EMITTANCE EXCHANGE (EEX)

I. Chaikovska, F. Fu, T. Grandsaert, A. Lueangaramwong, K. Poor Rezaei

• X-ray FELs demand ultra-low transverse emittance beam†

• State-of-the art photo-injectors cannot generate low 6-D emittance. Emittance exchange can, using TM110 mode of RF cavities instead of absorbers combining with dipole chicanes to exchange transverse emittance (too large) to longitudinal emittance (too small).

• Can also be used to suppress microbunching instability‡

† P. Emma et al. , Nature Photonics 4, 641 - 647 (2010) ; ‡ M. Cornacchia and P. Emma, PRSTAB 5, 084001 (2002)

Motivation

J. C. T. Thangaraj, “Experimental studies on an emittance exchange beamline at the A0 photoinjector”, Fermi National Accelerator Laboratory, Batavia, Illinois

Emittance Exchange Beamline

Dogleg 1

Dogleg 2

RF Cavity

T. Koeth, “An Observation of a Transverse to Longitudinal Emittance Exchange at the Fermilab A0 Photoinjector”, Rutgers, New Jersey

Dogleg

Trajectories of an electron at different phases through the TM110 Mode Cavity

(a) Depicts the peak εz field in the horizontal plane (b) Depicts the peak vertical magnetic field which occurs 90◦ later in time.

T. Koeth, “An Observation of a Transverse to Longitudinal Emittance Exchange at the Fermilab A0 Photoinjector”, Rutgers, New Jersey

TM110 Mode Cavity

T. Koeth, “An Observation of a Transverse to Longitudinal Emittance Exchange at the Fermilab A0 Photoinjector”, Rutgers, New Jersey

TM110 Mode Cavity

J. C. T. Thangaraj, “Experimental studies on an emittance exchange beamline at the A0 photoinjector”, Fermi National Accelerator Laboratory, Batavia, Illinois

Emittance Exchange Beamline

Emittance Exchange Beamline

J. C. T. Thangaraj, “Experimental studies on an emittance exchange beamline at the A0 photoinjector”, Fermi National Accelerator Laboratory, Batavia, Illinois

1

εx, in = 4.7 umεz, in = 21.1 um

J. C. T. Thangaraj, “Experimental studies on an emittance exchange beamline at the A0 photoinjector”, Fermi National Accelerator Laboratory, Batavia, Illinois

2

Emittance Exchange Beamline

εx, in = 4.7 umεz, in = 21.1 um

J. C. T. Thangaraj, “Experimental studies on an emittance exchange beamline at the A0 photoinjector”, Fermi National Accelerator Laboratory, Batavia, Illinois

3

Emittance Exchange Beamline

εx, in = 4.7 umεz, in = 21.1 um

J. C. T. Thangaraj, “Experimental studies on an emittance exchange beamline at the A0 photoinjector”, Fermi National Accelerator Laboratory, Batavia, Illinois

4

Emittance Exchange Beamline

εx, in = 4.7 umεz, in = 21.1 um

J. C. T. Thangaraj, “Experimental studies on an emittance exchange beamline at the A0 photoinjector”, Fermi National Accelerator Laboratory, Batavia, Illinois

5

Emittance Exchange Beamline

εx, in = 4.7 umεz, in = 21.1 um

J. C. T. Thangaraj, “Experimental studies on an emittance exchange beamline at the A0 photoinjector”, Fermi National Accelerator Laboratory, Batavia, Illinois

6

Emittance Exchange Beamline

εx, in = 4.7 umεz, in = 21.1 um

εx, out = 21.1 umεz, out = 4.7 um

Xiang, Dao, and Alex Chao. "Emittance and phase space exchange for advanced beam manipulation and diagnostics." Physical Review Special Topics-Accelerators and Beams 14.11 (2011): 114001.

Three Schemes for EEX

Xiang, Dao, and Alex Chao. "Emittance and phase space exchange for advanced beam manipulation and diagnostics." Physical Review Special Topics-Accelerators and Beams 14.11 (2011): 114001.

Three Schemes for EEX

Limitation:1. Thick-lens effect2. High Energy Particle

≠ 0

≠ 0

Xiang, Dao, and Alex Chao. "Emittance and phase space exchange for advanced beam manipulation and diagnostics." Physical Review Special Topics-Accelerators and Beams 14.11 (2011): 114001.

Three Schemes for EEX

Limitation:1. Thick-lens effect2. High Energy Particle

J. Ruan., et al. "First observation of the exchange of transverse and longitudinal emittances." FERMILAB-PUB-10-468-AD (2011).

First Observation of EEX

J. Ruan., et al. "First observation of the exchange of transverse and longitudinal emittances." FERMILAB-PUB-10-468-AD (2011).

First Observation of EEX

{εx , εy , εz } = {2.9 ± 0.1, 2.4 ± 0.1, 13.1 ± 1.3} ⇒ {11.3 ± 1.1, 2.9 ± 0.5, 3.1 ± 0.3} mm-mrad.

Flat Beam

Technology

εx <->

εz

Shorter Undulat

or Length

High-Gain FEL

Neil Thompson., et al. "The 4GLS VUV-FEL." University of Strathclyde (2011).

Applications: High Gain FEL

Neil Thompson., et al. "The 4GLS VUV-FEL." University of Strathclyde (2011).

Applications: High Gain FEL

Applications: THz Generation

Conversion of the transverse modulations to longitudinal modulations : beam shaping application.

Conversion of the transverse modulations to longitudinal modulations : beam shaping application.

Applications: THz Generation

Sun, Y. E., Piot, P., Johnson, A., Lumpkin, A. H., Maxwell, T. J., Ruan, J., & Thurman-Keup, R. (2010). Tunable subpicosecond electron-bunch-train generation using a transverse-to-longitudinal phase-space exchange technique. Physical review letters, 105(23), 234801.

Cross sectional view of the TM110 Mode Cavity with lN2

jacket

The fully brazed TM110 Mode Cavity without its liquid nitrogen jacket

T. Koeth, “An Observation of a Transverse to Longitudinal Emittance Exchange at the Fermilab A0 Photoinjector”, Rutgers, New Jersey

TM110 Mode Cavity

• Timing and energy jitter: X-ray pointing stability

• EEX is expensive due to RF and thermal considerations

• Modern photoinjectors produce low emittance beam (no need for EEX)

Limitations

Acknowledgments• Timothy Maxwell• Stanford• SLAC• SSSEPB Organizers/Students