[mcstas-users] thermal moderator

Peter Kjær Willendrup pkwi at fysik.dtu.dk
Thu Nov 20 10:48:37 CET 2014

Dear Anna,

Sorry for the delay in responding - I had other urgent matters to attend.

My first comment is that the “TDR” formulation is no longer very relevant. The “2014” realises the brilliances as function of height between 1 and 12 cm, including both the “pancake” and “volume” moderator - and gives BOTH the cold and thermal spectra with tunable statistics, i.e.

- cold_frac=1 gives cold only
- cold_frac=0 gives thermal only
- 0 < cold_frac < 1 chooses the any fraction in between

Please note however that the proposed “lower moderator” is NOT described in McStas yet, but the upper moderator at a relevant height should give a good approximation.

Please find attached the instrument file ESS_Brilliance_2014.instr which shows how to run the “2014” source. The instrument is also
- available within McStas 2.1
- released separately for use with older versions of the code on July 17th, 2014, see http://www.mcstas.org/download/share

I also attach a presentation from the ICANS conference by Troels Schönfeldt who did all the hard work of characterising the ESS source and extracting parameters for McStas.  (Troels is cc: here, jointly employed at DTU Nutech & ESS neutronics group)

Troels is in the process of preparing a paper with detailed information. You are welcome to also ask him in case of questions or for further information.



Peter Kjær Willendrup
Senior Research Engineer, Special Advisor

DTU Physics

[cid:c99f6005-a56f-4672-bfe8-f6c6cbc364ef at win.dtu.dk]

Technical University of Denmark

[cid:ae7dea5d-27e2-4933-8ae9-fcea404be25a at win.dtu.dk]

Department of Physics

Building 307

DK-2800 Kongens Lyngby

Direct +45 2125 4612

Mobil +45 2125 4612
Fax +45 4593 2399

pkwi at fysik.dtu.dk<mailto:pkwi at fysik.dtu.dk>

On 19 Nov 2014, at 15:49 , Anna Fedrigo <anna.fedrigo at fi.isc.cnr.it<mailto:anna.fedrigo at fi.isc.cnr.it>> wrote:

Dear mcstas users,

I finally moved to the new mcstas version and I have problems with the moderator. For the selection of the thermal source is this command (sourcedef="TDR") enough? I managed to get only a cold source.
Which parameters should I use? Sorry but it's not very clear from the manual to me.

Best regards,



Anna Fedrigo
PhD Student

Consiglio Nazionale delle Ricerche
Istituto dei Sistemi Complessi
Via Madonna del Piano, 10
50019 Sesto Fiorentino (Italy)

Phone: +39 055 522 6631
E_mail: anna.fedrigo at fi.isc.cnr.it<mailto:anna.fedrigo at fi.isc.cnr.it>

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