Odu / slac rf -dipole prototype
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Transcript of Odu / slac rf -dipole prototype
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Subashini De Silva
Center for Accelerator ScienceDepartment of Physics, Old Dominion University
andThomas Jefferson National Accelerator Facility
ODU/SLACRF-DIPOLE PROTOTYPE
LHC Crab Cavity Engineering Meeting – FNAL 13-14 December, 2012
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Introduction• An overview of the ODU-SLAC cavity development and
construction at 400 MHz toward a crab cavity for the LHC
• Cavity design and present status including– Deflecting mode characteristics– HOM spectra– Damping schemes– Coupler configurations and associated choices should be
addressed
• Cavity fabrication, treatment and recent test results
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Current LHC Crabbing Cavity Requirements
• Local crabbing scheme frequency – 400 MHz• Requires a crabbing system at two interaction
points (IP1 and IP5) Vertical crossing at IP1 Horizontal crossing at IP5
• Beam aperture diameter – 84 mm• Transverse dimensions ~ 145 mm • Transverse voltage – 10 MV per beam per
side• Transverse voltage per cavity – 3.4 MV• Awaiting on beam tolerances based on field
non-uniformity across the beam aperture 42 mm
<150 mm
194 mm
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RF Dipole Cavity Geometry• Operates in a TE-like mode
E Field
H Field
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Characteristics of the RF-Dipole Cavity• Properties depend on a few parameters
– Frequency determined by diameter of the cavity design– Bar Length ~λ/2– Bar height and aperture determine EP and BP
– Angle determines BP/EP
Cavity Length
Bar Length
θ
84 mm
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400 MHz Crabbing Cavity DesignsODU Design SLAC Design
Peak electric field (EP*) 3.86 3.75 MV/m
Peak magnetic field (BP*) 6.9 6.85 mT
BP* / EP* 1.79 1.83 mT / (MV/m)
Stored Energy (U*) 0.18 0.17 J
Geometrical factor (G = QRS)
115.0 152.9 Ω
[R/Q]T 315.7 331.1 Ω
RTRS 3.6×104 5.1×104 Ω2
At ET* = 1 MV/m
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Square RF-Dipole Cavity• Square-type rf-dipole cavity to further reduce the transverse dimensions• Frequency is adjusted by curving radius of the edges• Similar to cylindrical rf-dipole design
– Bar Length ~λ/2– Bar height and aperture determine EP and BP
– Angle determines BP/EP
Height and Width
< 290 mm
x
y
E Field H Field
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HOMs and Wakefields
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
• No lower order modes and widely separated HOMs
• Separation from the fundamental crabbing mode is ~200 MHz
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HOM Damping Options
Waveguide Damping• Strong damping can be achieved with
waveguide couplers
Coaxial Coupling• Coaxial couplers requires a high pass
filter to exclude the operating mode
• SLAC ACE3P Suite – Zenghai Li
Two-stage high-pass filter
Input Coupler
Three-stage high-pass filter
HOM Couplers & Damping, Zenghai Li
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Current Status on HOM DampingWaveguide Damping Coaxial Coupling
Two-stage high-pass filter
Input Coupler
Coupler configurations and associated choiceswill be presented in: HOM Couplers & Damping – Zenghai Li
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Multipacting Analysis• Particle tracking code in the SLAC ACE3P Suite – Zenghai Li and
Lixin Ge
- 0.5MV to 2.6 MV - 1.8 MV to 2.8MV - 3.0 MV to 6.0 MV
Modified end plates to suppress multipacting at lower fields
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Field Non-Uniformity and Multipoles(A) (B) At a transverse voltage of 1 MV
-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
/ VT
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%
Cylindrical Cavity
Square Cavity
Modified Square Cavity
Units
b3 3.0×102 4.1×102 1.0×102 mT/m
b4 0.0 0.0 0.0 mT/m2
b5 -4.6×104 -4.1×104 -2.2×104 mT/m3
b6 0.0 0.0 0.0 mT/m4
b7 -1.03×107 -2.0×107 -6.9×107 mT/m5
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Properties of RF-Dipole Designs
Parameter Cylindrical Cavity Square Cavity Unit
Nearest HOM 589.5 597.2 MHz
Deflecting voltage (VT*) 0.375 MV
Peak electric field (EP*) 3.9 3.86 MV/m
Peak magnetic field (BP*) 7.13 6.9 mT
[R/Q]T 287.3 315.7 Ω
Geometrical Factor (G) 138.7 115.0 Ω
RTRS 4.0×104 3.6×104 Ω2
Transverse voltage per cavity 3.4 MV
Peak magnetic field (BP) 35.4 35.0 mT
Peak electric field (EP) 64.7 62.6 MV
Operating temperature 2.0 4.2 2.0 4.2 K
Surface Resistance (RS)** (Rres = 10 nΩ) 11.3 70.0 11.3 70.0 nΩ
Static heat load per cavity ** From cryomodule design specifications W
Dynamic heat load per cavity ** 3.3 20.1 3.6 22.4 W
Q0 ** 12.2 1.2 10.2 1.6 ×109
At ET* = 1 MV/m ** Estimated
Cylindrical Cavity
Square Cavity
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Cavity Prototype Fabrication
110
500
220
499 MHz Prototype400 MHz Prototype
Input Power
CouplerPick Up
Probe
Pick Up
Probe
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Prototype Test Plan• Variable power coupler
– To process multipacting
• Cavity processing– Bulk BCP for 120 μm removal from the surface– High pressure rinsing– Baking for 10 hours at 6000C – Light BCP of 10 μm– In-situ baking
• Cavity assembly– Fixtures to support cavity in the test cage
• RF Test– Low power test while cooling down the cavity– High power test at 2 K and 4.2 K
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• Goal – To design a cavity for testing at SPS and future test at LHC, meeting the design requirements
• Optimize cavity geometry (ODU&SLAC) to,– Suppress multipacting levels– Revise the design to address mechanical specifications
• Stress• Pressure Sensitivity• Lorentz force detuning• Achieve design rigidity with adequate stiffening
– Power and HOM coupler designing• To achieve required damping requirements• Easy chemical processing of couplers
• Cyomodule design– Cavity tuning and He tank designing – HyeKyoung Park (ODU/JLAB)– Cryomodule designing – Dmitry Gorelov (Niowave)
Final 400 MHz Crab Cavity Design
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Summary• The current 400 MHz rf-dipole crabbing cavity design meets current
requirements on– Dimensional constraints– Electromagnetic peak surface field and transverse voltage specifications
• 400 MHz rf-dipole prototype– Is in preparation for surface treatment and VTA assembly – RF testing will be performed early 2013
• Ready to continue working on designing the final cavity desgin• Currently there are several viable electromagnetic design options• The final selection will be based on the requirements on
– Electromagnetic– Mechanical– Dimensional
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Acknowledgments• Work supported by the ODU-Niowave P1 & P2 STTR
• Work also supported by the US LHC Accelerator Research Program (LARP) through US Department of Energy contracts DE-AC02-07CH11359, DE-AC02-98CH10886, DE-AC02-05CH11231, and DE-AC02-76SF00515.
• ODU– Jean Delayen– Subashini De Silva– HyeKyoung Park– Julius Nfor– Alex Castilla
• SLAC– Zenghai Li– Lixin Ge
• Niowave– Terry Grimm– Dmitry Gorelov