A FIXED EXIT BEAM X-RAY MONOCHROMATOR FOR THE XACT FACILITY Carlo Pelliciari¹ (1) Osservatorio Astronomico G.S Vaiana, Palermo

What I am going to show An example of monochromator XACT facility present configuration: vacuum system, X ray source, monochromator. The Bragg law Perfect, mosaic and doped crystals, multilayers Monochromators double “reflection” The Project: configuration and technical characteristic Monochromator elements: crystals (perfect, mosaic, organic), multilayers, gratings Expected performances Conclusions

A monochromator is… …un attrezzo usa e getta (mono-uso) per cromare un’autovettura, una bici o quello che ti pare…ma una sola volta* *…A tool (use it once and throw it out) that permits one to plate a car or a bike with a chromium (it doesn’t matter) but only once…

A monochromator system What is it? It is a light-dispersing instrument which is used to obtain electromagnetic radiation of substantially one wavelength or at least of a very narrow band of the spectrum. Filters calibration Test for X ray optics Detector characterization

XACT Facility, vacuum beamline m 18 meter distance between x-ray source and test chamber. The beam travels in vacuum (10 -6 mbar) The vacuum system consists of several tubes with diameter varying from 150 mm up to 630 mm in order to minimize the air volume and thus the pumping time. Each section has a side port that permits to use it as a chamber test. Main test chamber: 1 meter long x 1 meter diameter. It can be isolated from the pipe by sliding gate valve. A clean room class 1000 is located at the end of the vacuum system. X ray source Test chamber

XACT Facility, the X ray source The X ray source is a multi anode system mounting up to 6 anodes and 4 filters that can be selected without breaking the vacuum. It is low power consuming, so it does not require anode cooling system. Flux = meters. The source produces 2 orthogonal beams. The second one is used to monitor the flux. The X ray source has a radius smaller then 0.1 mm. The laboratory has several anodes in order to cover the energy range keV: Cu(0.93; 8.04), Fe(6.4), Cr(5.41), Ti(4.51), Al(1.49), C (0.28) …

XACT Facility, the monochromator Original X ray white beam (before interaction with the grating) Monochromatic X-ray beam (after interaction with the grating) advantagesdisadvantage Grating (1000 lines/mm) E < 2 keV; Monochromatic beam can be obtained from the continuum. low efficiency (10%) No fixed exit, Image distorted. filters Fixed exit. Image of the source is not distorted Only the K fluorescence lines available

40 mm MCP (detector) 150 mm Linear stage 1 (direct beam) 22 150 mm 75 mm  x = 150 mm * tan (2  ) Slit 2 Slit 1 Rotational stage Source direction 55 Linear stage 2 (reflected beam)  Mirror sample Direct Beam Reflected Beam Mirror testing apparatus 1-st order Background 40 mm

The new monochromator system for the XACT facility Key features: 1.The system will provide a monochromatic beam for the full energy range: 0.1 up to 20 keV; 2.Energy resolution:  E / E = 10% ; 3.Fixed position of the monochromatic beam for all energies ; 4.Compatible vacuum mbar; 5.Beam section: 60 x meters.

Bragg’s law (crystals, multilayers) n = 2d sin  d = distance between atomic layers in crystal or bi-layer thickness in a multilayer  = wavelength of the incident X-ray beam n = diffraction order (integer);  grazing incidence angle; Bragg’s law defines the angle for constructive interference in the wave scattered by the crystal lattice. A multilayer consists of many alternating layers of high and low Z materials (ex. W/Si). The multilayer diffraction pattern is also described by Bragg’s law.

Perfect, mosaic and doped crystals (1) Perfect crystals: high efficiency, high resolution, low integrated reflectivity Mosaic crystals: Focusing properties, low transmission, low resolution, high integrated reflectivity. Doped crystals: Low resolution, high integrated reflectivity.

Perfect and mosaic crystals (2) Graphite, 10 keV, HOPG,  = 0.3°, FWHM= 600 eV Silicon, 20 keV, mosaic,  = 60”, FWHM= 90 eV Graphite, 10 keV, mosaic  = 3°, FWHM= 2 keV Silicon, 20 keV, perfect; FWHM= 3 eV

h Double reflection monochromators Configuration Laue-Bragg: 2 orthogonal elements in a monolithic structure. w = 2 h. h Channel cut: 2 or more elements etched in a monolithic structure. w = 2 h cos  ; rotation center

Fixed exit double diffraction monochromator The system consists of 2 monochromators. The incoming beam always hits crystal 2 in the same position. Crystal 2 translates orthogonally to its surface. Crystal 1 moves to intercept the beam. w = h sin(2  )/(sin  cos  ) = 2 h = w l w = l sin(2  ) l = p / sin  P = h / cos 

Choice of the configuration Systems advantagedisadvantage Channel cut Small, simple and inexpensive mechanical system. Exit not fixed. 1) complex machining 2) several and 3) large monolithic elements to cover the energy range LB Fixed exit. Small mechanical system. 1) piezoelectric 2) complex machining 3) several and 4) large monolithic elements to cover the energy range fixed exit separated crystals Versatile, up to 6 monochromators. Fixed exit. Mechanical system quite complex (8 axes). Large size.

Monochromator Project (1) Mechanical system : # 1 rotating stage for the rotation of the entire system. Res: 0.001° # 2 translation stages for the crystals position. Resolution 1  m. # 4 rotating stages for crystals alignment. # 1 translation stage to align and translate crystal 1. # 2 holders with 6 faces. # 1 translation stage for the collimator system. Res:1  m.

Monochromator Project (2)

Monochromator Project (3) The monochromator will be mounted in a vacuum chamber 1 meter from the X-ray source.

Monochromator elements Energy range: from 10 up to 20 keV few fluorescence lines continuum Energy range: from 0.1 up to 10 keV fluorescence lines; We investigated several materials as candidate for monochromators with different geometry (flat, concave and convex with different curvature radius). Monochromator/energy (keV) Graphite mosaic 0.4° Graphite mosaic 3.5° Silicon, Germanium mosaic 120” TlAP (organic) Multilayers ( Mo/Si, W/Si) Gratings ?

Multilayers (100 – 600 eV) Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 1.[AlO3(2.5 nm)/V(1.9 nm)]x 100 on V [ eV] 2.[AlO3(2.5 nm)/V(2.0 nm)]x 100 on V [ eV] 3.[Cr(0.76 nm)/Sc(0.86 nm)]x 200 on Cr [ eV] 4.[ Mo(3.5 nm)/Si(4.5 nm)]x 100 on Mo [ eV] 5.[ Mo(5.5 nm)/Si(4.5 nm)]x 100 on Mo [ eV] 6.[ Ni(2.5nm)/C(2.5nm)]x 200 on Ni [ eV] 7.[ Ni(1.2 nm)/C(2.8 nm)]x 200 on Ni [ eV] 8.[ W(3.0 nm)/Si(4.5 nm)]x 100 on W [ eV]

Organic crystals KAP, TlAP and RbAP crystals are based on the chemical structure of o-phtalic acid (Acid Phthalates [C6H4(COOH)2]). Crystallographic structure: orthorhombic (a  b  c;  =  =  = 90°). TlAP (001) : Thallium Acid Phthalates (CO2HC6H4CO2Tl); cell parameters (Å): a=6.63, b=10.54, c=12.95; 25.9 Å; RbAP (001) : Rubidium Acid Phthalates (CO2HC6H4CO2Rb ); cell parameters (Å): a=6.55, b=10.02, c= ; 2d = Å; KAP (001) : Potassium Acid Phthalates (CO2HC6H4CO2K); cell parameters (Å): a=6.46, b=9.61, c=13.32; 2d = Å;

Graphite, Silicon and Germanium Graphite, has an hexagonal structure (a 1 =a 2 = Å, c = Å). It grows with a very high mosaic degree (4°) After manipulation it is possible to have HOGP (high oriented pyrolytic graphite) with 0.4°. Low efficiency and resolution, high intensity. Silicon (a= Å ) and Germanium (a= Å ) have diamond crystallographic structure. It is possible to introduce a mosaic structure (2 arcmin mosaic = 0.03°) with several method (lapping, doping). High efficiency and resolution, low intensity. diamond hexagonal

Simulation results  = standard deviation of mosaic distribution;  =  ;  B = Bragg angle; r concave/convex = curvature radius 1 st and 2 nd crystal; xl z dim: z crystal dimension (mm); xls prj: crystal dimension projection (seen from source) div (rad): angular spread

Beam features: Graphite

Conclusions Mechanical system: the components are ordered and they will arrive soon. We plan to mount the system next month and to have the first test in January The system will be driven remotely. Monochromator elements: we are able to cover the full energy range; we are still analysing other materials in order to optimise the monochromator system. Contacts: Service d'Astrophysique (SAp), CEA, Saclay, France Laboratorio Astrofisica Alte Energie, Dip. Fisica, Ferrara, Italy (HOPG). ESRF, Grenoble, France (Silicon). Oss. Astronomico di Brera, Merate, Lecco, Italy, (multilayers). IMEM CNR, Fontanini, Parma, Italy (Silicon, Yttrium tungstate…).