Pre-conceptual study of the European DEMO neutron diagnostics

Abstract

A: This paper discusses the pre-conceptual design of the European DEMO neutron diagnostics aimed at the measurement of the fusion power, the plasma displacement and the fuel ion ratio for plasma burn control. The design has been based on the European DEMO design concept with a single divertor and on the so-called DEMO1 plasma scenario but limited only to the steady phased of the discharge. The suggested neutron diagnostics consist of neutron activation systems, fission chambers and vertical and horizontal collimated neutron flux monitors with spectroscopy capabilities. The fusion power can be measured with an accuracy of 1 % with a time resolution of one tenth of the energy confinement time and the plasma displacement with a time resolution of 1 ms. Central ion temperature and fuel ion ratio instead can be measured with a time resolution of about 1 s. Calibration and interfacing issues are discussed. K: Neutron detectors, Fast neutrons, Nuclear instruments and methods for hot plasma diagnostics.

Core ion measurements with collective Thomson scattering for DEMO burn control

“…Such measurements will generally require digitizer-based data with high frequency resolution. The results can complement estimates based on neutron spectroscopy [49] for improved burn control and help inform the optimum edge fuelling rate as well as the pacing and size associated with core pellet fuelling. Again, this can potentially be done on timescales below the pellet delivery rate for continuous optimization of the core isotope mix.…”

Neutronics Simulations for DEMO Diagnostics

“…The fits were obtained using Mathematica [36] for the simple expression f = c A, where f is the flux, A is the area of the duct and c is a constant, and they can be used as a first approximation to estimate the fluxes in ducts with different areas. Two diagnostics are currently expected to use straight ducts with even smaller crosssections than the ones simulated in the previous section (r = 1 cm): the neutron and gamma cameras [8,9] and the core radiated power and soft X-ray intensity system [10]. The aim of this section is to provide the neutron and gamma fluxes through the different ducts of these systems.…”

“…Two diagnostics are currently expected to use straight ducts with even smaller crosssections than the ones simulated in the previous section (r = 1 cm): the neutron and gamma cameras [8,9] and the core radiated power and soft X-ray intensity system [10]. The aim of this section is to provide the neutron and gamma fluxes through the different ducts of these systems.…”

“…Most sub-systems are designed to be integrated in equatorial port (EP) plugs dedicated to diagnostics (five or six EPs are foreseen), in some cases with additional lines of sight in the upper ports (UPs) if there is space reserved for diagnostics in the UPs. These include spectroscopy diagnostics [7], neutron/gamma cameras [8,9], radiated power and soft Xray intensity [10] and IR polarimetry/interferometry [11], with the eventual addition of collective Thomson scattering [12], still under study. For diagnostics that require access to the plasma from several poloidal positions, such as MW reflectometry [13] and ECE [14], the diagnostics slim cassette (DSC) concept has been developed [15][16][17] as a modular approach compatible with the remote handling operations of the breeding blanket (BB).…”