TTF and VUV-FEL Injector Commissioning

Transcription

1 TESLA Collaboration Meeting Sep. 6-8, 2004 Orsay TTF and VUV-FEL Injector Commissioning Siegfried Schreiber, Klaus Floettmann DESY Brief description of the injector Basic measurements Preliminary results on beam properties

2 TTF and VUV-FEL Injector Upgrade of injector II (Ph. Piot et al) Booster with 4 SC cavities + 4 to further accelerate 3 rd harmonic cavity to straighten out the RF banana Laser with longitudinal flat-hat profile Commissioning up to ACC2 operated all 8 cavities at 12 MV/m -> 100 MeV 3 rd harmonic cavity not yet installed Laser with longitudinal gaussian profile Commissioning up to ACC2 RF gun 12 MV/m 20 MV/m 3 rd harmonic cavity diagnostic section ACC2(M1*) ACC3(M3*) Laser ACC1 (M2*) bunch compressor 4 MeV 150 MeV beam dump 2

3 Schedule of the Commissioning RF Gun: 21-Feb Mar Mar Mar-2004 Injector: 15-Apr Jun-2004 Linac: End of Aug start conditioning 5 Hz, 900 us, 3 MW 10 Hz, 450 us, 3 MW first beam in gun section start injector commissioning end commissioning restart with complete machine 3

4 Injector Commissioning Overview We had three commissioning goals: 1. Gun 2. Module 2* at ACC1 3. BC section ad 1: a. Operation of RF gun without beam b. Operation of RF gun with beam in GUN section ad 2: a. Module conditioning (Möller, Kostin et al.) b. Accelerate beam with equal gradient in all cavities c. Accelerate with low gradient in first 4, high in last 4 cavities ad 3: a. Operation without bunch compressor b. Operation without bunch compressor and velocity bunching c. Operation with bunch compressor 4

5 The RF Gun Installed in the TTF Tunnel The RF gun has been installed into the TTF tunnel 8-Jan-2004 Alignment and survey finished, but not well understood yet Water system is OK Circulator close to the gun in the tunnel, filled with SF6 Diagnostics not yet complete: especially camera at diagnostic cross missing, slit needs repair 2 nd BPM not usable due to misalignment/steering? 2 nd pair of steerers not yet mounted (almost ready) Virtual cathode for laser not yet set-up (just finished now) 5

6 TTF 2 Laser Upgrade Together with Max-Born-Institute, Berlin (I. Will et al.) Upgrade has been tested at PITZ Doocs interface working, SPS upgrade soon Note: longitudinal flat diode-pumped profile by pulse stacker Nd:YLF only preamplifier σ l = 4.4 ps (UV) Pulse shaper (T = 5 %) Diode-pumped Nd:YLF oscillator AOM EOM AOM f round trip = 27 MHz Faraday pulse picker pump diode pump diode E micro = 16 µj P = 16 W pump diode pump diode E micro = 200µJ P = 200 W Pulse Stacker pump diode pump diode pump diode pump diode 2-stage diode-pumped Nd:YLF amplifiers pulse picker fast current control fast current control 2-stage flashlamp-pumped Nd:YLF amplifiers shot-to-shot optimizer fourth harm. 20 ps flat-top 4 ps edges E micro = 30 µj E burst = 24 mj UV (262 nm) 6

7 Beam in the straight section (3GUN) without steering with dark current ring (bucking = 50 A) with steering used to center laser beam on cathode 7

8 Charge Measurement With Faraday cups or toroid both on doocs via ADCs FCup close to T1 read about 20 % less charge then T1 charge jitter measured with the toroids about 1 % rms 1.2 nc 40 ns toroid signal of a single bunch of a bunch train (30 bunches 1 MHz) 8

9 Phase Scans Fit used to set the phase in a reproducible way: +/- 1.3 dg (rms) Several scans in a row: 1 dg 9

10 Quantum Efficiency Charge at T1 measured for various laser energies and electric fields in the gun for cathodes 42 and 37 QE is astonishing high therefore the results are only preliminary until we did all necessary cross checks (calibration of charge and laser energy) Charge (nc) Nb 42: QE from a straight line fit to the non-saturated data points: 9.6 % P fwd Quantum Efficiency (%) History of on-line QE of nb 37 after insertion Energy (uj) Time (h)

11 Darkcurrent measurement in March 2004 (10 Hz, 400 us, 3.2 MW): max. 230 ua and in June 2004 (5 Hz, 100 us, 3.2 MW): max. 160 ua 2 nd FC dark current (ua) dark current (ua) main solenoid current (A) 11

12 Transmission up to ACC1 entrance Full transmission through the narrow dipole chamber only for solenoid current above 280 A Focus on last screen before ACC1 I = 295 A Bucking off, 1 nc, 3 mm diam. laser, 40 dg phase Data don t fit well at focus: probably a resolution problem 280 A 12

13 Momentum Measurements momentum measurements dispersive section after RF gun reflected power is corrected for p vs Pfwd: data fit well with the simulation; vs phase: agreement less good 13

14 Beam based alignment RF Gun section Difficult due to missing camera at diagnostic cross this will improve Solenoid moved up by 2 mm Alignment issue not sattled yet 3 Imain=400A 6 y_bpm1gun, mm x_bpm1gun, mm Imain=0A ybpm1, mm Simul.pos+size ~'cavity centre acceptance' Simul.sol.center ~'BPM acceptance' xbpm1, mm ybpm1, mm after 2 step: dx=+1step: 1mm up xbpm1, mm after 1 step: 1mm up before 14

15 First Beam in Module ACC1 in this example: 30 us long bunch train, 4 nc/pulse transients are used to adjust the phase of each cavity with the 3-stub tuners this is usually been repeated to verify and further fine adjust the phases gradient 15-Apr-2004 transient time (us) phase (dg) 15

16 Energy Gain of C5 measured with beam Energy measured with BC dipole with and without C5 Dipole has not been cycled which leads to a small systematic error of about 7 % Data fit well with estimate of RF calibration which validates the results obtained in the horizontal cryostat RF calibration Spectrometer 16

17 Performance ACC1 (Module 2*) Cavities limits: C1 (Z54) 18 MV/m C2 (Z51) 16 MV/m Lower limit for ACC1 C3 (D42) 20 MV/m C4 (D37) 27 MV/m power limited C5 (AC72) 36 MV/m no FE C6 (C47) 23 MV/m C7 (Z53) 20 MV/m large FE large Lorentz forces C8 (AC69) 18 MV/m gradient phase time (us) 17

18 Energy and Energy Spread after ACC1 Energy set to 102 MeV, all 8 cavities at same gradient Minimum energy spread 220 kev rms as expected energy: + measured -- ASTRA energy spread: + measured -- ASTRA beam energy (MeV) rms energy spread (MeV) ACC1 phase (deg) ACC1 phase (deg) 18

19 Bunch Compressor Section No 3 rd harmonic cavity Magnetic chicane compressor Emittance measurement section with 4 OTR screens in a FODO lattice synchrotron radiation ports for bunch length measurements with - streak camera, - FIR interferometer, and - pyrodetector 19

20 Energy stability and Energy spread Measured in the BC dispersive section after acceleration llrf with closed loop energy stable within 0.1 %, rms = uncorrelated energy spread estimated from rising edge 25 to 30 kev Energy 20

21 Emittance: Four monitor method OTR WS OTR OTR QF QD QF QD QF QD WS WS OTR WS 0.95 m 0.46 m 0.49 m Beam sizes are measured at four screens with fixed quadrupole currents in a FODO lattice. - Emittance and twiss parametes calculated from beam sizes and beam size errors using Chi-square fitting. - Magnetic length the quadupoles: 270 mm, one common power supply. - Design phase advance of the FODO cell is 45 deg (smallest measurement error) FODO lattice with periodic beta function is not a requirement for the multi monitor method, but it provides a convenient measurement and a fast check of matching (with 45 dg phase advance, all beam sizes are equal) m

22 Standard optical set-up Mirror 3 Filters 3 Lenses Camera Lenses and filters are remotely controlled - one lens inserted at any time - any combination of filters possible 3 achromat doublets with focal lengths of 250 mm, 200 mm and 160 mm providing nominal magnifications of 1.0, 0.38, and neutral density filters transmission of 10 %, 25 %, and 40 % Basler A301f digital camera with firewire (IEEE1394) interface Small personal computers in the tunnel, server in control room 22

23 Examples of Beam Images at the four OTR stations, magnification = 1, 1 nc, matched optics 4DBC2 6DBC2 8DBC2 10DBC2 23

24 Emittance Data Smooth commissioning of the OTR set-up (incl. remote from Frascati) Suffered from changes in beam conditions during the measurements Nevertheless, a very promising though still preliminary result Study of systematics in beam size determination and measurement errors not completed yet - - simulation 24

25 Far-infrared spectrometer from RWTH Aachen Input beam Input polarizer Roof mirror Beam splitter Parabolic mirror Pyroelectric detectors removed 25

26 Bunch Compression with BC2 Bunch compression is indicated by a strong rise of coherent synchrotron radiation measured by a pyro-electric detector -10 dg on crest Bunch length mesured with interferometer: 1.5 ps (fwhh) signal of pyro-electric detector (mv) full compression phase of ACC1 26

27 Bunch Compression with velocity bunching 108 Velocity Bunching / 04 June 04 / BP JPC Momentum [MeV/c] Measurement ASTRA Phase first cavity ACC1 [Deg] Energy vs Phase of Cavity 1 Pyrodetector signal at -90 deg 27

28 HOM as a BPM The signal of a dipole mode in a cavity can be used as an indication of the beam position This works in both planes example for vertical steering and dipole mode response in C1 28

29 First Time of Flight measurements measured timing jitter ~1ps rms electronic noise needs clarification 29

30 Summary RF gun and module 2* installation finished mid February RF gun start-up smoothly First beam 16-Mar-2004 First beam through ACC1 15-Apr-2004 The program has been largely fulfilled: - first set of parameters and optics obtained. Machine well understood, fine tuning and systematic parameter scans still required. 30