Undulator X-Ray Diagnostics, R&D Plans

1. Undulator X-Ray Diagnostics, R&D Plans Bingxin Yang Argonne National Lab

2. Undulator X-Ray Diagnostics Scope X-ray optics / detector systems (low power) to aid tuning of undulator systems, and maximizing the FEL gain. • Past conceptual developments • Far-field x-ray diagnostics R & D plan and Argonne’s participation • Intra-undulator diagnostics R & D Contents

3. Evolution of the x-ray diagnostics plans • CDR (Apr. 2002) (ANL) Diagnostics for FEL start up in the undulator (LLNL) Diagnostics for x-ray beam out of the undulator • Re-examination (Jan. 2004, UCLA) Undulator commissioning workshop (Feb. 2004, SLAC) X-ray diagnostics planning meeting • Major issues Beam damage of optical components Getting sufficient information for FEL tuning?

4. Major issues at UCLA workshop • Beam damage of optical components • Example from Marc Ross’ coupon test, LINAC 2000 • Saturated FEL beam deposit higher energy density • Desirable information • Trajectory accuracy (Dx~1mm) • Effective K (DK/K ~ 1.5×10-4) • Relative phase (Df~10º) • Intensity gain (DE/E~0.1%, z-) • Undulator field quality

5. Rethink x-ray diagnostics (Galayda) • Intra-undulator diagnostics • Electron beam position monitor (BPM) • Electron beam profiler (OTR & wire scanner) • Low power x-ray Intensity measurements (R&D) • Far-field low-power x-ray diagnostics (R&D) • Clean signature from spontaneous radiation • Space for larger optics / detectors • Single set advantage (consistency, cost) • Goal = obtain “desirable information”

6. Two Essential Elements for Far-Field Measurements • Roll away undulators Spontaneous radiation is most useful when background is clean, with each undulator rolled in individually. • Adequate Far-field X-ray Diagnostics Adequate x-ray diagnostics extracts the beam / undulator information: • Electron trajectory inside the undulator (mm / mrad accuracy) • Undulator K-value (DK/K ~ 1.5 × 10-4) • Relative phase of undulators (Df ~ 10°) • X-ray intensity measurements (DE/E ~ 0.1%, z-dependent) • Micro-bunching measurements (z-dependent)

7. Far-Field measurement of x-ray beam centroid • Use center of the far-field pattern to determine e-beam trajectory and slope (x, x’) inside the undulator. • Need relative accuracy 0.25 mrad or better.

8. Far-Field measurement of Undulator K-value • Use angle-integrated spectrum to set all undulator to same K (or to a known taper). • Needed relative accuracy DK~0.0005 (DK/K ~ 1.5×10-4). • Issues: e-beam energy spread and jitter DE/E=2~5×10-4.

9. Far-field measurement of relative phase of undulators • Use interference of radiation from two undulators to tune their phase differences • Relative accuracy ~ 10 degrees or better • Reformulate the question for distributed phase shift?

10. Far-field measurement of FEL gain (z) • Measure monochromatic x-ray beam intensity as undulator segments are added, characterize the FEL start up and early gain process • Wide bandwidth monochromator (DE/E ~ 0.1%) • Multilayer reflectors • Mosaic or asymmetrically-cut crystals • Large dynamic range detector(s) • Low power only (before saturation)

11. More x-ray diagnostics of FEL physics? • Take single shot spectrum (DE/E ~ 0.5%, dE/E ~ 0.01%, z-dependent) • Measurement of electron beam micro-bunching (z-dependent)

12. FY04 effort in far-field x-ray diagnostics In the new R&D plan, Argonne is a part of the (SLAC/LLNL/ANL) collaboration on x-ray diagnostics: concept development, performance simulation, and system design. Develop concept from lessons learned from APS diagnostic undulator Design numeric tools for simulation of far-field x-ray diagnostics

13. Remaining intra-undulator diagnostics • Location: every long break (905 mm) • Diagnostics chamber length: 425 mm • Functional components RF BPM, Cherenkov detector, OTR profiler, wire scanner, x-ray (intensity) diagnostics

14. FY04 accomplishments • Layout of diagnostics chamber • OTR profiler • Camera module designed • Wire scanner • Scanner design in progress • Wire card adapt SLAC design • X-ray diagnostics design • Beam intensity: double crystal • Beam profile: imaging detector

15. Conclusions and current status • Plan for start-up x-ray diagnostics has been restructured, driven by the need of FEL tuning and existing experimental limitations. Center of gravity shifts significantly towards the end of undulators. Goals are clearly specified. • With roll away undulators, we have, at least conceptually, a good handle on relative measurements of trajectory direction (field quality), undulator K-value, and x-ray intensity gain. • Concept for undulator phasing and micro-bunching measurements need further development • Intra-undulator diagnostics development is nearly on-target.

16. R&D plan for x-ray diagnostics in FY05 • Wide bandwidth monochromator (DE/E ~ 0.1%) • Critical to FEL diagnostics inside / end-of undulator • Test multi-layer optics and asymmetrically cut crystals • Search for mosaic crystal (with APS/XFD/Optics) • Far-field undulator radiation diagnostics • Identify suitable spatial-spectral features • Simulation with non-ideal beam and non-ideal field • Estimate realistic measurement accuracy • Develop x-ray optics / detector requirements • Test core optical components