Transverse to Longitudinal Emittance Exchange Results

Transcription

1 Transverse to Longitudinal Emittance Echange Results Ray Fliller III NSLS-II Project Brookhaven National Laboratory (formerly of Fermilab) and Tim Koeth Rutgers University and Fermilab (now at University of Maryland) For the Fermilab A Team ICFA Mini Workshop

2 Acknowledgements Fermilab Helen Edwards Ray Fliller (now at BNL) Tim Koeth (now at University of Maryland) Jinhao Ruan Amber Johnson Yin-e Sun Artur Paytyan Mike Davidsaver (now at BNL) Grigory Kaakevich (now at Omega-P Inc.) Manfred Wendt Randy Thurman-Keup Vic Scarpine Ale Lumpkin Northern Illinois University Philippe Piot

3 Transverse to Longitudinal Emittance Echange How? There have been two proposals for EEX in a linac. Use a deflecting cavity in the middle of a chicane (Cornacchia and Emma, ). Use a deflecting cavity in the middle of two doglegs (Kim and Sessler, 6). Emma, et.al. in 6 combined this scheme with a round to flat beam transformer as well. Both FNAL and ANL use the Kim and Sessler scheme. Incoming beam is manipulated to have the appropriate transverse and longitudinal phase ellipses First dogleg provides dispersion at DMC. The deflecting cavity gives a longitudinal position dependant transverse kick and a transverse position dependant momentum kick. The second dogleg couples the remaining correlations to finish the echange. Initial e- bunch D 3.9 GH TM < D D3 D4 final e- bunch >

4 How does the echange work?? The transverse longitudinal transport matri R, and beam matri look like (in block mode) A R C B D The beam matri after the transport is given by R R If the R matri can be made to look like R C Then the beam matri looks like B B T T B C C T New Horiontal Emittance is the old longitudinal emittance New Longitudinal Emittance is the old Horiontal emittance

5 How does the echange work?? Assume that the beamline consists of a before cavity section, a DMC, and an after cavity section. R M Assume that the before cavity section produces some dispersion, η, with a slope η. Assume that the cavity is a ero length element What does the cavity strength need to be? What are the needed properties for the after cavity section? M M ac 6 ac 6 ac M M ac ac M η η' These equations come out of nothing more than the symplectic condition and the condition that the A and D blocks of the R matri are all eros. Note: The vertical emittance is unaffected by the transformation. M M cav ev ω k Ec η ac ac M bc FNAL Beams Doc 553

6 Fly s s in the Ointment There are many effects that may leave residual coupling, dilute, or obscure the emittance echange. Linear Flies can lead to residual coupling of the emittances, leading to an emittance increase I ve assumed an infinitely thin cavity, a finite length cavity will leave residual coupling Building an imperfect beamline such as using a chicane vs. a double dogleg as Cornacchia and Emma pointed out. Incorrect cavity strength too strong is as bad as too weak. These can be minimied or eliminated by manipulating the incoming beam phase spaces Ugly Flies these can blow up the emittances, possibly washing out the effect of the echange Space charge Coherent Synchrotron Radiation These can be minimied by lowering the beam charge.

7 Watching the Echange The Fermilab eperiment Input to the EEX line Before Dipole Before DMC After DMC Before Dipole 4 Echange Complete

8 A Photoinjector L band.5 cell NC RF gun with Cs Te photocathode 35 MV/m maimum cathode gradient TESLA technology accelerating cavity MV/m accelerating gradient Round to Flat beam transformer Transverse to Longitudinal Emittance Echange Beamline Quadrupole transport channel User eperimental area

9 Beam Parameters 6 MeV total energy Δp/p.%@ 6MeV (5 pc) Bunch length.75 mm (5 pc) γ mm-mrad 5 pc) γ,γ y 5 mm-mrad 5 pc)

10 Early EEX Signature from Spectrometer Preliminary investigations showed encouraging results. For instance, as we increased the TM cavity strength we saw a reduction in momentum spread Spectrometer Screen ~ 55keV Cavity Cavity Cavity Cavity Cavity: % 7% 8% 4% 5% 6% % % 3% OFF

11 Measuring the R 4 and R 34 through the EEX line Evolution of the beam trajectory as the cavity strength is increased, and energy is changed Horiontal BPM Difference (mm) k k5 k5 k75 k9 %k %k ideal ideal Momentum deviation removed, Converted into positions and angles! Lines: Model Dots : Horiontal BPM measured difference data δp ±.5 % in.35 % increments Vertical BPM Difference (mm)

12 OUT X Measured EEX Transport Matri EEX transport matri as a function of deflecting cavity strength FR5PFP IN X X Z X Z δ δ Circles are measurements, green lines are a weighted linear fit Red lines are calculated epected values Measured full 6 6; the vertical plane is unaffected by the cavity status

13 Emittance Echange Data Sets from A PRELIMINARY!!! Note: These numbers subject to change Plane [mm-mrad] input [mm-mrad] output Horiontal 4.7 Vertical Longitudinal 7. Successful echange of horiontal and longitudinal emittances!!!

14 Future of API EEX Program Re-measure R 3 and R 43 element Understand the emittance measurements Space Charge Studies transverse-modulation temporal Modulation (pictures from Piot and Sun)

15 Conclusion The A Photoinjector has constructed a transverse to longitudinal emittance echange beamline to swap a small transverse emittance with a large longitudinal emittance. A Photoinjector has successfully shown an emittance echange! Other ideas of how to use these manipulations are also around. Couple with a round to flat beam transformer Making a microbunch train

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17 TM Deflecting Mode Cavity (DMC) No longitudinal electric field on ais. Electric field imparts an energy kick proportional to distance off ais. Electro-magnetic field provides deflection as a function of arrival time. This type of cavity can be used as a crab cavity or for bunch length measurement. Derived from Figure of C&E. Electric field at synchronous phase. Magnetic field a quarter period later. M k Thin Cav evω Ec k k k is the integrated transverse kick normalied to the beam energy E.

18 Making an Emittance Echange Making an Emittance Echange Part I Part I The 44 emittance matri at two points in an accelerator are related by: R is the 44 transport matri between these points B and C typically have ero determinant and couple transverse and longitudinal emittances through dispersion. The emittances after the transport line are given by: T R R D C B A R ( ) [ ] ( ) [ ] T a T T a T D D C C tr B B A A tr D C B A λ λ λ ' ' ' δ δ δ Derivation follows C&E

19 Making an Emittance Echange Part II These equations show that for perfect echange we need: A B D C Follows from the symplectic condition λ How to get λ? A D ij ij If λ the emittances are coupled. Proper adjustment of the matri can reduce or remove the coupling. Derivation follows C&E