Exchange of Transverse and Longitudinal Emittance at the A0 Photoinjector

1. Exchange of Transverse and Longitudinal Emittance at the A0 Photoinjector Tim Koeth (this talk was initially prepared for TK’s committee meeting of March 11, 2008) Updated March 14th, 2008

2. Outline • Brief Photoinjector introduction • Motivation & Theory of Emittance Exchange • Exchange Apparatus at the A0 Photoinjector • Results to date… • Next Steps • Acknowledgements

3. The A0 Photoinjector Next, Artur will talk about the low level RF systems that keep the laser, two 1.3 GHz and one 3.9 GHz systems in sync. • Laser energy 16 mJ/pulse @ 263nm • <5nC/bunch (have had >12 nC in the past) • Typically 10 bunches/RF pulse. 1 Hz rep rate • 4 MeV gun output energy • 16 MeV total energy • Dp/p ≈ 0.3%@ 16MeV (1nC) • Bunch length ≈ 2 mm (1nC) • gez ≈ 120 mm-mrad (RMS @ 1nC) • gex,gey≈4 mm-mrad (RMS @ 1nC)

4. The Idea: Emittance Exchange (EEX) • In 2002 M. Cornacchia and P. Emma proposed using a TM110 deflecting mode cavity in the center of a chicane to exchange a smaller longitudinal emittance with a larger transverse emittance for a FEL. • Kim & Sessler in 2005 proposed using a flat beam (ex<<ey) combined with a deflecting mode cavity between 2 doglegs to produce a beam with very small transverse emittances and large longitudinal emittance to drive an FEL. • We are doing a proof of principle emittance exchange at A0 using the double dogleg approach with a round beam (ex=ey) . • We’ll be exchanging a larger longitudinal emittance with a smaller transverse emittance. • Keep in mind that emittance is the area beam phase space, • Why ? • Basic and unique beam dynamics manipulation – proof of principle • FEL’s - low transverse emittance, large brightness • This phase space manipulation could have application in a linear collider

5. TM110 (Deflecting) Mode Cavity • No longitudinal electric field on axis. • Electric field imparts an energy kick proportional to distance off axis. • Plan to use this to change the momentum deviation in presence of dispersion! • Electro-magnetic field provides deflection as a function of arrival time. • This is the type of cavity used as a crab cavity or for bunch length measurement. a (from Figure 1 of C&E) Electric field at synchronous phase. Magnetic field a quarter period later. k is the integrated longitudinal energy gain at a reference offset a normalized to the beam energy E.

6. Concept of Emittance Exchange A typical non-dispersive transport matrix: What we want to develop is a matrix like:

7. 3.9 GHz TM110 D1 Initial e- bunch D2 D3 final e- bunch D4 ex > ez EEX: Linear Optics Model First, break the EEX-line into three sections: Magnetic dogleg before cavity: Mbc TM110 cavity (thin lens): Mcav Magnetic dogleg after cavity: Mac and To get:

8. EEX: Linear Optics Model Now if we take the trivial case of k =0 we get: However, if we take the special case of k = -1/D = ko we get: All of the X-X and Z-Z coupling elements are zero !

9. EEX: Linear Optics Model With our k=ko We can transports the initial uncoupled beam (sigma) matrix through the EEX line And remember via : We know from above that A = D = 0, so this reduced to: Then take the determinate of σx, σz and we get: a complete swap of the emittances is seen.

10. EEX Beam Line at the Photoinjector Vertical bend avoids residual dispersion of X-plane Diagnostics: = Beam Position Monitor (BPM) - Transverse beam position = Diagnostic cross: viewing screen(s) & digital camera - Measuring transverse beam size = Slit/Screen pair for transverse emittances. = MagneticSpectrometer – P & ∆P Not shown: Streak camera & Interferometer – e- bunch length, Phase Mon – e- TOF

11. EEX Beam Line at the Photoinjector Vertical Spectrometer Dipoles TM110 Cavity Beam direction

12. EEX Beam Line at the Photoinjector (Cav off) Beamline Layout Deflecting Mode Cavity

13. TM110 Cavity Details Construction: 5 cells (of CKM design) Punched OFHC Copper Vacuum brazed Radio Frequency: 3.9 GHz (3x 1.3GHz) Q300K=14,900 Q80K=35,600 Coupling (β) = 0.7 Req’d RF power @ full gradient: 50kW

14. Cavity Polarizaton and Field Flatness Vertical • Longitudinal electric field vs angle in cells 2-4 determined by bead pull. • Cavity polarization is set by input coupler • Bead pull results of cavity field flatness tuning.

15. TM110 Cavity: 1st Deflection Operating phase for exchange • The induced kick is about 70% of what was expected for the input power, however, sufficient contingency was built into the cavity to accommodate this. BPM26

16. Early Vertical Spectrometer Images • Preliminary investigations showed encouraging results. For instance, as we increased the TM110 cavity strength we saw a reduction in momentum spread… ~ 550keV Spectrometer Screen Cavity 100% Cavity 70% Cavity 80% Cavity 40% Cavity 50% Cavity 60% Cavity 10% Cavity 20% Cavity 30% Cavity: OFF

17. Measuring the EEX Line Matrix Again, describing the beam line with linear optics we have: There is exciting evidence that the cavity was indeed modifying the momentum spread, so we have begun to systematically measure the EEX beam line matrix. Adjusting one input parameter at a time and measuring all output parameters we can map out the transport matrix. For example, introducing a momentum offset yields the 6th column: Do this with the TM110 cavity off, partially on, 100% on, and greater

18. EEX Beamline: Vertical Spectrometer BPM For a given TM110 strength, k, changed beam central momentum by ± 2.15 % in 0.70% increments by varying 9-Cell cavity gradient. Repeated for several TM110 k: TM110 cavity strength, ko OFF 73% 90% 100% 105% Intro dp from 9-Cell Intro dp from 9-Cell Vary k record vertical BPM reading

19. EEX: Beam Line Horizontal Dispersionmeasurement with TM11O cavity off Lines: ideal Dots : Horizontal BPM measured difference data D1 D2 D3 D4 TM110 SPECT. δP = ± 1.05 % in 0.35 % increments +1.05% +0.70% +0.35% 0 -0.35% -0.70% -1.05%

20. EEX: Beam Line with TM110 Cavity On,Ideal: Lines: ideal D1 D2 D3 D4 TM110 SPECT. 120% 100% 80% 60% 40% OFF 20% δP = ± 1.05 % in 0.35 % increments +1.05% +0.70% +0.35% 0 -0.35% -0.70% -1.05%

21. EEX: Beam Line with TM110 Cavity onMeasured: Cavity strength, ko D1 D2 D3 D4 TM110 SPECT. 100% OFF 44% 67% 85% +1.05% +0.70% +0.35% 0 -0.35% -0.70% -1.05%

22. Streak Camera TOF measurements Introduce dp from 9-Cell Streak camera ~ 1pSec resolution

23. Similar for 2nd Column: vary ∆xin’ Impart Dx’ by adjusting a horizontal corrector magnet k=62%ko … And Dx, Dy, Dy’… The Dz can be achieved by adjusting the TM110 cavity phase

24. Dx’in data from today

25. Today’s BPM8/30 Dispersion Measurements BPM8 & 30 Special 4-inch housing Ray’s cald XS4 Vert Disp : 865mm Tim’s measuremnt 855+/-5mm Ray’s calc of XS3 Horz Disp: 225mm Tim’s measurement 226mm Finally nice agreement ! Note non-lin > 8 mm

26. Summary of Today & yesterday data collection (March 13 thru 14) δ energy incriments calibration against BPM8 Now, off to analyze…

27. EEX: Next Steps • Continue to populate the matrix • Measure input and output emittances • Graduate !

28. Many thanks go to: • Helen Edwards - Advisor • Don Edwards - Voice of reason • Leo Bellantoni – [tor]Mentor & CKM • Ray Fliller – A0 Post Doc • Jinhao Ruan – Laser, All things optical • Jamie Santucci – fireman • Alex Lumpkin – streak camera • Uros Mavric – Ph.D. Student • Artur Paytan – Yerevan U. Ph.D. Student • Mike Davidsaver – UIUC staff, controls guru • Grigory Kazakevich – Guest Scientist, OTRI • Manfred Wendt & Co – Instrumentation, BPMs • Elvin Harms – kindly sharing a klystron • Randy Thurman-Keup – Instrumentation, Interferometer • Vic Scarpine – Instrumentation, OTR and cameras • Ron Rechenmacher – CD, controls • Lucciano Piccoli – CD, controls • Brian Chase, Julien Branlard, & Co – Low Level RF • Gustavo Cancelo – CD, Low Level RF • Wade Muranyi & Co – Mechanical Support • Bruce Popper – drafter & artist • Chris Olsen - assistant