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RF-Gun beam based alignment at PITZ/FLASH M.Krasilnikov, DESY Zeuthen LCLS Injector Commissioning Workshop (ICW) October 9-11, 2006.

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Presentation on theme: "RF-Gun beam based alignment at PITZ/FLASH M.Krasilnikov, DESY Zeuthen LCLS Injector Commissioning Workshop (ICW) October 9-11, 2006."— Presentation transcript:

1 RF-Gun beam based alignment at PITZ/FLASH M.Krasilnikov, DESY Zeuthen LCLS Injector Commissioning Workshop (ICW) October 9-11, 2006

2 M.Krasilnikov, DESY “RF-Gun BBA at PITZ/FLASH” 2 Outline Beam-Based Alignment (BBA) of RF gun: –Fields and geometry –BBA motivation Cathode laser BBA: –PITZ –FLASH –Limitations of laser BBA Main solenoid BBA: –Solenoid micromover system –Main problems and possible solutions –Limitations of solenoid BBA Conclusions

3 M.Krasilnikov, DESY “RF-Gun BBA at PITZ/FLASH” 3 RF-Gun: fields and geometry (PITZ and FLASH) sol.mech.axis ≠mag.axis sol.mech.axis ≠cavity el.axis solenoid tilt angles fields overlapping

4 M.Krasilnikov, DESY “RF-Gun BBA at PITZ/FLASH” 4 Solenoid tilt effect For Ecath=25MV/m solenoid tilt angle of ~3mrad is equivalent to 1 mm transverse offset RF-Gun Alignment Motivation Emittance growth due to RF -gun misalignment 5% emittance growth (lower limit estimations): laser  R<800um or solenoid  R<500um or solenoid  angle<1.5mrad (0.086deg) No effect in the matching section has been considered! ASTRA Simulations of FLASH (VUV-FEL) Injector (150MeV)

5 M.Krasilnikov, DESY “RF-Gun BBA at PITZ/FLASH” 5 Cathode Laser Alignment (FLASH) Laser spot positioning at the photo cathode: + Transverse displacement and angle of the laser beam can be independently changed - Iris position has to be adjusted for every mirror movement No VC and e-beam simultaneously

6 M.Krasilnikov, DESY “RF-Gun BBA at PITZ/FLASH” 6 Cathode Laser Alignment (PITZ)

7 M.Krasilnikov, DESY “RF-Gun BBA at PITZ/FLASH” 7 BBA of Laser on Cathode z=0 z=0.276m z=0.935m z=0.778m Basic measurement : Mean position of electron beam at LOW.Screen1 (DoubleDiagCross at z=0.778m) vs. RF gun launch phase (SP Phase) Conditions : Main and bucking solenoids off All steerers off Dipole (even it is ~0.2m after the screen) degaussed and off Bunch charge ~10pC, pulse train laser pulses Moderate RF power in the gun: MW (exclude dark current)→Pz~ MeV/c Preliminay (rough) laser alignment : Using scintillating cathode Centering in dark current images

8 M.Krasilnikov, DESY “RF-Gun BBA at PITZ/FLASH” 8 Beam spot at Diag.Cross screen (z=0.78m) “Normal” phases “Low” phases, rf focused beam Measurements&SimulationsSimulations Beam charge, Transverse rms Size, Mean Momentum Vs. RF Phase Beam Offset at z=0.78m Vs. RF Phase (0.5 mm vertical laser offset on the cathode has been assumed) Measured and Simulated beam charge at z=0.78m Vs. RF Phase Measured and Simulated beam rms size at z=0.78m Vs. RF Phase BBA of Laser on Cathode

9 M.Krasilnikov, DESY “RF-Gun BBA at PITZ/FLASH” 9 Cathode Laser BBA. Test Movement Step 1: Laser test movement One of results: (X0,Y0) – preliminary coordinates of the center at the screen Measurement: Beam offset vs. rf phase Step 2: Laser alignment

10 M.Krasilnikov, DESY “RF-Gun BBA at PITZ/FLASH” 10 Cathode Laser BBA. Difficulties Laser intensity non-homogeneity Laser position jitter Possible damage of YAG screen homogeneity Earth magnetic field (x,y,z)~(0.02mT,-0.03mT,-0.009mT) stdev =13um stdev =11um Extreme example of a damaged screen

11 M.Krasilnikov, DESY “RF-Gun BBA at PITZ/FLASH” 11 Main Solenoid BBA. Micromover system main solenoid beam axis

12 M.Krasilnikov, DESY “RF-Gun BBA at PITZ/FLASH” 12 Main Solenoid BBA z=0 z=0.276m z=0.935m z=0.778m Basic measurement : Mean position of electron beam at LOW.Screen1 (DoubleDiagCross at z=0.778m) vs. Main solenoid current Conditions : Bucking solenoid off All steerers off (or consider in simulations) Dipole (even it is ~0.2m after the screen) degaussed and off Bunch charge ~10pC, pulse train laser pulses – to be tuned for Imain Moderate RF power in the gun: MW (exclude dark current )→Pz~ MeV/c RF launch phase* Laser spot size possibly small

13 M.Krasilnikov, DESY “RF-Gun BBA at PITZ/FLASH” 13 Main Solenoid BBA Beam position (, ) at LOW.Scr1(z=0.778m) as a function Imain E-beam displacement with a main solenoid sweep. Possible reasons: Solenoid transverse offset (Xsol,Ysol) Solenoid tilt angles (AngleX, AngleY) Laser (small) offset (Xlas,Ylas) from the center Other factors to be considered: RF gun launch phase and gradient Small offset (from X0,Y0 obtained after laser BBA) Solenoid calibration From the laser BBA: X0=13.0mm Y0=14.8mm Imain=0A Imain=320A

14 M.Krasilnikov, DESY “RF-Gun BBA at PITZ/FLASH” 14 Main Solenoid BBA. RF-gun launch phase and gradient (21.4MV/m;22deg) streak-camera measurement  0=-18deg

15 M.Krasilnikov, DESY “RF-Gun BBA at PITZ/FLASH” 15 Simulation Tool Alignment Utility of the V-code - fast tracking code based on the method of moments of particle distribution function

16 M.Krasilnikov, DESY “RF-Gun BBA at PITZ/FLASH” 16 Main Solenoid BBA. Test movement Simultaneous simulations of beam position before and after test movement (  Xsol=0.4mm) Advantages: Same RF gun launch phase and gradient Same offset X0*,Y0* Same solenoid calibration Laser_Beam_CenterX0.20 mm Laser_Beam_CenterY-0.26 mm XSolMainCenter0.85 mm YSolMainCenter1.12 mm AngleXSolMain deg AngleYSolMain deg Ez_Field_At_Cathode22.2 MV/m Initial_Phase deg

17 M.Krasilnikov, DESY “RF-Gun BBA at PITZ/FLASH” 17 Main Solenoid BBA Before BBAAfter BBA Laser_Beam_CenterX0.20 mm0.11 mm Laser_Beam_CenterY-0.26 mm-0.27 mm XSolMainCenter0.85 mm0.041 mm YSolMainCenter1.12mm0.063 mm AngleXSolMain deg deg AngleYSolMain deg deg Ez_Field_At_Cathode22.2 MV/m22.4 MV/m Initial_Phase-147.2deg deg

18 M.Krasilnikov, DESY “RF-Gun BBA at PITZ/FLASH” 18 Main Solenoid BBA. Difficulties Laser BBA difficulties: Laser intensity non-homogeneity Laser position jitter Damaged YAG screen + RF phase and gradient jitter Some uncertainty in the solenoid micromover (especially angles), z-position

19 M.Krasilnikov, DESY “RF-Gun BBA at PITZ/FLASH” 19 RF-Gun BBA. Conclusions BBA of Laser on Cathode: –routine procedure at PITZ (FLASH) –based on a measurement of beam position vs. gun launch phase –test movement of the laser beam allows to determine a displacement vector for the laser beam centering Main solenoid BBA: –multi-parameter task –based on beam position simulation vs. main solenoid current –test movements of the main solenoid and/or cathode laser allows to reduce uncertainty in main solenoid misalignment Possible improvements: –implement earth magnetic field in BBA procedures –use BPM (LOW.BPM1) for solenoid BBA –more details on RF field profile –solenoid relative displacement online measurement

20 M.Krasilnikov, DESY “RF-Gun BBA at PITZ/FLASH” 20

21 M.Krasilnikov, DESY “RF-Gun BBA at PITZ/FLASH” 21 Reference RF Phase. Beam Size measurements Transverse Beam Size at Screen 3 as a Function of RF Launch Phase for Various Main Solenoid Currents  max

22 M.Krasilnikov, DESY “RF-Gun BBA at PITZ/FLASH” 22 PITZ1 Benchmark Problem: Fields Field balance in the rf gun cavity Solenoid calibration MF compensation Ibuck= *Imain

23 M.Krasilnikov, DESY “RF-Gun BBA at PITZ/FLASH” 23 Rough laser alignment using dark current symmetry. TTF Dark current at TTF at screen Gun3 (z = 1.27m) Without beam With beam Dark current rings originate from the edge of the Cs 2 Te coating and plug spring region A laser spot being aligned on the cathode center results in an electron beam centered with dark current rings BBA: Step 0 – Rough Laser Alignment on the Cathode

24 M.Krasilnikov, DESY “RF-Gun BBA at PITZ/FLASH” 24 Rough laser alignment using dark current symmetry. PITZ Without beamWith beam Screen Diag. Cross (z = 0.87m) Screen_PP (z = 2.62m) BBA: Step 0 – Rough Laser Alignment on the Cathode

25 RF Gun Alignment: Satellites “low phase” x y x x y Vacuum mirror

26 M.Krasilnikov, DESY “RF-Gun BBA at PITZ/FLASH” 26 SP phase = -130  SP phase = -125  SP phase = -120  SP phase = -116  SP phase = -114  SP phase = -112  SP phase = -110  SP phase = -106  SP phase = -100  SP phase = -90  SP phase = -70  SP phase = -50  SP phase = -30  BBA of laser on cathode SP phase = -20  SP phase = -16  precision of mirror adjustment: better than 20 µm

27 M.Krasilnikov, DESY “RF-Gun BBA at PITZ/FLASH” 27 RF-Gun Alignment Motivation ASTRA Simulations of FLASH (VUV-FEL) Injector (150MeV) trajectory emittance Emittance degradation in the matching section is not included


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