Fusion Engineering and Design 86 (2011) 1277–1281 Contents lists available at ScienceDirect Fusion Engineering and Design journal homepage: www.elsevier.com/locate/fusengdes Neutronic calculations in support of the design of the ITER High Resolution Neutron Spectrometer F. Moro a,∗ , B. Esposito a , D. Marocco a , R. Villari a , L. Petrizzi b , E. Andersson Sunden c , S. Conroy c , G. Ericsson c , M. Gatu Johnson c , M. Dapena d a Association EURATOM-ENEA, C.R. Frascati, Via E. Fermi, 45, I-00044 Frascati, Roma, Italy b IAEA Representative at OECD Nuclear Energy Agency 12, Boulevard des Îles, F-92130 Issy-les-Moulineaux, France c Department of Neutron Research, Uppsala University, EURATOM-VR Association, P.O. Box 525, S-75120, Uppsala, Sweden d Association Euratom-CEA, IRFM, Cadarache, 13108 Saint-Paul-lez-Durance, France article info Article history: Available online 15 March 2011 Keywords: ITER Neutron Diagnostic Spectrometer Design Analysis abstract This paper presents the results of neutronic calculations performed to address important issues related to the optimization of the ITER HRNS (High resolution Neutron Spectrometer) design, in particular con- cerning the definition of the collimator and the choice of the detector system. The calculations have been carried out using the MCNP5 Monte Carlo code in a full 3-D geometry. The HRNS collimation system has been included in the latest MCNP ITER 40 ◦ model (Alite-4). The ITER scenario 2 reference DT plasma fusion neutron source peaked at 14.1 MeV with Gaussian energy distribution has been used. Neutron fluxes and energy spectra (>1 MeV) have been evaluated at different positions along the HRNS collimator and at the detector location. The noise-to-signal ratio (i.e. the ratio of collided to uncollided neutrons), the breakdown of the collided spectrum into its components, the dependency on the first wall aperture and the gamma-ray spectra at the detector position have also been analyzed. The impact of the results on the design of the HRNS diagnostic system is discussed. © 2011 EURATOM ENEA Association - ENEA Fusion Unit. Published by Elsevier B.V. All rights reserved. 1. Introduction The HRNS (High Resolution Neutron Spectrometer) is a neu- tron diagnostic, located into the Equatorial Port Cell 1, conceived to provide information about several plasma parameters such as ion temperature, fuel ratio, fast ions’ density and energy spectrum and plasma rotation, requiring a tangential line of sight (LOS) (Fig. 1). The current ITER HRNS layout consists of a long, narrow conical collimator crossing the longitudinal axis of the port from the First Wall (FW) to the Cryostat and beyond the Bioshield. The main geo- metrical features of the HRNS can be found in [1]. The detection system, located at the end of the collimator, has not been defined yet: many instrumental devices are under investi- gation such as thin-foil proton recoil (magnetic and non-magnetic), time-of-flight and compact neutron spectrometers (proton recoil scintillators and diamonds) [1] For this purpose, an evaluation of the expected neutronic per- formance of the HRNS has been carried out by including the HRNS collimation system in the latest MCNP 40 ◦ ITER model. ∗ Corresponding author. Tel.: +39 0694005401; fax: +39 0694005417. E-mail addresses: fabio.moro@enea.it, moro@frascati.enea.it (F. Moro). The present paper summarizes the neutronic calculations per- formed in the frame of an EFDA contract [2] aiming at the optimization of the HRNS design, providing information useful for the definition of the interface characteristics and the choice of the detection system. The analysis has been focused on the following issues: (a) evaluation of neutron fluxes, energy spectra and signal- to-noise ratio at different positions along the collimator for two first wall aperture options (5 cm radius and 15 cm radius), (b) neutron and gamma spectra at the detector location, and (c) analysis of the components of the collided neutron spectrum. 2. Modeling and calculation tool 2.1. 3-D MCNP model and source The 40 ◦ ITER model, as officially distributed by ITER Organiza- tion (the Alite-4), has been updated in order to include the HRNS layout: the Port Plug has been modified to be consistent with all the diagnostic integration analyses performed so far [2]. Pictures of the model are shown in Figs. 2 and 3: the HRNS collimator extends in the whole Port Plug from the First Wall to the Cryostat and beyond the Bioshield. In this area a stainless steel sleeve and a con- crete collar surround the collimator in order to provide additional shielding. Two configurations of the conical collimator have been 0920-3796/$ – see front matter © 2011 EURATOM ENEA Association - ENEA Fusion Unit. Published by Elsevier B.V. All rights reserved. doi:10.1016/j.fusengdes.2011.02.049