NSLSII Soft Xray Undulator Beamlines Steve Hulbert NSLSII

NSLS-II Soft X-ray Undulator Beamlines Steve Hulbert NSLS-II User Workshop July 17, 2007 1 BROOKHAVEN SCIENCE

NSLS-II Soft X-ray Undulator Beamlines Steve Hulberta, Dario Arenaa, Cecilia Sánchez. Hankea, and Ruben Reiningerb a. Brookhaven National Laboratory b. Scientific Answers & Solutions, Madison, WI The extremely high brightness of NSLS-II in the soft x-ray range will enable the design and implementation of the next generation of soft x-ray beamlines. These beamlines will have (resolving power) flux (spot size)-1 product considerably greater than is available presently (2007), as well as fast (k. Hz) polarization switching capability. These beamlines can be optimally matched to a broad array of soft x-ray measurement techniques. 2 BROOKHAVEN SCIENCE

NSLS-II Soft X-ray Undulator Beamlines Outline • • • Source properties Example soft x-ray scientific programs & measurement techniques Beamline design, layout, and calculated performance Comparison with other US soft x-ray beamlines Outstanding technical issues Summary 3 BROOKHAVEN SCIENCE

NSLS-II source brightness 4 BROOKHAVEN SCIENCE

Soft x-ray EPU 45 source transverse coherence Vertical, horizontal, and total number of transverse coherent modes contained in the EPU 45 beam as a function of photon energy. 5 BROOKHAVEN SCIENCE

Soft x-ray EPU 45 source brightness Source polarization: linear (horiz. , vert. or any angle in between), circular, or elliptical Higher harmonic interference: use QEPU Soft x-ray mirror reflectivity • s-polarized reflectivity of 30 nmthick candidate mirror/grating coatings. • p-polarized reflectivities are similar at these small grazing angles. • Si substrate • assumed RMS surface roughness 0. 2 nm. 6 BROOKHAVEN SCIENCE

3 D schematic of soft x-ray undulator layout Experimental Station Side view, single beam mode Beam Chopper Plane Mirror Exit Slit Plane Grating EPU Elliptical cylinder KB refocusing mirrors Cylindrical Collimating Mirror EPU Side view, canted beam mode, fast switchable 7 BROOKHAVEN SCIENCE

Possible NSLS-II Soft X-ray Undulator Beamlines High flux High resolution Soft x-ray imaging and coherent scattering Soft x-ray resonant magnetic and inelastic scattering (XRMS, RIXS) Coherent XRMS Imaging RIXS Source for each beamline: Two 2 m-long EPU 45’s located in a 5 m NSLS-II straight section. Operating modes: (1) uncanted and phased as a single 4 m-long EPU 45, or (2) two 2 mlong EPU 45’s, canted by ~0. 25 mrad, for fast-switching polarization capability. 8 BROOKHAVEN SCIENCE

Possible High flux soft x-ray undulator endstations/techniques Coherent imaging endstation: coherent scattering, diffraction, coherent SAXS, diffraction imaging, holography Scientific themes / drivers: mesoscopic (few x 10 nm resolution) imaging, e. g. large cells, and magnetic domains; time correlation spectroscopy of fluctuations in materials; 3 D imaging of granular materials (with grains around 30 nm) Beamline requirements: beam size: ~few m on pinhole resolving power: ~104 flux: > 1013 photons/s on sample Microscopy endstation: STXM, phase contrast scope, full field scope, PEEM, spectro- scopy Scientific themes / drivers: simultaneous spectroscopic (electronic) and microscopic (structural) measurements on nano- and mesoscopic length scales, e. g. of single nano-elements , nano-contacts, or nano-magnets, to understand isolated behavior differences between boundaries/interfaces and bulk Beamline requirements: beam size: STXM: fill 250 m Fresnel zone plate (full transverse coherence), <10 nm x <10 nm on sample; coherent imaging: ~few m on pinhole; PEEM: ~few m on sample resolving power: ~104 flux: STXM: > 1012 photons/s on sample, coherent imaging: > few x 1013 photons/s through pinhole, PEEM: > few x 1013 photons/s on sample 9 Eisebit & Luening, Nature 432, 885 -888 (2004) Magnification Energy and angle selecti Acceleration, focusing and magnification http: //xraysweb. lbl. gov/peem 2 /PEEM 2 -02. html BROOKHAVEN SCIENCE

Possible High resolution soft x-ray undulator endstations/techniques XRS, XRMS (x-ray resonant [magnetic] scattering) endstation Scientific themes / drivers: ordering phenomena in correlated electron systems, magnetic & spintronic materials/devices, nanomagnetism, “soft” materials (C, N, O) Beamline requirements: - small spot size (small crystals, grazing incidence geometry) - high energy resolution (select different multiplet states) - high flux (detect weak, diffuse features in scattered beam) RIXS (resonant inelastic x-ray scattering) endstation Scientific themes / drivers: correlated electron materials (low energy excitations, phase transitions, bulk sensitivity), organic molecules (fullerenes, nanotubes) Beamline requirements: - small spot size (collect large solid angle, possibly no entrance slit) - very good energy resolution (precise selection of initial state) - highest flux possible (very low inelastic cross section) 10 BROOKHAVEN SCIENCE

Soft x-ray beamline design: VLS PGM illuminated by collimated light Possible planar M 1 • Rapid Switching: change M 2 and M 4 Side View Beamline High resolution High flux Source to M 1 27 m 30 m M 1 to M 2 1 m 1 m M 2 to M 3 PGM design M 2 to grating ~2 m Grating to exit slit 20 m 10 m Exit slit to M 4 1. 85 m M 4 to M 5 0. 5 m M 5 to sample 1. 0 m Total 53. 35 m 46. 35 m • 11 Horizontal Focusing by M 4 -52: 1 BROOKHAVEN SCIENCE

and divergence Sample spot size h =200 e. V: h=2. 3 m, v=1. 1 m h =1000 e. V: h=2. 1 m, v=1. 1 m Req’d figure error • • h =200 e. V: h’=1. 1 mrad, v’=0. 44 mrad h =1000 e. V: h’=0. 8 mrad, v’=0. 3 mrad 100 nrad RMS planes 0. 5 rad RMS Elliptical, cylinder meridional 12 BROOKHAVEN SCIENCE

Calculated flux & resolving power High resolution beamline 1010’s @ 105 rp; 1012’s @ 104 rp High flux beamline 1012’s @ 2 104 rp; 1013’s @ 5 103 rp Each soft x-ray undulator beamline would be equipped with at least 3 gratings, interchangeable under computer control 13 BROOKHAVEN SCIENCE

Spot sizes on sample, dual (canted) undulator beams Near, e. g. LCP, beam Far, e. g. RCP, beam h =200 e. V: h=2. 2 m, v=1. 1 m h =1000 e. V: h=2. 4 m, v=1. 1 m h =200 e. V: h=2. 6 m, v=1. 1 m h =1000 e. V: h=2. 0 m, v=1. 1 m To ensure complete overlap, defocus and/or trim with baffles 14 BROOKHAVEN SCIENCE

Comparisons of selected soft x-ray beamlines in the US 15 BROOKHAVEN SCIENCE

Sensitivity to electron beam motion Overall conclusions for soft x-ray beamlines: • • • Spectroscopy and diffraction experiments in the soft x-ray range are very forgiving: 10% criterion (in both position and angle) is sufficient for spectroscopy and scattering Imaging is another story (c. f. Chris Jacobsen) • STXMs/nanoprobes are very demanding on beam stability. • EPU 45 beam is ~7 modes horiz. by ~1 mode vert. The horiz. overfilling provides some tolerance to beam motion. The lack of vert. overfilling will require more stability than is now needed at NSLS and even APS, ALS. • Must have very stable flux on timescales of 0. 01 -100, 000 Hz, in order to match faster scan rates possible with high brightness beam • On that timescale, must have stability in flux to 1: 104 or better for transmission experiments (conclusion: need to use appropriatelydesigned I 0 normalization) Switched EPU with mechanical chopper: systematic differences between fixed sources and very stringent beamline alignment tolerances; hard to match source profiles– may end up using switched ID with subsequent stability requirements 16 BROOKHAVEN SCIENCE

Sensitivity to Horizontal Beam Motion: Large Demagnification Helps • NSLS-II: small divergence (~15 rad vert. , ~20 rad hor. @1000 e. V) Element Position From Source M 1 28 m M 2 ~29 m Grating ~30 m Exit Slit 50 m M 3 51. 8 m M 4 52. 3 m Sample 53. 3 m • CDR concept: no horizontal focusing until after exit slit (M 3) • Effective horizontal demagnification: ~50: 1 • Sample position: 4 - spot size ~ 4 mm (v) x 8 mm (h) • 3 m (10% of beam size) beam motion (horizontal) 0. 06 m beam motion on sample • Beam spot insensitive to vertical motion (imaging exit slit) 17 BROOKHAVEN SCIENCE

Sensitivity to Vertical Source Motion: Effect on Photon Energy Resolution Ultra-High Resolution (UHR, 3600 l / mm) UHR HF 1000 e. V Beamline Resolution Energy Shift 4 m beam motion High Flux (HF, 400 l / mm) HF 200 e. V (300 l/mm) UHR 200 e. V 11 me. V 114 me. V 21 me. V 0. 89 me. V 11 me. V 0. 08 me. V 18 (300 l/mm) BROOKHAVEN SCIENCE

Sensitivity to Beam Divergence (Angular) Motion At hv = 100 e. V: v’ ~ 40 rad, h’ ~ 45 rad • 10% values: ~ 4 rad (vert. ), ~ 4. 5 rad (hor. ) At hv = 2000 e. V: v’ ~ 10 rad, h’ ~ 20 rad • 10% values: ~ 1 rad (vert. ), ~ 2 rad (hor. ) • Dk ~ k * sin q ; Dk / k ~ sin q • Contribution to uncertainty of wavevector from beam angular motion is on order few parts in 106 (i. e. nada) 19 BROOKHAVEN SCIENCE

Technological issues (1) • • • For resolution and spot size, need better than 2007 state-ofthe-art mirror (and grating blank) figure, as well as extremely good finish • Require 100 nrad figure error on planar optics (M 3, VLS grating) • Require 0. 5 rad meridional figure error on cylinders (M 2) and plane ellipticals (M 4, M 5) For ultra-high resolution spectroscopy, need better than 2007 state-of-the-art in VLS PGM motion precision/accuracy/repeatability For optimum performance, alignment of optical elements, exit slit, and polarization chopper must be performed more accurately than has been required to date 20 BROOKHAVEN SCIENCE

Technological issues (2) • Thermal loading on M 2 and/or M 3 may be too high to maintain req’d figure error; solution is a combination of: • Insertion of planar first mirror (M 1) at more grazing angle of incidence than M 2 • LN 2 cooling of M 3 Power density absorbed by M 3 when the ID is tuned to 200 e. V in linear polarization mode and the mirror is tuned to the same energy with the VHR grating. Power density absorbed by M 2 when the 4 m-long EPU 45 is tuned to 200 e. V in linear polarization mode. 21 BROOKHAVEN SCIENCE

NSLS-II Soft X-ray Undulator Beamlines • • • Ultra-high-brightness NSLS-II accelerator design is well matched to the high-resolution, high-flux, polarizationswitchable, soft x-ray beamline design presented here. These beamlines will have (resolving power) flux (spot size)-1 product considerably greater than is available presently (2007), plus fast (k. Hz) polarization switching capability. Example soft x-ray scientific programs are well matched to this beamline design: XRMS, RIXS, imaging, coherent scattering. User groups (BATs) would be expected to define the mission of the NSLS-II soft x-ray beamlines, and carry out their detailed design, construction and operation. Successful implementation requires R+D in one major area: Next generation improvement in mirror figure and finish 22 BROOKHAVEN SCIENCE