kevin paul tech-x corporation
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Field Emission in the 805 MHz Cavity Update on the eSHIELD Phase I SBIR. Kevin Paul Tech-X Corporation. Muon Collider Design Workshop / BNL / Dec 3, 2009. Magnetic Insulation Primer. Introduced to achieve high voltages in transformers without arcing - PowerPoint PPT PresentationTRANSCRIPT
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Kevin PaulTech-X Corporation
Field Emission in the805 MHz Cavity
Update on the eSHIELD Phase I SBIR
Muon Collider Design Workshop / BNL / Dec 3, 2009
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Magnetic Insulation Primer
2
Introduced to achieve high voltages in transformers without arcing F. Winterberg, “Magnetically Insulated Transformer for Attaining
Ultrahigh Voltages,” Rev. Sci. Instrum., vol. 41, p. 1756, December 1970.
E. H. Hirsch, “The Concept of Magnetic Insulation,” Rev. Sci. Instrum., vol. 42, no. 9, p. 1371, 1971.
F. Winterberg, “On the Concept of Magnetic Insulation,” Rev. Sci. Instrum., vol. 43, p. 814, May 1972.
€
peB( )
Field emitted electrons are confined to a region near the surface Magnetic field is parallel to high-
voltage surface (high electric field) Thickness determined by Larmor
radius Limited time for acceleration by the
electric field (i.e., expect less energy deposition on surface)
€
r B
Muon Collider Design Workshop / BNL / Dec 3, 2009
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The eSHIELD Phase I SBIR“Magnetic Insulation and the Effects of External Magnetic Fields on RF Cavity
Operation in Muon Accelerators”
3
1. Accurate field/secondary emission and heating models VORPAL (3D Electromagnetic/Electrostatic PIC) Mostly complete (needs temperature dependent secondary
emission)2. Simulations of emitted electron propagation in cavities
In Progress (Discussed in this presentation!)3. Coupled small-scale micro-physics simulations with
large-scale macro-physics simulations Currently being studied in terms of non-uniform “mesh
refinement” Early in development (i.e., we ignore space charge for now)
4. Prototype integrated numerical simulations of the magnetic insulation concept To be developed further in Phase IIMuon Collider Design Workshop / BNL / Dec 3, 2009
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Simulation Challenges
4
Material and emission modeling / “The Physics” Temperature-dependent field and secondary electron emission
models are parameterized approximations (uncertainty) Material surfaces must be parameterized in terms of bulk
properties Microscopic surface geometries are unknown and evolve in
unknown ways
Need to resolve the “small scale” (How “small” is uncertain!)
Multi-scale resolution issues Microscopic surface properties / asperities: ~10-6 m RF Cavities: ~0.1 m to ~1 m EM PIC time scale (in small-scale simulations): ~10-15 s RF Time Scales: ~10-9 s to 10-8 s
Need “mesh refinement” (Hard in PIC!) – Ignoring space charge (for now)!
Muon Collider Design Workshop / BNL / Dec 3, 2009
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VORPAL Simulations of the 805 MHz “Button” Cavity
5Muon Collider Design Workshop / BNL / Dec 3, 2009
Full Diameter: 31.5 cm
Iris Diameter: 16 cm Central Length: ~8
cm Enclosed by windows
(asymmetric)
y
xz
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VORPAL Simulations of the 805 MHz “Button” Cavity
6Muon Collider Design Workshop / BNL / Dec 3, 2009
Full Diameter: 31.5 cm
Iris Diameter: 16 cm Central Length: ~8
cm Enclosed by windows
(asymmetric) Considered 3 points of
emission:A. On axis (“button”)B. Off axis / On window (4 cm)C. Off axis / On iris (~8.5 cm)
Emission Spots: ~1 mm radius
Fowler-Nordheim (300 K) Emits for only 1 RF cycle Magnetic Fields considered:
1. None2. “Parallel” (x-axis)3. “Perpendicular” (y-axis)
A
B
C
y
xz
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VORPAL Simulations of the 805 MHz “Button” Cavity
7Muon Collider Design Workshop / BNL / Dec 3, 2009
€
r J x (t)
Am 2[ ]
€
r E x (t)
Vm[ ]
€
t [s] Emission!
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CASE A1: On-axis / B = 0
8Muon Collider Design Workshop / BNL / Dec 3, 2009
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CASE A1: On-axis / B = 0
9Muon Collider Design Workshop / BNL / Dec 3, 2009
Total Energy:
7.2 MeV 0.85 MeV
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CASE A1: On-axis / B = 0
10Muon Collider Design Workshop / BNL / Dec 3, 2009
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CASE A2: On-axis / Bx = 1 T
11Muon Collider Design Workshop / BNL / Dec 3, 2009
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CASE A2: On-axis / Bx = 1 T
12Muon Collider Design Workshop / BNL / Dec 3, 2009
Total Energy:
7.2 MeV 0.86 MeV
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CASE A2: On-axis / Bx = 1 T
13Muon Collider Design Workshop / BNL / Dec 3, 2009
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CASE A3: On-axis / By = 1 T
14Muon Collider Design Workshop / BNL / Dec 3, 2009
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CASE A3: On-axis / By = 1 T
15Muon Collider Design Workshop / BNL / Dec 3, 2009
Total Energy:
0.96 MeV 0.48 eV
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CASE A3: On-axis / By = 1 T
16Muon Collider Design Workshop / BNL / Dec 3, 2009
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CASE B1: On-window / B = 0
17Muon Collider Design Workshop / BNL / Dec 3, 2009
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CASE B1: On-window / B = 0
18Muon Collider Design Workshop / BNL / Dec 3, 2009
Total Energy:
7.3 MeV 43 eV
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CASE B1: On-window / B = 0
19Muon Collider Design Workshop / BNL / Dec 3, 2009
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CASE B2: On-window / Bx = 1 T
20Muon Collider Design Workshop / BNL / Dec 3, 2009
SUSPICIOUS!
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CASE B2: On-window / Bx = 1 T
21Muon Collider Design Workshop / BNL / Dec 3, 2009
Total Energy:
1.5 MeV 688 eV
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CASE B2: On-window / Bx = 1 T
22Muon Collider Design Workshop / BNL / Dec 3, 2009
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CASE B3: On-window / By = 1 T
23Muon Collider Design Workshop / BNL / Dec 3, 2009
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CASE B3: On-window / By = 1 T
24Muon Collider Design Workshop / BNL / Dec 3, 2009
NOTHING!
Total Energy:
6.2 keV
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CASE B3: On-window / By = 1 T
25Muon Collider Design Workshop / BNL / Dec 3, 2009
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CASE C1: On-iris / B = 0
26Muon Collider Design Workshop / BNL / Dec 3, 2009
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CASE C1: On-iris / B = 0
27Muon Collider Design Workshop / BNL / Dec 3, 2009
Total Energy:
13.8 MeV 43.5 keV
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CASE C1: On-iris / B = 0
28Muon Collider Design Workshop / BNL / Dec 3, 2009
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CASE C2: On-iris / Bx = 1 T
29Muon Collider Design Workshop / BNL / Dec 3, 2009
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CASE C2: On-iris / Bx = 1 T
30Muon Collider Design Workshop / BNL / Dec 3, 2009
Total Energy:
13.8 MeV 175 keV
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CASE C2: On-iris / Bx = 1 T
31Muon Collider Design Workshop / BNL / Dec 3, 2009
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CASE C3: On-iris / By = 1 T
32Muon Collider Design Workshop / BNL / Dec 3, 2009
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CASE C3: On-iris / By = 1 T
33Muon Collider Design Workshop / BNL / Dec 3, 2009
NOTHING!
Total Energy:
1.15 MeV
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CASE C3: On-iris / By = 1 T
34Muon Collider Design Workshop / BNL / Dec 3, 2009
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Conclusions & Future Work
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Preliminary simulations of field emission in the 805 MHz cavity Not a thorough exploration of configuration space, but… Most of the energy deposited is on the “near” wall (very little on
“far”) Suggest that “magnetic insulation” can reduce the energy
deposited on the near wall by approximately an order of magnitude!
Probably depends (greatly!) on the cavity field-strength, dimensions, etc.
Need to account for space charge Requires finer mesh Suggests non-uniform “mesh refinement” techniques (or risk
prohibitively large simulations) Need to include secondary electrons
Multi-pactoring could be significant (amplification and resonance) Means simulating longer times (many RF cycles)
Need to investigate better data analysis techniques
Muon Collider Design Workshop / BNL / Dec 3, 2009