measurement principle and tuning of the clic crab cavity
DESCRIPTION
Measurement Principle and Tuning of the CLIC Crab Cavity. 12. Feb. 2014. Outline. General information on the Crab Cavity and motivation for this talk Electromagnetic field pattern close to the axis [Ex, Ey , Ez , Hx , Hy , Hz] - PowerPoint PPT PresentationTRANSCRIPT
Measurement Principle andTuning of the CLIC Crab Cavity
12. Feb. 2014
2
Outline
12.02.2014 Tuning of CLIC Crab Cavity
1. General information on the Crab Cavity and motivation for this talk
2. Electromagnetic field pattern close to the axis [Ex, Ey, Ez, Hx, Hy, Hz]
3. Strategy for Bead-pull measurements: basing them on Ey only
4. Results of 1st Bead-pull measurements
5. Tuning and measurement results of the Crab Cavity
6. Summary
Tuning of CLIC Crab Cavity 3
CLIC Crab Cavity
12.02.2014
• designed by Cockcroft Institute, Lancaster University, EDMS 1159170
• very good support from Graeme Burt and Praveen-Kumar Ambattu
• extracted fields on axis and off-axis (CST) from Praveen-Kumar Ambattu
• .sat Model from Praveen-Kumar Ambattu,(here simulated with HFSS)
• symmetric structure (constant impedance)
• directions: z: beamy: deflection
4
General information, Goal, Suggestions
12.02.2014 Tuning of CLIC Crab Cavity
General information:• Crab Cavity designed by Cockcroft Institute, Lancaster University and CERN• production coordinated by CERN (BE/RF/PM)• tuning by CERN (BE/RF/LRF)• preparation (bake out, etc.), installation and high power testing by CERN (BE/RF/PM,
BE/RF/MK, BE/RF/LRF)
Goal: develop a reliable tuning method and tune the CLIC Crab in short time=> no need to re-study RF design, data provided by Cockcroft Institute, Lancaster University=> no need to measure all electromagnetic field components=> find a reliable method and apply it !
Suggestions:• using a double bead-pull with a dielectric bead and a metallic bead + data processing to determine
the electric and the magnetic field (as Ben Hall used for his PhD)• using a double bead-pull with 2 different bead shapes (e.g. a small cylinder = needle and a
disc = washer) to couple to different field components complicated !
5
Is there a simple method for Bead-pulling?
12.02.2014 Tuning of CLIC Crab Cavity
Background:• the CLIC Crab Cavity is a multi-cell cavity• most important is the correct phase advance per cell for synchronism with the beam
=> automatically for good RF designs, the correct amplitude patterns settles• all cells need to be tuned = adjusted in volume to reach desired frequency / phase
advance=> several bead-pull measurements need to be performed to verify effect of tuning=> ideally a bead-pull measurement after each tuning operation=> about 30 (+ 10 at different frequencies) bead-pull measurements in total (best case)
• Reliability: Performing several bead-pull measurements in the same state shall give the same information (mainly phase advance per cell and amplitude profile)
• => we are looking for a way to get the necessary information for tuning (= phase advance per cell, amplitude profile) with a single, reliable bead-pull measurement
Tuning of CLIC Crab Cavity 6
Electromagnetic field pattern
12.02.2014
• beam is deflected in y-direction by Ey and vz*μ0*Hx=ZF0*Hx(! fields taken at different moments in time)
observations for x~0, y~0:
• max(|Ey(z)|) @ location of irises
• max(|Hx(z)|) in middle of cells
• max(|Ez(z)|) in middle of cells
• max(|Ez(z)|)<max(|Ey(z)|)
Tuning of CLIC Crab Cavity 7
z- dependency: backward travelling wave
12.02.2014
• negative group velocity at operation point
• wide pass band (11.9 to 12.8 GHz)
0 20 40 60 80 100 120 140 160 18011.9
12
12.1
12.2
12.3
12.4
12.5
12.6
12.7
phase advance per cell [°]
frequ
ency
[G
Hz]
Brillouin Diagram
Tuning of CLIC Crab Cavity 8
EM-fields, deflecting Ey
12.02.2014
Ey(x,y) nearly homogeneous close to symmetry axis (here R0.5 mm)0 20 40 60 80 100 120 140
0
1000
2000
3000
4000
z [mm]
|E(x
,y,z
)| [V
/m]
Ey(x,y,z)
0 20 40 60 80 100 120 140-2000
-1000
0
1000
z [mm]
arg(
E(x
,y,z
)) [°
]
x=0.5mm, y=0x=0. y=0.5mmx=0, y=0
-1 0 1
x 107
-1
-0.5
0
0.5
1
x 107
Re(E^2)
Im(E
^2)
! Ey^2 in preparation for bead-pull pattern
Tuning of CLIC Crab Cavity 9
EM-fields, deflecting Hx
12.02.2014
Hx(x,y) nearly homogeneous close to symmetry axis (here R0.5 mm)
peaks of ZF0*Hx are ~20% lower than peaks of Ey
0 20 40 60 80 100 120 1400
1000
2000
3000
4000
z [mm]
|ZF0
*Hx(
x,y,
z)|
[V/m
]
ZF0*Hx(x,y,z)
0 20 40 60 80 100 120 140-1500
-1000
-500
0
z [mm]
arg(
c0*H
x(x,
y,z)
) [°
]
x=0.5mm, y=0x=0. y=0.5mmx=0, y=0
-5 0 5
x 106
-5
0
5
x 106
Re(E 2̂)
Im(E
^2)
Tuning of CLIC Crab Cavity 10
EM-fields, accelerating Ez
12.02.2014
Ez(x,y): ~lin. dependent on y, close to beam axis
smaller than Ey and Hx(here factor 3 for R0.5 mm)
Ez(0,0) not 0 in first and last cells => single feed effect
0 20 40 60 80 100 120 1400
500
1000
1500
z [mm]
|E(x
,y,z
)| [V
/m]
Ez(x,y,z)
0 20 40 60 80 100 120 140-6000
-4000
-2000
0
2000
z [mm]
arg(
E(x
,y,z
)) [°
]
x=0.5mm, y=0x=0. y=0.5mmx=0, y=0
-1 0 1
x 106
-1
-0.5
0
0.5
1x 10
6
Re(E^2)
Im(E
^2)
Tuning of CLIC Crab Cavity 11
EM-fields, small Ex
12.02.2014
Ex negligible close to symmetry axis(factor >70 in respect to Ey for R0.5 mm)0 20 40 60 80 100 120 140
0
20
40
60
z [mm]
|E(x
,y,z
)| [V
/m]
Ex(x,y,z)
0 20 40 60 80 100 120 140-15000
-10000
-5000
0
5000
z [mm]
arg(
E(x
,y,z
)) [°
]
x=0.5mm, y=0x=0. y=0.5mmx=0, y=0
-2000 0 2000
-2000
-1000
0
1000
2000
Re(E 2̂)
Im(E
^2)
Tuning of CLIC Crab Cavity 12
EM-fields, small Hy
12.02.2014
ZF0*Hy negligible close to symmetry axis(factor >100 in respect to Ey for R0.5 mm)
0 20 40 60 80 100 120 1400
10
20
30
40
z [mm]
|ZF0
*Hy(
x,y,
z)|
[V/m
]
ZF0*Hy(x,y,z)
0 20 40 60 80 100 120 140-15000
-10000
-5000
0
5000
z [mm]
arg(
c0*H
y(x,
y,z)
) [°
]
x=0.5mm, y=0x=0. y=0.5mmx=0, y=0
-1000 0 1000
-1000
-500
0
500
1000
Re(E^2)
Im(E
^2)
Tuning of CLIC Crab Cavity 13
EM-fields, Hz
12.02.2014
different simulation (HFSS of .sat file)=> field worse adapted for 120°/cell compared to simulations from Praveen-Kumar Ambattu
Hz depends lin. on x close to beam axis
ZF0*Hz has similar magnitude as Ez
0 20 40 60 80 100 120 1400
500
1000
1500
z [mm]
|ZF0
*Hz(
x,y,
z)|
[V/m
]
ZF0*Hz(x,y,z)
0 20 40 60 80 100 120 140-1
0
1
2x 10
4
z [mm]
arg(
c0*H
z(x,
y,z)
) [°
]
x=0.5mm, y=0x=0. y=0.5mmx=0, y=0
-1 0 1
x 106
-1
-0.5
0
0.5
1
x 106
Re(E 2̂)
Im(E
^2)
Tuning of CLIC Crab Cavity 14
Field summary and Bead-pull measurements
12.02.2014
• Summary of fields:Ex and Hy can be neglected in vicinity of beam axis (~100 smaller)=> only Ey, Hx, Ez, Hz need to be consideredEy(x,y), Hx(x,y) ~ y0 x0 (deflecting fields)Ez(x,y)~ y1 x0, Hz(x,y) ~ y0 x1
Ex(x,y), Hy(x,y) ~ 0
• Bead-pull measurement principle: monitoring change of input reflectionCharles W. Steele, IEEE Trans. on microwave theory and techniques, Vol. MTT-14, No.2 (February, 1966), p.70:
S11= S11,perturbed – S11,unperturbed = _{x,y,z} {(e.*E.)^2 – (ZF0*h.*H.)^2}E2, H2: complex fields squared (phase !) at position of beade, h: complex factors describing polarisation & magnetisation effect ofthe bead's material in the local EM field
• Study of different factors e., h. to investigate if bead-pull measurements can be bases on a single field component => making tuning procedure simple
Tuning of CLIC Crab Cavity 15
Simulation of bead-pull measurement
12.02.2014
1 2 3 4 5 6 7 8 9 101112-0.1
-0.05
0
0.05
0.1
z [cells]
Re(
indi
v. c
ontr.
to d
S11
)
position: x=0.00 mm, y=0.00 mm
ey=1.00
1 2 3 4 5 6 7 8 9 101112
-0.1
-0.05
0
0.05
z [cells]
Im(in
div.
con
tr. to
dS
11)
1 2 3 4 5 6 7 8 9 1011120
0.05
0.1
z [cells]
abs(
indi
v. c
ontr.
to d
S11
)
1 2 3 4 5 6 7 8 9 1011120
0.05
0.1
z [cells]
|dS
11|
dS11=sum_{x,y,z} (e.*E.) 2̂ - (ZF0*h.*H.) 2̂
1 2 3 4 5 6 7 8 9 101112
-200
-100
0
z [cells]
sub-
rang
e ar
g(dS
11)
[°]
-0.1 0 0.1
-0.1
-0.05
0
0.05
0.1
Re(dS11)
Im(d
S11
)
Ey only =
reference
Tuning of CLIC Crab Cavity 16
Simulation of bead-pull measurement
12.02.2014
small off-set y=0.5mmEy & Ez
=> changes seen for dS11 at locations min(|Ey|)
=max(|Ez|)
1 2 3 4 5 6 7 8 9 101112-0.1
-0.05
0
0.05
0.1
z [cells]
Re(
indi
v. c
ontr.
to d
S11
)
position: x=0.00 mm, y=0.50 mm
ex=1.00ey=1.00ez=1.00
1 2 3 4 5 6 7 8 9 101112
-0.1
-0.05
0
0.05
z [cells]
Im(in
div.
con
tr. to
dS
11)
1 2 3 4 5 6 7 8 9 1011120
0.05
0.1
z [cells]
abs(
indi
v. c
ontr.
to d
S11
)
1 2 3 4 5 6 7 8 9 1011120
0.05
0.1
z [cells]
|dS
11|
dS11=sum_{x,y,z} (e.*E.) 2̂ - (ZF0*h.*H.) 2̂
1 2 3 4 5 6 7 8 9 101112
-200
-100
0
z [cells]
sub-
rang
e ar
g(dS
11)
[°]
-0.1 0 0.1
-0.1
-0.05
0
0.05
0.1
Re(dS11)
Im(d
S11
)
Tuning of CLIC Crab Cavity 17
Simulation of bead-pull measurement
12.02.2014
off-set y=0.5mmEy & Ez
but ez^2=4
=> changes seen for dS11 at locations min(|Ey|)
=> peaks of dS11
dominated by Ey stay in
the same location
(amplitude & phase)
1 2 3 4 5 6 7 8 9 101112-0.1
-0.05
0
0.05
0.1
z [cells]
Re(
indi
v. c
ontr.
to d
S11
)
position: x=0.00 mm, y=0.50 mm
ey=1.00ez=2.00
1 2 3 4 5 6 7 8 9 101112
-0.1
-0.05
0
0.05
z [cells]
Im(in
div.
con
tr. to
dS
11)
1 2 3 4 5 6 7 8 9 1011120
0.05
0.1
z [cells]
abs(
indi
v. c
ontr.
to d
S11
)
1 2 3 4 5 6 7 8 9 1011120
0.05
0.1
0.15
z [cells]
|dS
11|
dS11=sum_{x,y,z} (e.*E.) 2̂ - (ZF0*h.*H.) 2̂
1 2 3 4 5 6 7 8 9 101112
-200
-100
0
z [cells]
sub-
rang
e ar
g(dS
11)
[°]
-0.1 0 0.1
-0.1
-0.05
0
0.05
0.1
Re(dS11)
Im(d
S11
)
Tuning of CLIC Crab Cavity 18
1 2 3 4 5 6 7 8 9 101112-0.1
-0.05
0
0.05
0.1
z [cells]
Re(
indi
v. c
ontr.
to d
S11
)
position: x=0.00 mm, y=0.50 mm
ey=1.00ez=3.00
1 2 3 4 5 6 7 8 9 101112
-0.1
-0.05
0
0.05
z [cells]
Im(in
div.
con
tr. to
dS
11)
1 2 3 4 5 6 7 8 9 1011120
0.05
0.1
z [cells]
abs(
indi
v. c
ontr.
to d
S11
)
1 2 3 4 5 6 7 8 9 1011120
0.05
0.1
0.15
z [cells]
|dS
11|
dS11=sum_{x,y,z} (e.*E.) 2̂ - (ZF0*h.*H.) 2̂
1 2 3 4 5 6 7 8 9 101112-50
0
50
100
z [cells]
sub-
rang
e ar
g(dS
11)
[°]
-0.1 0 0.1
-0.1
0
0.1
Re(dS11)
Im(d
S11
)
Simulation of bead-pull measurement
12.02.2014
off-set y=0.5mmEy & Ez
but ez^2=9
=> changes seen for dS11 at
locations min(|Ey|)
=> weird phase behaviour due to
"minimum passage"
=> peaks of dS11: phase locations
identic, small changes of amplitude
Tuning of CLIC Crab Cavity 19
1 2 3 4 5 6 7 8 9 101112-0.1
-0.05
0
0.05
0.1
z [cells]
Re(
indi
v. c
ontr.
to d
S11
)
position: x=0.00 mm, y=0.00 mm
ey=1.00hx=0.50
1 2 3 4 5 6 7 8 9 101112
-0.1
-0.05
0
0.05
z [cells]
Im(in
div.
con
tr. to
dS
11)
1 2 3 4 5 6 7 8 9 1011120
0.05
0.1
z [cells]
abs(
indi
v. c
ontr.
to d
S11
)
1 2 3 4 5 6 7 8 9 1011120
0.05
0.1
z [cells]
|dS
11|
dS11=sum_{x,y,z} (e.*E.) 2̂ - (ZF0*h.*H.) 2̂
1 2 3 4 5 6 7 8 9 101112-300
-200
-100
0
100
z [cells]
sub-
rang
e ar
g(dS
11)
[°]
-0.1 0 0.1
-0.1
-0.05
0
0.05
0.1
Re(dS11)
Im(d
S11
)
Simulation of bead-pull measurement
12.02.2014
Ey & Hx
=> changes seen for dS11 at
locations min(|Ey|)
=> peaks of dS11: amplitude and
phase of peaks as for reference
=> difference seen for cell 1 &
12
Tuning of CLIC Crab Cavity 20
1 2 3 4 5 6 7 8 9 101112-0.1
-0.05
0
0.05
0.1
z [cells]
Re(
indi
v. c
ontr.
to d
S11
)
position: x=0.00 mm, y=0.50 mm
ex=1.00ey=1.00ez=3.00hx=0.70
1 2 3 4 5 6 7 8 9 101112
-0.1
-0.05
0
0.05
z [cells]
Im(in
div.
con
tr. to
dS
11)
1 2 3 4 5 6 7 8 9 1011120
0.05
0.1
z [cells]
abs(
indi
v. c
ontr.
to d
S11
)
1 2 3 4 5 6 7 8 9 1011120
0.05
0.1
0.15
z [cells]
|dS
11|
dS11=sum_{x,y,z} (e.*E.) 2̂ - (ZF0*h.*H.) 2̂
1 2 3 4 5 6 7 8 9 101112
-200
-100
0
100
z [cells]
sub-
rang
e ar
g(dS
11)
[°]
-0.1 0 0.1
-0.1
0
0.1
Re(dS11)
Im(d
S11
)
Simulation of bead-pull measurement
12.02.2014
Ey, Ez & Hx
=> phases of peaks at
locations as reference,
=> amplitudes similar, only
different for first and last irises
Tuning of CLIC Crab Cavity 21
Strategy for bead-pull measurements:
12.02.2014
• dielectric bead => bead does not perturb magnetic field => no (or negligible) S11
• close to beam axis (x=0,y=0):• Ex negligible• peaks(|Ey|^2) >> peaks(|Ez|^2)• moreover, Ez small where |Ey| reaches maxima in regular cells
==> Strategy for measuring and evaluating fields of operating mode in regular cells: • bead-pull with dielectric bead on axis (x=0,y=0) => S11
• search for peaks(S11) => Ey(zn)^2 + very small error==> amplitude and phase advance profile of regular cells can be evaluated accurately at the same time a sensitive method to validate the accuracy is provided by
comparing max(|Ez|) to min(|Ey|) (in the middle of cells) by looking at thecomplex bead-pull pattern S11
Coupling cells:• output coupling cell is adjusted to minimise the standing wave pattern• input coupling cell is adjusted to minimise the overall input reflection S11
Tuning of CLIC Crab Cavity 22
Results of 1st RF measurements
12.02.2014
• nearly no frequency shift due to wire (for accelerating structures typically -0.50 MHz, here |df|0.04 MHz)
• perturbation by bead is quite small due to relatively low field strength (typical S11 usually ~ 0.1, here ~ 0.01)=> noise is was seen on the first measurements (VNA setting IF 200 Hz)=> simple solution: decrease VNA IF bandwidth to 100 Hz for measurements during tuning – signal was clean enough, no need for making a bigger bead
• due to an (un)fortunate setup-error the effect of going off-axis could be analysed
Tuning of CLIC Crab Cavity 23
Results of 1st RF measurements
12.02.2014
flange was skewed (soft after brazing) => bead not on axis for the upper (first) cells
Tuning of CLIC Crab Cavity 24
Results of 1st RF measurements
12.02.2014
dS11
iris number (iris 1 between cell 1 and 2)
arg(
dS11
) [°
]
off-axis
on-axisd_E~-120°
Tuning of CLIC Crab Cavity 25
Tuning of the Crab Cavity
12.02.2014
centring V guiding the wire for bead-pull measurements
nitrogen supply
input (chosen and marked)
tuning pins (4 per cell)
temperature sensor
cooling block
output (marked)
Tuning of CLIC Crab Cavity 26
Before tuning
12.02.2014
11.8 11.9 12 12.1 12.2 12.3 12.4-60
-50
-40
-30
-20
-10
0
f / GHz
S /
dB
-34.8
-26.3
11.9922
simulated by Graeme BurtS11
11.96 11.98 12 12.02 12.04-60
-50
-40
-30
-20
-10
0
f / GHz
S /
dB
-34.8
-26.3
11.9922
simulated by Graeme BurtS11
input reflection bead-pull @ 11.9922 GHz
1 5 100
0.02
0.04
0.06
0.08
sqrt(
abs(
S
11))
Bead-pulling at 11992.2 MHz,
1 5 10-122-120-118-116-114
/ cel
l (D
EG
)
phase advance between cells
cell#
-0.032 -0.03 -0.028 -0.026 -0.024 -0.022 -0.02 -0.018
-0.045
-0.044
-0.043
-0.042
-0.041
-0.04
-0.039
-0.038
-0.037
Real(S11)
Imag
(S11
)
combined S11 in complex plane
12
3
2
4
6
8
10
12
Tuning of CLIC Crab Cavity 27
Tuning - E. Daskalaki, A. Degiovanni, C. Marrelli, M. Navarro Tapia, R. Wegner, B. Woolley
12.02.2014
cell
tuning record of |ds11|*sign(df) (mU)
1 2 3 4 5 6 7 8 9 10 11 12 13 141 in 2 3 4 5 6 7 +4.88 +9.6 +14.0 9 -8.9 -3.4
10 +7.0 +4.0 11 +7.4 +12.0 12 out +8.1 +10.2 +12.3 +8.7 -7.5 -3.2
celltuning record of |ds11|*sign(df) (mU)
15 16 17 18 19 20 21 22 23 24 25 26 sum1 in +9.8 +9.82 +10.5 +9.9 +20.43 +6.2 +21.7 +27.94 +5.3 +3.8 +9.15 +6.4 +3.1 +9.56 +5.0 +5.7 +10.77 +7.0 -3.4 +8.48 +23.69 -12.3
10 +11.011 +19.412out +28.6
Tuning of CLIC Crab Cavity 28
Tuning of the Crab Cavity
12.02.2014
tuning pins (4 per cell)
Tuning of CLIC Crab Cavity 29
After tuning
12.02.2014
input reflection bead-pull @ 11.9922 GHz
11.8 12 12.2 12.4 12.6 12.8-60
-50
-40
-30
-20
-10
0
f / GHz
S /
dB
-34.8-37.9
11.9922
simulated by Graeme BurtS11
11.96 11.98 12 12.02 12.04-60
-50
-40
-30
-20
-10
0
f / GHz
S /
dB
-34.8-37.9
11.9922
simulated by Graeme BurtS11
1 5 100
0.02
0.04
0.06
0.08
sqrt(
abs(
S
11))
Bead-pulling at 11992.2 MHz,
1 5 10
-120
-119
-118
/ cel
l (D
EG
)
phase advance between cells
cell#
-4 -2 0 2 4 6 8
x 10-3
-0.018
-0.016
-0.014
-0.012
-0.01
Real(S11)
Imag
(S11
)
combined S11 in complex plane
12
3
2
4
6
8
10
12
Tuning of CLIC Crab Cavity 30
Summary
12.02.2014
• a simple and reliable bead-pull method has been identified to determine the phase advance and amplitude profile of the CLIC Crab Cavity with a single bead-pull measurement
• the CLIC Crab Cavity could easily be tuned. A few remarks: • the cells were initially very well in shape• the tuning range per cell is about 4 to 5 times smaller than for other accelerating
structures (T(D)24, T(D)26, DDS, etc.)* for the Crab Cavity the group velocity is higher (~3.3%)* the tuning pins placed ~45° off the max. magnetic field regionsbut due to the good initial shape, the tuning range was largely sufficient for tuning
• we had to hammer slightly harder for tuning compared to other structures
Tuning of CLIC Crab Cavity 31
Thank you for your attention
12.02.2014