- Email: [email protected]
The concept of the new small-angle scattering instrument SANS-1 at the FRM-II
ARTICLE IN PRESS
Physica B 385–386 (2006) 1174–1176 www.elsevier.com/locate/physb
The concept of the new small-angle scattering instrument SANS-1 at the FRM-II Ralph Gillesa,, Andreas Ostermanna, Christian Schanzerb, Bernhard Krimmera, Winfried Petrya a
Technische Universita¨t Mu¨nchen, Lichtenbergstr. 1, 85747 Garching near Munich, Germany b Paul Scherrer Institut, 5232 Villigen, Switzerland
Abstract The new small-angle scattering instrument SANS-1, a project of the Technische Universita¨t Mu¨nchen, the Universita¨t Go¨ttingen, the GKSS Research Centre and other collaboration partners is currently set up at the new neutron source Heinz Maier-Leibnitz (FRM-II) in Garching near Munich. This contribution describes the concept and the technical features of the instrument. The first task was to implement the instrument concept within the suite of instruments in the neutron guide hall of the FRM-II. Monte Carlo simulations were performed to optimise the neutron guide with respect to the available space for the instrument and the possibility to include components later in a flexible way. The advantage of the installed vertical S-shaped neutron guide will be compared to a standard single-curved neutron guide. A sharp wavelength cut off and a more homogeneous divergence distribution with higher intensity for neutrons with small wavelengths are important improvements. r 2006 Elsevier B.V. All rights reserved. PACS: 61.12.Ex; 28.41.Rc; 02.70.Uu Keywords: Small-angle scattering; Neutron instrumentation; Monte Carlo simulations
1. Concept of the instrument SANS-1 The new small-angle scattering instrument SANS-1 is currently built at the new neutron source Heinz MaierLeibnitz (FRM-II) of the Technische Universita¨t Mu¨nchen. Monte Carlo simulations with the program MCSTAS [1] have been carried out to optimise the neutron guide system and optical components. Fig. 1 shows a schematic drawing of the instrument. The neutron guide starts at the cold source with a straight neutron guide (partly coated with m ¼ 2) which is followed by a vertically S-shaped guide section. The cross section of the neutron guide is 50 50 mm2 . A consequence of the vertically S-shaped neutron guide [2,3] is an increased height of the neutron beam centre to 1.57 m, which allows easier handling of the sample environment. Actually the S-shaped neutron guide Corresponding author. Tel.: +49 89 289 14683; fax: +49 89 289 14666.
E-mail address: [email protected] (R. Gilles). 0921-4526/$ - see front matter r 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.physb.2006.05.403
ends at the beginning of the neutron guide hall. This concept has the advantage to dump fast neutrons still inside the tunnel of FRM-II which provides ideal shielding. The next component of the concept is a selector tower with two selectors to choose from (one for high intensity with Dl=l ¼ 11% to another one for high resolution with Dl=l ¼ 6%) and a third position for a neutron guide segment. A polarization device will be installed prior to the collimation system. To guarantee high polarization and transmission over a wavelength range of 4 to 20 A˚ two V-shaped transmission polarizer are planned with different angles of the polarizer planes with respect to the neutron beam direction. The collimation system will consist of seven segments. Each segment houses four selectable positions filled with i.e. neutron guides, apertures, optical elements like lenses, laser etc. including a position for future developments. The space at the sample position is planned with 1.2 m to ensure flexible installation of sample environments. To cover a wide Q-range (Qmin o102 nm1
ARTICLE IN PRESS R. Gilles et al. / Physica B 385–386 (2006) 1174–1176
1175
Fig. 1. Schematic drawing of the new SANS-1 instrument at the FRM-II in Garching.
1e+08
neutron flux [a.u.]
flux at sample position [a.u.]
100.0
10.0
1.0
6e+07 -50
0.1
0
5
10
15
20
100.0
flux at sample position [a.u.]
8e+07
-25 0 25 position [mm]
50
-50
-25 0 25 position [mm]
50
Fig. 3. Intensity distribution at the end of the collimation system with guide (18 m) of a horizontal single curved neutron guide (open circles) and of a vertical S-shaped neutron guide (closed circles). Left: Sum along the horizontal direction for the S-shaped guide and the vertical direction for the single curved guide. Right: Sum along the vertical direction for the S-shaped guide and along the horizontal direction for the single curved guide. A wavelength of 4:7 A˚ was used in the simulation.
10.0
2. Results and discussion of Monte Carlo simulations 1.0
0.1
0
5
10
15
20
wavelength [Å]
Fig. 2. Comparison of intensity versus wavelength between a single curved (open circles) and a S-shaped (closed circles) neutron guide. Top: The collimation part (18 m) contains a neutron guide of Ni58 . Bottom: The collimation part contains 50 50 mm2 apertures.
and Qmax 16 nm1 ) an area detector of 1 1 m2 will be used. In addition the detector can be translated horizontally by 0.5 m perpendicular to the beam direction along the whole detector tube.
For the neutron guide system Monte Carlo simulations have been carried out. A comparison of different neutron guide systems (a standard horizontally single curved guide with radius r ¼ 1210 m and Ni58 coating and a vertical S-shaped type r ¼ 480 m with coatings of Ni58 and supermirrors with m ¼ 2) shows a few advantages for the S-shaped neutron guide. The latter neutron guide provides a sharp wavelength cut off at lc 3 A˚ for a collimation part with neutron guide and apertures as well (Fig. 2). Single curved neutron guides transport these undesired neutrons below 3 A˚ to the selector position where background will be generated. Figs. 3 and 4 show the intensity and divergence distribution for the two types of neutron guides. The difference in the intensity distribution is small with a slightly higher intensity (5%) at the sample position for the S-shaped neutron guide. The asymmetry in the intensity distribution (Fig. 3) due to the curvature is very similar for both guide systems. A more pronounced
ARTICLE IN PRESS R. Gilles et al. / Physica B 385–386 (2006) 1174–1176
1176
neutron flux [a.u.]
1.5e+08
1e+08
5e+07
0 -1.5
-1
-0.5 0 0.5 divergence [°]
1
-1.5
-1
-0.5 0 0.5 divergence [°]
1
Fig. 4. Divergence distribution at the end of the collimation system with guide 18 m of a horizontal single curved neutron guide (left) and of a vertical S-shaped neutron guide (right) for the horizontal divergence (triangles, dashed line) and the vertical divergence (circles, solid line). A wavelength of 4:7 A˚ was used in the simulation.
difference is visible in the divergence profiles (compare Fig. 4). The standard single curved guide shows a clear asymmetry between the horizontal and vertical divergence. Even with two sample apertures (+ ¼ 10 mm, collimation
length 1 m) in front of the sample this asymmetry is still present and leads to an anisotropy. Last but not least only the vertical S-shaped guide allows an adequate positioning of the instrument in the neutron guide hall. All simulations include the real illumination from the cold source of the FRM-II, the proper neutron guide cross section, the desired coatings of enriched 58Ni and supermirror with m ¼ 2 and the required space for neighbour instruments. A standard selector of company EADS for high intensity ðDl=l ¼ 11%Þ with 72 lamellae, screwing angle of 48:3 and maximum selector speed at 4:5 A˚ was used in the Monte Carlo simulations. This concept aims to realise the most powerful SANS instrument.
References [1] K. Lefman, K. Nielsen, Neutron News 10 (1999) 20. [2] R. Gilles, C. Schanzer, W. Petry, G. Eckold, Proceedings of German Neutron Scattering Conference, Dresden, 2004. [3] R. Gilles, C. Schanzer, W. Petry, G. Eckold, Proceedings of CANSASIV Meeting, 2004, May 12–14th, RAL: Chilton, Didcot, Oxfordshire, England.
Physica B 385–386 (2006) 1174–1176 www.elsevier.com/locate/physb
The concept of the new small-angle scattering instrument SANS-1 at the FRM-II Ralph Gillesa,, Andreas Ostermanna, Christian Schanzerb, Bernhard Krimmera, Winfried Petrya a
Technische Universita¨t Mu¨nchen, Lichtenbergstr. 1, 85747 Garching near Munich, Germany b Paul Scherrer Institut, 5232 Villigen, Switzerland
Abstract The new small-angle scattering instrument SANS-1, a project of the Technische Universita¨t Mu¨nchen, the Universita¨t Go¨ttingen, the GKSS Research Centre and other collaboration partners is currently set up at the new neutron source Heinz Maier-Leibnitz (FRM-II) in Garching near Munich. This contribution describes the concept and the technical features of the instrument. The first task was to implement the instrument concept within the suite of instruments in the neutron guide hall of the FRM-II. Monte Carlo simulations were performed to optimise the neutron guide with respect to the available space for the instrument and the possibility to include components later in a flexible way. The advantage of the installed vertical S-shaped neutron guide will be compared to a standard single-curved neutron guide. A sharp wavelength cut off and a more homogeneous divergence distribution with higher intensity for neutrons with small wavelengths are important improvements. r 2006 Elsevier B.V. All rights reserved. PACS: 61.12.Ex; 28.41.Rc; 02.70.Uu Keywords: Small-angle scattering; Neutron instrumentation; Monte Carlo simulations
1. Concept of the instrument SANS-1 The new small-angle scattering instrument SANS-1 is currently built at the new neutron source Heinz MaierLeibnitz (FRM-II) of the Technische Universita¨t Mu¨nchen. Monte Carlo simulations with the program MCSTAS [1] have been carried out to optimise the neutron guide system and optical components. Fig. 1 shows a schematic drawing of the instrument. The neutron guide starts at the cold source with a straight neutron guide (partly coated with m ¼ 2) which is followed by a vertically S-shaped guide section. The cross section of the neutron guide is 50 50 mm2 . A consequence of the vertically S-shaped neutron guide [2,3] is an increased height of the neutron beam centre to 1.57 m, which allows easier handling of the sample environment. Actually the S-shaped neutron guide Corresponding author. Tel.: +49 89 289 14683; fax: +49 89 289 14666.
E-mail address: [email protected] (R. Gilles). 0921-4526/$ - see front matter r 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.physb.2006.05.403
ends at the beginning of the neutron guide hall. This concept has the advantage to dump fast neutrons still inside the tunnel of FRM-II which provides ideal shielding. The next component of the concept is a selector tower with two selectors to choose from (one for high intensity with Dl=l ¼ 11% to another one for high resolution with Dl=l ¼ 6%) and a third position for a neutron guide segment. A polarization device will be installed prior to the collimation system. To guarantee high polarization and transmission over a wavelength range of 4 to 20 A˚ two V-shaped transmission polarizer are planned with different angles of the polarizer planes with respect to the neutron beam direction. The collimation system will consist of seven segments. Each segment houses four selectable positions filled with i.e. neutron guides, apertures, optical elements like lenses, laser etc. including a position for future developments. The space at the sample position is planned with 1.2 m to ensure flexible installation of sample environments. To cover a wide Q-range (Qmin o102 nm1
ARTICLE IN PRESS R. Gilles et al. / Physica B 385–386 (2006) 1174–1176
1175
Fig. 1. Schematic drawing of the new SANS-1 instrument at the FRM-II in Garching.
1e+08
neutron flux [a.u.]
flux at sample position [a.u.]
100.0
10.0
1.0
6e+07 -50
0.1
0
5
10
15
20
100.0
flux at sample position [a.u.]
8e+07
-25 0 25 position [mm]
50
-50
-25 0 25 position [mm]
50
Fig. 3. Intensity distribution at the end of the collimation system with guide (18 m) of a horizontal single curved neutron guide (open circles) and of a vertical S-shaped neutron guide (closed circles). Left: Sum along the horizontal direction for the S-shaped guide and the vertical direction for the single curved guide. Right: Sum along the vertical direction for the S-shaped guide and along the horizontal direction for the single curved guide. A wavelength of 4:7 A˚ was used in the simulation.
10.0
2. Results and discussion of Monte Carlo simulations 1.0
0.1
0
5
10
15
20
wavelength [Å]
Fig. 2. Comparison of intensity versus wavelength between a single curved (open circles) and a S-shaped (closed circles) neutron guide. Top: The collimation part (18 m) contains a neutron guide of Ni58 . Bottom: The collimation part contains 50 50 mm2 apertures.
and Qmax 16 nm1 ) an area detector of 1 1 m2 will be used. In addition the detector can be translated horizontally by 0.5 m perpendicular to the beam direction along the whole detector tube.
For the neutron guide system Monte Carlo simulations have been carried out. A comparison of different neutron guide systems (a standard horizontally single curved guide with radius r ¼ 1210 m and Ni58 coating and a vertical S-shaped type r ¼ 480 m with coatings of Ni58 and supermirrors with m ¼ 2) shows a few advantages for the S-shaped neutron guide. The latter neutron guide provides a sharp wavelength cut off at lc 3 A˚ for a collimation part with neutron guide and apertures as well (Fig. 2). Single curved neutron guides transport these undesired neutrons below 3 A˚ to the selector position where background will be generated. Figs. 3 and 4 show the intensity and divergence distribution for the two types of neutron guides. The difference in the intensity distribution is small with a slightly higher intensity (5%) at the sample position for the S-shaped neutron guide. The asymmetry in the intensity distribution (Fig. 3) due to the curvature is very similar for both guide systems. A more pronounced
ARTICLE IN PRESS R. Gilles et al. / Physica B 385–386 (2006) 1174–1176
1176
neutron flux [a.u.]
1.5e+08
1e+08
5e+07
0 -1.5
-1
-0.5 0 0.5 divergence [°]
1
-1.5
-1
-0.5 0 0.5 divergence [°]
1
Fig. 4. Divergence distribution at the end of the collimation system with guide 18 m of a horizontal single curved neutron guide (left) and of a vertical S-shaped neutron guide (right) for the horizontal divergence (triangles, dashed line) and the vertical divergence (circles, solid line). A wavelength of 4:7 A˚ was used in the simulation.
difference is visible in the divergence profiles (compare Fig. 4). The standard single curved guide shows a clear asymmetry between the horizontal and vertical divergence. Even with two sample apertures (+ ¼ 10 mm, collimation
length 1 m) in front of the sample this asymmetry is still present and leads to an anisotropy. Last but not least only the vertical S-shaped guide allows an adequate positioning of the instrument in the neutron guide hall. All simulations include the real illumination from the cold source of the FRM-II, the proper neutron guide cross section, the desired coatings of enriched 58Ni and supermirror with m ¼ 2 and the required space for neighbour instruments. A standard selector of company EADS for high intensity ðDl=l ¼ 11%Þ with 72 lamellae, screwing angle of 48:3 and maximum selector speed at 4:5 A˚ was used in the Monte Carlo simulations. This concept aims to realise the most powerful SANS instrument.
References [1] K. Lefman, K. Nielsen, Neutron News 10 (1999) 20. [2] R. Gilles, C. Schanzer, W. Petry, G. Eckold, Proceedings of German Neutron Scattering Conference, Dresden, 2004. [3] R. Gilles, C. Schanzer, W. Petry, G. Eckold, Proceedings of CANSASIV Meeting, 2004, May 12–14th, RAL: Chilton, Didcot, Oxfordshire, England.