FLASH. FLASH Training: RF Gun. FLASH: the first soft X-ray FEL operating two undulator beamlines simultaneously. Siegfried Schreiber, DESY

Transcription

1 FLASH Training: RF Gun FLASH: the first soft X-ray FEL operating two undulator beamlines simultaneously Siegfried Schreiber, DESY FLASH Training DESY 17-Mar-2017 FLASH1

2 RF Gun History

3 RF Guns operated at FLASH since 2004 Gun Gun2: 5 Hz, 3.5 MW, 350 µs, 5 kw, 680 GJ Window: G29 Gun2 breakdown Gun 4.2 Gun 4.1 Gun 3.1 1/2010 6/2010 9/2011 5/2012 6/2012 3/2013 Gun4.2: 10 Hz, 3.9 MW, 400 µs, 15 kw, 1200 GJ Window: Gxx Window break down; G67 Window break down; G29 Gun4.2 breakdown Gun4.1: 10 Hz, 4 MW, 550 µs, 21 kw, 930 GJ Window: G29 Gun3.1: 10 Hz, 5 MW, 550 µs, 27 kw, 2400 GJ(*) Window: Thales 5 4/2014 Window leak; G64 6/2016 Window leak; G57 Integrated RF-power (*) until 17-Mar-2017 RF gun controlled by a MTCA.4 based LLRF system since Jan 2015

4 Status RF-gun June 2016 > RF-gun 3.1 in operation since 8/2013 window exchanged in Apr 2014 (vacuum leak) no breakdown events since June 2014 > RF-pulse length slowly increased stable operation with ~500 µs flat top reached end of 2014 > April 2016: continued to lengthen the flat top to 600 µs > Phase stability improved by a factor of 3 Pulse width modulation feedback implemented > Fast interlock implemented if increase in reflected RF power is detected, RF is switched off within 3 µs; next pulse full power (not at start-up)

5 RF-Gun: again RF-Window vacuum leak > 27-Jun-2016: Hard breakdown event shortly after restart from the summer shutdown Actually the first one since June 2014 We had a few breakdowns at the air(!) part close to the window We have 1.5 bar air at the window > Then: continues problems to keep power and pulse length in the gun > increase of vacuum pressure > 4-July: leak detected at RF window > Window G64 has been exchanged with G57 this took 69.5 h incl. pumping > Conditioning up to 100 µs w/o beam h > 13-July: beam back after 9 days G64: 1.5 TJ of integrated RF RF Gun 3.1: 2.1 TJ up to now

6 RF-Gun breakdown event > RF-Gun vacuum pressure at the breakdown event Pressure (mbar) Serious breakdown event during ramp-up small e- event Vacuum base level increased by an order of magnitude 12 h 14 h 16 h 18 h 27-Jun-2016 Time

7 RF Gun recovered with very short pulses 175 µs <1 µs e- event (from 600 us) RF pulse length 20 µs Pressure (mbar) Serious breakdown event during ramp-up 12 h 14 h 16 h 18 h 27-Jun-2016 Time

8 RF Gun full RF power difficult to achieve 54 MV/m RF Power Pressure (mbar) h 14 h 16 h 18 h 27-Jun-2016 Time

9 RF-Gun 3.1 with window G64 > In 2014, we installed a special waveguide with 8 pick-ups to measure the RF wave and to compare with simulations Simulations agree with measured data > From this, we concluded, that the window should be mounted ¾ λ further away to reduce RF field load on the window during operation Gun 3.1 with Window G64 Light and electron sensor ¾ λ Knee with sensors Coupler Window G64 8 pick-up s Directional couplers

10 RF-Gun section with window G57 > We installed the new window with an intermediate piece of ¾ λ in length Intermediate piece with pump RF-window G57 Gun coupler RF

11 RF Gun Set-up

12 RF Gun Overview Laser Beamline Box TSP/IGP 2GUN IGP 1GUN IGP - 0GUN Cathode System Transfer Box with spare cathodes

13 GUN section Darkcurrent Kicker Laser Mirror BPM Dipol Steerer Steerer

14 RF Gun: Coupler Interlocks Sensors Photomultiplier (LUVA) Electron Pick-up (e- WG) Vacuum (2GUN) Temperature Window (PT1000 WG)

15 RF Gun interlock Sensors Vacuum Waveguide filled with air (1.5 bar)

16 RF Gun: Coupler Interlocks Sensors IR Detector (IR Temp. Win) Circulator Spark Detector (LUWG) Directional Coupler

17 RF Gun Gun Body Solenoid Cathode Chamber Bucking

18 RF Gun > Laser driven photo emission from a Cs 2 Te cathode Iris 3 h Temperature Sensor

19 RF Gun Start-up

20 RF Gun panel > Main Injector Gun Conditioning Startup Help Solenoid Coupler interlocks PM Coupler interlock spectra e- Spark GUN vacuum

21 RF Gun LLRF panel > Main Injector Gun LLRF FSM Fast Protection Pulse Width Modulation Feed Forward Feedback etc

22 RF Gun Water System Cold water Gun Temperature Hot water

23 RF Gun tuning panel > Main Injector Temperature Tuning RF off Refl. Power: Keep minimum below ~1.4 Start-up with 58.3 dg dt to correct temperature: keep positive around 0.1 K Temperature needs to rise when RF pulse length is increased

24 RF Gun tuning panel > T=58.3 dgc > Start with 20 us > ramp up forward power rather quickly to SP=53 MV/m > Observe vacuum and interlock signals Refl. Power: Keep well below 1.4 Start-up with 58.3 dg and 20 us pulse length

25 RF Gun temperature vs RF pulse length End with dg for 640 us Start with 58.3 dg

26 After Ramp-up: close feedback 1. Output vector correction (use with care, if you know how: manually) 2. Feedback Feed-Forw. Correction Learning FF 3. Activate fast protection

27 Activate Pulse width modulation feedback > Before the feedback is activated: > Wait for a good proposed SP You may need to adjust the SP temperature And/or try to set it manually > Best SP detuning Temp.: dt = Positive around 0.04 K

28 What you never should do

29 After a trip: be careful before reset > Vacuum trip at gun coupler > FSM was off Thus: gun is not in a safe state to reset 1. Feed-forward off 2. Ampl. SP to pulse length to 20 us > Check vacuum > Then reset interlocks > Switch FSM on

30 Never leave the gun alone during ramp-up

31 Never leave the gun alone during ramp-up Pfwd SP 53 MV/m Pfwd >5 MW RF pulse 200 us Prfl 1.8 full reflection T=60.5 dgc