Angular momentum dominated electron beam and flat beam generation. FNPL video conference Feb. 28, 2005 Yin-e Sun 1

Transcription

1 Angular momentum dominated electron beam and flat beam generation FNPL video conference Feb. 8, 5 Yin-e Sun 1

2 outline angular momentum dominated electron beam and its applications production and measurements of angular momentum dominated beam removal of the angular momentum and generation of flat beam: a bit of theory measurement method data analysis and recent results comparison with simulations conclusion FNPL video conference Feb. 8, 5 Yin-e Sun

3 beam dynamics: three different regimes emittance canonical angular momentum space charge ε L σ '' 3 3 σ σ envelope equation in a drift: where. K 4σ = K = I I 3 β γ 3 FNPL video conference Feb. 8, 5 Yin-e Sun 3

4 Applications of angular momentum dominated beam electron cooling for heavy ion τ mag c ρ ( ) v ion v e z z τ c free ρ v e flat beam for linear e + e - collider: reduce beamstrahlung 1 1 luminosity δ E σ σ ( σ + σ ) x y e.g.tesla 5GeV 1/. 3mm mrad for 3 nc FNPL video conference Feb. 8, 5 Yin-e Sun 4 x y

5 Applications of angular momentum dominated beam flat beam for light sources Linac based ultra-short X-ray pulse (LBNL) l = y sin θ sin( θ sin α + α) time Smith-Purcell radiator or image charge undulator Bragg angle time U of Chicago, Dartmouth U. JLab. FNPL video conference Feb. 8, 5 Yin-e Sun 5

6 Generation of angular momentum dominated e - beam L = γ mr φ & + 1 eb r On the photocathode: z L = σ eb c Bz = : mechanical angular momentum 15 B z (Gauss) 1 5 FNPL 1.65-cell RF gun, 1.3 GHz Z (cm) FNPL video conference Feb. 8, 5 Yin-e Sun 6

7 Fermilab/NICADD Photoinjector Lab. (FNPL) 4 MeV 16 MeV RF gun TESLA superconducting cavity Round-to-flat Beam transformer (skew quadrupoles) FNPL video conference Feb. 8, 5 Yin-e Sun 7

8 Measurement of canonical angular momentum on the photocathode L = eb σ c B : B-field on cathode s c :RMS beam size on cathode FNPL video conference Feb. 8, 5 Yin-e Sun 8

9 Measurement of mechanical angular momentum in a drift space σ1σ sin θ L = pz D D z1 z FNPL video conference Feb. 8, 5 Yin-e Sun 9

10 Measurement of mechanical angular momentum vs B-field FNPL video conference Feb. 8, 5 Yin-e Sun 1

11 Demonstration of conservation of canonical angular momentum as a function of magnetic field on cathode 11 B (G) <L> = p z σ 1 σ sin θ/d (nev s) σ c =.97 ±.4 mm experiment <L> = eb σ (nev s) c FNPL video conference Feb. 8, 5 Yin-e Sun 11

12 Parametric dependencies of angular momentum Angular momentum versus beam longitudinal position z bunch charge beam size on the cathode L = eb σ c FNPL video conference Feb. 8, 5 Yin-e Sun 1

13 Round-to-flat beam transformation Σ round ε eff β = L ε eff L β ε L eff β ε eff L β General form of a round beam (K.-J. Kim) e eff = ε u + L Σ ~ flat = M Σ round M Un-correlated emittance normalized canonical angular momentum Transfer matrix of the round-to-flat beam transformer Σ flat = ε β ε β ε + β ε + β Flat beam emittances given by: ε u + L ± FNPL video conference Feb. 8, 5 Yin-e Sun 13 e.g. ε ± = L L= mm mrad, e u =1 mm mrad e + =47 mm mrad; e - =. mm mrad

14 Round-to-flat beam transformation using skew quadrupoles Flat beam: large transverse emittance ratio, zero average angular momentum. q 1 q q 3 d d 3 τ total = q i xi yi 3 Two sets of solutions: 1-1 S N N S q q 1 = ± d S = d d q + 1 q + ds11q1q + S1 q3 = ( d ) ( ) Tq1 + d 3q S11 + dd3q S1 + q1 FNPL video conference Feb. 8, 5 Yin-e Sun 14 S 11 + S1 dd d d S + dt S (1 + S q 1 1 ) T T 1 S 1 + d T S (D. Edwards)

15 Position and velocity snap shots at the entrance/exit of the transformer -3 x x x y x 1-3 x x 1-4 Round beam x 1-4 flat beam FNPL video conference Feb. 8, 5 Yin-e Sun

16 Beam evolution through the transformer for the first solution 1 mm 5 x x 1-3 Right before 1 st quad Right after 1 st quad x x x x 1-3 Right before nd Quad Right after nd Quad x x x x 1-3 Right before 3 rd quad Right after 3 rd quad x x 1-3 FNPL video conference Feb. 8, 5 Yin-e Sun 16

17 Removing of angular momentum and generating a flat beam 1345 experiment simulation FNPL video conference Feb. 8, 5 Yin-e Sun 17

18 single slit emittance measurement method Blue: flat beam at X7; green: H or V slit inserted at X7; red: slit image at X8..6 mm 6 mm FNPL video conference Feb. 8, 5 Yin-e Sun 18

19 Recent flat beam experiment 1 Data of Jan. 6, 5 Solenoid setting: main=19a, buck=a, secondary=75a UV drive-laser rms size =.76 mm, rms pulse length = 3 ps beam energy = 15.8 MeV bunch charge =.5 ±.5 nc y (mm) y (mm) y (mm) X7 X8 Hslit X8 Vslit x (mm) x (mm) x (mm) FNPL video conference Feb. 8, 5 Yin-e Sun 19

20 Data analysis: RMS beam size calculation 1. Choose area of interest y (pixel) y (pixel) x (pixel) area of interest x (pixel). Decide the background level x (pixel) FNPL video conference Feb. 8, 5 Yin-e Sun Intensity (arb. unit) 4 3 1

21 Data analysis: RMS beam size calculation 1. area of interest σ x (pixel) Number of pixels used for rms calculation σ x (pixel) Percentage FNPL video conference Feb. 8, 5 Yin-e Sun 1

22 . background level Data analysis: RMS beam size calculation 35 3 σ x (pixel) Number of pixels used Rising background level Red line: using average background level FNPL video conference Feb. 8, 5 Yin-e Sun

23 Compare experiment 1 with simulation Experiment Simulation 9% 95% (ASTRA) rms_cathode(mm).71±.5.76±.6.76 B_cathode(Gauss) I_Quad1 (A) I_Quad (A).4.57 I_Quad3 (A) rms_x7y (mm).59±.3.63±.4.56 rms_x7x (mm).77±.5.87±.6.47 rms_x8_hslit (mm) 1.15±. 1.4±. 1.5 rms_x8_vslit (mm).1±.1.13±.1.81 emitx (mm mrad).36± ± emity (mm mrad) 6± 3± 3 emit ratio 73±1 68±1 165 (emitx emity) mm mrad FNPL video conference Feb. 8, 5 Yin-e Sun 3

24 ASTRA Simulation with 1/6/5 experiment conditions mm mrad emit. ratio ε x (mm mrad) ε y (mm mrad).18 mm mrad z (m) FNPL video conference Feb. 8, 5 Yin-e Sun 4

25 3 Recent flat beam experiment Data of Feb. 5, 5 Solenoid setting: main=195a, buck=a, secondary=75a UV drive-laser rms size =.97 mm, rms pulse length = 3 ps (?) beam energy = MeV bunch charge =.51 ±.17 nc X X X X X X FNPL video conference Feb. 8, 5 Yin-e Sun 5

26 Compare experiment with simulation Experiment Simulation 9% 95% (ASTRA) rms_cathode(mm) B_cathode(Gauss) I_Quad1 (A) I_Quad (A) I_Quad3 (A) rms_x7y (mm).58±.1.63±.1.77 rms_x7x (mm).84±.1.95±.1.58 rms_x8_hslit (mm) 1.57± ± rms_x8_vslit (mm).1±.1.13±.1.11 emitx (mm mrad).39±...49±...7 emity (mm mrad) 35.±.5 41.±.5 53 emit ratio 9±5 83±4 196 (emitx emity) mm mrad FNPL video conference Feb. 8, 5 Yin-e Sun 6

27 conclusion A series of experimental investigation of angular momentum dominated electron beam was carried out; Simulations show that an emittance ratio >1 is possible when the chromatic effect and space charge are taking into account. Recent flat beam emittance measurements are very encouraging: at.5 nc, normalized emittance of.4 ~.5 mm mrad was measured (LUX design value but at 1nC); emittance ratio of 7 ~ 9 was achieved; ideas and simulations of further improving the emittance ratio is underway. However as beam size approaches to 1 s of µm, dispersion and camera resolution come to play. laser pulse length and temporal profile FNPL video conference Feb. 8, 5 Yin-e Sun 7

28 acknowledgements Contributors to the work presented here: Guidance and leadership Helen Edwards, Don Edwards, Kwang-je Kim, Philippe Piot Laser work: Jianliang Li, Rodion Tikhoplav, Jamie Santucci, Nick Barov Cryogenics and vacuum: Wade Muranyi, Brian Degraff, Mike Heinz, Rocky Rauchmiller RF: Markus huening, Peter Prieto, Renee Padilla, John Reid Software: Jason Wennerberg Discussions: Court Bohn, Klaus Flöttmann FNPL video conference Feb. 8, 5 Yin-e Sun 8

29 Chromatic effects q? transfer matrix? thermal emittance =1 mm mrad. space charge force is turned off. FNPL video conference Feb. 8, 5 Yin-e Sun 9

30 RF asymmetry caused by gun RF coupler kick Accelerating mode center is shifted? time-dependent dipole kick? vertical emittance growth (Khabiboulline) E z 1 mm r FNPL video conference Feb. 8, 5 Yin-e Sun 3

31 Quadrupole alignment: rotation and displacement around each axis Quad 1 Quad Quad 3 emittance ratio Q1 tilt Q tilt Q3 tilt Q13 tilt emit ratio quadrupole tilt angle (deg) emittance ratio angle of rotation around vertical axis Q1 DY Q DY Q3 DY quadrupole center dy (mm) FNPL video conference Feb. 8, 5 Yin-e Sun 31