PAC for Condensed Matter Physics A proposal for a bent neutron guide at beam line 7A of the modernized fast pulsed reactor IBR-2M for the diffractometers EPSILON-MDS and SKAT Christian Scheffzük Frank Laboratory of Neutron Physics Dubna & FU Berlin PAC for Condensed Matter Physics Dubna, April 16, 2007 1/23

outline scientific subject instrumentation at beamline 7A: EPSILON-MDS SKAT neutron guide at present state new neutron guide: requirements simulations conclusions 2/23

mainly investigation of geological samples: scientific subject mainly investigation of geological samples: - better understanding of deformation processes - strain-stress distributions / redistibutions - formation of texture as a result of applied stresses - texture / strain relation EPSILON-MDS: - in-situ applied strain - residual strain distribution - surface strain - acoustic emission during deformation processes SKAT: - bulk texture determination - in-situ texture changes - deconvolution of deformation history 3/23

beam layout at channel 7A 4/23

Experimental hall with neutron diffractometers EPSILON SKAT NSWR NERA 5/23

The EPSILON-MDS strain/stress diffractometer 3He detectors and preamplifiers sample goniometer 6/23

SKAT at present by Ullemeyer, K. 7/23

Intended improvement of SKAT by Ullemeyer, K. 8/23

Present state of the neutron guide construction of the neutron guide in the mid-eighties the neutron guide is straight starts at a long distance from the surface of the moderator ( > 6 m distance) 9/23

Present state of the neutron guide construction of the neutron guide in the mid-eighties the neutron guide is straight starts at a long distance from the surface of the moderator ( > 6 m distance) d. the neutrons have to fly a path through between moderator and neutron guide head e. misfit of the moderator surface size ([HxW]: 270 x 200 mm2) and the cross section of the neutron guide ([HxW]: 170 x 50 mm2) 10/23

Moderator size and neutron guide cross section distance: moderator – neutron guide: 6 m limitation by: Liouville-Theorem: beam cross section x beam divergency = const. 11/23

Present state of the neutron guide construction of the neutron guide in the mid-eighties the neutron guide is straight starts at a long distance from the surface of the moderator ( > 6 m distance) the neutrons have to fly a path through between moderator and neutron guide head misfit of the moderator surface size ([HxW]: 270 x 200 mm2) and the cross section of the neutron guide ([HxW]: 170 x 50 mm2) f. at a distance of about 47 m from the moderator is an interrupt (pillar) -> gap g. misfit of beam cross section and sample dimensions 12/23

Neutron guide and sample dimensions 13/23

Neutron intensity distribution view to the neutron source by Churakov, A.V. & Bogdsel, A.A. 14/23

Present state of the neutron guide construction of the neutron guide in the mid-eighties the neutron guide is straight starts at a long distance from the surface of the moderator ( > 6 m distance) the neutrons have to fly a path through between moderator and neutron guide head misfit of the moderator surface size ([HxW]: 270 x 200 mm2) and the cross section of the neutron guide ([HxW]: 170 x 50 mm2) at a distance of about 47 m from the moderator is an interrupt (pillar) -> gap low neutron flux => the experimental possibilities by improved diffractometers can not be used to full capacity 15/23

Basic requirements for the new neutron guide improvement of the resolution (low divergency) b) increasing of the neutron flux at sample position: i) effective use of the interface moderator – neutron guide head for intensity gain ii) adaptation of the neutron guide exit cross section to sample‘s dimensions => splitting of the neutron guide into two sub-beams => different exit cross sections for SKAT: 50 x 50 mm2 EPSILON-MDS: [HxB]: 40 x 5 mm2 iii) neutron guide splitter for beams 7A and 7B c) reduction of the background (removal of the fast neutrons) => bent neutron guide 16/23

Horizontal cross section of the reactor IBR-2M and the environment VII VII VII VIII VIII VIII 2 4 2 1 1 1 2 2 5 3 3 3 at 5.95 m at 6.05 m at 6.0625 m 1 - surface of the orthogonal beam line No. 7 2 - comb-shaped water moderator 3 - pre-moderator 4 - post-moderator 5 - cryogenic mesithylen moderator by Kulikov, S.A. & Shabalin, E.P. 17/23

by Kulikov, S.A. & Shabalin, E.P. Differential neutron density as function of energy and wavelength: beamline 7, IBR-2M by Kulikov, S.A. & Shabalin, E.P. 18/23

Thermal neutron distribution: beam line 7, IBR-2M 0.957 meV 2.1 meV 23.5 meV 5 meV modified after Kulikov, S.A. & Shabalin, E.P. 19/23

Simulations of neutron distribution: beamline 7, IBR-2M E < 0.957 meV 0.957 meV < E < 2.1 meV (a) (b) 2.1 meV < E < 5 meV 5 meV < E < 23.5 meV (c) (d) view from the neutron source by Kulikov, S.A. & Shabalin, E.P. 20/23

I. As conclusion: favourite neutron guide  incident cross section: 50 mm (w) x 125 mm (h) cold source (mesithylen 20 K) neutron flux: 2.3 x 1014 n / (cm2 s)  exit cross section: - EPSILON-MDS: [HxW]: 40 x 5 mm2 - SKAT: 50 x 50 mm2  10 m straight neutron guide (m = 1) ([HxW]: 125 x 50 mm2)  88 m bent neutron guide ([HxW]: 125 x 50 mm2), r = 13,400 m (m=1) - including 10 m „anti-trumpet“ (focusing element) for vertical reduction for the SKAT-neutron guide: condenser: from [HxW]: 125 x 50 mm2 down to 50 x 50 mm2 - at the end: neutron guide segments with lower cross-section for the EPSILON-neutron guide: [HxW]: 40 x 5 mm2  neutron flux: 2.6 x 109 n / (cm2 s)  Divergence: Δα = 0.008 rad. (0.45°), Δβ = 0.016 rad. (0.9°) 21/23

II. As conclusion: geometry of the favourite neutron guide distance, mm horizontal shift : 1.2 m 22/23

Acknowledgement - K. Walther (FU Berlin) A. Frischbutter, F. Schilling (GFZ Potsdam) V.M. Pusenkov, V.A. Ulyanov (PNPI Gatchina) A.I. Ioffe (FZ Jülich) V.V. Zhuravlov, A.V. Churakov, A.A. Bogdsel, S.A. Manoshine, S.A. Kulikov & E.P. Shabalin (JINR Dubna) the BMBF Germany and the FLNP Dubna for support 23/23