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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) - PowerPoint PPT Presentation
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01.10.2009 F. Le Pimpec 1
PAUL SCHERRER INSTITUT
history in 25’
F. Le Pimpec, PSI
On behalf of the SwissFEL dudesLCLS meeting
SLAC Oct 2009
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 Machine1. The PSI-XFEL project (2005-2008)
2. The SwissFEL project (2009+) a “standard” photogun machine
III A Bottom line
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 screensEmittance 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 2007LEG – Phase II (4 MeV beam line)
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 εn ~ 5x10-3 mm mrad(σx~1 μm, δθ ~ 15°, Ue~100 V)
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)
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
01.10.2009 F. Le Pimpec 5
PAUL SCHERRER INSTITUT
Vacuum chamber and cavitySystem parametersMax accel. diode voltage -
500kVDiode pulse length FLHM –
250nsTwo cell RF cavity 1.5GHz Max RF power - 5MWRF pulse length – 5us Beam energy - 4MeVRep. rate - 10HzLaser pulse length – 10psLaser wave length – 262nmMax laser pulse energy – 250uJ
FeaturesVariable anode cathode distanceAdjustable cathode positionExchangeable electrodesDifferential vacuum systemBolts-free vacuum chamberScintillator based dark current
monitoring system
e- beame- beam
UV laserUV laser
CathodeCathode
RF cavityRF cavity
AnodeAnode
Vacuum chamber
Vacuum chamber
Differential vacuum
Differential vacuum
Vacuum chamber and cavity cross section
01.10.2009 F. Le Pimpec 6
PAUL SCHERRER INSTITUT
500 kV Pulser in operation
-600.0
-400.0
-200.0
0.0
200.0
400.0
600.0
1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0
t, usCourtesy M. Paraliev
- 500 kV
Electron Back Bombardment
Ion Back Bombardment
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
01.10.2009 F. Le Pimpec 7
PAUL SCHERRER INSTITUT
Field emitter array survival
+
Anode
+
+e-
: AdsorbatesBreakdowns
Heat induced desorption
Local Heat Up
Ionization of neutrals
Ion Back bombardment
Most likely to killthe entire array
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 HardnessLiterature is full of correlation tables between material properties and breakdown
Configuration AISI DIN Surface Deposition Av. Gradient Samples Note
St. Steel (ref.) ~316L 1.443 polished No 87 MV/m 7 Range 61..128 MV/m
SS (Decolletage) ~316L 1.4404+S+Cu polished No 119MV/m 4 Range 90..142 MV/m
SS (Implant) ~316LVM 1.4441 polished No 99 MV/m 7 Range 57..137 MV/m
Mo coating ~316L 1.443 polished Mo 2m 138 MV/m 1 Without plasma cleaning
Mo coating ~316L 1.443 polished Mo 2m 212 MV/m 1 Plasma cleaning before deposition
ZrN coating ~316L 1.443 polished ZrN 0.5m 38 MV/m 1 Bad adhesion
“Hollow” cathode geometry:Emission from other materials
- small sample
- reduced surface fieldEmission from FEA chipsExplore 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.
01.10.2009 F. Le Pimpec 9
PAUL SCHERRER INSTITUT
DLC – parametric study (our best cathode holder results)
First configuration – 2m thick DLC on polished stainless steel, ~ 5x106 .cm (PSI 080815-UF ) – 3 pairs
Thicker coating layer - 4m thick DLC , ~ 5x106 .cm (PSI 080815-UF) – 4 pairs
Higher conductivity - 2m thick DLC , ~ 5x104 .cm (PSI 080815-RG) – 4 pairs
Low conductivity - 2m thick DLC , Resistivity ~ 5x1011 .cm (PSI-080815-HR) – 4 pairs
Base metal - 2m thick DLC , ~ 5x106 .cm (PSI 080815-UF) – bronze 8 pairs, copper 5 pairs
Base metal roughness 2m thick DLC , ~ 5x106 .cm (PSI 080815-UF) rougher stainless steel – 1pair
Thicknes
s
Base Metal
Condu
ctivi
ty
Base
Rough
ness
DLCDLC
DLC types tested to study the influence of coating layer parameters.
Configuration Thickness Resistivity Base Av. Gradient Samples Note
First configuration 2 m DLC 5.106 .cm Polished st. steel 248 MV/m 2 (+11)) Range 227..270 MV/m1) Used for photo emission
Thicker layer 4 m DLC 5.106 .cm Polished st. steel 145 MV/m 4 Range 140..150 MV/m
Higher conductivity 2 m DLC 5.104 .cm Polished st. steel 200 MV/m 2 (+22)) Range 167..233 MV/m2) 2 samples died at ~55MV/m
Low conductivity 2 m DLC 5.1011 .cm Polished st. steel 185 MV/m 4 Range 137..291 MV/m
Copper base 2 m DLC 5.106 .cm Polished copper >200 MV/m3) 2 (+34)) 3) Used for emission4) Used in other configurations
Bronze base 2 m DLC 5.106 .cm Polished bronze 232 MV/m 5 (+25)) Range 150..324 MV/m5) 2 samples died at ~50MV/m
Rough surface 2 m DLC 5.106 .cm Rough st. steel 122 MV/m 1
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
Thermal emitance
0
0.2
0.4
0.6
0.8
1
1.2
1.4
0 0.2 0.4 0.6 0.8
Laser spot size (s ), mm
No
rma
lize
d e
mit
tan
ce
, m
m.m
rad
Cu eps xCu eps y
DLC eps xDLC eps y
0.43 mm.mrad / mm
Measured points
Emittance
Beam
size
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
01.10.2009 F. Le Pimpec 12
PAUL SCHERRER INSTITUT
SwissFEL : Possible Sites 2005-07 PSI – XFEL Project 800m long machine – Reuse of injector bldg2008-09 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
01.10.2009 F. Le Pimpec 13
PAUL SCHERRER INSTITUT
Project Goals (comparisons in 2007)
E-XFEL LCLS SCSS PSI-XFEL
Beam Energy 10-20 14.3 2 - 8 6.0 4.7 GeV
Peak Current 5 3.4 3.5 1.5 1.5 kA
Bunch Charge 1 1 1.6 0.2 0.2 nC
Norm.Emittance 1.4 1.5 0.6 (0.8) 0.2 0.2 mm mrad
Target h 0.1 (0.085) 0.15 0.1 0.1 0.1 nm
Facility length 3.6 ~2 0.75 0.8 <0.7 km
Cost 850 315* 260 140 ? M€
* existing linac
Hamburg (De) Palo-alto(USA) Spring8 (Jp)
Photocathode Thermionic FEA
01.10.2009 F. Le Pimpec 14
PAUL SCHERRER INSTITUT
PSI-XFEL Facility (up to 2007)
BC1K
SPlinac-1injector linac-2
linac-4
BC2
userstations
linac-3
FEL-1
K MFEL-3
FEL-2
beamline specificationsFEL 1 FEL 2 FEL 3 SPontaneous
0.1 – 0.3 0.3 – 1 1 – 10 0.1 – 0.3 nmelectron beam energy 3.1 – 5.8 3.1 – 5.8 3.7 3.1 – 5.8 GeVbeam current 1.5 1.5 1.5 1.5 kA
norm. slice emittance (rms) 0.2 0.2 0.2 0.2mm
mradrepetition rate 10 – 100 10 – 100 10 – 100 10 – 100 Hzundulator period 15 (smlr ?) 36.6 52 18.3 mm
undulator type planarapple(Pol h)
apple planar
wavelength tuning mechanism
energyEnergy
gapgap gap
400 m400 m
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
compressionacceleration
electron bunchQ = 200 pCI = 350 A (slice emittance)n < 0.2 mm mradE = 250 MeVcontrolled 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 GHz 3 GHz
12 GHz
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 L21 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 fictionA pulsed Gun using its cathode as a photoelectron source is fine, but is not much better than LCLS gun (for now…) Obvious conclusion
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
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”
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 2014http://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)
01.10.2009 F. Le Pimpec 20
PAUL SCHERRER INSTITUT
01.10.2009 F. Le Pimpec 21
PAUL SCHERRER INSTITUT
PSI-XFEL(SwissFEL)e.g.,
- BESSY- FERMI@ELETTRA
SCSS
2007 2009