Linac Coherent Light Source
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Linac Coherent Light Source Update. John N. Galayda LCLS Project Manager Basic Energy Sciences Advisory Committee Meeting 2-3 August 2001. R&D progress Gun Bunch compression Undulator X-ray optics FEL experiments Near-term R&D goals Determine baseline gun performance

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Linac Coherent Light Source Update

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Linac coherent light source update

Linac Coherent Light Source

Update

John N. Galayda

LCLS Project Manager

Basic Energy Sciences Advisory Committee Meeting

2-3 August 2001


Linac coherent light source update

  • R&D progress

    • Gun

    • Bunch compression

    • Undulator

    • X-ray optics

    • FEL experiments

  • Near-term R&D goals

    • Determine baseline gun performance

    • Improve understanding of coherent synchrotron radiation effects

    • Sub-Picosecond Photon Source (SPPS)


Linac coherent light source update

1977-1990

National Synchrotron Light Source, Brookhaven National Lab

1990-2001

Advanced Photon Source,

Argonne National Lab


Linac coherent light source update

LINAC COHERENT LIGHT SOURCE

I-280

Sand Hill Rd


Linac coherent light source update

Performance Characteristics of the LCLS

Peak and time

averaged brightness

of the LCLS and other facilities operating or under construction

~ TESLA

Performance


Linac coherent light source update

Self-Amplified Spontaneous Emission

Electrons are bunched under the influence of the light that they radiate.

The bunch dimensions are characteristic of the wavelength of the light.

Excerpted from the TESLA Technical Design Report, released March 2001


Linac coherent light source update

At entrance to the undulator Exponential gain regime Saturation(maximum bunching)

Excerpted from the TESLA Technical Design Report, released March 2001


Linac coherent light source update

  • R&D progress – Gun

  • BNL Accelerator Test Facility

    • Measurement of 0.8 mm-mrad emittance with 0.5 nC of charge

    • Such high performance could make shorter LCLS pulses possible

    • Details to be published in NIM-A, 2001 FEL Conference Proceedings


Linac coherent light source update

  • R&D progress – Gun

  • SLAC gun test facility

    • Comparison of computed and measured emittances

    • Agreement is good for configurations tested thus far

    • Facility upgrades planned to study configurations with lower emittance

ge, mm-mrad

LCLS Specification

Charge, picocoulombs


Linac coherent light source update

Producing short bunches

At low energy, space charge repulsion degrades the beam properties

Accelerate the bunch, then compress it.

250 MeV

z  0.19 mm

  1.8 %

4.54 GeV

z  0.022 mm

  0.76 %

14.35 GeV

z  0.022 mm

  0.02 %

7 MeV

z  0.83 mm

  0.2 %

150 MeV

z  0.83 mm

  0.10 %

Linac-X

L0.6 m

rf=180

RF

gun

Linac-1

L9 m

rf -38°

Linac-2

L330 m

rf -43°

Linac-3

L550 m

rf -10°

new

Linac-0

L6 m

undulator

L120 m

21-1b

21-1d

21-3b

24-6d

25-1a

30-8c

X

...existing linac

BC-1

L6 m

R56 -36 mm

BC-2

L24 m

R56 -22 mm

DL-1

L12 m

R56 0

DL-2

L66 m

R56 = 0

SLAC linac tunnel

undulator hall


Linac coherent light source update

DE/E

DE/E

DE/E

Over-compression

Under-compression

2sz0

z

z

z

2sz

V = V0sin(wt)

Dz = R56DE/E

RF Accelerating

Voltage

Path Length-Energy

Dependent Beamline


Linac coherent light source update

Coherent Synchrotron Radiation (CSR)

sz

Coherent radiation for:

lr >> sz

lr

A

|AB|

B

e–

R

<<1

...from Derbenev, et. al.

Free space radiation from bunch tail at pointAovertakes bunch head, a distancesahead of the source, at the pointBwhich satisfies...

s = arc(AB) – |AB| = R– 2Rsin(/2)  R 3/24

and fors = sz(rms bunch length) the overtaking distance is...

L0  |AB|  (24szR2)1/3, (LCLS: L0 ~ 1 m)


Linac coherent light source update

CSR Effects  Bunch Energy Gradient

Charge distribution

sz

TAIL

DE/E

HEAD

(mean loss)

~CSR wakefield

z


Csr effects emittance growth

CSR Effects  Emittance Growth

Energy loss in bends causes

transverse position spread after

bends x-emittance growth

Radiation in bends

s

DE/E = 0

DE/E < 0


Linac coherent light source update

minimum compression

Elegant

model

  • R&D Progress – Coherent Synchrotron Radiation

    • CSR sets a lower limit on LCLS as a laser

    • LCLS could produce ~50 fsec pulses of spontaneous radiation

    • New ANL model fits latest data – is the model accurate?

    • LCLS bunch compression can be retuned to accommodate

energy

spread [%]

rms bunch length [ps]

emittance [mm-mrad]

Q 0.3 nC

M. Borland, PRST-AB v.4, 074201(2001)

Borland, Braun, Doebert, Groening, & Kabel, CERN/PS 2001-027(AE)

Courtesy M. Borland, J. Lewellen, ANL


Linac coherent light source update

  • R&D Progress – Prototype Undulator

    • Titanium strongback mounted in eccentric cam movers

    • Magnet material 100% delivered

    • Poles >90% delivered

    • Assembly underway


Linac coherent light source update

Helmholtz Coil – magnet block measurement Translation stages for undulator segment

Poletip alignment fixture Magnet block clamping fixtures


Linac coherent light source update

Planned beam diagnostics in undulator include pop-in C(111) screen

To extract and observe x-ray beam, and its superposition on e-beam


Linac coherent light source update

  • R&D Progress – Undulator diagnostics

    • P. Krejcik, W. K. Lee, E. Gluskin

    • Exposure of diamond wafer to electron beam in FFTB-

    • Same electric fields as in LCLS

    • No mechanical damage to diamond

    • Tests of crystal structure planned

Before After


Linac coherent light source update

  • R&D Progress – X-ray optics

    • LLNL tests of damage to silicon crystal

      • Exposure to high- power laser with similar energy deposition

      • Threshold for melting 0.16 J/cm2, as predicted in model

    • Fabrication/test of refractive Fresnel lens

      • Made of aluminum instead of carbon

      • Machined with a diamond point

      • Measurements from SPEAR presently under analysis


Linac coherent light source update

Warm Dense Matter Experiment

250 mm

aperture

Back-scatter

x-ray

spectrometer

Incident Beam

Monitors

Laser

FEL

Beam

Spectrometer

100 mm thick sample

Outgoing

Beam

Monitor

Focusing

Optic

50-100 mm

aperture

Imaging

detector

Variable

beam

attenuator

Sample

Tank

PPS beam stops

Optics

Tank

WDM Shielded Room

13 m


Linac coherent light source update

  • R&D Progress – FEL physics

    • More complete analysis of HGHG

      • A. Doyuran, et al. PRL vol. 86, Issue 26, pp. 5902-5905, June 25, 2001

    • LEUTL experiments ongoing

      • Milton, et al. Science vol. 292, Issue 5524, 2037-2041, June 15, 2001

    • VISA experiment saturation

      • To be published in proceedings of 2001 FEL conference

Data from BNL/ANL

High-Gain Harmonic

Generation(HGHG)

Experiment


Linac coherent light source update

LEUTL Gain Curve @ 530 nm on March 10, 2001

107

106

105

104

Radiated Energy (a.u.)

103

October,2000

102

101

100

10

25

5

20

15

0

Distance Traversed in Undulator (m)


Linac coherent light source update

16 March 2001

Visible to Infrared SASE Amplifier

BNL-LLNL-SLAC-UCLA

VISA Pulse Energy vs. Position

Wavelength 830 nm

Onset of Saturation

Data Points taken along VISA Undulator

Wavelength830nm

RMS Bunch Length:900 fs

Average Charge:170 pC

Peak Current:~200 A

Measured Projected Emittance:1.7 mm mrad

Energy Spread:7×10-4

Gain Length18.5 cm

Equivalent Spontaneous Energy:5 pJ

Peak SASE Energy:10 mJ

Total Gain: 2×106

Pop-In Diagnostics

Enclosure for 4-m long VISA undulator

Direction of Electron Beam

Preliminary recent results (unpublished) from VISA showing large gain (2 106) in SASE FEL radiation and evidence of saturation at 830 nm.


Linac coherent light source update

  • Near-term R&D goals

    • Gun R&D

      • Thorough investigation of gun operation at LCLS parameters

        • Laser upgrade

        • Linac energy upgrade

      • Experiment/model comparison at 1 mm-mrad emittance, 0.5-1 nC

    • Bunch compression, coherent synchrotron radiation

      • Install a bunch compressor in the SLAC linac

      • Continue start-to-end modeling


Linac coherent light source update

  • Bunch compression studies with SLAC linac in 2003

    • Compatible with PEP-II injection

    • Capable of producing 80 fsec electron bunches

    • Goal: first studies in 1/2003, 1 year of tests

      • pump/probe techniques

      • Accelerator physics opportunities to study wake fields

  • Of great importance to LCLS

  • Short bunches are ideal for advanced accelerator R&D; Strong SLAC support


Linac coherent light source update

DE/E

z

LCLS – X-ray Laser Physics

The “sixth” experiment – Produce < 230 fsec pulses of SASE radiation

LCLS will be used to explore means of producing ultra short bunches (< 50 fs). Alternative techniques will be investigated:

  • Stronger compression of the electron bunch

    • No new hardware is required

  • Photon bunch compression or slicing

    • Principle:spread the electron and photon pulses in energy; recombine optically or select a slice in frequency

  • Seeding the FEL with a slice of the photon pulse

    • Principle: select slice in frequency, then use it to seed the FEL


Linac coherent light source update

Two-Stage Chirped-Beam SASE-FEL for High Power Femtosecond X-Ray Pulse Generation

C. Schroeder*, J. Arthur^, P. Emma^, S. Reiche*, and C. Pellegrini*

^ Stanford Linear Accelerator Center

*UCLA

Strong possibility for shorter-pulse operation


Linac coherent light source update

DEFW/E = 1.0%

Energy

Energy

1.010-4

time

time

DtFW = 230 fsec

DtFW < 10 fsec

UCLA

Si monochromator

(T = 40%)

x-ray pulse

time

time

e-

30 m

52 m

43 m

SASE gain (Psat/103)

SASE Saturation (23 GW)

Two-stage undulator for shorter pulse

Mitigates e- energy jitter and undulator wakes

Also a DESY scheme which emphasizes line-width reduction (B. Faatz)


Linac coherent light source update

  • LCLS Construction

  • FY2003: $6M for project engineering and design, $3M for R&D

    • Prepare bid packages

  • FY2004: Start of Construction

    • Injector construction and installation

    • Bunch compressor construction

    • Start construction of near hall

    • Undulator procurement

  • FY2005:

    • Injector commissioning

    • Bunch compressor installation

    • Start construction of far hall

    • Undulator, experiment construction

  • FY2006: Installation

    • Linac commissioning

    • Undulator and experiment installation

    • LCLS commissioning


Linac coherent light source update

LCLS research activities span the full range of challenges to be met in creating and exploiting an x-ray laser

SLAC has supplemented its extraordinary capabilities with the expertise and resources at partner labs to make LCLS possible

LCLS can be a reality by 2007


Linac coherent light source update

End of Presentation


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