DESY / Hans Weise TTF / VUV-FEL Status and Some Words of Fast Kickers Hans Weise / DESY DESY meeting with KEK ILC Delegation (March 7th 2005)

DESY / Hans Weise RF gun FEL experimental area bypass 4 MeV150 MeV450 MeV1000 MeV undulatorscollimator bunch compressor Laser bunch compressor accelerator modules TESLA Test Facility Linac – Phase II FEL User Facility in the nm Wavelength Range (VUV) and R&D for the ILC

DESY / Hans Weise TTF / VUV-FEL Status as of January 13th, 2005 The VUV-FEL Set-up: installation completed until end of 2004 includes RF gun five accelerator modules two bunch compressors electron beam collimation electron and photon beam diagnostics undulator section still missing are the 3.9 GHz rf system at the end of the first accelerator module (needed for short wavelength FEL operation, scheduled for 2006) some electron beam diagnostics, esp. beam position monitors sixth accelerator module to increase the electron beam energy to 1 GeV the photon beam transport to the user‘s experimental hall the user‘s photon beam lines (to be commissioned until 5/2005)

DESY / Hans Weise Electron beam commissioning done with single bunches per bunch train Measured beam emittance (90%) at 120 MeV (BC2 section) is 1.3 pi mm mrad in both planes without compression at 0.5 nC; compression slightly decreases beam quality (as expected) but the beam quality seems to be good enough for lasing at 30 nm; shorter wavelengths need 3.9 GHz system in order to keep the emittance small. Chosen beam energy is 450 MeV, thus corresponding to 30 nm First spontaneous spectrum was taken in 12/2004 At present beam based alignment is used to find the correct electron beam orbit inside the undulator, i.e. first lasing should happen soon. VUV-FEL Status as of January 13th, 2005

DESY / Hans Weise VUV-FEL Status as of January 14th, 2005 We now have six weeks of SASE operation Photon pulse energy increased to typ. 5 µJ (a factor 2 below saturation) Photon beam parameters measured with excellent agreement to theoretical predictions Stable FEL operation over typ. 15 minutes; then slight tuning necessary 90% emittance of compressed bunches approx. 1.6 mm mrad in both planes some control loops established in order to stabilize SASE still some trouble with the beam orbit inside the undulator First lasing established on January 14th!!! average bunch charge 0.6 nC first accel.module ACC1 approx 6 deg off-crest electron beam energy at BC2 set for 125 MeV accel.modules ACC2/3 on-crest (within 1-2 degrees) accel. BC3 (bunch compressor) on with currents set for 380 MeV beam energy in undulator 450 MeV undulator optic: FOFO and all undulator correctors off, quadrupole movers have not been activated. FEL gain: 1E5 (saturation would correspond to 1E7) Photon pulse energy ~1 micro-Joule Photons per pulse 5E11 photons/sec*mm2*mrad2*0.1BW At present some shut-down activities connect undulator beamline with user‘s photon beam lines modify interlock system Restart on March 21st.

DESY / Hans Weise RF gun FEL experimental area bypass 4 MeV150 MeV450 MeV1000 MeV undulatorscollimator bunch compressor Laser bunch compressor accelerator modules undulator section VUV-FEL Setup / Overall Layout

DESY / Hans Weise The goals for the XFEL: charge 1nC  x,y 1.4 µm  z ~ 20 µm (80 fs)  E, uncorr < 2.5 MeV At TTF and PITZ (DESY) we are already close to these parameters. TTF / VUV-FEL as Prototype for the XFEL Injector σ z = 2.0 mm 112 µm 22 µm RF Gun s.c. Acc. 3rd harm. Structure s.c. Booster LinacBunch CompressorMain Linac 100 MeV 500 MeV

DESY / Hans Weise The TTF2 Tunnel installation basically follows the old TESLA design… With all its advantages and disadvantages. TTF2 / VUV-FEL Tunnel Layout

DESY / Hans Weise TTF2 Installation / Warm Beam Line Sections

DESY / Hans Weise Accelerator is housed in a 5.2 m diameter tunnel ~ m underground. Klystrons in tunnel are connected to modulators in an external hall by 10kV pulse cables. Preferred installation concept is suspension from tunnel ceiling RF pulse cable accelerator module klystron XFEL Linac Tunnel Layout

DESY / Hans Weise De-rated 10MW MBK Bouncer-type modulator var. Q_ext with adjustable coupler and/or waveguide tuner 12m TTF- like acc. modules eight 9-cell Nb cavities at 2K, Q 0 = MW RF source Acc 1Acc 2Acc 3Acc 4 RF Unit of the XFEL (32 cavities)

DESY / Hans Weise Mechanical tuner (frequency adj.) DAC ADC Low Level RF System vector sum vector demodulator pickup signal MBK Klystron vector modulator cavity #1 cavity #8 coaxial coupler circulator stub tuner (phase & Q ext ) accelerator module 1 of 2 RF Operation of s.c. Cavities TTF RF Unit 1 klystron for 2 accelerating modules 8 nine-cell cavities each

DESY / Hans Weise Cavity quench detection algorithms and exeption handling procedures analyze the probe signals... 1 st quench: Cavity 2 E acc =19 MV/m 2 nd quench: Cavity 6 E acc =21 MV/m 3 rd quench: Cavity 1 E acc =24 MV/m Stable Module #1* operation with slowly but steadily increased gradient RF Operation of Accelerator Modules Above its Performance Limit (e.g. Module 1*)

DESY / Hans Weise RF Operation of Accelerator Modules Above its Performance Limit (e.g. Module 1*) The maximum operating gradient of s.c. cavities is set by cavity quench, field emission, or Q-degradation – not by structure breakdown is not a hard limit. A too high gradient results in increased cryogenic load, radiation, and dark current does not trip off cavities in ns but in typ. 100 µs if cavities are operated at the threshold An exception handler as part of the LLRF can avoid quenches. Action can be taken prior to the next pulse. Consequences for the machine safety are very positive, i.e. correctly injected bunches will not be lost in the linac. In a high gradient long pulse run in spring 2002, an accelerator module was operated with stable beam (5 mA, 800 µs) close to its gradient limit. The acc. module was operated with a typ. module on-time of 90% at increasing gradients: 39 days at 19.5 MV/m, 800 µs, 5 Hz 4 days at 20.0 MV/m, 800 µs, 1 Hz 1 Hz operation due to beam oper. 6 days at 21.5 MV/m, 800 µs, 1 Hz laser + gun were limited

DESY / Hans Weise TTF Cavities above 25 MV/m Gradient 10 out of 16 cavities in modules ACC4 / ACC5 can be operated flat top at approx. 29 MV/m ACC1 was electropolished and reaches 35 MV/m flat top after module installation

DESY / Hans Weise Dark Current Measurement The on-axis dark current was measured for modules ACC4 / ACC5. Only one cavity in module ACC5 produced a mentionable dark current. captured dark current could be measured at the exit of ACC5 there was no d.c. from this cavity at the entrance of ACC4 the d.c. decreased as a function of time after module commissioning (August 2003) 100 nA at 16 MV/m increasing by a factor 10 for each 4.4 MV/m gradient step i.e. approx. 10 µA at 25 MV/m May 4th 100 nA at 20 MV/m increasing by a factor 10 for each 3.7 MV/m gradient step, i.e. 1.2 µA at 25 MV/m September 22nd after a few weeks on-time at 20 – 25 MV/m 250 nA at 25 MV/m detuning of cavity no. 6 left over an integrated dark current of the order of 20 to 25 nA at 25 MV/m average gradient Reminder: The TESLA limit is defined by additional cryogenic losses: The captured d.c. has to stay below 50 nA per cavity. (see TESLA Report ). Dark Current vs. RF phase with respect to neighbouring cavities is just as expected (max min) over pi/2

DESY / Hans Weise 1 st beam (bypass) re-commissioning of gun + injector setup cavity phases ACC2-5  beam energy setup bunch compression setup beam linear optics, optimize orbit commissioning of diagnostics re-commissioning of gun + injector setup cavity phases ACC2-5  beam energy setup bunch compression setup beam linear optics, optimize orbit commissioning of diagnostics done on-going First measurement before adjustment after adjustment TTF2 / VUV-FEL Beam Commissioning

DESY / Hans Weise FEL 30 nm 1 bunch setup collimation emittance measurements and optics matching beam-based alignment in undulator section commiss. of photon diag. with spon. emission Beam wirescanner quadrupole beam Ion pump stretched wire position control system granite baseplate A. Fateev et al., Dubna MCP Diagn. TTF2 / VUV-FEL Beam Commissioning

DESY / Hans Weise Saturation & nm commissioning of FEL diagnostics study of FEL beam, compression schemes, etc. establish reproducible settings, etc. FEL hallPETRA tunnel beam dump gas absorberphoton diagnostics photon diagnostics LINAC tunnel TTF2 / VUV-FEL Beam Commissioning

DESY / Hans Weise Long time operation of all 5 acc. Modules. VUV-FEL Commissioning. First lasing achieved. Stable operation / saturation spring Start user operation in spring 2005 TTF2 / VUV-FEL Outlook Accelerator Module ACC6 with electro-polished cavities should first be tested in a separate test stand. Schedule: a.s.a.p., but not before end of Electro-polished Cavities Measured in Vertical Test Accelerating Gradient (MV/m) Unloaded Quality Factor

DESY / Hans Weise VUV-FEL Program for 2005 The 2005 operation time is divided in different blocks. Under the assumption of no unexpected shut downs, all requests can be full-filled. Some reserve is within the individual operation periods.

DESY / Hans Weise The actually used pulser ready for the connection to a fast kicker or the ATF kicker A Fast Pulser for a Fast ATF Kicker Frank Obier & (Hans Weise)

DESY / Hans Weise Test kicker (stripline in vacuum); matching not optimized 1.5 m cable RG213 between pulser and kicker reflection at both stripline ends (right plot) and some ringing as a consequence of the reflection (left plot) Stripline used for pulser tests Frank Obier & (Hans Weise)

DESY / Hans Weise Schalter HTS 80-12UF t on =10ns 10 ns switch 6.5 kV 70 A All pictures show the same signal but have different scaling in order to look at ripple and ringing. The 10 ns Switch Frank Obier & (Hans Weise)

DESY / Hans Weise Schalter HTS 80-12UF t on =10ns 40ns 6,8‰ 3,7 % Same pulse, different scaling (zoom) Picture shows ringing at almost acceptable amplitude. Ringing at the end of the pulse. Frank Obier & (Hans Weise)

DESY / Hans Weise Schalter HTS 80-12UF t on =10ns And now a ceramic kicker… Frank Obier & (Hans Weise)