Developing an Eletron source for the XFEL -

Transcription

1 Developing an Eletron source for the XFEL - the Photo Injector Test Facility at Zeuthen, PITZ Introduction, Motivation & Parameters Examples of International Experimental Results on Photo Injector Developments Results obtained in Zeuthen Further Developments needed to reach the XFEL Requirements Summary F. Stephan, DESY in Zeuthen, talk at the University of Hamburg, January 28th,

2 Acknowledgements, PITZ Collaboration colleagues from DESY in Zeuthen: J. Bähr, U. Gensch, H.-J. Grabosch, J.H. Han, S. Khodyachykh, M. Krasilnikov, V. Miltchev, A. Oppelt, B. Petrosyan, S. Riemann, L. Staykov, F. Stephan. colleagues from DESY in Hamburg: I. Bohnet, J.P. Carneiro, K. Flöttmann, S. Schreiber. colleagues from collaboration partners: BESSY (E. Jaeschke, M.v. Hartrott, D. Krämer, D. Lipka, D. Richter) INFN Milano (P. Michelato, L. Monaco, C. Pagani, D. Sertore) INR Troitsk (V. Paramonov) INRNE Sofia (G. Asova, G. Dimitrov, I. Tsakov) MBI Berlin (W. Sandner, I. Will) TU Darmstadt (W. Ackermann, W.F.O. Müller, S. Schnepp, S. Setzer, T. Weiland) University of Hamburg (J. Rönsch, J. Rossbach) YERPHI Yerevan (K. Abrahamyan) [CCLRC Daresbury, Humboldt University Berlin, INFN Frascati, LAL Orsay] F. Stephan, DESY in Zeuthen, talk at the University of Hamburg, January 28th,

3 General Goal of the PITZ Facility develop an electron source with minimum transverse emittance! for the operation of the VUV-FEL and the XFEL F. Stephan, DESY in Zeuthen, talk at the University of Hamburg, January 28th,

4 ε x,y ~ (e - beam size) (e - beam angular divergence) ε z ~ (e - bunch length) (energy spread of e - bunch) ε = 6 dimensional phase space volume acceleration (adiabatic damping): What is Emittance? Θ 2 < Θ 1 angular divergence is reduced normalized transverse emittance: ε = ß γ σ 2 σ (ε n is conserved in general) cov (x, x ) n 2 2 x x x' = = = 2 1- ß F. Stephan, DESY in Zeuthen, talk at the University of Hamburg, January 28th, ; ß v c, γ 1, x dx ds

5 Slice Emittance vs. Projected Emittance transverse coordinate x or y tail head flight direction longitudinal coordinate z transverse phase space x px transverse phase space x px momentum px momentum px coordinate x large projected emittance small coordinate x meas. projected emittance slice emittance FEL process F. Stephan, DESY in Zeuthen, talk at the University of Hamburg, January 28th,

6 Motivation: Why small emittance is important VUV-FEL length of the undulator output peak power of the 6.4 nm (GW) peak power εn = 1 mm mrad εn = 2 mm mrad εn = 4 mm mrad Q = 1 nc path length in the undulator (m) F. Stephan, DESY in Zeuthen, talk at the University of Hamburg, January 28th,

7 Motivation: Why small emittance is important XFEL output peak power of the XFEL 0.1 nm (GW) peak power length of the undulator εn = 1 mm mrad εn = 2 mm mrad εn = 3 mm mrad peak current: 5 ka energy spread: 2.5 MeV path length in the undulator (m) XFEL goal: 0.9 mm mrad@injector = 1.2 mm mrad@undulator smaller emittance new horizons: shorter wavelength, less energy required F. Stephan, DESY in Zeuthen, talk at the University of Hamburg, January 28th,

8 Some Parameters of the VUV-FEL and the XFEL pulse trains: repetition rate train length bunch spacing bunch length micro pulses: Parameters final energy bunch charge max. repetition rate max. train length bunch spacing required injector emittance SASE output wavelength 1 GeV 1 nc 10 Hz 800 µs µs 2 mm mrad nm European XFEL 20 GeV 1 nc 10 Hz 650 µs µs 0.9 mm mrad nm F. Stephan, DESY in Zeuthen, talk at the University of Hamburg, January 28th,

9 Schematic of the RF Gun used at PITZ animation F. Stephan, DESY in Zeuthen, talk at the University of Hamburg, January 28th,

10 related problems are e.g.: RF Guns FELs need high space charge density (small εx,y, small εz, launchof e at optimal rf phase: medium Q ) E r start end time defocussing space charge force: F SC r Q r γ 2 focussing solenoid strength: F sol r laser parameters (trans., long.): homogenous r SC F r, I time F. Stephan, DESY in Zeuthen, talk at the University of Hamburg, January 28th,

11 Projected Emittance Measurements at parameters: * 0.5 nc * 110 MV/m at gun * beam energy: 60 MeV methode: * fitting Twiss parameters to 4 subsequent beam size measurements * transport optics adjusted to maximize beam size at screen locations V. Yakimenko et. al., FEL 01 fit result: εn = 0.8 mm mrad for 0.5 nc, accuracy: better than 15% F. Stephan, DESY in Zeuthen, talk at the University of Hamburg, January 28th,

12 Transverse Laser Shape Studies from cylindical symmetric parameters: nc phase: 30º from zero crossing emittance measured at 40 MeV via quad scan non-cylindical symmetric additional study: emittance vs charge ~ linear F. Zhou et. al., EPAC 02 F. Stephan, DESY in Zeuthen, talk at the University of Hamburg, January 28th, 2005

13 Slice Emittance Measurements from setup: parameters: 300 pc laser: 1.8 ps FWHM 2 mm diameter on cathode phase: 30º from zero crossing slice width fs beam size: signal cut at 5% of max. D.H. Dowell et. al., LCLS-TN-03-2 (corr.) E r Spectrometer Image head Energy/Time F. Stephan, DESY in Zeuthen, talk at the University of Hamburg, January 28th, 2005 time Current (A) ε n (µm) tail Time (ps) B sol = kg B sol = kg B sol = kg Time (ps) projected emittance

14 WR on Emittance from 1.6 cell S-band gun ( 4 MeV) + 70 cm SW linac ( 14 MeV) Ti:Saphire laser system ( 50 fs long pulses at 800 nm) + pulse shaping (e.g. gratings + liquid crystal spatial light modulator) temporal shape of laser pulses: (x-ray streak camera, resolution: ~2 ps) Gaussian Square rise/decay time: 1.5 ps, limited by streak camera transverse laser distributions: (cathode) F. Sakai et. al., ICFA workshop 2002, SPring8 F. Stephan, DESY in Zeuthen, talk at the University of Hamburg, January 28th,

15 World Record on Emittance Methode: quad 14 MeV, gaussian fit to background subtracted signal frames 1.2 For 1 nc: εn 1.2 mm mrad F. Sakai et. al., ICFA workshop 2002, SPring8 F. Stephan, DESY in Zeuthen, talk at the University of Hamburg, January 28th,

16 Photo Injector Test Facility at Zeuthen (PITZ) Test facility for photo injectors: focus on VUV-FEL, XFEL very small transverse emittance (0.9 mm 1 nc) stable production of short bunches with small energy spread Extensive R&D on photo injectors in parallel to TTF operation Compare detailed experimental results with simulations: benchmark theoretical understanding of photo injectors Test and optimize RF guns for subsequent operation at VUV- FEL and XFEL Test new developments (laser, cathodes, beam diagnostics) F. Stephan, DESY in Zeuthen, talk at the University of Hamburg, January 28th,

17 Short History and PITZ 1 Layout Short History of PITZ: autumn 1999: decission to built PITZ 2000: civil construction of buildings 2001: installation of infrastructure January 2002: first photo electrons 2002/2003: upgrade facility December 2003: characterization of gun prototype 2 finished VUV-FEL 2004: install gun prototype 1, increase rf power, do characterization (1.3 GHz) F. Stephan, DESY in Zeuthen, talk at the University of Hamburg, January 28th,

18 Laser system from the MBI in Berlin diode-pumped Nd:YLF preamplifier Pulse shaper diode-pumped Nd:YLF oscillator AOM EOM AOM f round trip =27MHz Faraday isolator pump diodes pulse picker 1MHz E micro =16µJ P burst =16W 800µs Amplified output train Pulse train from the oscillator E micro =200µJ P burst = 200 W pump diodes to photocathode pump diodes pulse picker fast current control fast current control fourth harm. flat-top pulses E micro =30µJ E burst =24mJ UV (262 nm) 2-stage diode-pumped Nd:YLF amplifier 2-stage flashlamp-pumped Nd:YLF booster amplifier shot-to-shot optimizer F. Stephan, DESY in Zeuthen, talk at the University of Hamburg, January 28th,

19 Temporal and Transverse Laser Profiles in 2003 (VUV-FEL gun): in 2004 (gun prototype #1): a.u Measured(524 nm) Flat Top Fit Measured (262 nm) Flat Top Fit FWHM ps 60 rise/fall ps t / ps a.u t / ps FWHM ps rise/fall 7-9 ps σx = 0.51 ± 0.02 mm σx = 0.57 ± 0.02 mm 0 3 σy = 0.62 ± 0.02 mm 0 3 σy = 0.58 ± 0.02 mm 2 x,mm y,mm 2 x,mm y,mm F. Stephan, DESY in Zeuthen, talk at the University of Hamburg, January 28th,

20 VUV-FEL Gun: long RF pulses, high power RF Power source: 5 MW Klystron RF Gun cavity: 1.5-cell copper cavity operated at 1.3 GHz a.u. 0.7 ~ log(power) Forward power Reflected power 9cm e.g. 800 µs ~25cm t / µsec - rf pulse lenght: 900 µs, repetition rate: 10 Hz - gradient: 42 MV/m at the cathode (~ 3 MW) duty cycle: 0.9 %, average rf power: 27 kw (results only limited by conditioning time) fulfills VUV-FEL RF parameter requirements F. Stephan, DESY in Zeuthen, talk at the University of Hamburg, January 28th,

21 VUV-FEL Gun: Longit. Phase Space p mean / MeV/c φ / degree p RMS / kev/c Q = 1 nc max. mean momentum: 4.72 MeV/c min. rms momentum spread: 33 kev/c good agreement with simulations! bunch length: minimum bunch length: FWHM = (21.04 ± 0.45stat ± 4.14syst) ps = (6.31 ± 0.14stat ± 1.24syst) mm F. Stephan, DESY in Zeuthen, talk at the University of Hamburg, January 28th,

22 Transverse Emittance Measurements Single Slit Scan Technique beamlets at screen 3 ε single slit positions 2 2 nx = βγ x x xx beam spot at screen 2 2 beamlet size is measured screen 2 for 3 slit positions: n { 1,0,1} y n = Y + n 0.7σ screen 2 y F. Stephan, DESY in Zeuthen, talk at the University of Hamburg, January 28th,

23 norm. emittance / mm mrad VUV-FEL Gun: Transverse Emittance requirement for VUV-FEL (30 nm) = 3 Ex Ey SQRT(Ex*Ey) ASTRA sim. requirement for VUV-FEL (6 nm) = 2 WR=1.2 requirement for XFEL = 0.9 Main Solenoid I buck, A Q = 1 nc, Φ = Φm 5 Imain = 305 A Bucking Solenoid 1.3 GHz 1 1/2 cell RF Gun Start-up requirement of TTF2 is clearly fulfilled! F. Stephan, DESY in Zeuthen, talk at the University of Hamburg, January 28th,

24 Picture from the VUV-FEL at Hamburg PITZ gun was installed at VUV-FEL in Jan F. Stephan, DESY in Zeuthen, talk at the University of Hamburg, January 28th,

25 Prototype #1: RF Conditioning Results conditioning results obtained in 2004: limited by 5 MW klystron and water cooling system!! upgrade Dec 04 March MW klystron goals for the XFEL: ~ 6.5 MW, 650 µs, 10 Hz delivered on 1.E+01 rf power (MW) E E-01 repetition rate 1.E-02 rf pulse length peak power at gun mean power duty cycle forward power reflected power time (µs) 10 Hz 0.5 ms 4 MW 20 kw 0.5 % 1300 µs 5 Hz 1.3 ms 4 MW 26 kw 0.65 % 10 Hz 1.0 ms 3 MW 30 kw 1.0 % F. Stephan, DESY in Zeuthen, talk at the University of Hamburg, January 28th,

26 Prototype #1: Longit. Phase Space p mean / MeV/c φ / degrees old data from VUV- FEL gun: p mean / MeV/c φ / degree p RMS / kev/c p RMS / kev/c Q = 1 nc max. mean momentum: 5.20 MeV/c (+ 10%) min. rms momentum spread: 16 kev/c (- 50 %) phase difference max between p mean min and p RMS only ~5 degrees F. Stephan, DESY in Zeuthen, talk at the University of Hamburg, January 28th,

27 Prototype #1: Thermal Emittance methode: ε = σ th 2Ek 3m c 0 2 E k = 1.5 m c 0 2 dε dσ th 2 norm. emittance/ mm mrad slit measurement Ex Ey pc, 32 MV/m r.m.s. size / mm cross check with solenoid scan yielded same result: E k = 0.8± 0.1eV for laser r.m.s. size = 0.58 mm ε th 0.6 mm mrad F. Stephan, DESY in Zeuthen, talk at the University of Hamburg, January 28th,

28 Prototype #1: Transverse Emittance norm. emittance / mm mrad VUV-FEL (30 nm) VUV-FEL (6 nm) WR XFEL Ex Ey SQRT(Ex*Ey) I main, A current status! Q = 1 nc Φ = Φm Ibuck = Imain * min. emittance and geom. average improved! still long way to go for XFEL requirements! F. Stephan, DESY in Zeuthen, talk at the University of Hamburg, January 28th,

29 PITZ 2 large extension of the facility and its research program study emittance conservation principle: (booster cavity + new diagnostics beam line + beam dynamics) reach XFEL requirements: 0.9 mm 1 nc: (increased RF field on photo-cathode + improved laser system + beam dynamics + improved photo-cathodes) study XFEL parameter space: (low charge and short bunches + vice versa) operate at higher repetition rates: (more cooling + new RF system + new gun cavity + diagnostics) F. Stephan, DESY in Zeuthen, talk at the University of Hamburg, January 28th,

30 The Emittance Conservation Principle Solenoid strength, drift length, and accelerating gradient of booster definded by invariant envelope technique: simulation for XFEL matching condition (M. Ferrario) Like for LCLS: place entrance of booster at local emit. max. and beam size min. define accelerating gradient by: ' γ boost = ' γ boost σ w = = 2 σ w energy rms ˆ = peak I γ = mean I = 0 Alvfen beam gain current beam Iˆ 3I γ size current (17 ka for electrons) 0 booster energy F. Stephan, DESY in Zeuthen, talk at the University of Hamburg, January 28th,

31 ASTRA Simulation of PITZ2 (40MV/m, 20ps FWHM, 2ps rise/fall time) emittance and beam size matching condition (M. Ferrario) CDS booster diagnostics section Xrms(TESLA) / mm EmX(TESLA) / um µm Xrms(CDS14) / mm EmX(CDS14) / µ µm um Xrms(no booster) / mm EmX(no booster) / µ µm um z / m distance from photo cathode (m) check that principle works and optimize it! F. Stephan, DESY in Zeuthen, talk at the University of Hamburg, January 28th,

32 Preliminary Layout of PITZ2 transverse emittance longitudinal phase space quads masks booster gun rf deflector new ~ PITZ 1 F. Stephan, DESY in Zeuthen, talk at the University of Hamburg, January 28th,

33 How to reach the beam quality required for the XFEL Goal: 0.9 mm mrad from the injector for 10 Hz, 650 µs!! upgrades with ~ 40 MV/m at the cathode: improved homegenous transverse laser profile: remotely controllable diaphragm close to the cathode εn ~ 1.5 mm 1 nc improved longitudinal laser profile (20 ps FWHM, 2 ps rise/fall time): use a broadband laser medium, solve problem of high average power, conserve stability εn ~ 1.2 mm 1 nc in addition, with 60 MV/m at the cathode: εn ~ 0.9 mm 1 nc F. Stephan, DESY in Zeuthen, talk at the University of Hamburg, January 28th,

34 Setup for the Laser Beam Line to the Cathode I. Will (MBI), status: in preparation L in,1 L out,1a f = 750 mm f = < M = > L out,1b f = 3000 mm beam-shaping aperture d = 2 mm L in,2a L in,2b f = 750 f = -750 L out,2a f = -750 L out,2b f = 750 mm - 50 cm ± 0 cm + 50 cm Gaussian input beam FWHM = 2mm pinhole <--- M = 1:1 ---> M1 M2 M3 M4 MV <----- laser table -----> < shaft > <- wall -> < optical rail > photocathode marginal rays 0 m 5 m 10 m 15 m 20 m Z 0-50 cm Z 0-25 cm Z 0 Z cm Z cm 3 mm V - 50 cm V - 25 cm V - 00 cm V + 25 cm V + 50 cm F. Stephan, DESY in Zeuthen, talk at the University of Hamburg, January 28th,

35 Transverse Beam Parameters for the XFEL Injector 11.5 MV/m 25.0 MV/m 13.9 MV/m gun param.: rms laser spot assumed therm. emittance laser pulse length gun acc. gradient injecting phase 0.75 mm, uniform 0.74 mrad mm 20 ps, uniform 60 MV/m 44 proj. emittance 0.5 mrad mm (no th. emittance) Courtesy of Ph. Piot, FNAL εn = 0.9 mrad mm (including th. emittance) F. Stephan, DESY in Zeuthen, talk at the University of Hamburg, January 28th,

36 High Gradient, High Duty Cycle thermal calculations: Courtesy of Frank Marhauser, BESSY 27 kw of average RF power: 80 C (40MV/m, 900µs, 10 Hz) done 130 kw of average RF power: 170 C!!! (60MV/m, 650µs, 30 Hz) vacuum, dark current, new cathodes!!! (new gun geometry?) F. Stephan, DESY in Zeuthen, talk at the University of Hamburg, January 28th,

37 Summary different developments for achieving small emittance electron beams are ongoing worldwide (WR 1 nc = 1.2 mm mrad) results at PITZ up to now: VUV-FEL gun: minimum normalized emittance (one plane): 1.5 mm mrad minimum geometrical average (both planes):1.7 mm mrad good agreement with simulations next gun installed at PITZ (2004): increased rf power: <P> = 30 kw, 1 % duty cycle, Ppeak = 4 MW, rf pulse lenght = 1.3 ms beam characterization: transverse emittance improved (1.3 / 1.6 mm mrad) goal for XFEL: 0.9 mm mrad PITZ 2 will start operation in spring 2005: further improve emittance from gun (high gradient, laser parameters) studies on conserving small emittance to higher beam energies F. Stephan, DESY in Zeuthen, talk at the University of Hamburg, January 28th,

38 Zugabe : F. Stephan, DESY in Zeuthen, talk at the University of Hamburg, January 28th,

39 Slice Parameters for VUV-FEL Gun horizontal / vertical slice emittance pi mm mrad slice EmX slice EmY z, 6m m ASTRA simulation of slice parameters for z = 1.62 m (EMSY location) Ibuck = 20 A projected emittance = 1.7 mm mrad charge density / slice energy spread Density, a.u. Erms, kev z, 6 m m8 F. Stephan, DESY in Zeuthen, talk at the University of Hamburg, January 28th,