EMITTANCE EXCHANGE (EEX)
I. Chaikovska, F. Fu, T. Grandsaert, A.
Lueangaramwong, K. Poor Rezaei
Motivation
• 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)
Emittance Exchange Beamline
Dogleg 1
Dogleg 2
RF Cavity
J. C. T. Thangaraj, “Experimental studies on an emittance exchange beamline at the A0 photoinjector”, Fermi
National Accelerator Laboratory, Batavia, Illinois
Dogleg
T. Koeth, “An Observation of a Transverse to Longitudinal Emittance Exchange at the Fermilab A0
Photoinjector”, Rutgers, New Jersey
TM110 Mode Cavity
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
Emittance Exchange Beamline
J. C. T. Thangaraj, “Experimental studies on an emittance exchange beamline at the A0 photoinjector”, Fermi
National Accelerator Laboratory, Batavia, Illinois
Emittance Exchange Beamline
1
εx, in = 4.7 um
εz, 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
Emittance Exchange Beamline
2
εx, in = 4.7 um
εz, 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
Emittance Exchange Beamline
3
εx, in = 4.7 um
εz, 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
Emittance Exchange Beamline
4
εx, in = 4.7 um
εz, 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
Emittance Exchange Beamline
5
εx, in = 4.7 um
εz, 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
Emittance Exchange Beamline
εx, out = 21.1 um
εz, out = 4.7 um
6
εx, in = 4.7 um
εz, 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
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 effect
2. High Energy Particle
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 effect
2. High Energy Particle
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.
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.
J. Ruan., et al. "First observation of the exchange of transverse and longitudinal emittances."
FERMILAB-PUB-10-468-AD (2011).
Applications: High Gain FEL
Flat Beam
Technology
εx <-> εz
Shorter
Undulator
Length
Neil Thompson., et al. "The 4GLS VUV-FEL." University of Strathclyde (2011).
High-Gain
FEL
Applications: High Gain FEL
Neil Thompson., et al. "The 4GLS VUV-FEL." University of Strathclyde (2011).
Applications: THz Generation
Conversion of the transverse modulations to longitudinal modulations :
beam shaping application.
Applications: THz Generation
Conversion of the transverse modulations to longitudinal modulations
: beam shaping application.
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.
TM110 Mode Cavity
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
Limitations
• 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)
Acknowledgments
• Timothy Maxwell
• Stanford
• SLAC
• SSSEPB Organizers/Students