McStas - A neutron ray-trace simulation package

McStas is a general tool for simulating neutron scattering instruments and experiments. It is actively supported by DTU Physics, NBI KU, ESS, PSI and ILL.

Simulated scattering from a hollow-cylinder vanadium sample.

The plot shows the intensity of scattered neutrons (red is highest intensity). The sample is at the center of the sphere with the neutron beam coming from the left. Clearly seen is the shadowing effect of the sample causing a lower intensity opposite the beam. Also seen is the effect of the non-symmetric geometry of the sample, causing lower intensity directly above and to the side of the sample.

Recent news

Migrating from McStas 2.x to 3.x? - Use the wiki-based guides

April 6th, 2025: Component doc pages back online

We are now in the air with new server hardware.

Among other things this means that component mcdoc pages are back online - by popular demand!

April 5th, 2025: Ongoing webserver upgrade

We are in the process of upgrading the webserver for McStas, McXtrace and other sites. Please bear with us if you experience service interruptions. :-)

February 19th, 2025: McStas and McXtrace 3.5.24 released

Dear all,
McStas and McXtrace release 3.5.24 is now available - McStas installation instructons on GitHub .

What's Changed

Important note

McStas and McXtrace will soon change organisation-name on GitHub - from McStasMcXtrace -> mccode-dev

User interfaces and tools

[Feature] mcgui/mxgui Let configuration dialogue spawn your EDITOR to edit your local mccode_config.json by @willend in https://github.com/mccode-dev/McCode/pull/1838 (available also by --edit-user-config from mcrun/mxrun)
[Feature] mcrun/mxrun: New switch --cogen to allow on-demand switch to non-standard code generator. See also interoperability with mccode-antlr below by @willend in https://github.com/mccode-dev/McCode/pull/1851
[Feature] mcrun/mxrun Solution for picking up code generator from PATH if not found where expected by @willend in https://github.com/mccode-dev/McCode/pull/1840
[Feature] pygen minor revision: Build importable make() function and call from generic notebook by @willend in https://github.com/mccode-dev/McCode/pull/1827
[Fix] Support Scintilla editor on Debian with Qt6 by @willend in https://github.com/mccode-dev/McCode/pull/1813
[Fix] Drop hard-coded check for PyQt5 by @willend in https://github.com/mccode-dev/McCode/pull/1814
[Fix] No more hidden Perl dependencies! (perl -> python 1-liner readlinkf()) by @willend in https://github.com/mccode-dev/McCode/pull/1824
[Fix] too-restrictive mcdisplay/mxdisplay instrument line parsing by @g5t in https://github.com/mccode-dev/McCode/pull/1834
[Fix] Patches for mcdisplay/mxdisplay in Windows from @LelandWH https://github.com/mccode-dev/McCode/issues/1853

Components and instruments

[Fix] McStas Vertical_bender: Add max iteration criterion for while loop (default 1000). by @willend in https://github.com/mccode-dev/McCode/pull/1815
[Fix] McStas NCrystal_sample: Remove possible out-of-bounds memory access by @g5t in https://github.com/mccode-dev/McCode/pull/1821
[Fix] McStas Elliptic_guide_gravity and Pol_mirror: Minor comp revisions, suppresses compilation warnings from clang by @willend in https://github.com/mccode-dev/McCode/pull/1826
[Fix] McStas SNS_ARCS.instr edits by @willend in https://github.com/mccode-dev/McCode/pull/1838
[Fix] McStas ISIS_IMAT.instr DEPENDENCY " @NEXUSFLAGS@ " added by @willend in https://github.com/mccode-dev/McCode/pull/1839
[Fix] McStas Union_master Adjustment of default parameter by @willend in https://github.com/mccode-dev/McCode/pull/1840
[Fix] McStas Union-related fixes and imports from DMSC school by @willend in https://github.com/mccode-dev/McCode/pull/1841
[Fix] McStas Elliptical_guide_gravity did not work in GROUPS as it always SCATTERS by @mads-bertelsen in https://github.com/mccode-dev/McCode/pull/1843
[Fix] Monitor_nD on GPU: Adjustments for coherence between CPU and GPU particle lists by @willend in https://github.com/mccode-dev/McCode/pull/1816

Core simulation toolkit

[Feature] NeXus: sort comp instances by index and include comp parameter information by @willend in https://github.com/mccode-dev/McCode/pull/1828
[Fix] Increased stability in NeXus x wide MPI by @willend in https://github.com/mccode-dev/McCode/pull/1811
[Fix] Portability, Windows + cl.exe: Remove variable length array allocations for issue #1817 by @g5t in https://github.com/mccode-dev/McCode/pull/1819 and https://github.com/mccode-dev/McCode/issues/1818 by @willend in https://github.com/mccode-dev/McCode/pull/1822

Interfaces and interoperability with other codes

NCrystal

Thanks to @tkittel for ping-pong on this :)
[Feature] McStas 3.5.24 and later now depends on NCrystal 4.0.0 and later. NCrystal is now available also on Windows! by @willend in https://github.com/mccode-dev/McCode/pull/1848 and https://github.com/mccode-dev/McCode/pull/1855

`mccode-antlr`

Thanks to @g5t for ping-pong on this :)
[Feature] mccode-antlr is an alternative code-generator for McStas and McXtrace - a new development by @g5t and based on ANTLR instead of lex/yacc. The new tool is mainly written in python and thus has a lower barrier for changes in language syntax and code generation. The tool implementations mcstas-antlr and mcxtrace-antlr are thus a candidate implementations to potentially replace the classic mcstas and mcxtrace code generators in the future. Current status is that
- McStas: mcstas-antlr is fully feature complete wrt. mcstas for CPU simulations and close to complete for GPU simulations
- McXtrace: Not all instruments will compile using mcxtrace-antlr but basic functionality is in place
- To try:
  1. Install mccode-antlr from conda-forge or via pip
  2. Adapt your configuration to use e.g. mcstas-antlr by
    - Setting the new --cogen=mcstas-antlr option in mcrun
    - Enable or edit the MCCOGEN field of mccode_config.json using the new Save/Edit configuration in mcgui
    - (The antlr tools default to download comps etc. to an internal cache: Add e.g. -I${MCSTAS} to prefer ingredients fromyour local library)
  3. Use the mcrun-antlr/mxrun-antlr tools provided directly by mccode-antlr

Platform support

Debian/Ubuntu
- [Fix] Make hidden numpy dependency explicit also on Debian by @willend in https://github.com/mccode-dev/McCode/pull/1825
- [Fix] McXtrace meta-pkgs for Debian add libgsl-dev as dependency by @farhi in https://github.com/mccode-dev/McCode/pull/185
Windows
- [Feature] NCrystal is now available with McStas on Windows
- [Info] Windows via cross-compiled .exeinstaller from mccode.org: Please place the MCPL-related .bat files from the extras folder in e.g. c:\mcstas-3.5.24\bin to enable MCPL (May require giving your user 'full access' permissions to the bin folder)
- [Info] Windows via conda-forge: MCPL is not yet available but expected during the spring

Full Changelog: https://github.com/mccode-dev/McCode/compare/v3.5.16...v3.5.24

January 8th, 2025: Monte Carlo Satellite to ICNS2025

Dear all,

The ICNS2025 conference is taking place in Copenhagen and Lund this summer, and the abstract submission is closing January 15th - in one week.

Of special interest to McStas users:
A satellite event is being planned for July 11th, arranged by Mads Bertelsen, ESS and Peter Willendrup DTU/ESS. We envision a one-day event with contributed talks on instrument simulation and its use, abstract submission will open soon:

Advanced computer simulations methods for neutron scattering instruments

Abstract:
Neutron scattering relies heavily on computer simulations of neutron scattering instrumentation to optimize their performance. These simulation tools are also evolving to be more relevant for a running facility, aiding in both preparation and analysis for individual experiments. It is even becoming possible to make better decisions during experiments by running simulations in parallel.

All the best and hope to see you this summer in Copenhagen,
Peter Willendrup

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Last Modified: Sunday, 06-Apr-2025 20:25:01 CEST