1 / 21

history in 25’

history in 25’. F. Le Pimpec, PSI On behalf of the SwissFEL dudes LCLS meeting SLAC Oct 2009. I The Low Emittance Gun project (2003-2005) A FEA based electron gun (online - xmas 2007) II Evolving from LEG to a Machine The PSI-XFEL project (2005-2008)

hide
Download Presentation

history in 25’

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. history in 25’ F. Le Pimpec, PSI On behalf of the SwissFEL dudesLCLS meeting SLAC Oct 2009

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

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

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

  5. Vacuum chamber and cavity Differential vacuum Anode RF cavity Cathode e- beam UVlaser Vacuum chamber 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  Vacuum chamber and cavity cross section

  6. Electron Back Bombardment - 500 kV Ion Back Bombardment Courtesy M. Paraliev 500 kV Pulser in operation At 200 KeV Ve- ~ 88% c (light) VH2 ~ 1.6% c VCO ~ 0.4% c 4 mm Gap transit time te- ~ 15 ps tH2 ~ 0.9 ns tCO ~ 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. Local Heat Up Heat induced desorption Anode e- Ionization of neutrals + Ion Back bombardment + + Breakdowns Most likely to killthe entire array : Adsorbates Field emitter array survival

  8. Material Testing (2007-2009) Anode e- beam Emission depth Cathode DLC coated surface e- beam Sample 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 “Hollow” cathode geometry: • Emission from other materials • - small sample • - reduced surface field • Emission from FEA chips • Explore the effect of electrostatic focusing Electrostatic simulation of the field in the accelerating diode. Hollow cathode cross-section

  9. DLC – parametric study (our best cathode holder results) Thickness Conductivity DLC Base Roughness Base Metal DLC types tested to study the influence of coating layer parameters. • First configuration– 2m thick DLC on polished stainless steel,  ~ 5x106 .cm (PSI 080815-UF ) – 3 pairs • Thicker coating layer- 4m thick DLC ,  ~ 5x106 .cm (PSI 080815-UF) – 4 pairs • Higher conductivity- 2m thick DLC ,  ~ 5x104 .cm (PSI 080815-RG) – 4 pairs • Low conductivity- 2m thick DLC , Resistivity ~ 5x1011 .cm (PSI-080815-HR) – 4 pairs • Base metal- 2m thick DLC ,  ~ 5x106 .cm (PSI 080815-UF) – bronze 8 pairs, copper 5 pairs • Base metal roughness 2m thick DLC ,  ~ 5x106 .cm (PSI 080815-UF) rougher stainless steel – 1pair

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

  11. 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. 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. Project Goals (comparisons in 2007) Hamburg (De) Palo-alto(USA) Spring8 (Jp) Photocathode Thermionic FEA * existing linac

  14. 400 m 400 m PSI-XFEL Facility (up to 2007)

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

  16. The Photocathode based SwissFEL (2009+) Compact X-ray Free Electron Laser 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 L21 Xband (12GHz) Investment cost < 300 MCHF Estimated > 450 MCHF (without any electronic at 400 Hz) A pulsed Gun, driving an FEA source is still science fictionA pulsed Gun using its cathode as a photoelectron source is fine, but  is not much better than LCLS gun (for now…)  Obvious conclusion

  17. 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. 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. Summary The LEG project will phase out fall 2010, hopefully we will have tested reliably a single/double gated electrode (Q -) 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) 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) The bottom line The SwissFEL project design and planning starts at FEL09.

  20. SCSS PSI-XFEL(SwissFEL) e.g., - BESSY - FERMI@ELETTRA 2009 2007

More Related