Status of JRA6 - MCNSI

Kim Lefmann

NMI3, ISIS, 28/9-05

What is MCNSI ?

• Monte Carlo Simulations for Neutron Scattering Instruments

• Development of packages, Vitess, ResTrax, and McStas

• Cross comparison between codes and with exp.

• Tools for virtual experiments

• HMI, NPI, Risø, PSI, ISIS, ILL, INFM (+SNS, +ANSTO)

Packages I

• RESTRAX, NPI/ILL, version 4.8 (April 2005)+ both ray-tracing and data analysis- continuous sources only

• VITESS, (HMI), version 2.6 (June 2005)+ polarization included, also pulsed sources-

• McStas, Risø/ILL, version 1.9 (October 2005, beta yesterday!)+ detailed samples++ , also pulsed sources- no polarisation (yet)

Packages II

• Use of MC packagesa) Enable users to simulate new instruments

(FRM-2, ISIS TS2, FZJ, ANSTO, J-PARC, SNS, …) b) Understand/upgrade existing instrumentsc) Lay the foundation for all simulation activities

• Why not just one package?a) Scientific; intercomparisons reveal subtle errorsb) Innovative; good ideas survive and spread

Packages III .

Optimization of optics:

• Guide dimensions (VITESS)• Beam focusing device

(RESTRAX; automatic optimization)

50 cm30 cm

50 cm

8 cm

0.0 0.2 0.4 0.670

80

90

100

110

120

V [m-1

]

exit

heig

ht [m

m]

Packages IV: The grid

Code validation I

• Cold neutron powder diffractometer DMC @ PSI

• McStas vs. Real exp.• Sample Na2Ca3Al2F14

• Background from V can

• Very good agreement!… but intensity scaling

• Many other efforts, e.g. OSIRIS@ISIS; FOCUS@PSI; ILL; FRM2

Virtual experiments I

• What is a ”true” virtual experiment?a) Simulation of a complete instrument, source to detector b) …including a realistic sample modelc) Input from instrument control programd) Data analyzed by standard data analysis programs

• What can virtual experiments be used for?a) Virtual tests of proposed instrumentsb) Feasibility studies of planned experimentsc) Understanding of data (background, multiples)d) Teaching (Students, general public)

Virtual experiments, II

• REXTRAX model of IN20@ILL with 32 analyzers in flat-cone geometry

• Sample: phonons in Si

• Q-map at constant-E (20 meV)

Virtual experiments, III

• Course on neutron scattering

• Univ. Copenhagen, 2005

• 9 students, 3 groups

• 4th year undergraduates

• 3 virtual experiments

• 1 real experiment (PSI)

• VERY good learning progress!

Virtual experiments, IV .

• Realistic sample simulation (multiples, sample environment)

• FOCUS @ PSI; McStas

• New component: Isotropic S(q,ω); concentric

MCNSI - prospects

• Packages: – Standard modules: truly reliable and user friendly

– Approaching detailed sample description

– Still few major features and many details missing

• Virtual experiments:– Proof of concept performed

– Potentially a very powerful tool (training, data analysis, …)

– Much work needed! (in collaboration with facilities)