jpg)
Beam Loading
• As the electric field in dipole cavities vary with offset the beam-loading changes with time and cannot be predicted.
• The beam is too short for feedback.
• Need to design to minimise the effect (increase convection or dissipation)
E Beam
)1n(U
Q
R
cxfq
QUv
L
UU
dt
dUnrepng
cell
n1nn
For each cell solve energy equation
convection - dissipation - beamloading
![Page 13: LLRF for EUCARD Crab Cavities Graeme Burt (on behalf of Amos Dexter) Paris May 2011.](https://reader031.fdocuments.us/reader031/viewer/2022013012/56649f435503460f94c631ae/html5/thumbnails/13.jpg)
Luminosity loss
0.000%
0.005%
0.010%
0.015%
0.020%
3 4 5 6 7 8
Lum
inos
ity
loss
for
am
plit
ude
fluct
uati
on
Iris radius (mm)
Luminosity loss for a beam offset of 0.125 mm
Increasing dissipation increases heating, this is not recommended
We can increase power convection by increasing the structure group velocity.
The group velocity is dependant on the iris radius.
However we have limited power (20 MW) so we can only increase the convection so much.
Possible solutions
![Page 14: LLRF for EUCARD Crab Cavities Graeme Burt (on behalf of Amos Dexter) Paris May 2011.](https://reader031.fdocuments.us/reader031/viewer/2022013012/56649f435503460f94c631ae/html5/thumbnails/14.jpg)
Wakefactor ~ R/Q times cells
0
200
400
600
800
1,000
1,200
2 3 4 5 6 7 8
wak
efac
tor
Iris radius (mm)
R/Q multiplied by cell number plotted against iris radius to give figure of merit for wakefields
![Page 15: LLRF for EUCARD Crab Cavities Graeme Burt (on behalf of Amos Dexter) Paris May 2011.](https://reader031.fdocuments.us/reader031/viewer/2022013012/56649f435503460f94c631ae/html5/thumbnails/15.jpg)
Choice
0
5
10
15
20
25
30
2 3 4 5 6 7 8
Num
ber o
f cel
ls
Iris radius (mm)
0
10
20
30
40
50
2 3 4 5 6 7 8
Pow
er R
equi
rem
ent (
MW
)
Iris radius (mm)
0.000%
0.005%
0.010%
0.015%
0.020%
3 4 5 6 7 8
Lum
inos
ity
loss
for
am
plit
ude
fluct
uati
on
Iris radius (mm)
0
200
400
600
800
1,000
1,200
2 3 4 5 6 7 8
wak
efac
tor
Iris radius (mm)
Initial studies have started with the 10 cell
option
![Page 16: LLRF for EUCARD Crab Cavities Graeme Burt (on behalf of Amos Dexter) Paris May 2011.](https://reader031.fdocuments.us/reader031/viewer/2022013012/56649f435503460f94c631ae/html5/thumbnails/16.jpg)
Waveguide choiceAssume 40 m waveguide run from Klystron to each Crab cavity
Available klystron has nominal output of 50 MWDivide output for two beam lines = 25 MW For standard rectangular waveguide we have 10.2 MW available (OK for 15 cells)For special rectangular waveguide we have 12.8 MW available (OK for 11 cells)For circular 12mm TE11 waveguide we have 15.1 MW available (OK for 11 cells)
(note that mode conversion from circular TE11 to circular TM10 is vanishingly small for properly designed bends)
For copper s =5.8e7 S/m and at 11.994 GHz Attenuation Transmission Over moded
Rectangular TE10 EIA90 (22.9 x 10.2 mm) 0.098 dB/m 40.6% no
Rectangular TE10 special (24 x 14 mm) 0.073 dB/m 51.3% no
Circular TE11 (r = 9.3 mm) 0.119 dB/m 33.3% no
Circular TE11 (r = 12 mm) 0.055 dB/m 60.4% TM10
Circular TE01 (r = 40 mm) 0.010 dB/m 91.2% extremely
![Page 17: LLRF for EUCARD Crab Cavities Graeme Burt (on behalf of Amos Dexter) Paris May 2011.](https://reader031.fdocuments.us/reader031/viewer/2022013012/56649f435503460f94c631ae/html5/thumbnails/17.jpg)
CLIC LLRF Timing
Booster Linac561 m2.2 to 9.0 GeV
IP
Bunch timing pick-ups
Klystron
LLRF LLRFLLRF LLRF
Bunch timing pick-ups
Drive beams12 GHzChicane
stretchingChicane
stretching
PETS PETS
0.05 km 2.75 km2.75 km 21 km21 km
Crab cavity
Crab cavity
electronspositrons
compressorcompressor linaclinac
Synchronisation to main beam after booster linac.For a 21 km linac we have 140 ms between bunches leaving the booster and arriving at the crab cavities.
2 GHz bunch rep
LLRF
Crab bunch timing pickups could be 2.75 km away from LLRF
![Page 18: LLRF for EUCARD Crab Cavities Graeme Burt (on behalf of Amos Dexter) Paris May 2011.](https://reader031.fdocuments.us/reader031/viewer/2022013012/56649f435503460f94c631ae/html5/thumbnails/18.jpg)
Crab Cavity RF• Beamloading constrains us to high power pulsed operation• Intra bunch phase control looks impossible for a 140 ns bunch
SOLUTION• One Klystron (~ 20 MW pulsed) with output phase and amplitude control • Intra bunch delay line adjustment for phase control (i.e. between bunch trains)• Very stable cavities
Dual Output
or Magic
Tee
Laser interferometer
Waveguide with micron-level adjustment
Waveguide with micron-level adjustment
12 GHz Pulsed Klystron
( ~ 20 MW )Pulsed
Modulator Vector modulationControl
Control
travelling wave cavity
Phase Shifter
LLRFLLRF
12 GHz Oscillator
Main beam outward pick up
main beam outward pick up
From oscillator
![Page 19: LLRF for EUCARD Crab Cavities Graeme Burt (on behalf of Amos Dexter) Paris May 2011.](https://reader031.fdocuments.us/reader031/viewer/2022013012/56649f435503460f94c631ae/html5/thumbnails/19.jpg)
RF Layout and Procedure
Splitter
Laser interferometer
Waveguide with micron-level adjustment
Waveguide with micron-level adjustment
12 GHz Pulsed Klystron
( ~ 20 MW )Pulsed
Modulator Vector modulationControl
Control
travelling wave cavity
Phase Shifter
LLRFLLRF
Once the main beam arrives at the crab cavity there is insufficient time to correct beam to cavity errors. These errors are recorded and used as a correction for the next pulse.
0. Send pre-pulse to cavities and use interferometer to measure difference in RF path length (option1)
1. Perform waveguide length adjustment at micron scale (option 2 use measurements from last pulse)2. Measure phase difference between oscillator and outward going main beam3. Adjust phase shifter in anticipation of round trip time and add offset for main beam departure time4. Klystron output is controlled for constant amplitude and phase5. Record phase difference between returning main beam and cavity6. Alter correction table for next pulse
main beam outward pick up
From oscillator 12 GHz
Oscillator
Main beam outward pick up
![Page 20: LLRF for EUCARD Crab Cavities Graeme Burt (on behalf of Amos Dexter) Paris May 2011.](https://reader031.fdocuments.us/reader031/viewer/2022013012/56649f435503460f94c631ae/html5/thumbnails/20.jpg)
Phase measurement
vector modulation
Load
Load
Load
11.996 GHz Pulsed
Klystron ( ~ 70 MW )
10 MHz Master
Oscillator
analogue control
10.700 GHz
11.996 GHz
11.996 GHz signal
long transmission paths with
controlled RF length adjustmentas computed by
laser interferometer
Hittite digital phase detector
HMC493Calibration
ADC ADC ADC ADC ADC
Multiplexer
DSP
D flip/flop array providing delayed clock for triggering
ADC sampling
Need to make 8 to 12 accurate phase measurements during pulse to check that the phases of the two
cavities are moving as one in synchronism.
sample at ~ 10 ns intervals andread back to DSP at an appropriate rate.
The DSP manages the time delay between outward beam pickup and firing Klystron. It controls pulse length and manages the
overall phase offset for the drive
Phasing to beam
120 ns pulse
120 ns pulse
![Page 21: LLRF for EUCARD Crab Cavities Graeme Burt (on behalf of Amos Dexter) Paris May 2011.](https://reader031.fdocuments.us/reader031/viewer/2022013012/56649f435503460f94c631ae/html5/thumbnails/21.jpg)
Distribution Stability Requirement
CERN April 2011
• r.m.s. cavity to cavity synchronisation requirement is 4.4 fs
• hence r.m.s klystron to cavity stability requirement is 3.1 fs (two paths)
• phase velocity of light in the waveguide will be just over 3.0×108
• hence waveguide length must be steady at the precision of 10-6 metres
(Expansion example without expansion joints)Control waveguide temperature to say 0.3oC. Copper expansivity 17 x 10-6 K-1. 40 metre waveguide could vary in length by 200 m.Waveguide wavelength ~ 25 mmExpansion ~ 200 m Phase shift ~ 2.9 degrees which is 150 times the allowance!
It is probably that the waveguide will have expansion joints and so the real question is about the lateral stability of the cavity and the klystron.
![Page 22: LLRF for EUCARD Crab Cavities Graeme Burt (on behalf of Amos Dexter) Paris May 2011.](https://reader031.fdocuments.us/reader031/viewer/2022013012/56649f435503460f94c631ae/html5/thumbnails/22.jpg)
Distribution Experiment
CERN April 2011
11.996 GHz Pulsed Klystron ( ~ 50 MW )
long waveguide transmission paths
Double balanced mixer Mini-circuits SIM-24MH+RF 7.3 GHz to 20 GHz, IF DC to 7.2 GHzNeed about 24 dB of amplification to resolve 1 milli-degree at 12 GHz,signal to noise before amplifier for 40 MHz bandwidth ~ 6 dBMeasurement looks feasible.
But need digital phase detection as before for calibration
![Page 23: LLRF for EUCARD Crab Cavities Graeme Burt (on behalf of Amos Dexter) Paris May 2011.](https://reader031.fdocuments.us/reader031/viewer/2022013012/56649f435503460f94c631ae/html5/thumbnails/23.jpg)
Board Development10 MHz Master
Oscillator
10.700 GHz
11.996 GHz
Hittite digital phase detector
HMC493
Calibration
DBM
The calibration of the DBM is performed using a digital phase detector after down-conversion to 1.3 MHz.
This hardware is underdevelopment but is so far not meeting the resolution specification.