Intra-Undulator X-ray Diagnostics for the LCLS Undulator

1. Intra-Undulator X-ray Diagnostics for the LCLS Undulator Bingxin Yang, Advanced Photon Source

2. Intra-Undulator X-ray Diagnostics for the LCLS Undulator • History of the conceptual development • Far-field x-ray diagnostics R & D and ANL’s participation • Intra-undulator diagnostics R & D

3. Old plan for intra-undulator x-ray diagnostics Electron beam diagnostics (CDR, G. Decker and A. Lumpkin) • RF BPM, Cherenkov detectors, current monitors • Wire scanners • OTR imaging cameras 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, 2q = 90, CCD detector. 20-20 Hindsight • Good starting point, but • Low photon energy (800 eV) diagnostics was not addressed • High-power and beam damage was not addressed

4. IMPLICATION OF HIGH PEAK POWER

5. 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 mC in 30 mm 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.

6. 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/g-beam alignment and errors in K, F, and field quality. • Far-field spontaneous radiation has cleaner signature of these spoilers: DK, DF, field quality, e/g-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.

7. Far-field x-ray diagnostics (SLAC, LLNL, ANL) Jointly develop x-ray diagnostics concept through analytical work and computer simulation: characterize errors in K, F, 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? ANL’s New Role in LCLS X-Ray Diagnostics 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).

8. 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, F, 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, F, and trajectory. • Error / tolerance estimate.

9. 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.

10. Intra-undulator x-ray diagnostics R & D 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.

11. Intra-undulator x-ray diagnostics R & D 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 K, F, and field quality? • On-axis x-ray intensity measurements: Gas, beam, or solids.

12. Intra-Undulator X-ray Diagnostics for the LCLS Undulator 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.