HFSS

1. Reentrant cavity resonator for low
intensities proton beam measurements
ESR: Sudharsan Srinivasan
Supervisor: Dr. Pierre André Duperrex
Project Start Date: 01/01/2017

2. Contents
• Project Description
• Comparison of Diagnostics
• Principle of Operation
• ANSYS HFSS for BCM
• Test bench Characterization
• Simulation Vs Measurement
• ANSYS HFSS for BPM
• Future work
OMA Workshop on Beam Diagnostics,
05/06/2018
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3. OMA Workshop on Beam Diagnostics,
05/06/2018
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Beam Parameters Value
Repetition Rate 72.85 MHz
RMS Bunch Length 2 ns
Beam Intensity of Interest 1 – 800 nA
Resonator Frequency 145.7 MHz

4. Project Description
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05/06/2018
Proton Beam
Proton
Beam
RF based Measurement of
Ultra Low charges
Proton Beam
Ionization
Chamber
Non-
interceptive
Beam
Diagnostic
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5. Comparison of Diagnostics
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05/06/2018
Passive Transformer
• Short pulsed beams
• Low number of windings
• Low stray capacitance
• High permeability metal
shielding
5
P. Forck, Lecture Notes on Beam Instrumentation and Diagnostics. 2011.

6. Comparison of Diagnostics
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05/06/2018
Button
Active Transformer
• Operational amplifier with
feedback resistor
• Higher sensitivity
• Low bandwidth
• High permeability torus
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P. Forck, Lecture Notes on Beam Instrumentation and Diagnostics. 2011.

7. Comparison of Diagnostics
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05/06/2018
DC Transformer
• DC beam current
• High sensitivity
• High SNR
• Complex realization
• Typical resolution 1 μA
7
P. Forck, Lecture Notes on Beam Instrumentation and Diagnostics. 2011.

8. Comparison of Diagnostics
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05/06/2018
Resistive WCM
Resistive WCM
• Bunch structure observation
• Emittance measurement
• Shielding
• Rarely used
• Thermal noise
• Coupling impedance
• Beam instability
8
P. Forck, Lecture Notes on Beam Instrumentation and Diagnostics. 2011.

9. Comparison of Diagnostics
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05/06/2018
Inductive WCM
Inductive WCM
• Azimuthal image current
distribution
• Positional sensitivity
• Large bandwidth
• Installation is outside beam
pipe
• Easy accessibility
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P. Forck, Lecture Notes on Beam Instrumentation and Diagnostics. 2011.

10. Comparison of Diagnostics
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05/06/2018
Pillbox
Pillbox
• Short pulse and single pulse
• Superior signal sensitivity
• Size limitations
• Mode contamination
10
R. Lorenz, “Cavity beam position monitors,” pp. 53–73, 1998.

11. Comparison of Diagnostics
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05/06/2018
Reentrant
Reentrant
• Proven cryogenic and
cleanroom
compatability
• Smaller size
• Lower Q
• Better damping
• Good linearity
• Radial symmetry
11
H. S. M. Gasior, R. Jones, T. Lefevre, “Introduction to Beam Instrumentation,”
2013.

12. Principle of Operation
1/
o LC
 
1
2
f
LC


ln
2
c
b
L
a




2 / ln
c
b
C
a



2
gap
a
C
s




 
0.5
1
( )
2
c c gap
f L C C


 
OMA Workshop on Beam Diagnostics,
05/06/2018
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“Microwave Phase Modulators for Smoothing by Spectral
Dispersion,” LLE Rev., vol. 68, pp. 192–208, 1996.
Increasing a increases Cgap. Increasing S reduces Cgap

13. ANSYS HFSS Simulation
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Design Modeler
Boundaries
Excitations
Solution Setup
Frequency Sweep
Adaptive Mesh
Convergence
2D reports
Fields plot

14. ANSYS HFSS Simulation
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50 Ω Port impedance
Waveport Excitation
Across all ports
i.e. beam entry and exit
All pickup ports

15. ANSYS HFSS Simulation
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E Field
H Field

16. ANSYS HFSS SIMULATION
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Simulation result: Optimetric
Analysis of Pickup position
S13 for different Pickup position Vs Resonance Frequency
Maximum
Minimum

17. ANSYS HFSS SIMULATION
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Resonance Frequency Vs Pickup Position

18. ANSYS HFSS SIMULATION
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S13 Vs Pickup Position
Pickup position 35 mm chosen

19. ANSYS HFSS SIMULATION
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S13 for Ceramic Thickness Vs Resonance Frequency
Simulation result:
Optimetric
Analysis of
ceramic thickness
145.7 MHz
130 MHz 160 MHz
-6.89
dB

20. ANSYS HFSS Simulation
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E Field
H Field
Resonance Frequency
Signal Level

21. Mechanical Prototype
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Optimized Pickup position
Optimized Ceramic
thickness
Dimensions derived
from HFSS

22. Test Bench Design
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23. Simulation Vs Measurement
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2% deviation due to Dielectric
constant of the Ceramic

24. Status of BCM
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• The prototype built and characterized
• Simulation Vs Test bench measurement good agreement
• Deviation from Simulation investigated
• Frequency dependent dielectric constant of MACOR
• Install in the beam line in the coming weeks

25. Reentrant BPM
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Monopole
Dipole
Beam Entering into the page
2mm offset
Beam Shifting in the upward direction
Y
X

26. Reentrant BPM
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Monopole
Dipole

27. OMA Workshop on Beam Diagnostics,
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Reentrant BPM
Y Direction
2 mm offset in Y
plane.
X plane cavities
see no difference
in induced fields
Y plane cavities
see considerable
difference in
induced fields
X direction
Near by Far by

28. First Observations
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29. Future Works
• BPM prototype middle of July, 2018
• BPM Test bench measurement
• Fine-tuning of Prototype
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30. Thank You
Questions???
This project has received funding from the
European Union’s Horizon 2020 research and
innovation programme under the Marie
Skłodowska-Curie grant agreement No 675265
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05/06/2018
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