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 systemWhat is it? It is a light-dispersing instrumentwhich is used to obtain electromagneticradiation of substantially one wavelengthor at least of a very narrow band of the spectrum.

Filters calibration

Test for X ray optics

Detector characterization

XACT Facility, vacuum beamline

100 100 100 100 100 200

2020 25 25 30

100

30 35

200

40 50

200

55

200

63

20050

100

100

18 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 sourceTest chamber

XACT Facility, the X ray sourceThe 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 = 105 photons/s/cm2 @ 16 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 0.1- 20 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)

advantages disadvantage

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

150

mm

75 m

mx = 150 mm * tan (2)

Slit 2

Slit 1

Rotational stage

Source direction

5 5

Linear stage 2 (reflected beam)

Mirror sample

Direct Beam

Reflected Beam

Mirror testing apparatus

1-st order

Background

40 m

m

The new monochromator system forthe 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 10-7 mbar;5. Beam section: 60 x 60 cm2 @ 20 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

rotation center

Fixed exit double diffraction monochromatorThe 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

= wl

w = l sin(2) l = p / sinP = h / cos

Choice of the configurationSystems advantage disadvantage

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 elementsEnergy 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)

0.1 0.3 0.5 0.7 1.0 2.0 5.0 10.0 20.0

Graphite mosaic 0.4°

Graphite mosaic 3.5°

Silicon, Germaniummosaic 120”

TlAP (organic)

Multilayers (Mo/Si, W/Si)

Gratings

?

Multilayers (100 – 600 eV)

Figure 1Figure 2Figure 3Figure 4Figure 5Figure 6Figure 7Figure 8

1. [AlO3(2.5 nm)/V(1.9 nm)]x 100 on V [480-520 eV]

2. [AlO3(2.5 nm)/V(2.0 nm)]x 100 on V [480-520 eV]

3. [Cr(0.76 nm)/Sc(0.86 nm)]x 200 on Cr [350-450 eV]

4. [ Mo(3.5 nm)/Si(4.5 nm)]x 100 on Mo [80-160 eV]

5. [ Mo(5.5 nm)/Si(4.5 nm)]x 100 on Mo [80-160 eV]

6. [ Ni(2.5nm)/C(2.5nm)]x 200 on Ni [200-400 eV]

7. [ Ni(1.2 nm)/C(2.8 nm)]x 200 on Ni [150-600 eV]

8. [ W(3.0 nm)/Si(4.5 nm)]x 100 on W [100-120 eV]

Organic crystalsKAP, TlAP and RbAP crystals are based on the chemical structure of o-phtalic acid (Acid Phthalates [C6H4(COOH)2]). Crystallographic structure: orthorhombic (abc; = == 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=13.069.61; 2d = 26.12 Å;• KAP (001) : Potassium Acid Phthalates (CO2HC6H4CO2K); cell parameters (Å): a=6.46 , b=9.61 , c=13.32; 2d = 26.64 Å;

Graphite, Silicon and GermaniumGraphite, has an hexagonal structure (a1=a2=2.4613 Å, c = 6.708 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=5.43095 Å) and Germanium (a=5.64613 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;• = 2.355 ;• B = Bragg angle;• r concave/convex = curvature radius 1st and 2nd crystal;• xl z dim: z crystal dimension (mm);• xls prj: crystal dimension projection (seen from source) • div (rad): angular spread

Beam features: Graphite

ConclusionsMechanical 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 2005. 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…).