history in 25’

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


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


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


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


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


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


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


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


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


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


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


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


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


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


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


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


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


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


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


01.10.2009 F. Le Pimpec 21


PSI-XFEL(SwissFEL)e.g.,

- BESSY- FERMI@ELETTRA

SCSS

2007 2009

history in 25’

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