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Numerical and Experimental Design Study of Quasi-Optical (QO) Multi-Gap Output
Cavity for W-band Sheet Beam Klystron
Numerical and Experimental Design Study of Quasi-Optical (QO) Multi-Gap Output
Cavity for W-band Sheet Beam Klystron
10th International Vacuum Electronics Conference (IVEC2009)
April 28 - 30th 2009
10th International Vacuum Electronics Conference (IVEC2009)
April 28 - 30th 2009
(Presentation #: 1558349)
15:20 Session 20 - Klystron II
Thursday, 30 April 2009
Young-Min Shin, Larry R. Barnett, Jianxun Wang, and Neville C. Luhmann Jr.
Department of Applied Science, University of California-Davis (UCD), CA 95616, USA
This work is supported by the Marine Corps Systems Command (MCSC), Grant No. M67854-06-1-5118.
Acknowledgements
•We wish to acknowledge informative discussions with Dr. Glenn P. Scheitrum and Dr. Aaron Jensen on the SLAC WSBK
•We also wish to Dr. Ali Farvid at the Stanford Linear Accelerator Center (SLAC) for his generous help, advice, and assistance in setting up the electroforming system, and to acknowledge informative discussions with Dr. Frank Yaghmaie, Director of the Northern California Nanotechnology Center (NCNC) in the University of California – Davis (UCD)
Outline
Motivation and Objectives
Electron Gun and Focusing Magnet
QO Output Cavity Design and Analysis
Simulation Examination and Cold-Test
Full Tube Design (AJDISK) and PIC Simulation (MAGIC3D) Analysis
UV LIGA Microfabrication
Summary and Future Plans
Motivation
• Develop a transportable, modular system, employing four novel W-band Sheet Beam Klystron (SBK) devices (each capable of 2.5 kW of average power) and producing a minimum of 10 kW of 95 GHz radiation. Higher powers can be produced by adding more SBKs and combining their output powers either by waveguide multiplexing, or in space.
Original SLAC MURI Concept
Original SLAC MURI WSBK Design Parameters
Beam voltage: 74 kVBeam current: 3.6 A Peak power: 50 kWAverage power: 2.5 kW Efficiency: 20%Gain: 40 dBBrillouin Magnetic field: 1000 Gauss (RMS)Number of cavities: 8 Circuit length (wg to wg): 9 cmBeam size (elliptical): 6 mm x 0.5 mm (12 : 1)Drift tube size (rectangular): 8 mm x 0.72 mm
WSBK Problems
Output Cavity: Incorrectly Designed
Input Cavity: Correctly Designed/Incorrectly Fabricated
Magnetic Anode Body
Windows: High VSWR
Need for Tuners
PCMSensitivity
Full Peak Power WSBK Demo Tube
• Seven gap velocity tapered output circuit with three gaps in other cavities
• MAGIC 3-D simulations predicted stability and 50 kW peak output
• Gun redesign: the original beam stick gun which produced high efficiency (91 %) transport was extremely sensitive to alignment ( 0.002” vertical misalignment would lose 40% of the beam in the gun). The anode aperture was therefore opened to reduce the anode hole effects
•Magnet stack redesigned.
Maximum beam transmission of 78 % at full design voltage and cathode current-attributed to magnetization of the gun weld ring resulting in beam rotation** Maximum output power of > 11 kW and ~ 48 dB gain observed using sensitive external adjustments of the shunts and cavity tuning using retrofitted cavity tuners. Low output is (as indicated by the test data) due to a combination of poor output coupling involving higher modes, field cancellation at the design frequency, beam and bunch formation, and cavity mistuning.
*Summary of initial tests at SLAC and subsequent tests at UC Davis.**Magnetization problem eliminated by proper choice of stainless steel
• Summary of Prototype WSBK Test Results
Amelioration of Technical Issues(1) Anode Flange Magnetization
• Replace 304L S.S. with 310 S.S. which cannot be magnetized
• Carry out complete 3D Gun and Magnetic field (re-)simulations to verify/modify design using CST Particle-Studio, Advanced Charged-particle Design Suite from Field Precision, and Ansoft Maxwell 3D simulation packages.
• Independent modeling assessment by Stan Humphries of Field Precision(2) Incorrectly Machined Input Cavity
• Proper input cavity design/fabrication eliminates/ameliorates mode competition problem
(3) Incorrectly Designed Output Cavity (7-Gap)
• Re-design the output cavity Quasi-Optical (QO) cavity
(4) Incorporation of cavity tuners
(5) Extensive MAGIC3D simulations to determine optimum design
Quasi-Optical (QO) WSBK Output Concept
QO Cavity Design and Sensitivity Analysis
• Original 7-Gap Output
Most critical dimension: cavity height (dy)
s
z
W
dzE
Q
R
2
2
dzE
dzeE
M
z
ziz
Replacement of WSBK Output Cavity (7-Gap QO)
• Original 7-Gap Output • Pocket Machining • QO Output Circuit
• QO Circuit Assembly • Brazing Assembly • Assembled Circuit
3-Gap 2-Mode QO Output Cavity Being Installed in Modified Tube
Signal Response and Eigenmode Analysis
• Port-to-Port Transmission and Reflection Coefficients (S21 and S11)
- FDTD simulation (CST MS) -
Total Q (Qt) of the operation TE10 mode (2-mode) of 95.4 GHz is about 450 - Experimental measurement -
f0 (unloaded) = 95.3GHz
fL (loaded) = 95.3504GHz
Q0 = 1652
Qe = 621
Qtot = 451
• Eigenmodes of Multi-Gap QO Cavities
- 3-Gap QO Cavity -
f0 (unloaded) = 95.3527GHz
fL (loaded) = 95.4074GHz
Q0 = 1665
Qe = 646
Qtot = 465
- 4-Gap QO Cavity -
f0 (unloaded) = 95.3731GHz
fL (loaded) = 95.385GHz
Q0 = 1663
Qe = 655
Qtot = 467- 5-Gap QO Cavity -
Young-Min Shin, Larry R. Barnett, and Neville C. Luhmann Jr. “Quasi-Optical Output Cavity Design for 50kW Multi-Cavity W-Band Sheet Beam Klystron”, IEEE Trans. Elec. Dev. (submitted, 2009)
QO WSBK Tube Design
• AJDISK Simulation Result of Optimized WSBK Tube Design
MAGIC3D Simulation of Full Circuit
1-Port Driving (~ 18.2 mW)
- Input Power and Frequency Spectrum -
- Output Power and Frequency Spectrum -
Beam Voltage = 74 kV
Beam Current = 3.6 A
Input Frequency = 94.5 GHz
Input Power = 18.2 mW
Output Power = 53 kW ( = 2 × 26.5 kW)
Efficiency = 20 %
Gain = 64.64 dB
• Multi-Cell (Export-Import) MAGIC3D Simulation
94.5 94.64 94.5 94.64 94.82 95.6 94.85 94.5Units: GHz
53 kW 2 × 26.5 kW = 53 kW
Parameter Sweep of QO-WSBK Models
3-Gap Output Cavity 5-Gap Output Cavity 7-Gap Output Cavity
3-Gap
Intermediate
Cavity
(2th – 4th)
1-Gap
Intermediate
Cavity
(2th – 4th)
2-Mode (f = 94.5GHz)
2-Mode (f = 94.5GHz)
2-Mode (f = 94.5GHz)
2-Mode (f = 94.5GHz)
2-Mode (f = 94.5GHz)
2-Mode (f = 94.5GHz)
(Conductivity: = 5.8 × 107 [-1m-1])
3-Gap Intermediate Cavities (MAGIC3D)
• Time History of Output Power
- 3-Gap Output Cavity - - 5-Gap Output Cavity - - 7-Gap Output Cavity -
Single Gap Intermediate Cavities:MAGIC3D
• Time History of Output Power
- 3-Gap Output Cavity - - 5-Gap Output Cavity - - 7-Gap Output Cavity -
Summary of MAGIC3D Simulations
3-Gap Output Cavity 5-Gap Output Cavity 7-Gap Output Cavity
3-Gap Intermediate
Cavity
- Pin (Max. Pout) ~ 12.13 mW
- Pout (Max.) ~ 40 kW
- Gain (Max.) ~ 69 dB
- Pin (Max. Pout) ~ 20 mW
- Pout (Max.) ~ 53 kW
- Gain (Max.) ~ 70 dB
- Pin (Max. Pout) ~ 24.27 mW
- Pout (Max.) ~ 54.76 kW
- Gain (Max.) ~ 63.54 dB
1-Gap Intermediate
Cavity
- Pin (Max. Pout) ~ 300 mW
- Pout (Max.) ~ 39.5 kW
- Gain (Max.) ~ 53.3 dB
- Pin (Max. Pout) ~ 300 mW
- Pout (Max.) ~ 52.5 kW
- Gain (Max.) ~ 56 dB
- Pin (Max. Pout) ~ 500 mW
- Pout (Max.) ~ 56.14 kW
- Gain (Max.) ~ 50.5 dB
Demountable Tube Concept for Hot-Tests
• Assembly of the Demountable Tube • Body of the Demountable Tube (currently being machined)
• Cover with a gold seal (machining in progress) • Support for the cover
Demountable Tube
UV LIGA Fabrication of QO WSBK Circuit
- UV lithography fabricated mold structure (thickness: ~ 450 m) -
• KMPR UV Lithography Patterning
• Electroplating and Mold Removal
• Lapping and Polishing
Summary and Future Plans
1. Summary
2. Future Plans
- Electron gun and magnet being redesigned Beam transport simulation is underway
PCM Magnetic field is being measured
- QO output cavity has been designed Dimension parameters optimized
Dimensional sensitivity analysis done
Cold-test and signal response simulation done
- Full Power WSBK tube has been redesigned Tube design finished using AJDISK
MAGIC3D simulation verification done
Parametric analysis done
- UV LIGA Fabrication Multi-Step UV LIGA development is underway
- Full WSBK circuit engineering design - Demountable tube design - Hot-Test