1. D. Lipka DESY Hamburg Dark current Monitor for the European XFEL, tests at PITZ and FLASH

2. 2 Content European XFEL layout Principle of dark current detection Monitor Setup at PITZ and FLASH Electronics Measurement of dark current and bunch charge Summary D. Lipka; MDI; DESY Hamburg; UBW 2012; Berlin

3. Dark current Monitor for the European XFEL, tests at PITZ and FLASH Dark current Production of dark current due to field emission in accelerator Causes radiation background in the tunnel: destroys electronics and activate components Decrease dark current due to kickers, chicane and collimators 3 D. Lipka; MDI; DESY Hamburg; UBW 2012; Berlin Need non-destructive monitor to measure efficiency of dark current reduction, few monitors will be installed Beamline of the European XFEL

4. Dark current Monitor for the European XFEL, tests at PITZ and FLASH European XFEL layout and Dark current Monitor Proposed monitor position are indicated by arrows 4 D. Lipka; MDI; DESY Hamburg; UBW 2012; Berlin

5. Dark current Monitor for the European XFEL, tests at PITZ and FLASH Principle of detecting weakly charged bunches with a resonator 5 D. Lipka; MDI; DESY Hamburg; UBW 2012; Berlin Induced voltage in a resonator from a beam oscillates with resonance frequency f and decays with decay time . Q L : loaded quality factor. By measuring U 0 the charge of the beam q is determined. Field distribution of 1. monopole mode Simulation view Sensitivity S can be determined by resonance frequency f, line impedance Z=50Ω, external quality factor Q ext and normalized shunt impedance (R/Q). for monopole modes A passive resonator will be used because the induced field strength due to electrons has the potential to detect very low beam charges

6. Dark current Monitor for the European XFEL, tests at PITZ and FLASH Principle of detecting dark current with resonator 6 D. Lipka; MDI; DESY Hamburg; UBW 2012; Berlin t I  t = 1/(1.3 GHz) = 1/f Expected/simulated voltage f=1.3 GHz, Q L =205 for I =1 mA and 1000 dark current bunches Dark current bunches within 2 RF oscillations Transient oscillation finished after 150 ns Charge of one dark current bunch too weak to be detected: superimposing of induced fields from the dark current bunches when resonance frequency of resonator harmonic of accelerator

7. Dark current Monitor for the European XFEL, tests at PITZ and FLASH The monitor The monitor consist of 2 stainless steel discs, brazed together, with 2 antennas and feedthroughs 7 D. Lipka; MDI; DESY Hamburg; UBW 2012; Berlin 2 versions available: injector with 34 mm and beamline with 40.5 mm diameter Parameter goals: f=1.3 GHz, Q L =205 Cross section

8. Dark current Monitor for the European XFEL, tests at PITZ and FLASH Setup at the Photo Injector Test Facility at DESY Zeuthen (PITZ) 8 D. Lipka; MDI; DESY Hamburg; UBW 2012; Berlin PITZ: characterize, optimize and prepare electron source for FEL Dark current Monitor (DaMon) situated 2.36 m behind cathode followed by booster 0.68 m Measurement: f l =1299.3±0.1 MHz, Q L =193±5, Q ext =252±4 Expectation agree with measurement (resonator without tuner) Shunt impedance from simulation, results in sensitivity of 11.83 V/nC Photo: J. Lund-Nielsen NWA measurement result in tunnel to detect resonator properties

9. Dark current Monitor for the European XFEL, tests at PITZ and FLASH Setup of the monitor in FLASH 9 D. Lipka; MDI; DESY Hamburg; UBW 2012; Berlin A 34 mm type is installed at the first bunch compressor like in PITZ Measurement: f l =1299.0±0.1 MHz, Q L =192±5, Q ext =248±4 Shunt impedance from simulation, results in sensitivity of 11.88 V/nC

10. Dark current Monitor for the European XFEL, tests at PITZ and FLASH Electronics This autumn produced 3 new electronics; up to this only 1 prototype was available Two inputs according of two outputs of DaMon:  Beam charge  Dark current Includes circulator, band-pass filters, limiter, pre-amplifier, down conversion to IF, logarithmic detector, offset and gain control Two outputs for ADC 10 D. Lipka; MDI; DESY Hamburg; UBW 2012; Berlin

11. Dark current Monitor for the European XFEL, tests at PITZ and FLASH Calibration Calibration is done by adapting the laboratory calibration measurement of electronics input/output to a function provided by the control group for the available ADC Therefore non-linearity values for low and high values are not successful adapted, e.g. if the charge below 3 pC the line shows still 3 pC but the data are below. In addition the base line of 3 pC does not need to be corrected because for the given measurement range the calibration line is in agreement with the laboratory data 11 D. Lipka; MDI; DESY Hamburg; UBW 2012; Berlin

12. Dark current Monitor for the European XFEL, tests at PITZ and FLASH Measurement of dark current at PITZ 12 D. Lipka; MDI; DESY Hamburg; UBW 2012; Berlin ADC observed dark current, scale logarithmic output without electronics is at sensitivity limit of oscilloscope Analyzed data after electronics show about 30 µA Distribution of both measurement in agreement Without electronics With electronics

13. Dark current Monitor for the European XFEL, tests at PITZ and FLASH Measurement of dark current at PITZ 13 D. Lipka; MDI; DESY Hamburg; UBW 2012; Berlin RF power Solenoid used such that DC was maximized Here FC1 used. Error bars are standard deviations. DC at DaMon 2.5 times lower compared to FC1 DC at FC2 about 2 times lower compared to FC1 → Calculated DC at DaMon in agreement with FC DaMon FC2 Dipole FC1 98 cm 58 cm Beam direction Observation limit of FC: few µA

14. Dark current Monitor for the European XFEL, tests at PITZ and FLASH Measurement of dark current at PITZ 14 D. Lipka; MDI; DESY Hamburg; UBW 2012; Berlin Measured dark currrent with DaMon as a function of injector solenoid current FC can not resolve these low values Lowest observed dark current is 52 ± 13 nA Observation limit of DaMon system about 40 nA For very low beam charges the dark current electronics can be used to observe the charge One beam: dark current electronics in saturation Log scale Linear scale

15. Dark current Monitor for the European XFEL, tests at PITZ and FLASH Measurement of bunch charge at PITZ 15 D. Lipka; MDI; DESY Hamburg; UBW 2012; Berlin Beam charge 0.34 nC (measured with Faraday Cup: FC) Signal after low-pass filter on oscilloscope Electronics provides voltage amplitude which will be re-calculated in bunch charge and dark current Base line Voltage amplitude Photo: J. Lund-Nielsen Signal from electronics

16. Dark current Monitor for the European XFEL, tests at PITZ and FLASH Measurement of bunch charge at PITZ 16 D. Lipka; MDI; DESY Hamburg; UBW 2012; Berlin Voltages calibrated with electronics response function, attenuation of cables and attenuators. smaller fluctuation compared to Faraday Cup for low charges Sub-Pico-Coulomb resolution with DaMon visible Still 20 dB attenuation used DaMon 2% higher charge compared to FC (loss of charge at FC) Good agreement between laboratory calibration measurement including simulated shunt impedance and measured charge with FC

17. Dark current Monitor for the European XFEL, tests at PITZ and FLASH Measurement of bunch charge at PITZ 17 D. Lipka; MDI; DESY Hamburg; UBW 2012; Berlin q ≈ 0.34 nC Signal without electronics Signal with electronics Comments The bunch spacing at PITZ is 1  s, decay time withouth and with electronics measurement sufficient Bunch spacing for European XFEL is 222 ns, decay time is sufficient for single bunch measurements Response function of electronics calibrated Due to logarithmic detection lower amplitudes amplified Results in high dynamic range: 70 dB

18. Dark current Monitor for the European XFEL, tests at PITZ and FLASH Measurement of dark current at PITZ Strong dark current in backward direction from booster, on calibration limit Gun dark current much lower, can be separated by different RF pulse duration 18 D. Lipka; MDI; DESY Hamburg; UBW 2012; Berlin Only gun RF on Gun and booster RF on Measurements Spring 2011

19. Dark current Monitor for the European XFEL, tests at PITZ and FLASH Measurement of dark current at PITZ A vacuum event in the gun produced an additional charge spike in the dark current output This can be seen in the time domain compared to the RF pulse 19 D. Lipka; MDI; DESY Hamburg; UBW 2012; Berlin Measurement Dec. 2012

20. Dark current Monitor for the European XFEL, tests at PITZ and FLASH Measurement of beam charge at PITZ Beam charge is monitored as well with higher resolution (compared to Toroids) Charge spike is visible in dark current output 20 D. Lipka; MDI; DESY Hamburg; UBW 2012; Berlin Measurements Spring 2011

21. Dark current Monitor for the European XFEL, tests at PITZ and FLASH Measurement of dark current at FLASH Measured behind second accelerator module Gun and module are producing dark currents 21 D. Lipka; MDI; DESY Hamburg; UBW 2012; Berlin

22. Dark current Monitor for the European XFEL, tests at PITZ and FLASH Measurement of dark current at FLASH At the history of the dark current measurement a gap was visible This was verified by the beam loss system (with lower resolution) 22 D. Lipka; MDI; DESY Hamburg; UBW 2012; Berlin Beam loss output, z=177 m Measurement Dec. 2012 A RF event stops RF in the gun and restarted after several µs, therefore such gap can be produced z=32m

23. Dark current Monitor for the European XFEL, tests at PITZ and FLASH Summary Design of a dark current monitor to detect dark current and beam charge non-destructively for the European XFEL Described: principle, monitor, electronics, calibration Shown: measurement of dark current and bunch charge at PITZ and FLASH Different dark current sources are visible due to different RF time durations Better beam charge resolution compared to Toroids 23 D. Lipka; MDI; DESY Hamburg; UBW 2012; Berlin

24. Dark current Monitor for the European XFEL, tests at PITZ and FLASH Acknowledgement Mechanics: W. Kleen, S. Vilcins, Electronics: J. Lund-Nielsen, F. Schmidt-Föhre, J. Neugebauer Support: D. Nölle, PITZ team FLASH team Thanks for your attention! 24 D. Lipka; MDI; DESY Hamburg; UBW 2012; Berlin

25. Dark current Monitor for the European XFEL, tests at PITZ and FLASH Spare slides 25 D. Lipka; MDI; DESY Hamburg; UBW 2012; Berlin

26. Dark current Monitor for the European XFEL, tests at PITZ and FLASH Principle of detecting bunch length 26 D. Lipka; MDI; DESY Hamburg; UBW 2012; Berlin Amplitude from monopole mode is corrected by form factor Ratio of amplitude for different monopole modes should dependent on bunch length TM01 TM11 TM21 TM02 TM12 TM22 TM03 First three monopole modes frequencies: 1.299; 3.236; 5.074 GHz Complete spectrum up to 6 GHz Measured with spectrum analyzer

27. Dark current Monitor for the European XFEL, tests at PITZ and FLASH Principle of detecting bunch length Form factor as a function of expected bunch length after injector After compressor bunch length < 1 ps: form factor tends to be unity; therefore this method applicable only at injector area at the European XFEL Best resolution by using largest frequency difference 27 D. Lipka; MDI; DESY Hamburg; UBW 2012; Berlin

28. Dark current Monitor for the European XFEL, tests at PITZ and FLASH Measurement of bunch length 28 D. Lipka; MDI; DESY Hamburg; UBW 2012; Berlin DaMon Streak Station 4 m Beam direction Amplitude at different frequencies taken with spectrum analyzer Measurement as a function of injector acceleration phase; highest energy gain at phase 0 Compare DaMon results (combination TM01 and TM03, because best resolution) with aerogel radiator and streak camera method, detector positions differs by 4 m Streak measurement differs from simulation for phases < 0, same as it is for DaMon Both show same behavior (maybe simulation parameters not perfect) Result: agreement of bunch length taken with DaMon to the streak camera results DaMon Streak camera

29. Dark current Monitor for the European XFEL, tests at PITZ and FLASH DaMon at REGAE Relativistic Electron Gun for Atomic Exploration Femtosecond Electron Diffraction (FED) has the potential to directly observe the most venerable concepts in chemistry and biology most notably enabling a direct atomic level view of transition states.FED 29 D. Lipka; MDI; DESY Hamburg; UBW 2012; Berlin charge about 3 pC Charge about 200 fC DaMon as a charge monitor for both channels because accelerator with 3 GHz. Dark current channel for higher resolution possible. Observation limit 5 fC. Resolution 4 fC at 200 fC taking into account scope 8 bit ADC. Courtesy S. Bayesteh Bayesteh

30. Dark current Monitor for the European XFEL, tests at PITZ and FLASH Design for European XFEL 30 D. Lipka; MDI; DESY Hamburg; UBW 2012; Berlin FLASH/PITZ and European XFEL injector design 34 mm diameter tube 8 cm length E-XFEL standard design 40.5 mm diameter tube 9 cm length Three monopole modes below pipe cut-off frequency for bunch length measurement Welded feedthrough Two monopole modes available for bunch length measurement because of lower cut-off frequency. Due to flanged feedthrough: better cleaning for vacuum requirements

31. Dark current Monitor for the European XFEL, tests at PITZ and FLASH Design for European XFEL 31 D. Lipka; MDI; DESY Hamburg; UBW 2012; Berlin Produced 5 DaMons (European XFEL design) without tuners Measured resonance frequency 1299.0 ± 0.2 MHz Photo: D. Nölle

32. Dark current Monitor for the European XFEL, tests at PITZ and FLASH 32 D. Lipka; MDI; DESY Hamburg; UBW 2012; Berlin Clip board – copy and paste  keyword Result headline Result text, result text, result text Keyword 1.Keyword 2.Keyword Headline Texttext texttext texttext texttext texttext texttext Result headline result text Result Headline  result text Headline first level  second level  third level