vasim khan 4th annual x-band structure collaboration meeting, cern. 03.05.10 1/36 clic_dds &...
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Vasim Khan 4th Annual X-band Structure Collaboration Meeting, CERN. 03.05.10 1/36
CLIC_DDS & Test Structure03.05.2010
V. Khan, A. D’Elia, R. JonesA. Grudiev, W. Wuensch, R. Zennaro
Vasim Khan 4th Annual X-band Structure Collaboration Meeting, CERN. 03.05.10 2/36
Overview
• Initial designs: CLIC_DT
• DDS design: DDS1_C
• Modified DDS: DDS2_E
• Test Structure: CLIC_DDS_A
• Next : 1) CLIC_DDS_B ?
2) DDS_SiC
Vasim Khan 4th Annual X-band Structure Collaboration Meeting, CERN. 03.05.10 3/36
Initial designs : CLIC_ DT
Ref: Khan, Jones. Proc. of EPAC08
<a>/λ=0.155 , ∆f = 3.6σ= 3.3 GHz, ∆f/favg= 20 %
Large bandwidth structure
RF breakdown constrains: Not satisfiedBeam dynamics constraints : Satisfied
Ref: Khan, Jones. Proc. Of LIAC08
Small bandwidth structure
<a>/λ=0.102 , ∆f = 3σ= 0.83 GHz, ∆f/favg= 4.5 %
RF breakdown constrains: SatisfiedBeam dynamics constraints : Not satisfied
Vasim Khan 4th Annual X-band Structure Collaboration Meeting, CERN. 03.05.10 4/36
192 cells8-fold interleaving
Summary of CLIC WS’09 : DDS1_C
24 cellsNo interleaving
192 cells8-fold interleaving
Manifold
Coupling slot
Dipole mode Manifold mode
∆fmin = 65 MHz∆tmax =15.38 ns∆s = 4.61 m
∆fmin = 8.12 MHz∆tmax =123 ns∆s = 36.92 m
∆f=3.6 σ =2.3 GHz∆f/fc=13%
Vasim Khan 4th Annual X-band Structure Collaboration Meeting, CERN. 03.05.10 5/36
Shortcomings of DDS1_C• High surface fields : It does not satisfy RF breakdown
constraints (results consistent in various ver. of HFSS and CST microwave studio)
Solution* : Major change in cavity shape : circular to elliptical
[*] R. Zennaro & A. D’Elia
• Use of surface approximation (2nd ord. soln.) for meshing the geometry for accurate simulation results rather than volume mesh
Suggestions from CERN collaborators*
Problems encountered during post CLIC WS’09 visit• No consistency in freq. and fields in different
ver. of HFSS and CST microwave studio
Vasim Khan 4th Annual X-band Structure Collaboration Meeting, CERN. 03.05.10 6/36
DDS1_C
Parameters CLIC_DDS1_corrected(8-fold interleaved)
Bunch space (rf cycles/ns) 8/0.67
Limit on wake (V/pC/mm/m) 6.3
Number of bunches 312
Bunch population (109) 4.2
Pin (MW) 74.6
Esur max. (MV/m) 290
Pulse temperature rise (K) 65
RF-beam-eff. 22.5
Vasim Khan 4th Annual X-band Structure Collaboration Meeting, CERN. 03.05.10 7/36
10ε 5ε
3.33ε 2ε
Circular
Square
Ellipticala)Convexb)Concave
a
b
ε = a/b
Vasim Khan 4th Annual X-band Structure Collaboration Meeting, CERN. 03.05.10 8/36
a
b
ε = a/bReference line
Vasim Khan 4th Annual X-band Structure Collaboration Meeting, CERN. 03.05.10 9/36
10ε 5ε
3.33ε
Circular Square
ε=20ε=10
ε=5
Convex ellipticity
Concave ellipticity
Single un-damped cell Iris radius=4.0 mm
Vasim Khan 4th Annual X-band Structure Collaboration Meeting, CERN. 03.05.10 10/36
Circular Rectangular Elliptical(Convex)
Elliptical(Concave)
ε=10 ε=5 ε=3.33 ε=2.0 ε=1 ε=20 ε=10 ε=5
Facc(GHz) 12.24 12.09 11.98 12.0 11.99 11.98 11.98 11.9911 11.9919 11.9935
Eacc(V/m) 0.43 0.43 0.42 0.43 0.43 0.42 0.42 0.43 0.43 0.42
Hsur max
/Eacc (mA/V)
3.64 4.86 4.71 4.54 4.29 3.75 3 4.94 4.99 5.11
Esur max
/Eacc2.27 2.27 2.33 2.28 2.28 2.33 2.33 2.27 2.27 2.33
Undamped cell with various geometries
Iris radius = 4. 0 mmIris thickness = 4.0 mm
Vasim Khan 4th Annual X-band Structure Collaboration Meeting, CERN. 03.05.10 11/36
Optimisation scan for DDS2_E
Optimisation of cavity shape for min. H surmax
Circular
Rectangular
ε=10
ε=5
ε=3
ε=2
ε=1
Single undamped cell Iris radius=4.0 mm
Optimised parameters for DDS2
Circular cell
ε=2
ε=3
Single cell with manifold
Vasim Khan 4th Annual X-band Structure Collaboration Meeting, CERN. 03.05.10 12/36
E surmax
Efficiency
∆f _dipole
∆T
Pin
Manifold damped structures3 cell simulations
Optimisation of E surmax , ∆f and efficiency
Optimised parameters for DDS2
Vasim Khan 4th Annual X-band Structure Collaboration Meeting, CERN. 03.05.10 13/36
b
2b
2bemajor
emajor3.0eminor
Detailed cell geometry : CLIC_DDS2_E
Rc
hr1
2*r2
r2
h1
r1+h+2*r2
r1
a1
a2g=L - t
L a
t= 2*a2
Radius = 0.5 mm
Variable parameters (mm)
Cell #1 Cell#24
a 4.0 2.3
b 11.01 10.039
a2 2.0 0.65
a1 1*a2 2*a2
Rc 6.2 6.8
r2 3.25 2.3
Constant parameters (mm)
All cells
L 8.3316
r1 0.85
h 4.5
h1 1.25
Fillet @ cavity and manifold joint
1.0
Rounding of cavity edge
0.5
Vasim Khan 4th Annual X-band Structure Collaboration Meeting, CERN. 03.05.10 14/36
DDS1_C
DDS2_E
Parameters DDS1_C DDS2_E Changes for
Shape Circular Elliptical Min. H-field
<Iris thickness> (mm) 2.35 2.65 Min. E-field
Rc 1/24 (mm) 6.2-7.5 6.2-6.8 Critical coupling
Changes : DDS1_C to DDS2_E
DDS1_C
DDS2_E
Vasim Khan 4th Annual X-band Structure Collaboration Meeting, CERN. 03.05.10 16/36
Dipole mode : circuit parameters
DDS1_C
DDS2_E
DDS1_C
DDS2_E
DDS1_C
DDS2_E
Vasim Khan 4th Annual X-band Structure Collaboration Meeting, CERN. 03.05.10 17/36
a1=4mma24=2.3mm
∆f=3.5 σ =2.2 GHz∆f/fc=13%
DDS1_C
DDS2_E
DDS1_C
DDS2_E
DDS1_C
DDS2_E
DDS1_C
DDS2_E
DDS1_C
DDS2_E
Vasim Khan 4th Annual X-band Structure Collaboration Meeting, CERN. 03.05.10 18/36
A. Grudiev & A. D’Elia : Potential final design with all roundings incorporated
To move all this part (coupling guide+manifold) up
Rounding
Change : Rc needs to be increasedProblem : Poor dipole coupling resulting in wake-suppression degradation
DDS2_EDDS2_ER
Rc
Vasim Khan 4th Annual X-band Structure Collaboration Meeting, CERN. 03.05.10 19/36
Dispersion curves
Light line
Uncoupled 1st mode
Uncoupled manifold mode
Avoided crossing
Uncoupled 2nd mode
Cell # 1
Cell # 24
Vasim Khan 4th Annual X-band Structure Collaboration Meeting, CERN. 03.05.10 20/36
DDS2_E :Rc=6.2 - 6.8 mm
DDS2_ER : Rc=6.8 mm const
Vasim Khan 4th Annual X-band Structure Collaboration Meeting, CERN. 03.05.10 21/36
High Power Test: CLIC_DDS_A
It has been decided to build 1st out of 8-fold interleaved structures for High Power Testing
Vasim Khan 4th Annual X-band Structure Collaboration Meeting, CERN. 03.05.10 22/36
Cell # 1
Cell # 24
CLIC_DDS_ANon interleaved 24 cell structureMotivation: High power testing (71 MW)Uniform manifolds
CLIC_DDS_A
Vasim Khan 4th Annual X-band Structure Collaboration Meeting, CERN. 03.05.10 23/36
mc=14.45
mr = 2.2Uniform manifold throughout the structure : Mechanical ease
Manifold geometry for CLIC_DDS_A
Rc=6.8
Dimensions are in mm
Cell 1
Cell 24
mc = 14.45mm
mc = 15mm
mc = 14.45mm
mc = 15mm
Vasim Khan 4th Annual X-band Structure Collaboration Meeting, CERN. 03.05.10 24/36
)/(E
ESImagSReS 2
2
cell singleacc
ULureacc_struct
61
c mW
Where S= Poynting vector
Cell # 1
E-field H-field Sc
6.75 W/μm2
40 o K
50 o K
@ 95 MV/mOpposite sides Selected contours
Vasim Khan 4th Annual X-band Structure Collaboration Meeting, CERN. 03.05.10 25/36
@ 138 MV/m
Cell # 24E-field H-field Sc
220 MV/m
Opposite sides Selected contours
Vasim Khan 4th Annual X-band Structure Collaboration Meeting, CERN. 03.05.10 26/36
CLIC_DDS_A Parameters
∆a
∆t
∆b
Vasim Khan 4th Annual X-band Structure Collaboration Meeting, CERN. 03.05.10 27/36
CLIC_DDS_A : Surface fields
Vasim Khan 4th Annual X-band Structure Collaboration Meeting, CERN. 03.05.10 28/36
CLIC_DDS_A : Fundamental mode properties
Vasim Khan 4th Annual X-band Structure Collaboration Meeting, CERN. 03.05.10 29/36
CLIC_DDS_A : RF properties
Max. Values
Esur=220 MV/m∆T = 51 KPin= 70.8Eacc_UL=131 MV/mSc=6.75 W/μm2
RF-beam-eff=23.5%
∆T
35*Sc
Esur
Eacc
Pin
Dashed curves : Unloaded conditionSolid curves: Beam loaded condition
CLIC_G Values
Esur=240 MV/m∆T = 51 deg.Pin= 63.8Eacc_UL=128 MV/mSc=5.4 W/μm2
RF-beam-eff=27.7%
Vasim Khan 4th Annual X-band Structure Collaboration Meeting, CERN. 03.05.10 30/36
CLIC_DDS_A : Dipole mode properties
f0
fxfsyn, fπ
Vasim Khan 4th Annual X-band Structure Collaboration Meeting, CERN. 03.05.10 31/36
24 cellsNo interleaving
CLIC_DDS_A
24 cellsNo interleaving
Undamped
Damped
Qavg ~1700
Vasim Khan 4th Annual X-band Structure Collaboration Meeting, CERN. 03.05.10 32/36
Matching cell design procedure
ma =
mg
• Two options• Vary ma and mb : very small room to vary mb vary ma and mg
mb
Matching cell
Mode launcher
Regular cell Matching cell
N=1-3
Regular iris
Matching iris Matching iris
Mode launcher
Vasim Khan 4th Annual X-band Structure Collaboration Meeting, CERN. 03.05.10 35/36
11.994 GHz
0.00035
dB 34.5S max11
First matching cell
11.994 GHz
0.000035
dB 44.5S max11
Last matching cell
Vasim Khan 4th Annual X-band Structure Collaboration Meeting, CERN. 03.05.10 36/36
2
b2b1b1.5
2
b25b24b24.5
In progress : Full structure
mb1 = b1mb24 = b25
ma1ma24a1 a2 a24 a25
mb1 mb24b1.5 b24.5
First matching cell Last matching cell
Mode launcherb2.5
........Mode launcher
Vasim Khan 4th Annual X-band Structure Collaboration Meeting, CERN. 03.05.10 37/36
Potential design for DDS_SiC
• Motivation : Better damping
• DDS3 Geometry : SiC running through manifolds
• Possible advantage(s) :
• 1) Relaxed tolerances
2) Short coupling slots → reduced ∆T
• Possible disadvantage :
• Need to think about locating BPM’s
Vasim Khan 4th Annual X-band Structure Collaboration Meeting, CERN. 03.05.10 38/36
Initial study
Monopole
Dipole
Sicεr = 10μr = 1tanδ = 0.06mr = 3.2 mmr = 2.0 mm
Iris radius = 4. 0 mmIris thickness = 4.0 mm
Vasim Khan 4th Annual X-band Structure Collaboration Meeting, CERN. 03.05.10 39/36
Summary
• DDS1_C : Adequate damping but high surface fields
• DDS2_E : Surface fields within acceptable limits but damping is relatively poor but still acceptable
• CLIC_DDS_A : First out of 8 structures of DDS2_E, RF design is done and will be built in 2010-11
Vasim Khan 4th Annual X-band Structure Collaboration Meeting, CERN. 03.05.10 40/36
Next in 2010-11 ?
Task May Jun Jul Aug Sept. onwards
Matching end cells In progress
HFSS: Full structure(N+2 cells) simulations
To do
Comparison of results (wakefield)in GdfidL
To do
Mechanical design To do
Fabrication To do
DDS_SiC Schedule to be discussed
CLIC_DDS_B Schedule to be discussed
Vasim Khan 4th Annual X-band Structure Collaboration Meeting, CERN. 03.05.10 41/36
Acknowledgements• Thanks to Igor Syratchev for suggesting to look into
DDS_SiC
• We acknowledge all our collaborators from CERN, KEK and SLAC for providing all the necessary information and many-many useful suggestions.
Vasim Khan 4th Annual X-band Structure Collaboration Meeting, CERN. 03.05.10 42/36
DDS1 revised simulations with surface approximation 5micron+aspect ratio of 5
Cells esur hsur eacc ttf Eacc*ttf Esur/eaccttf hsur./eaccttf
1 0.67 1.5 0.2748 0.96 0.26 2.54 5.76
5 0.94 2.5(2.7) 0.4963 0.953 0.473 1.987 5.28
9 0.93 2.2(2.3) 0.538 0.946 0.509 1.827 4.32
13 0.94(0.97) 2.2(2.3) 0.5532 0.939 0.519 1.81 4.23
17 0.78 1.7(1.8) 0.4742 0.932 0.442 1.765 3.85
21 0.89 1.88(1.9) 0.5574 0.925 0.516 1.725 3.64
24 0.67(0.72) 1.0 0.3272 0.92 0.3 2.23 3.33
Vasim Khan 4th Annual X-band Structure Collaboration Meeting, CERN. 03.05.10 43/36
DDS1 : Plain curve ; DDS2 : Curve with dots
Vasim Khan 4th Annual X-band Structure Collaboration Meeting, CERN. 03.05.10 44/36
DDS2
Cell # 1Rc=6.2
Cell # 1Rc=6.5
Cell # 1Rc=6.8
Cell # 13Rc=6.8
Cell # 13Rc=6.6
Cell # 13Rc=6.5
Cell # 13Rc=6.2
Vasim Khan 4th Annual X-band Structure Collaboration Meeting, CERN. 03.05.10 45/36
Cell # 24Rc=6.2
Cell # 24Rc=7.2
Cell # 24Rc=7.0
Cell # 24Rc=6.8
Cell # 24Rc=6.6
Cell # 24Rc=6.4
DDS2
Vasim Khan 4th Annual X-band Structure Collaboration Meeting, CERN. 03.05.10 46/36
Damped Detuned Structure overview• Gaussian distribution of cell parameters is chosen in this (CLIC_DDS) structures
which causes wakefield to decay in nearly Gaussian fashion for short time scale (few nsec)
• Limited number of cells (N=24) in a structure (poor sampling of a Gaussian) leads to recoherence of the wake (t=1/∆fmin)
• Recoherence of the wake is suppressed by coupling out the higher order modes using a waveguide like structures i.e. manifolds running parallel to the accelerating cells
• Interleaving neighbouring structure frequencies can be envisaged to improve the wake suppression
Vasim Khan 4th Annual X-band Structure Collaboration Meeting, CERN. 03.05.10 47/36
DDS2_HPT structure
Cell Eacc Q R’/Q vg/c Es/Eacc Hsur/Eacc Sc/Eacc2
# (V/m) kΩ/m (%) mA/m W/(x10-4)
1 0.4488 5020 10.179 2.07 2.23 4.9 7.3
2 0.4563 5091 10.649 1.85 2.2 4.82 6.9
5 0.4882 5325 11.723 1.62 2.05 4.5 5.5
9 0.5255 5604 12.899 1.51 1.89 4.15 4.5
13 0.5555 5838 13.952 1.42 1.8 4.0 4.0
17 0.5828 6061 15.049 1.34 1.7 3.75 3.4
21 0.6021 6307 16.416 1.22 1.66 3.5 2.9
23 0.4217 6451 17.411 1.11 1.65 3.3 2.9
24 0.5749 6534 18.130 1.0 1.67 3.3 2.98
ma (mm)
mg
(m
m)
noc=1
4 5 6
4.5
5
5.5
6
6.5
7
-20
-15
-10
-5
ma (mm)
mg
(m
m)
noc=2
4 5 6
4.5
5
5.5
6
6.5
7
-20
-15
-10
-5
ma (mm)
mg
(m
m)
noc=3
4 4.2 4.4 4.6 4.8 5 5.2 5.4 5.6 5.8 6
4.5
5
5.5
6
6.5
7
-40
-30
-20
-10
ma (mm)
mg
(m
m)
noc=1
5 5.2 5.4 5.6 5.8
6.4
6.6
6.8
7
7.2
-20
-15
-10
-5
ma (mm)
mg
(m
m)
noc=2
5.2 5.4 5.6 5.8
6.2
6.4
6.6
6.8
7
7.2
-20
-15
-10
-5
ma (mm)
mg
(m
m)
noc=3
5.2 5.25 5.3 5.35 5.4 5.45
6
6.5
7
-40
-30
-20
-10
common_minimum = ma mg S11 S11 S11 (noc=1) (noc=2) (noc=3) 5.0000 6.3316 -4.7483 -9.9892 -8.3322 5.3000 6.8316 -19.5343 -19.0196 -50.6180 5.5000 7.3316 -12.6941 -10.2416 -6.6752 5.6000 7.3316 -5.7225 -24.0994 -6.4650 5.7000 7.3316 -2.7236 -10.7502 -4.1787
global_min = ma mg S11 S11 S11 (noc=1) (noc=2) (noc=3) 5.3000 6.8316 -19.5343 -19.0196 -50.6180
Contour plots for first cell
Vasim Khan 4th Annual X-band Structure Collaboration Meeting, CERN. 03.05.10 51/36
a1=4mma24=2.3mm
∆f=3.5 σ =2.2 GHz∆f/fc=13%
DDS1_C : Plain curve DDS2_E : Curve with dots
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