December 20th, 2022: Minor update on the new releases

For 2.7.2 users on arm64 macOS - if you downloaded before December 20th:
Yesterday, a small mishap in the macOS Silicon / arm64 release of McStas 2.7.2, it actually contained a set of 3.x binaries and tools.
A fresh build of 2.7.2 for arm64 macOS was immediately uploaded.

For Ubuntu users where your browser can not access the documentation:
Please consult for a solution

For those of you on CentOS (v8):
We have decided to released a last set of packages:
- This will be the last packages released for CentOS and are not offered from the repo - they must be manually installed.

December 12th, 2022: McStas 2.7.2 and McStas 3.2 released

Dear all, A new PAIR of releases of McStas:

are both built and ready for download!

Download and installation instructions are available via our GitHub INSTALL-doc pages.

Selected highlights from the releases are listed below. The full list of changes for both releases is also available at

Please start your migration to 3.x:

- If you are still in trouble, please write us a GitHub issue or an email to

Fixes of issues from last releases:
A good number of issues from the earlier 2.7.1 and 3.1 releases were addressed, see the relevant GitHub issues for details:
Full 2.7.1 issue list
Full 3.1 issue list

Release highligts
(!!3.2 only denotes features or improvements that are 3.2 specific!!)

We still support 64bit Windows 10/11 on Intel, all recent 64bit macOS including 11.x - 13.x Monterey on both Intel and Apple Silicon/M1 processors. Debian/Ubuntu-based distros on Intel and Arm, our RPM-based distro is Fedora on Intel. (Official support for CentOS has been dropped, but you should be able to "roll your own" from the src packages.)

Our Docker and binder containers will be updated within the following weeks.

We hope you will enjoy these new releases!!!

November 1st, 2022: macOS 13 Ventura issues

Dear all,

If you upgrade to macOS 13 Ventura (intel/x86_64), your already installed Python tools of McStas 2.7.1 / 3.1 and /Application bundles may not work after the upgrade.

A workaround is to:

New releases 2.7.2 and 3.2 are in preparation and should be released during November or December.

November 1st, 2022: Python 3.10 / pyqtgraph issues in current releases.

Dear all,

Several users have reported "yet another Python issue" that arise in current releases of McStas (2.7.1 / 3.1). After following the advice from September 23rd to replace mcgui/ and mccodelib/, mcplot-pyqtgraph fails with

mcplot error: scale(self): too many arguments
Traceback (most recent call last):
File "C:\mcstas-2.7.1\lib\tools\Python\mcplot\pyqtgraph\", line 67, in 
File "C:\mcstas-2.7.1\lib\tools\Python\mcplot\pyqtgraph\", line 57, in main
raise e
File "C:\mcstas-2.7.1\lib\tools\Python\mcplot\pyqtgraph\", line 51, in main
File "C:\mcstas-2.7.1\lib\tools\Python\mcplot\pyqtgraph....\mccodelib\", line 62, in runplot
plot_node(node, self.plot_func, plt_layout, viewmodel)
File "C:\mcstas-2.7.1\lib\tools\Python\mcplot\pyqtgraph....\mccodelib\", line 144, in plot_node
viewbox_lst.append(add_plot(layout, node, plot_func, i, n, viewmodel))
File "C:\mcstas-2.7.1\lib\tools\Python\mcplot\pyqtgraph....\mccodelib\", line 382, in add_plot
view_box, plt_itm = plot_node_func(node, i, plt, options)
File "C:\mcstas-2.7.1\lib\tools\Python\mcplot\pyqtgraph\", line 33, in plot
view_box, lyt = plot_Data2D(data, plt, log=opts['log'], legend=opts['legend'], icolormap=opts['icolormap'],
File "C:\mcstas-2.7.1\lib\tools\Python\mcplot\pyqtgraph\", line 203, in plot_Data2D
TypeError: scale(self): too many arguments'
To fix this issue, please replace your

New releases 2.7.2 and 3.2 are in preparation and should be released during November or December.

September 23rd, 2022: Python 3.10 issues in current releases.

Dear all,

We have recently become aware of a couple of issues that arise with all current releases of McStas (2.7.1 / 3.1)

On system with the newest Python versions (3.10 and beyond) you may experience that

In case you experience these problems you may replace the following files within your installation folder:

New stable releases of McStas should be released during November/December this year.

Best and sorry for the inconvenience,

Peter Willendrup

August 20th, 2022: Preview of ICNS 2022 presentation available.

On behalf of the McStas team, Peter Willendrup is giving an ICNS2022 presentation, entitled:

Speeding up legacy: GPU-accelerating the McStas instrument simulation code using OpenACC.


The McStas neutron ray-tracing simulation package is a versatile tool for producing accurate simulations of neutron scattering instruments at reactors, short- and long-pulsed spallation sources such as the European Spallation Source.
McStas is extensively used for design and optimization of instruments, virtual experiments, data analysis and user training. McStas was founded as an scientific, open-source collaborative code in 1997 and thus celebrates 25 years of service to the neutron community in 2022.
The contribution presents the project at its current state, with emphasis on recent modernisation-efforts and GPU-acceleration. Using the OpenACC precompiler-mechanism, McStas and its X-ray counterpart McXtrace have received speedups in the range of 10-600 depending on problem size and model complextiy.
By a detailed walk-through of a selected instrument example including the utilised components, we will illustrate the few simple steps users should carry out to port their existing instrument-models.

The video has been pre-recorded and is now available at or on YouTube

May 14th, 2022: Neutron-optics and McStas/Union related Post Doc position at PSI:

Dear all,

An interesting Post Doc position is available within the Neutron Optics and Scientific Computing Group at PSI:

A central part of the position is expanding features of the McStas Union by adding support for reflectivity (and potentially refraction).

Main tasks are:

For more information please refer to the link below or contact Dr. Christine Klauser <>

Peter Willendrup

February 18th, 2022: New ready-to-run McStas box in a browser

We are happy to provide a ready-to-run system with McStas pre-installed. It typically pulls-out an 8-cores computer running at Binder, for free, with both McStas 2.x and 3.x (with MPI multi-core support but no GPU). Perfect for running McStas from anywhere, for training/schools/workshops.

Start it in a single click here:

(Please note that load-time can be a couple of minutes.)



The above docker image has been pushed to dockerhub and can also be run locally at your machine using docker:

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