Intra-Undulator X-ray Diagnostics for the LCLS Undulator

A U.S. Department of EnergyOffice of Science LaboratoryOperated by The University of Chicago

Argonne National Laboratory

Office of ScienceU.S. Department of Energy

Intra-Undulator X-ray Diagnostics for the LCLS Undulator

Bingxin Yang, Advanced Photon Source

2

Pioneering Science andTechnology

Office of Science U.S. Department

of Energy

Undulator Systems Review, March 3 – 4, 2004Argonne National Lab


• History of the conceptual development

• Far-field x-ray diagnostics R & D and ANL’s participation

• Intra-undulator diagnostics R & D

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Old plan for intra-undulator x-ray diagnostics

X-ray diagnostics (E. Gluskin and P.Ilinski)

• On-axis diagnostics

Diamond(111), 4-9 keV, cooled Si PIN diode

• Off-axis diagnostics

Holy crystal, 2 = 90, CCD detector.

Electron beam diagnostics (CDR, G. Decker and A. Lumpkin)

• RF BPM, Cherenkov detectors, current monitors

• Wire scanners

• OTR imaging cameras

20-20 Hindsight

• Good starting point, but

• Low photon energy (800 eV) diagnostics was not addressed

• High-power and beam damage was not addressed

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IMPLICATION OF HIGH PEAK POWER (Extrapolation from CDR Section 9.1)

Table 9.1 Characteristics of the FEL x-ray beam (Adapted) 0.828 keV (4.54 GeV) 8.27 keV (14.35 GeV)

FEL Spontaneous FEL Spontaneous Energy per pulse (mJ) 3 1.4 2.5 22

Peak power (GW) 11 4.9 9 81 Spot size at 50 m (m FWHM) 610 Aperture limited 130 Aperture limited

Spot size in undulator (m FWHM) 75 66 Average power (W) 0.4 0.2 0.3 2.6

Average power density (W/mm2) 52 42

Table 9.2 Normal-incidence peak energy dose and damage to materials (Adapted) Dose at 50 m (eV/atom) Dose in undulator (eV/atom)

Material Melt

(eV/Atom) Evaporation*

(eV/atom) 827 eV 8.27 keV 827 eV 8.27 keV Li 0.1 1.8 0.02 0.0005 1.3 0.002 Be 0.3 3.8 0.08 0.001 5 0.004 B 0.5 4.8 0.2 0.003 13 0.01

C (graphite) 0.9 0.4 0.007 26 0.03 Al 0.2 3.9 0.4 0.2 26 0.8 Si 0.4 5.2 0.6 0.2 40 0.8 Cu 0.3 1.1 0.4 73 1.6

* Data from thermal measurements: fusion and evaporation latent heat, plus heating up with specific heat (25 C).

Screen material is lost similar to laser ablation!

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Commissioning Workshop (UCLA, 1/19/2004)

A workshop was called to draft a commissioning procedure.

Too many questions on the intra-undulator x-ray diagnostics. - Are the diagnostics sufficient to obtain start-up?

- Will the diagnostics survive the onslaught of the beams?

A case in point: Total dose limit on diamond crystals in e-beam:

SLAC Coherent Bremsstrahlung Facility (1970-1980’s) found severe radiation damage after 5*1019 e/cm2, equivalent to 8 C/cm2 or 450 C in 30 m spot, ~ 1 hours LCLS beam at 120 Hz.

The damage is expected to accelerate for short bunch.

Other crystals are expected to be less durable.

John Galayda reduced expectations on most intra-undulator x-ray diagnostics: from construction item to R & D.

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X-ray Diagnostics R & D Plan (SLAC, 2/10/2004)

John Arthur (SLAC) called a one-day meeting to discuss setting R & D plans for the x-ray diagnostics (report pending?)

Personal observations: - Spoiler of FEL action: peak current, emittance, e/-beam

alignment and errors in , , and field quality.- Far-field spontaneous radiation has cleaner signature of these

spoilers: , , field quality, e/-beam alignment.- Roll-away undulator allows cleaner measurements- Need 6 to 12 months simulation/studies time to define useful x-

ray diagnostics and our realistic expectations for them.- Most intra-undulator x-ray diagnostics are to be R & D items.

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ANL’s New Role in LCLS X-Ray Diagnostics

Far-field x-ray diagnostics (SLAC, LLNL, ANL)• Jointly develop x-ray diagnostics concept through analytical work and

computer simulation: characterize errors in , , and field quality.

• Jointly develop specifications and designs for some technical components.

• Develop SDDS software tools for data processing and interpretation.

• Join the commissioning activity and validate these tools.

• Other responsibilities?

Intra-undulator x-ray diagnostics (scope reduced)• X-ray diffraction wire-scanner (powder ring).

• X-ray intensity measurements with scanning diamond blades (R & D).

• FEL start-up diagnostics (R & D).

• High-power annular crystal (R & D, signal interpretation).

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Short-Term Goals for Far-Field Diagnostics R & D

• Simulation of far-field radiation.

- Undulator model with gaps, dipoles, and quads

- LCLS beam emittance and energy spread

• Answer questions about K, , and trajectory errors :

- Signatures in radiation pattern

- Sensitivities

- Impact of beam jitter

- Automation of data processing?

Figure from M. Tischer et al., FEL 2002

• Develop data processing software tools for future use in LCLS commissioning.

- Extract quantitative information for errors in K, , and trajectory.

- Error / tolerance estimate.

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Intra-undulator x-ray diagnostics R & D

Short term tasks• Develop diagnostics characterizing initial FEL start-up

- Start-up is a main concern at the commissioning workshop- Based on powder / poor crystal diffraction - Survives the electron beam. X-ray damage is low at start.- Incremental cost is not high.- Calibration and validation issues.

• Beam scattering calculation from diagnostics screens- Undulator radiation damage concerns- Screen / crystal dose limit due to electron / x-ray beam damage.- Material selection for wire, OTR mirror, and x-ray screen.

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X-ray diamond blade scanner (short term task)• X-ray wire scanner was proposed by R. Tatchyn of SLAC (PAC 1999)

• Mosaic diamond blade has much higher diffraction signals. It can stand higher beam dose than single crystal diamond.

• z-dependent intensity and profile information.

• Need crystal rotation stage and detector upgrade.

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High-power Diagnostics (long term task)

Simulations of

• Near-field off-axis x-ray radiation

• Optical diffraction radiation

-Proposed in CDR but not sufficiently studied

-Correlation and sensitivity to changes in e-beam properties?

-Correlation and sensitivity to errors in , , and field quality?

•On-axis x-ray intensity measurements: Gas, beam, or solids.

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Conclusions• The original plan for intra-undulator x-ray diagnostics has been

replaced by a blend of far-field x-ray diagnostics and intra-undulator devices.

• We will participate in the research, development, design and commissioning of the far-field diagnostics. Our involvement in the construction is not specified at this point.

• We will continue R & D of the intra-undulator x-ray diagnostics. High priority is given to mosaic crystal based FEL start-up diagnostics due to its high benefit and risk ratio.

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Intra-Undulator X-ray Diagnostics for the LCLS Undulator