Bingxin Yang Undulator / FEL October 12, 2004 Undulator / FEL Diagnostics Bingxin Yang Argonne National Lab

Bingxin Yang Undulator / FEL October 12, 2004 Undulator / FEL diagnostics scope Electron beam diagnostics in the undulator RF BPM (beam centroid) OTR imager (beam profile) Wire scanner (beam profile) Cherenkov counters (beam loss) Low-power x-ray diagnostics (R&D) Intra-undulator x-ray diagnostics Far-field undulator x-ray optics / detector systems Specifically designed to aid the commissioning and tuning of the undulator systems.

Bingxin Yang Undulator / FEL October 12, 2004 Past conceptual developments and current plan Intra-undulator diagnostics: design and R&D activities in FY2004 R & D for far-field x-ray diagnostics Conclusions Contents

Bingxin Yang Undulator / FEL October 12, 2004 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 (Sep. 2004, SLAC) Diag. and commissioning workshop Major issues Beam damage of optical components Getting sufficient information for FEL tuning?

Bingxin Yang Undulator / FEL October 12, 2004 Major issues at UCLA workshop Beam damage of optical components Example from Marc Ross’ coupon test (LINAC 2000) Saturated FEL beam deposit even higher energy density Desirable information Trajectory accuracy (  x~1  m) Effective K (  K/K ~ 1.5×10 -4 ) Relative phase (  ~10º) Intensity gain (  E/E~0.1%, z-) Undulator field quality

Bingxin Yang Undulator / FEL October 12, 2004 Rethink x-ray diagnostics (Galayda) Intra-undulator diagnostics Electron beam position monitor (RF BPM) Electron beam profiler (OTR & wire scanner) Beam loss Monitor 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, lower cost) Goal = obtain “desirable information”

Bingxin Yang Undulator / FEL October 12, 2004 LCLS Undulator hall schematic

Bingxin Yang Undulator / FEL October 12, 2004 Intra-undulator diagnostics (short breaks) Location: short breaks (482 mm × 22) Diagnostics components RF BPM (work to start in FY05) Cherenkov detector (work to start in FY05)

Bingxin Yang Undulator / FEL October 12, 2004 Intra-undulator diagnostics (long breaks) Location: long breaks (909 mm × 10) Diagnostics components RF BPM, Cherenkov detector OTR profiler, wire scanner x-ray diagnostics (intensity / profile)

Bingxin Yang Undulator / FEL October 12, 2004 FY04 activities: diagnostics chamber Chamber length: 425 mm Layout of diagnostics chamber Sharing space side-by-side OTR profiler Wire scanner X-ray diagnostics provision Double crystal optics Integrating detector (intensity) Imaging detector (distribution) Smooth bore pass-through

Bingxin Yang Undulator / FEL October 12, 2004 FY04 activities: OTR camera module Modular design Camera module design complete Waiting for funds to make prototype Features Commercial 2 inch lens tube, magnification adjustable with change of lens Integral tungsten shield Stepper driven remote focus Digital video camera, 30-fps at 1 MP, or 120 fps at VROI (250L), programmable gain. Manual iris control

Bingxin Yang Undulator / FEL October 12, 2004 FY04 activities: wire scanner Based on SLAC design. Adapted for tighter space. Features Mounted on 8-inch flange On-axis drive mechanism in air Share space with other diagnostics (OTR and x-ray) Wire card to adapt SLAC design A motor-in-vacuum design is being evaluated

Bingxin Yang Undulator / FEL October 12, 2004 FY05 plan for intra-undulator diagnostics Complete and test OTR profiler prototype Fabricate prototype Bench test (resolution) and APS(?)/FFTB beam test Performance review and plan production Complete and test wire scanner prototype Compatibility test of in-vacuum motors Fabricate prototype Bench test (accuracy) and APS(?)/FFTB beam test Performance review and plan production Continue x-ray diagnostics R&D Start work on RF BPM (cavity type) Start work on Cherenkov detector

Bingxin Yang Undulator / FEL October 12, 2004 Far-field x-ray diagnostics: essential elements Roll away undulators Spontaneous radiation is most useful when background is clean, with each undulator rolled in individually. Adequate far-field x-ray diagnostics to extract the beam / undulator information: –Electron trajectory in undulators (1  m / 0.25  rad accuracy) –Undulator K-value (  K/K ~ 1.5 × ) –Relative phase of undulators (  ~ 10°) –X-ray intensity measurements (  E/E ~ 0.1%, z-dependent) –Micro-bunching measurements (z-dependent)

Bingxin Yang Undulator / FEL October 12, 2004 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 mono (  E/E ~ 0.1%) Multilayer reflectors Asymmetrically-cut crystals Large dynamic range detector(s)

Bingxin Yang Undulator / FEL October 12, 2004 Effective K measurement with angle- integrated undulator spectrum The angle-integrated spectrum has a distinct, sharp edge at all odd-order harmonics X-ray intensity is very sensitive to effective K changes. For  1  F/F ~ 400  K/K  detect < 6% intensity change. Only 1 – 2 sec. to acquire data How can we make use of this feature to measure effective K?

Bingxin Yang Undulator / FEL October 12, 2004 Angle integrated spectrum is robust Beam of interest is within 35  rad cone angle Spectra independent of aperture size / location as long as the beam is fully contained in the detector. Spectra independent of emittance for adequate aperture.

Bingxin Yang Undulator / FEL October 12, 2004 X-ray intensity fluctuates proportionally with electron bunch charge (10-20%). Electron beam energy jitter (  E/E ~ 0.1%) has the same effect as  K/K! Impact of electron bunch fluctuations!! Differential measurement cancels beam jitter Shoot e-beam through two undulator segments. Intensities of both x-ray beams fluctuate together as e-beam jitters. Taking their difference removes the effect of jitter. Signal is proportional to  K of the two undulator segments. A very high resolution (<10 -5 ) can be obtained.

Bingxin Yang Undulator / FEL October 12, 2004 Differential Measurements of Two Undulators Insert only two segments from the entire undulator. Kick the e-beam to separate the x-rays Use one mono to pick the same x-ray energy Use two detectors to detect the x-ray flux separately Use differential electronics to get the difference in flux

Bingxin Yang Undulator / FEL October 12, 2004 A simulation: input and approach

Bingxin Yang Undulator / FEL October 12, 2004 Differential measurements: simulation Select x-ray energy at the edge (Point A). Record difference in flux from two undulators. Boxcar average of 64 points Peaks for effective K above and below the reference value are distinctly resolved  K/K =  ! We can also use it to detect minor radiation damage!

Bingxin Yang Undulator / FEL October 12, 2004 Generation of coherent x-ray transition radiation (Alex Lumpkin, LCLS diag. & comm. Workshop, 9/04) Coherent XTR peaks ~ 5  rad

Bingxin Yang Undulator / FEL October 12, 2004 CXTR intensity measures micro-bunch fraction (Alex Lumpkin, LCLS diag. & comm. Workshop, 9/04) ~ 10 6 photons/nC saturation

Bingxin Yang Undulator / FEL October 12, 2004 Incoherent XTR to be tested in SPPS in FY05 (Alex Lumpkin, LCLS diag. & comm. Workshop, 9/04)

Bingxin Yang Undulator / FEL October 12, 2004 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  rad or better.

Bingxin Yang Undulator / FEL October 12, 2004 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?

Bingxin Yang Undulator / FEL October 12, 2004 Summary of 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. Developed a differential technique for high resolution measurement of undulator effective K. Developing micro-bunching diagnostics concept and planning initial tests. Developing concept for broadband mono for z- dependent x-ray intensity measurements

Bingxin Yang Undulator / FEL October 12, 2004 R&D plan for x-ray diagnostics in FY05 Test broadband mono elements (  E/E ~ 0.1%) Critical to FEL diagnostics inside / outside of undulator Multi-layer optics and asymmetrically cut crystals Far-field undulator radiation diagnostics Continue to identify suitable spatial-spectral features for FEL start-up x-ray diagnostics Simulation with non-ideal beam and non-ideal field Develop x-ray optics / detector requirements Test core optical components

Bingxin Yang Undulator / FEL October 12, 2004 Conclusions 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 measurements of undulator K-value, x-ray intensity gain, and micro-bunching. Concept for relative measurements of trajectory direction (field quality) and undulator phasing need further development for practical use. Intra-undulator diagnostics design is nearly on-target. Funding delays have had severe impact on prototype schedule.