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LHC – CC-13, CERN. December 9-11, 2013. CAVITY II – RF-DIPOLE CAVITY TEST RESULTS. Proof–of–Principle RF–Dipole Design. 34 cm. 53 cm. B Field. E Field. Proof–of–Principle Cavity Fabrication. Proof-of-Principle cavity fabricated at Niowave Inc. Cavity thickness – 3 mm. Teflon Bead. - PowerPoint PPT Presentation
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Page 1
Subashini De Silva
Center for Accelerator ScienceOld Dominion University
CAVITY II – RF-DIPOLE CAVITY
TEST RESULTS
LHC – CC-13, CERN December 9-11, 2013
Page 2
Proof–of–Principle RF–Dipole Design
Parameters Value Units
Frequency 400 MHz
Deflecting Voltage (VT*) 0.375 MV
Peak Electric Field (Ep*) 4.02 MV/m
Peak Magnetic Field (Bp*) 7.06 mT
Bp*/Ep
* 1.76 mT/(MV/m)
Stored Energy (U*) 0.195 J
[R/Q]T 287.0 Ω
Geometrical Factor (G) 140.9 Ω
RTRS 4.0×104 Ω2
At ET* = 1 MV/m
34 cm
53 cm
E Field B Field
Page 3
Proof–of–Principle Cavity Fabrication• Proof-of-Principle cavity fabricated at Niowave Inc.• Cavity thickness – 3 mm
-100.0
0.0
100.0
200.0
300.0
400.0
500.0
-0.5 -0.3 -0.1 0.1 0.3 0.5
0E
2 /U
[m
-3]
z [m]
MeasurementSimulation
-100.0
0.0
100.0
200.0
300.0
400.0
500.0
-0.5 -0.3 -0.1 0.1 0.3 0.5
0E
2 /U
-μ 0
H2 /
2U [
m-3
]
z [m]
MeasurementSimulation
Teflon Bead Al Bead• Bead pull measurements of on axis electric and magnetic field components
Page 4
Proof–of–Principle Cavity Surface Treatment• Surface treatment and rf testing done at
Jefferson Lab
• Procedure:– Bulk BCP
• Average removal – 85 μm• Planned total removal – 120 μm• Reduced etch rate from 2.7-2.8 μm /min to 1.8 μm/min due
acid mixture contamination with glycol
– Heat treatment – At 6000 C for 10 hours– Light BCP – ~10 μm– High Pressure Rinse – 3 passes
• Cavity assembly and leak check in clean room
Page 5
Multipacting in Proof–of–Principle Design• Multipacting analysis using Tack3P in SLAC – ACE3P suite
• A multipacting barrier was observed in the first 2 K test at very low fields
• Increasing the power processed the cavity and no multipacting was observed in the following 4.2 K and 2 K tests
Expected multipacting levels at very low VT of low orders with low impact energies
Page 6
P-o-P Cavity – 4.2 K and 2.0 K Test Results• Design goal can be achieved
with three cavities
• Multipacting levels observed below 2.5 MV and processed easily
• Achieved fields at 2.0 K:– ET = 18.6 MV/m
– VT = 7.0 MV
– EP = 75 MV/m
– BP = 131 mT
• RF performance was limited at 7.0 MV due to high field emission
• At 2.0 K with Rs = 11.3 nΩ (Rres = 10 nΩ)– Expected Q0 = 1.25×1010
– Measured Q0 = 4.0×109
• Total design requirement – 13.4 MV• Design requirement per cavity – 3.4 MV
1.0î 109
1.0î 1010
0.0 1.5 3.0 4.5 6.0 7.5
Rad
iati
on [
mR
/hr]
Q0
VT (MV)
Q0 2.0 K Q0 4.2 K
Rad 2.0 K Rad 4.2 K
1.0î 108
1.0î 109
1.0î 1010 1.0î 103
1.0î 102
1.0î 101
1.0
1.0î 10-1
1.0î 10-2
1.0î 10-3
0.0 5.0 10.0 15.0 20.0R
adia
tion
[m
R/h
r]
Q0
ET (MV/m)
Q0 2.0 K Q0 4.2 K
Rad 2.0 K Rad 4.2 K
1.0î 109
1.0î 1010 1.0î 103
1.0î 102
1.0î 101
1.0
1.0î 10-1
1.0î 10-2
0.0 35.3 70.6 105.9 141.2
Rad
iati
on [
mR
/hr]
Q0
BP (mT)
Q0 2.0 K Q0 4.2 K
Rad 2.0 K Rad 4.2 K
1.0î 109
1.0î 1010 1.0î 103
1.0î 102
1.0î 101
1.0
1.0î 10-1
1.0î 10-2
0.0 35.3 70.6 105.9 141.2
Rad
iati
on [
mR
/hr]
Q0
BP (mT)
Q0 2.0 K Q0 4.2 K
Rad 2.0 K Rad 4.2 K
1.0î 109
1.0î 1010 1.0î 103
1.0î 102
1.0î 101
1.0
1.0î 10-1
1.0î 10-2
0.0 20.1 40.2 60.3 80.4
Rad
iati
on [
mR
/hr]
Q0
EP (MV/m)
Q0 2.0 K Q0 4.2 K
Rad 2.0 K Rad 4.2 K
1.0î 109
1.0î 1010 1.0î 103
1.0î 102
1.0î 101
1.0
1.0î 10-1
1.0î 10-2
0.0 20.1 40.2 60.3 80.4
Rad
iati
on [
mR
/hr]
Q0
EP (MV/m)
Q0 2.0 K Q0 4.2 K
Rad 2.0 K Rad 4.2 K
1.0î 109
1.0î 1010
0.0 1.5 3.0 4.5 6.0 7.5
Rad
iati
on [
mR
/hr]
Q0
VT (MV)
Q0 2.0 K Q0 4.2 K
Rad 2.0 K Rad 4.2 K
1.0î 108
1.0î 109
1.0î 1010 1.0î 103
1.0î 102
1.0î 101
1.0
1.0î 10-1
1.0î 10-2
1.0î 10-3
0.0 5.0 10.0 15.0 20.0
Rad
iati
on [
mR
/hr]
Q0
ET (MV/m)
Q0 2.0 K Q0 4.2 K
Rad 2.0 K Rad 4.2 K
Quench
Limited by rf power
Multipacting
3.4 5.0
Page 7
P-o-P Cavity Test Results
-50.0
-40.0
-30.0
-20.0
-10.0
0.0
10.0
0.0 50.0 100.0 150.0 200.0 250.0 300.0 350.0
Δf
[kH
z]
Et2 [MV/m]2
2.0 K 4.2 K
kL = - 121.94 Hz/(MV/m)2
Simulated kL–
117.3 Hz/(MV/m)2
• For a Rres = 10 nΩ– At 2.0 K RS = 11.3 nΩ, Q0 = 1.25 ×1010
– At 4.2 K RS = 81.3 nΩ, Q0 = 1.8 ×109
• Measured Q0 at 2.0 K = 4.0×109
• Q0 due to power losses at the beam port stainless steel blank flanges 3.8×109
Surface Resistance
df /dP = - 483.0 Hz/torr
-0.45
-0.40
-0.35
-0.30
-0.25
-0.20
-0.15
-0.10
-0.05
0.00
0 200 400 600 800 1000
Δf
[MH
z]
Pressure [torr]
Measured Simulated
df /dP = - 407.9 Hz/torr
Pressure Sensitivity Lorentz Detuning
Rres = 34 nΩ
10
100
0.2 0.3 0.4 0.5 0.6 0.7
RS
[nΩ
]
1/T [K-1]
Measurements BCS Fit
42.6 10 18.67[n ] exp 33.9
[K] [K]sRT T
Magnetic field and surface field on the beam port
Page 8
499 MHz RF-Dipole Cavity
Surface Processing Procedure• Bulk BCP of ~150 μm• Average removal
– 1st treatment: 108 μm– 2nd treatment: 200 μm
• Heat Treatment H2 degassing at 6000C – 10 hours
24 cm
44 cm
RF Properties – 499 MHz Cavity
Aperture Diameter (d)
40.0 mm
Nearest HOM 777.0 MHz
Ep* 2.86 MV/m
Bp* 4.38 mT
[R/Q]T 982.5 Ω
Geometrical Factor (G)
105.9 Ω
RTRS 1.0×105 Ω2
At ET* = 1 MV/m
• Light BCP – Removal of 10 μm (2nd time: 20 μm) after heat treatment
• High pressure rinsing in 2 passes
• Cavity Assembly – with fixed coupling
Page 9
499 MHz – 4.2 K and 2.0 K Test Results• Multipacting was easily
processed during the first rf test at 4.2 K rf test
• No multipacting levels were observed in the reprocessed cavity
• Hard quench observed at 4.2 MV
• Achieved fields at 2.0 K– ET = 14 MV/m
– VT = 4.2 MV
– EP = 40 MV/m
– BP = 61.3 mT
1.0î 108
1.0î 109
1.0î 1010
1.0î 1011 1.0î 103
1.0î 102
1.0î 101
1.0
1.0î 10-1
1.0î 10-2
1.0î 10-3
0.0 5.0 10.0 15.0
Rad
iati
on [
mR
/hr]
Q0
ET (MV/m)
Q0 4.2 K - Test 1 Q0 2.0 K - Test 1Q0 4.2 K - Test 2 Q0 2.0 K - Test 2Rad 2.0 K Rad 4.2 K
1.0î 108
1.0î 109
1.0î 1010
1.0î 1011 1.0î 103
1.0î 102
1.0î 101
1.0
1.0î 10-1
1.0î 10-2
1.0î 10-3
0.0 5.0 10.0 15.0
Rad
iati
on [
mR
/hr]
Q0
ET (MV/m)
Q0 4.2 K - Test 1 Q0 2.0 K - Test 1Q0 4.2 K - Test 2 Q0 2.0 K - Test 2Rad 2.0 K Rad 4.2 K
1.0î 109
1.0î 1010
1.0î 1011
0.0 1.5 3.0 4.5
Rad
iati
on [
mR
/hr]
Q0
VT (MV)
Q0 4.2 K - Test 1 Q0 2.0 K - Test 1Q0 4.2 K - Test 2 Q0 2.0 K - Test 2Rad 2.0 K Rad 4.2 K
1.0î 109
1.0î 1010
1.0î 1011 1.0î 103
1.0î 102
1.0î 101
1.0
1.0î 10-1
1.0î 10-2
0.0 21.9 43.8 65.7
Rad
iati
on [
mR
/hr]
Q0
BP (mT)
Q0 4.2 K - Test 1 Q0 2.0 K - Test 1Q0 4.2 K - Test 2 Q0 2.0 K - Test 2Rad 2.0 K Rad 4.2 K
1.0î 109
1.0î 1010
1.0î 1011 1.0î 103
1.0î 102
1.0î 101
1.0
1.0î 10-1
1.0î 10-2
0.0 21.9 43.8 65.7
Rad
iati
on [
mR
/hr]
Q0
BP (mT)
Q0 4.2 K - Test 1 Q0 2.0 K - Test 1Q0 4.2 K - Test 2 Q0 2.0 K - Test 2Rad 2.0 K Rad 4.2 K
1.0î 109
1.0î 1010
1.0î 1011
0.0 1.5 3.0 4.5
Rad
iati
on [
mR
/hr]
Q0
VT (MV)
Q0 4.2 K - Test 1 Q0 2.0 K - Test 1Q0 4.2 K - Test 2 Q0 2.0 K - Test 2Rad 2.0 K Rad 4.2 K
1.0î 109
1.0î 1010
1.0î 1011 1.0î 103
1.0î 102
1.0î 101
1.0
1.0î 10-1
1.0î 10-2
0.0 14.3 28.6 42.9R
adia
tion
[m
R/h
r]
Q0
EP (MV/m)
Q0 4.2 K - Test 1 Q0 2.0 K - Test 1Q0 4.2 K - Test 2 Q0 2.0 K - Test 2Rad 2.0 K Rad 4.2 K
1.0î 109
1.0î 1010
1.0î 1011 1.0î 103
1.0î 102
1.0î 101
1.0
1.0î 10-1
1.0î 10-2
0.0 14.3 28.6 42.9
Rad
iati
on [
mR
/hr]
Q0
EP (MV/m)
Q0 4.2 K - Test 1 Q0 2.0 K - Test 1Q0 4.2 K - Test 2 Q0 2.0 K - Test 2Rad 2.0 K Rad 4.2 K
Quench
Page 10
499 MHz – Surface Resistance
• Measured Q0
– 1st Test: 1.6×1010
– 2nd Test: 8.1×109
• Reduced Q0 at 2.0 K with surface reprocessing– 1st bulk BCP removal: 108 μm– 2nd bulk BCP removal: 200 μm
Rres = 5.5 nΩ
1
10
100
0.2 0.3 0.4 0.5 0.6 0.7 0.8
RS
[nΩ
]
1/T [1/K]
Measurements BCS Fit
42.6 10 18.12[n ] exp 5.53
[K] [K]sRT T
• Q0 dropped with the increase in residual surface resistance
• Residual resistance– 1st Test: 5.5 nΩ– 2nd Test: 9.0 nΩ
42.6 10 18.12[n ] exp 8.97
[K] [K]sRT T
Page 11
Prototype RF–Dipole Design
54 cm
28.1 cm
Parameters Prototype P-o-P Units
Frequency 400.79 400 MHz
Deflecting Voltage (VT*) 0.375 0.375 MV
Peak Electric Field (Ep*) 3.65 4.02 MV/m
Peak Magnetic Field (Bp*) 6.22 7.06 mT
Bp*/Ep
* 1.71 1.76 mT/(MV/m)
Stored Energy (U*) 0.13 0.195 J
[R/Q]T 427.4 287.0 Ω
Geometrical Factor (G) 106.7 140.9 Ω
RTRS 4.6×105 4.0×104 Ω2
At ET* = 1 MV/m
• Electromagnetic mode is the same• Prototype design has improved rf-
properties
B FieldE Field
Page 12
Prototype Design – FPC and Pick Up Ports
Pick Up Port Options
(1)
Fundamental Power Coupler
• Outer conductor = 62 mm
• Inner conductor = 27 mm
• Qext = 1.0×106
• All penetrations to the He tank will be from top
• Magnetic coupling Field enhancement at the port
• 75 Ω inner conductor
• Outer conductor = 36 mm• Inner conductor = 27 mm• To achieve 1.0 W at 3.4 MV• Qext = ~3.0×1010
(2)
• Electric coupling No field enhancement
• 50 Ω inner conductor
• Port losses at the SS flanges on the beam pipes
• Beam port 1 (shorter): 1.1 mW• Beam port 2 (longer): 0.3 μW
• Is not an issue on assembled cavity in the cryomodule
Page 13
Prototype Design – HOM Damping• Analysis of HOM damping – Zenghai Li
1.0E-02
1.0E-01
1.0E+00
1.0E+01
1.0E+02
1.0E+03
0 500 1000 1500 2000
R/Q
(Ω
)
Frequency (MHz)
Ex, Hy Ez Ey, Hx
• Horizontal HOM Coupler– Ridged waveguide coupler – Couple to both horizontal dipole and
accelerating HOM modes– Operating mode below cutoff – naturally
reject operating mode – Groove reduces multipacting levels at the
waveguide
• Vertical HOM coupler– Selective WG-stub-coaxial coupler,
does not couple to operating mode - no filter needed
– Damps both vertical HOM and accelerating HOM modes
– Modified V-HOM coupler meets impedance threshold requirements
Horizontal HOM Waveguide
Vertical HOM WG-Coax Coupler
Page 14
Prototype Design – HOM Damping• Current design specifications per cavity
– Longitudinal impedance threshold – 0.2 MΩ– Transverse impedance threshold – 0.125 MΩ
• Vertical and horizontal HOM couplers optimized to damp high Q modes at 1.265 and 1.479 GHz
Page 15
Prototype Design – Field Non-Uniformity
(A) (B)
-0.06
-0.04
-0.02
0
0.02
0.04
0.06
0 2 4 6 8 10 12 14 16 18 20
δVT
/ V
T
Offset (mm)
Design (A) in xDesign (B) in xDesign (A) in yDesign (B) in y
Voltage deviation at 20 mm– Horizontal: 5.0% 0.2%– Vertical: 5.5% 2.4%
-0.05
-0.03
-0.01
0.01
0.03
0.05
0.0 5.0 10.0 15.0 20.0
δVT/ V
T
Offset [mm]
Proof of Principle - x
Proof of Principle - y
Prototype - x
Prototype - y
• Curvature around beam aperture to– Reduce field non-uniformity– Suppress higher order multipole
components
Full Cavity with
Couplers
Units
VZ 0.0 0.0 0.0 0.46 kV
VT 1.0 MV
b3 300 410 100 37.4 mT/m
b4 0.0 0.0 0.0 -1.8 mT/m2
b5 -4.6×104 -4.1×104 -2.2×104 -1.9×105 mT/m3
Higher Order Multipole Components
• Multipole component b3 is reduced below requirements
• Any specifications for other higher order multipole components?
Page 16
Prototype Design – Multipole Analysis
Pitch 5°
• (A) Yaw (rotation about y-axis) of one pole. • (B) Pitch (rotation about x-axis) of one pole.• (C) Roll (rotation about z-axis) of one pole.• (D) Horizontal displacement of one pole. • (E) Vertical displacement of one pole. • (F) Blending radius at the outer corner of one pole. • (G) Blending radius of the feather-like structure
near the beam line of one pole. • (H) Aperture radius in one pole.
• Strength of the multipole components is mainly determined by the aperture region of the poles near the beamline.
• Initial analysis focused on individual imperfections or departures from the ideal cavity poles due to fabrication or welding errors (no deformations due to tuning processes considered).
Shift of electrical center observed
• Effect of cavity imperfections on multipole components – R. Olave
* Small individual imperfections have negligible effects on the multipole components, but may shift the electrical center and operating frequency.
Page 17
Prototype Design – Multipole AnalysisThe largest effect on the multipole components observed is produced by the roll of a pole
Roll 5°
Imperfection
-6 -4 -2 0 2 4 6
Fre
qu
ency
(M
Hz)
390
392
394
396
398
400
402
404
yaw, degreespitch, degreesroll, degreesHorizontal pole displacement, mmVertical pole displacement, mm
The largest frequency shift observed is produced by the horizontal displacement of a pole
So far there are no individual imperfections that would make the cavity non-compliant with the multipole component requirements for the LHC system.
Studies of the effects of individual imperfections due to fabrication and welding of the cavity + couplers are underway.
(A) Yaw(B) Pitch(C) Roll
Page 18
Prototype Cavity CryomoduleCryomodule design for rf-dipole cavity
Room Temp Cavity• Mechanical analysis
• Prototype cavity
fabrication by Niowave Inc.
Cryomodule Design• He tank• Cryostat
Tom Nicol – FermilabStiffening
ribs
Ofelia Capatina – CERN
Jim Henry – JLab
Page 19
Current Status and Future PlansProof-of-Principle Cavity
• First cryogenic tests of proof-of-principle cavity is completed• Cavity performance reached higher gradients and is capable of achieving
design specifications• Achieved a total transverse deflection of 7 MV CW (twice the design voltage)• Multipacting conditions were processed easily and did not reoccur• Retesting the cavity on improving Q0 Further testing at CERN is on the plan
Prototype Cavity• Electromagnetic design is complete including multipacting levels, HOM
damping, reduced multipole components– Multipole analysis on design sensitivities shows that cavity design is extremely robust against
mechanical imperfections – Higher order mode damping meets current impedance threshold requirements
• Mechanical model study for SPS test and SM18 test cryostat stress requirements are ongoing
• Several approaches of He tank design has been studied Converging the ideas into a single design
Page 20
Acknowledgments
• ODU – Jean Delayen, HyeKyoung Park, Rocio Olave, Chris Hopper, Alex Castilla, Kevin Mitchell
• JLab – Peter Kneisel, Tom Powers, Kirk Davis, Joe Preble, Tony Reilly
• SLAC – Zenghai Li
• Niowave – Terry Grimm, Dmitry Gorelov, Chase Boulware• Fermilab – Tom Nicol• CERN – Rama Calaga, Ofelia Capatina