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McStas: ILL_H13_IN20

[ Identification | Description | Input parameters | Links ]

The ILL_H13_IN20 Instrument

Thermal neutron three-axis spectrometer IN20@ILL (unpolarized configuration)

Identification

Description

IN20 is installed at the H13 thermal beam tube (Phi 170 mm) in the reactor hall.

Both the primary and the secondary spectrometer employ a monochromatic
horizontal focusing geometry. A heavy input slit of an adjustable size, placed
in the casemate, serves as a virtual source, providing a large solid angle for
the monochromatic beam, while reducing, together with a sapphire filter window,
the fast neutron background. The neutron energy is selected either by a doubly
focusing polarizing Heusler 111 monochromator (230 x 150 mm2 w x h) or by an
unpolarised Si 111 monochromator (elastically bent crystals, 195 x 200 mm2 w x
h) free of higher-order contamination in the incident beam at wave-numbers ki >
3 Angs-1. The analysis of the energy and polarisation state of the scattered
neutrons is effectuated by a similar horizontally focusing Heusler crystal
analyzer. Further PG 002 and Si 111 analyzers are available for occasional
unpolarised work.

The energy transfer range accessible in the present configuration of IN20
extends to 100 meV with maximum incident neutron energies reaching 150 meV. The
typical energy widths (FWHM) measured with a reference vanadium sample at the
graphite filter wave-numbers ki = 2.66 A-1 and 4.1 A-1 are 0.82(3) meV and 3.05
(15) meV, respectively.

This model uses two Si111 monochromator and analyzers (unpolarized
configuration).

Input parameters

Parameters in boldface are required; the others are optional.
NameUnitDescriptionDefault
KFAngs-1Outgoing neutron wavevector3
KIAngs-1Incoming neutron wavevector0
QMAngs-1Wavevector transfer in crystal0.5
ENmeVEnergy transfer in crystal0
verbose1print TAS configuration. 0 to be quiet1
WMmWidth of monochromator0.20
HMmHeight of monochromator0.19
RMHmMonochromator horizontal curvature, 0 for flat, -1 for automatic setting-1
RMVmMonochromator vertical curvature, 0 for flat, -1 for automatic setting-1
DMAngsMonochromator d-spacing3.155
NHM1Number of horizontal slabs composing the monochromator15
NVM1Number of vertical slabs composing the monochromator15
WAmWidth of analyzer0.16
HAmHeight of analyzer0.08
RAHmAnalyzer horizontal curvature, 0 for flat, -1 for automatic setting-1
RAVmAnalyzer vertical curvature, 0 for flat, -1 for automatic setting-1
DAAngsAnalyzer d-spacing3.155
NHA1Number of horizontal slabs composing the analyzer15
NVA1Number of vertical slabs composing the analyzer15
L1mSource-Monochromator distance. Contains 1st Collimator of length 5.342.33
ALF1arc minHorizontal collimation from Source to Monochromator60
ALF2arc minHorizontal collimation from Monochromator to Sample A60
ALF3arc minHorizontal collimation from Sample to Analyzer60
ALF4arc minHorizontal collimation from Analyzer to Detector60
BET1arc minVertical collimation from Source to Monochromator120
BET2arc minVertical collimation from Monochromator to Sample A120
BET3arc minVertical collimation from Sample to Analyzer120
BET4arc minVertical collimation from Analyzer to Detector120

Links

  • Source code for ILL_H13_IN20.instr.
  • Rescal for Matlab at http://www.ill.eu/instruments-support/computing-for-science/cs-software/all-software/matlab-ill/
  • Restrax at http://omega.ujf.cas.cz/restrax/

[ Identification | Description | Input parameters | Links ]

Generated on 2023-09-19 20:01:36


Last Modified: Wednesday, 03-Jan-2024 19:59:10 CET
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