1. 01.10.2009 F. Le Pimpec 1 PAUL SCHERRER INSTITUT history in 25’ F. Le Pimpec, PSI On behalf of the SwissFEL dudes LCLS meeting SLAC Oct 2009

2. 01.10.2009 F. Le Pimpec 2 PAUL SCHERRER INSTITUT I The Low Emittance Gun project (2003-2005) A FEA based electron gun (online - xmas 2007) II Evolving from LEG to a Machine 1.The PSI-XFEL project (2005-2008) 2.The SwissFEL project (2009+) a “standard” photogun machine III A Bottom line

3. 01.10.2009 F. Le Pimpec 3 PAUL SCHERRER INSTITUT Test stand overview 500kV pulse generator Vacuum chamber with pulsed accelerating diode Two cell 1.5GHz RF cavity Focusing solenoids Diagnostic screens Emittance monitor (pepper pot, slits) Quadrupole magnets Dipole magnet Beam dumps with faraday caps 5 degree of freedom mover Laser table Diagnostic screens BPMs 5.43 m Clean cubicle and air filter 3D CAD model of 4MeV test stand Phase I (no RF) operational in 2007 LEG – Phase II (4 MeV beam line)

4. 01.10.2009 F. Le Pimpec 4 PAUL SCHERRER INSTITUT Single-gated emitter array Field Emitter Arrays (FEA) as a low emittance electron beam source Field emitter array cross section Phase space Transverse momentum dx/dz Transverse direction x Individual emitter ε n ~ 5x10-3 mm mrad (σ x ~1 μm, δθ ~ 15°, Ue~100 V) Envelope of whole array (single gate) ε n ~ 2.5 mm mrad (σ x ~0.5 mm, δθ ~ 15°, Ue~100 V) Envelope (double gate) ε n < 0.1 mm mrad (σ x ~0.5 mm, δθ ~ 0.5°, Ue~100 V) Double-gated emitter array  First emitter gate controls the emission  Second emitter gate focuses individual beamlets (reduces overall emittance)  High gradient acceleration Density of electron extracted higher than for a photogun

5. 01.10.2009 F. Le Pimpec 5 PAUL SCHERRER INSTITUT Vacuum chamber and cavity System parameters  Max accel. diode voltage - 500kV  Diode pulse length FLHM – 250ns  Two cell RF cavity 1.5GHz  Max RF power - 5MW  RF pulse length – 5us  Beam energy - 4MeV  Rep. rate - 10Hz  Laser pulse length – 10ps  Laser wave length – 262nm  Max laser pulse energy – 250uJ Features  Variable anode cathode distance  Adjustable cathode position  Exchangeable electrodes  Differential vacuum system  Bolts-free vacuum chamber  Scintillator based dark current monitoring system e - beam UV laser Cathode RF cavity Anode Vacuum chamber Differential vacuum  Vacuum chamber and cavity cross section

6. 01.10.2009 F. Le Pimpec 6 PAUL SCHERRER INSTITUT 500 kV Pulser in operation Courtesy M. Paraliev - 500 kV Electron Back Bombardment Ion Back Bombardment At 200 KeV V e- ~ 88% c (light) V H2 ~ 1.6% c V CO ~ 0.4% c 4 mm Gap transit time t e- ~ 15 ps t H2 ~ 0.9 ns t CO ~ 3.4 ns (21ns at 5keV) Electrons of high E do damage (+ESD) Ions : E 1 ≥ 100keV implantation, < E 1 sputtering (+ISD) Vacuum – Surface - preparation Back Bombardment will be limiting the lifetime of the e - source and will damage the electrodes

7. 01.10.2009 F. Le Pimpec 7 PAUL SCHERRER INSTITUT Field emitter array survival + Anode + + e- : Adsorbates Breakdowns Heat induced desorption Local Heat Up Ionization of neutrals Ion Back bombardment Most likely to kill the entire array

8. 01.10.2009 F. Le Pimpec 8 PAUL SCHERRER INSTITUT Material Testing (2007-2009) Even the detailed vacuum breakdown mechanism is not yet well understood there is some evidence that following mechanical properties affect the vacuum breakdown strength.  Melting temperature  Hardness  Literature is full of correlation tables between material properties and breakdown ConfigurationAISIDINSurfaceDepositionAv. GradientSamplesNote St. Steel (ref.)~316L1.443polishedNo87 MV/m7Range 61..128 MV/m SS (Decolletage)~316L1.4404+S+CupolishedNo119MV/m4Range 90..142 MV/m SS (Implant)~316LVM1.4441polishedNo99 MV/m7Range 57..137 MV/m Mo coating~316L1.443polished Mo 2  m 138 MV/m1Without plasma cleaning Mo coating~316L1.443polished Mo 2  m 212 MV/m1Plasma cleaning before deposition ZrN coating~316L1.443polished ZrN 0.5  m 38 MV/m1Bad adhesion “Hollow” cathode geometry:  Emission from other materials - small sample - reduced surface field  Emission from FEA chips  Explore the effect of electrostatic focusing DLC coated surface Sample e - beam Hollow cathode cross-section Anode Cathode e - beam Emission depth Electrostatic simulation of the field in the accelerating diode.

9. 01.10.2009 F. Le Pimpec 9 PAUL SCHERRER INSTITUT DLC – parametric study (our best cathode holder results)  First configuration – 2  m thick DLC on polished stainless steel,  ~ 5x10 6 .cm (PSI 080815-UF ) – 3 pairs  Thicker coating layer - 4  m thick DLC,  ~ 5x10 6 .cm (PSI 080815-UF) – 4 pairs  Higher conductivity - 2  m thick DLC,  ~ 5x10 4 .cm (PSI 080815-RG) – 4 pairs  Low conductivity - 2  m thick DLC, Resistivity ~ 5x10 11 .cm (PSI-080815-HR) – 4 pairs  Base metal - 2  m thick DLC,  ~ 5x10 6 .cm (PSI 080815- UF) – bronze 8 pairs, copper 5 pairs  Base metal roughness 2  m thick DLC,  ~ 5x10 6 .cm (PSI 080815-UF) rougher stainless steel – 1pair Thickness Base Metal Conductivity Base Roughness DLC DLC types tested to study the influence of coating layer parameters. ConfigurationThicknessResistivityBaseAv. GradientSamplesNote First configuration 2  m DLC5.10 6 .cm Polished st. steel248 MV/m2 (+1 1) ) Range 227..270 MV/m 1) Used for photo emission Thicker layer 4  m DLC5.10 6 .cm Polished st. steel145 MV/m4 Range 140..150 MV/m Higher conductivity 2  m DLC5.10 4 .cm Polished st. steel200 MV/m2 (+2 2) ) Range 167..233 MV/m 2) 2 samples died at ~55MV/m Low conductivity 2  m DLC5.10 11 .cm Polished st. steel185 MV/m4 Range 137..291 MV/m Copper base 2  m DLC5.10 6 .cm Polished copper>200 MV/m 3) 2 (+3 4) ) 3) Used for emission 4) Used in other configurations Bronze base 2  m DLC5.10 6 .cm Polished bronze232 MV/m5 (+2 5) ) Range 150..324 MV/m 5) 2 samples died at ~50MV/m Rough surface 2  m DLC5.10 6 .cm Rough st. steel122 MV/m1

10. 01.10.2009 F. Le Pimpec 10 PAUL SCHERRER INSTITUT Electron beam characterization OPAL simulation of beam emittance and beam envelope, compared with measurements Measured thermal emittance vs laser spot size (extraction field 50MV/m, laser = 262) Cathode imaging helps to study the beam propagation and laminarity PSI logo projected on the cathode Electron beam images on YAG screen two Measured points Emittance Beam size

11. 01.10.2009 F. Le Pimpec 11 PAUL SCHERRER INSTITUT Summary of LEG operation, up to 2009  Very encouraging results with DLC coated electrodes (present limits): - Breakdown field up to 300 MV/m - Photo emission at up to 170 MV/m - Stable emission at 100 MV/m (~40 pC) - Charge up to 80pC (~10 ps laser) (200 pC on Cu and SS – full laser) - Quantum efficiency ~10 -6 (SS and Cu, 10 -6 < QE < 10 -4 )  200 MV/m breakdown with 2 µm Mo on stainless steel - The emission properties are to be explored further  Beam parameters evaluation - Low energy beams emittance preservation - Improvement of low emittance measurement techniques - Comparison of different emitting materials  Progress with single and double gated FEA devices - Demonstrated working double gated device - Control apex radius in 10 nm scale (single gate FEA – current homogeneity) - Single tip current capability – 3 – 20 µA per tip for small arrays LEG will operate until fall 2010

12. 01.10.2009 F. Le Pimpec 12 PAUL SCHERRER INSTITUT SwissFEL : Possible Sites 2005-07 PSI – XFEL Project 800m long machine – Reuse of injector bldg 2008-09 PSI – XFEL Project 900-960 m long machine – Orientation change (no reuse of the Inj bldg) 2009 SwissFEL back to 800m with 2 possible sites

13. 01.10.2009 F. Le Pimpec 13 PAUL SCHERRER INSTITUT Project Goals (comparisons in 2007) E-XFELLCLSSCSSPSI-XFEL Beam Energy10-2014.32 - 86.04.7GeV Peak Current53.43.51.5 kA Bunch Charge111.60.2 nC Norm.Emittance1.41.50.6 (0.8)0.2 mm mrad Target h 0.1 (0.085)0.150.1 nm Facility length 3.6~20.750.8<0.7km Cost 850315*260140 ?M€ * existing linac Hamburg (De)Palo-alto(USA)Spring8 (Jp) PhotocathodeThermionicFEA

14. 01.10.2009 F. Le Pimpec 14 PAUL SCHERRER INSTITUT PSI-XFEL Facility (up to 2007) beamline specifications FEL 1FEL 2FEL 3SP ontaneous 0.1 – 0.30.3 – 11 – 100.1 – 0.3nm electron beam energy3.1 – 5.8 3.73.1 – 5.8GeV beam current1.5 kA norm. slice emittance (rms)0.2 mm mrad repetition rate10 – 100 Hz undulator period15 (smlr ?) 36.65218.3mm undulator typeplanar apple ( Pol h ) appleplanar wavelength tuning mechanism energy Energy gap 400 m

15. 01.10.2009 F. Le Pimpec 15 PAUL SCHERRER INSTITUT cathode emittance compensation coils 2-frequency RF capture cavity (1.5 GHz + 4.5 GHz) electron beam focusing high-gradient acceleration Electron Gun (4 MeV) 250 MeV injector – based on the LEG RF + ballistic Compression (30 MeV - 20A) magnetic compression acceleration electron bunch Q=200pC I=350A (slice emittance)  n <0.2mm mrad E=250MeV controlled longitudinal phase space Space charged dominated beam Conventional RT accelerator technology RF system :(1.5, 4.5) – 3, and 12GHz structures Small beam → fancy diagnostic, NO undulator 1.5 GHz3 GHz 12 GHz

16. 01.10.2009 F. Le Pimpec 16 PAUL SCHERRER INSTITUT The Photocathode based SwissFEL (2009+) SwissFEL Tunable : 1 - 100 Å Pulse duration : 1 - 20 fs Repetition rate : 100 - 400 Hz Bunches/train : 1 (3) Construction period : 2012 - 2015 Operation : 2016 S band Photogun & injector C band L1 and L2 1 Xband (12GHz) Investment cost < 300 MCHF Estimated > 450 MCHF (without any electronic at 400 Hz) Compact X-ray Free Electron Laser A pulsed Gun, driving an FEA source is still science fiction A pulsed Gun using its cathode as a photoelectron source is fine, but  is not much better than LCLS gun (for now…)  Obvious conclusion

17. 01.10.2009 F. Le Pimpec 17 PAUL SCHERRER INSTITUT SwissFEL expected performance More than 18 optimization including : Solely an S band linac Hybrid S band and C band (probably what we will bet on) Even a quick study on an S band - Xband linac. Good Performance is to be expected just ask Y. Kim for the details

18. 01.10.2009 F. Le Pimpec 18 PAUL SCHERRER INSTITUT 250 MeV injector – based on a S-band Photogun Mandate of the 250 MeV injector has changed No more reserved space for the LEG gun. Photogun is a CLIC gun (not what we need but we need something to start with) Still suppose to create and propagate a small emittance beam We might be able to test FEA or different photocathode. The CLIC gun allows this. Plans to do a EE-HG seeding beam line of 17m total length. More info at FEL09 conference S. Reiche (MOPC06) PSI will build a PSI gun (2.5 Cell). Hybrid of LCLS (scaled to euro freq) and PHIN (CLIC) gun. Why ? “mismatch of the slices along the bunch should be better than LCLS gun but it takes more space for the emittance compensation”

19. 01.10.2009 F. Le Pimpec 19 PAUL SCHERRER INSTITUT Summary The bottom line The SwissFEL project design and planning starts at FEL09. The 250 MeV injector will partially operate in 2009 and should test EEHG – other potential electron source – prove our design and train our physicist/operators - until 2014 http://user.web.psi.ch/newsletter/09-03/ (SwissFEL special edition – Director’s corner) The LEG project will phase out fall 2010, hopefully we will have tested reliably a single/double gated electrode (Q -  ) PSI has a very ambitious project. Can potentially lead to major advancement in high brightness e - source (2007) PSI would like to build an XFEL based on standard technology (S-X-C) (if $ approved in 2012 by the federal gov) (2009)

20. 01.10.2009 F. Le Pimpec 20 PAUL SCHERRER INSTITUT

21. 01.10.2009 F. Le Pimpec 21 PAUL SCHERRER INSTITUT PSI-XFEL (SwissFEL) e.g., - BESSY - FERMI@ELETTRA SCSS 2007 2009