[ Identification | Description | Examples | Input parameters | Links ]
Test_Dispersion_relation_TAS InstrumentA simple triple axis spectrometer with a flat PG(002) monochromator and analyzer, operated at fixed final energy. For a given (h, 0, l) and energy transfer dE the instrument calculates the monochromator, sample and analyzer angles, so scans over h, l and dE map the dispersion of the sample, for example a constant energy cut in (h, l) or a dispersion curve in (h, dE). The samples take the scattering vector as Q = k_i - k_f in the sample frame, with h along the sample x axis, k along y and l along z, so the horizontal scattering plane holds h and l. The sample rotation A3 turns (h, 0, l) into the scattering vector set up by the scattering angle A4. sample_choice selects the sample. The phonon samples (0, 1) share the Pb phonon of Phonon_simple, and the magnon samples (2, 3) the MnF2 magnon of SpinWave_BCO: 0: Dispersion_relation reading the phonon files written by generate_phonon_dispersion.py 1: Phonon_simple, the phonon reference 2: SpinWave_BCO, the magnon reference. Its shared functions are prefixed with disp_SBCO_ so it can be in the same instrument as Phonon_simple 3: Dispersion_relation reading the magnon files written by generate_magnon_dispersion.py All samples get the same geometry, absorption, incoherent scattering, Debye-Waller factor and temperature. For the phonon, h and l are in units of 4 pi/a of Pb (a = 4.95 AA): the dispersion files are written on the cube of side a/2, over which the fcc dispersion repeats, and the files hold the cross section for the zone around (1, 0, 1). With primitive_cell = 1, Dispersion_relation instead gets the primitive fcc lattice vectors, a non-orthogonal cell with 60 degree angles, and reads the files written with --cell primitive; h and l keep their units. For the magnon, h, k, l are the MnF2 indices (a = b = 4.873 AA, c = 3.130 AA, along x, y, z for both samples), and (h, l) = (1, 0) is the magnetic zone centre MnF2 (1 0 0). Example: mcrun Test_Dispersion_relation_TAS.instr -M -N 21,21 -n 2e5 h=0.6,1.4 l=0.6,1.4 dE=5 sample_choice=0 The dispersion files are written by the SHELL command below when the instrument is compiled, if they do not exist yet, by generate_dispersion_files.py (Python with numpy).
| Name | Unit | Description | Default |
| h | r.l.u. | Scattering vector component along a* (sample x axis) | 1 |
| l | r.l.u. | Scattering vector component along c* (sample z axis) | 1 |
| dE | meV | Energy transfer to the sample, positive for neutron energy loss | 5 |
| Ef | meV | Fixed final energy selected by the analyzer | 14.7 |
| T | K | Sample temperature | 300 |
| sigma_abs | barns | Absorption cross section of the samples | 0 |
| sigma_inc | barns | Incoherent scattering cross section of the samples | 0 |
| sample_choice | 1 | 0: Dispersion_relation (phonon), 1: Phonon_simple, 2: SpinWave_BCO, 3: Dispersion_relation (magnon) | 0 |
| primitive_cell | 1 | setting this to 1 gives the phonon Dispersion_relation sampling the primitive fcc lattice vectors | 0 |
Test_Dispersion_relation_TAS.instr.
[ Identification | Description | Examples | Input parameters | Links ]
Generated for mcstas 3.9.2