# Presentation: 482579

## Design of Advanced Photonic Bandgap Accelerator Structures

**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** **

## OUTLINE

- Introduction to PBG Accelerator Research
- HOM and Wakefields Simulation
- Advanced PBG Structures
- Conclusions

## Motivation

- Advanced Structures Needed for Wakefield Damping** **

- Slots for damping

- SLAC Damped Detuned Structure

- Shintake Choke-
- Mode Structure

- MIT PBG Structure

## Photonic Bandgap Cavity

- Pillbox Cavity, TM01 mode

** **Fundamental mode TM01 in bandgap
** **2D Lattice theory says: no HOM confined in defect
-  For a/b<0.2, only low frequency bandgap exists

## Accelerator with PBG cells

- Disk loaded PBG structure.
- Open to free space for HOM damping.
- Irises as in disk loaded waveguide.

- Accelerator parameters

## 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

## OUTLINE

- Introduction to PBG Accelerator Research
- HOM and Wakefields Simulation
- Advanced PBG Structures
- Conclusions

## 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

## Spectrum of Lattice HOMs

- Log Amp (dB)

- Cold test

- HFSS

- Lattice HOMs

** **Simulations explain HOM continuum spectrum measured

## 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.

## Animation of Beam Transit

**Animation of Beam Transit**

## OUTLINE

- Introduction to PBG Accelerator Research
- HOM and Wakefields Simulation
- Advanced PBG Structures
- Conclusions

## 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

## 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

## Pulsed Heating 

- SLAC DDS Structure
- ΔT=55OC for 70 MV/m
*(Z. Li et al., SLAC-PUB-8647, 2000)*

- PBG Structure
- H-field distribution
- ΔT=40OC for 70 MV/m gradient, Hmax=0.56 MA/m, 100 ns pulse length

## 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

## 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