interfacing mcnp/mcnpx and mcstas for cold neutron ......interfacing mcnpx and mcstas - why bother...

General rights Copyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights.

Users may download and print one copy of any publication from the public portal for the purpose of private study or research.

You may not further distribute the material or use it for any profit-making activity or commercial gain

You may freely distribute the URL identifying the publication in the public portal If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim.

Downloaded from orbit.dtu.dk on: Jun 05, 2021

Interfacing MCNP/MCNPX and McStas for cold neutron moderator calculations

Klinkby, Esben Bryndt; Lauritzen, Bent; Nonbøl, Erik; Willendrup, Peter Kjær

Publication date:2011

Document VersionPublisher's PDF, also known as Version of record

Link back to DTU Orbit

Citation (APA):Klinkby, E. B., Lauritzen, B., Nonbøl, E., & Willendrup, P. K. (2011). Interfacing MCNP/MCNPX and McStas forcold neutron moderator calculations. Abstract from IAEA Technical Meeting on Advanced Moderators toEnhance Cold Neutron Beam Production for Materials Research and Applications, Tsukuba (JP), 22-25 Nov, .

https://orbit.dtu.dk/en/publications/023a196b-16a4-461d-b798-f2bf50ad42e7

Interfacing MCNPX and McStas - why bother and what are the possible applications?

Peter Willendrup1,5

Erik Nonbøl2,5

Esben Klinkby2,5(*)

Bent Lauritzen2,5

Input from / collaboration with

Emmanuel Farhi3

Uwe Filges4

1Materials Research Division, Risø DTU, Roskilde, Denmark

2Radiation Research Division, Risø DTU, Roskilde, Denmark

3Calcul Scientifique, Institut Laue-Langevein (ILL), Grenoble, France

4Paul Scherrer Institut, Villigen, Switzerland

5ESS collaboration

(*) New PostDoc from october 1st

DK contribution, to ESS target station design update

• Built around 2-year project at Risø DTU, Radiation Research Division (collaboration with Materials Research Division) and PSI

• Part I: Integration work on MCNP/X and McStas for better description of cold-thermal energy range and “exotic”

geometries/materials

• Part II: Application of the new tool in optimization of moderator-beam extraction

• Contribution to target station update phase, WP 2 (WU 2.6)

Agenda

• Quick intro to McStas

• Complementarity to MCNP/X

• What we hope to achieve

• Possible implementation

• Possible application areas

Advanced Moderators to enhance cold neutron beam production, Tsukuba, Japan, Nov 22-25 2011

McStas Introduction

• Flexible, general simulation utility for neutron scattering experiments.

• Original design for Monte carlo Simulation of triple axis spectrometers

• Developed at RISØ DTU, KU, PSI and ILL, Grenoble.

• V. 1.0 by K Nielsen & K Lefmann (1998)

• Currently 2.5+1 people full time plus students

[email protected] mailinglist Project website at http://www.mcstas.org

• Synergy, knowledge transfer, shared infrastructure

GNU GPL License Open Source


mailto:[email protected]:[email protected]:[email protected]://www.mcstas.org/


McStas Introduction

• Used at all major neutron sources (or instrumentation efforts)

•Instrumentation

•Virtual experiments

•Data analysis

•Teaching

What is McStas used for?

(KU 2005-2011)


Reliability - cross comparisons

P. Willendrup et al., Physica B, 386, (2006), 1032. E. Farhi, P. Willendrup et al., in preparation


A few facts about physics in McStas

• Under usual circumstances, the source for us effectively means the moderator surface

• Moderator described via analytical expressions of neutron velocities etc. (fitted spectra) or or direct input of events via tally-ptrac files from MCNP/X (or similar in case of Tripoli4)

• Our neutrons are typically “statistical events” meaning not single neutron particles, but rather “neutron rays” with a given weight

• Cold and thermal neutrons are described very well, including

Coherent and incoherent scattering (possibility to move particlewave)

Elastic and inelastic scattering

• Structure and dynamical properties of matter in different states are well described, e.g. liquids/amorpheus, powders, single crystals, small angle scattering

• We handle structures of “any shape” Advanced Moderators to enhance cold neutron beam production, Tsukuba, Japan, Nov 22-25 2011

MCNP/X and related codes, “shortcomings” (- for our use: effective production of cold-thermal neutrons)

• Mainly focused on high energy neutrons (extrapolations apply in many cases)

• Coherent scattering (Bragg etc.) from atomic planes is not implemented.

• -> Accurate simulation of alternatives for e.g. geometry and materials that interact with the moderated neutrons is currently not possible.


Materials databases in McStas vs. neutronics codes

• McStas builds a material data base from molecular dynamics and TOF-TAS measurements which provide S(q,w) and F2.

• MD for most metals (powders, liquids), F2 from McStas for common crystals, measurements for hydrogenated materials.

• All neutronics codes use ENDF-derivated databases. They use total cross section measurements together with analytical models. Most users will say that they are not satisfactory/accurate, and need to modify the files (NJOY).

• ILL: Ongoing task to improve the accuracy of cold-thermal range S(q,w) for MCNP, based on MD and measurements. (Improved scattering kernel for water will be made available through IAEA - meeting in J-PARC in november) Experimental technique: combination of IN5 and IN4 experiments on water, large total dynamical range

• -> Collaboration for new scattering kernels (based on McStas code) is expected for improving description of cold moderators and surroundings.


What we hope to achieve

• Improved handling of cold-thermal neutrons, especially in relation to coherent scattering

• Easier description of geometrical effects, e.g. vanes/voids/grooves/inserts/sawtooth-moderators (Dubna and others have demonstrated an improvement experimentally - existing code does not exactly reproduce this)

• A seamless way to effectively ping-pong events between the codes (without intermediate files)

• Some experience already at PSI (U. Filges) - reflecting mirrors partially implemented in PSI-internal MCNPX code... - That knowledge will be expanded.

• -> Link to “heavy” MCNPX knowledge via U. Filges / F. Gallmeier @SNS


• Current MCNP ESS target station geometry (developed by ESS-Bilbao) includes

bi-spectral moderator • Relevant beamline will get transmitted thermal beam through mirror and cold

beam reflected by mirror (so-called supermirror switch, as implemented at HZB in Berlin)

• Current MCNP distribution does not handle (imperfect) mirrors, but

physics/algorithms readily available in McStas


Primary area of interest

Modify MCNP: mimic the existing perfect mirror to make a new mirror type with non-perfect, q-depending reflection

➢ Pro's: relatively straight forward (given that the reflectivity dependence on q is known)

➢ :Would enable one to optimize brilliance

➢ Con's: Doesn't solve the general request: an interface between McStas and MCNP

➢ :Not clear when to exit MCNP and enter McStas ➢ :Tricky to take out coherent contribution from MCNP's total cross-section

Use existing PTRAC interface

➢ Pro's: It works!

➢ Con's: Does not easily allow neutrons to re-enter MCNP after being handed to McStas

Possible solutions


Compile together (a McStas Cell?)

➢ Pro's: Principle proven (next slide) Would allow to use the best of the worlds, since one could have a neutron: Generated in MCNP →

Transported to McStas → Scatter coherently Re-enter MCNP (with different momentum, coordinates, time and weight)

➢ Con's: perhaps a bit of an overkill(?) Licensing is a mess → very limited # of users

Possible solutions


Generated in MCNP →

➢ Transported to McStas →

➢ Scatter

➢ Autogenerated ANSI C McStas code examples are copied to MCNP source directory, and compiler is setup of to compile the C code with the

Fortran codes of MCNP, so that C routines of McStas can be called

directly from MCNP

➢ Present setup involves a new operater (-) on a MCNP surface, defined in the MCNP input files (where all surfaces, cells etc are defined)

➢ Once a neutron arrives at a “minus” surface, the C-routine is called, with all arguments needed: mom, pos, weight, energy

➢ McStas code is presently dummy, but with a little work and expertise, something useful could be done here.

Present setup (compiling option)


Present setup (compiling option)

MCNP McStas

“-surface”

~n

Coherent scat ·n

·n

Code example:

C -- segment

planes

C

-110 PX -0.2

-120 PX -0.4

~n

“Figure of Merit” or interface unit

• A main challenge for interfacing neutronics and instrument simulations is ”language”

• Neutron scatterers and instrument designers think in terms of Brilliance, i.e.:

Neutrons / s / ster / mod. area / energy bin – as a function of particle energy (even better wavelength than energy)

• This could be defined by means of an MCNP tally formulation like


Expected main areas of application

• Beam-extraction area / crossover between moderation and beam transport (WU 2.6) – as described above

• Likely also interesting for WU 2.4 (Advanced moderators)

• Potentially also interesting for far-from-source estimates of e.g. shielding dimensions (MCNP/X -> McStas in the guide -> MCNP/X), cf. WU’s where

PSI is also involved

• Potentially also interesting for other work units (but is long-term/maybe inside construction phase)


Current work-force and work plan

• Two-year PostDoc Esben Klinkby (has background in particle physics and knows Geant4 and McStas already, extensive coding experience with c, c++ and Fortran)

• Phase-I: Gaining neutronics experience / thinking through algorithm

• Phase-II: Implementation of prototype

• Phase-III: Application of the prototype to at least one selected beam-extraction problem


Summary

• McStas handles all scattering processes used for neutron instruments, in the cold-thermal region.

• Neutron transport (MCNP, PHITS, GEANT, FLUKA, …) codes handle reactor/source neutronics and moderation for hot-epithermal neutrons and other fancy particles.

• We are now promoting interfaces between McStas and other codes. Work is starting in the framework of the TS collaboration WU2.6. Primary goal is set for MCNP/X - as written in application to DK ministry (FLUKA and/or GEANT could also be considered.)

• Already have a more basic MCNP and Tripoli -McStas interface through PTRAC files.


interfacing mcnp/mcnpx and mcstas for cold neutron ......interfacing mcnpx and mcstas - why bother...

Documents