Post on 28-Jan-2016
description
AAC 2008
Design of Advanced Photonic Bandgap Accelerator
Structures
M. A. Shapiro, R. A. Marsh, B. J. Munroe, R. J. Temkin
MIT Plasma Science and Fusion Center
(see also R. A. Marsh et al., PBG Wakefields Expt.)
Work supported by DOE HEP
AAC 2008
OUTLINE
• Introduction to PBG Accelerator Research
• HOM and Wakefields Simulation
• Advanced PBG Structures
• Conclusions
AAC 2008
Motivation
Advanced Structures Needed for Wakefield Damping Slots for damping
SLAC Damped Detuned Structure
Shintake Choke-Mode Structure
MIT PBG Structure
AAC 2008
Photonic Bandgap Cavity
Pillbox Cavity, TM01 mode
2a
PBG Cavity, triangular lattice a/b=0.15, TM01 –like mode
bdefect
Fundamental mode TM01 in
bandgap 2D Lattice theory says: no
HOM confined in defect For a/b<0.2, only low
frequency bandgap exists
AAC 2008
Accelerator with PBG cells
6.97 mmLattice vector, b
2.16 mmIris radius
25.2 P[MW] MV/m Gradient
1.08 mmRod radius, a
17.140 GHzFrequency
2/3Phase shift per cell
0.013cGroup velocity
23.4 kΩ /m[rs/Qw]
98 MΩ /mrs
4188Qw
6.97 mmLattice vector, b
2.16 mmIris radius
25.2 P[MW] MV/m Gradient
1.08 mmRod radius, a
17.140 GHzFrequency
2/3Phase shift per cell
0.013cGroup velocity
23.4 kΩ /m[rs/Qw]
98 MΩ /mrs
4188Qw
Disk loaded PBG structure.Open to free space for HOM damping.Irises as in disk loaded waveguide.
Accelerator parameters
AAC 2008
Accomplishments: PBG Accelerator Expt.
E. I. Smirnova et al., Physical Review Letters (2005).
First successful experimental PBG accelerator demonstration.
Tested to gradient 35 MeV/m, limited by available power
AAC 2008
OUTLINE
• Introduction to PBG Accelerator Research
• HOM and Wakefields Simulation
• Advanced PBG Structures
• Conclusions
AAC 2008
Lattice Dipole HOMs
HFSS simulations show HOMs in PBG structure Field not confined in central region (defect), but in lattice Low Q, Q<300
Pillbox Dipole Mode 23 GHz Q = 9500
Lattice Dipole Mode 24.9 GHz Q = 63
AAC 2008
Spectrum of Lattice HOMsLo
g A
mp
(dB
)
16 18 20 22 24 26-100
-80
-60
-40
-20
0S21
[dB
]
Frequency [GHz]
Your text
Cold test
HFSS
Lattice HOMs
Simulations
explain HOM continuum spectrum measured
AAC 2008
Wakefields Theory and Simulations
• Conventional wakefield theory (K. Bane et al., 1987) can
be used for PBG wakefields calculation
– Requires r, Q for each mode
– Calculations underway at MIT
• SLAC codes (T3P) can be used to simulate wakefields in
PBG structure
– We collaborate with SLAC and STAAR, Inc. on wakefields
simulations in PBG structures.
AAC 2008
Animation of Beam Transit
AAC 2008
OUTLINE
• Introduction to PBG Accelerator Research
• HOM and Wakefields Simulation
• Advanced PBG Structures
• Conclusions
AAC 2008
Plans for Advanced PBG Structures
• First PBG structure built at 17 GHz
– Tested at MIT for gradient, wakefields
• Second PBG structure being built for gradient
testing at 11.424 GHz (MIT/SLAC collaboration)
• Future PBG structures at 11, 17 GHz are being
designed
– Reduced pulsed heating
– Gradient 100 MeV/m
– Low breakdown rate
– Free of wakefields
AAC 2008
PBG Structure Detuning
23.0 GHz TM11, Q=72
Structure allows detuning dipole modes TM11
17.13 GHz TM01
Lattice rotated by 30 deg. from cell to cell
AAC 2008
Pulsed Heating
SLAC DDS StructureΔT=55OC for 70 MV/m
(Z. Li et al., SLAC-PUB-8647, 2000)
PBG StructureH-field distribution
ΔT=40OC for 70 MV/m gradient,
Hmax=0.56 MA/m, 100 ns pulse
length
AAC 2008
New Ideas for Optimized PBG Structures
Optimize structure for dipole mode
damping and reduced pulsed heating Shaped rods, not circular Distortion of lattice geometry
Similar to proposal of G. Werner et al.
(Colorado) for dielectric PBG design
Example of PBG structure with elliptical
rods to improve pulsed heating
Complex Mag E
Complex Mag H
ΔT=11OC for 70 MV/m gradient,
Hmax=0.3 MA/m, 100 ns pulse length
AAC 2008
Conclusions
• PBG structure under investigation for linear collider
• Wakefields in form of Dipole HOMs calculated.
– Lattice HOMs with low Q
• Calculation results can be compared to PBG wakefields experiment (next talk).
• Collaboration with SLAC and STAAR Inc. on wakefields in PBG structure
• Advanced PBG accelerator under design for testing 11 and 17 GHz
– 17 GHz structure for test at MIT, 11 GHz at SLAC
– Reduced pulsed heating, comparable to DDS
– Extremely low HOM wakefields, much lower than in DDS