Relationship between neutron yield rate of tokamak plasmas and spectrometer measured flux for different sight lines

Abstract

A parametric relationship between total neutron yield rate and collimated fluxes related to the brightness (B) of plasma chords (λ) is developed for different emissivity distributions of tokamak plasmas. Specifically, the brightness was expressed as a function of chord coordinates of radial position using a simple model for the emissivity profiles of width parameter w. The functional brightness dependence B(λ,w) was calculated to examine the relationship between measured flux and deduced yield rate, and its plasma profile dependence. The results were used to determine the chord range of minimum profile sensitivity in order to identify the preferred collimator sight for the determination of yield rate from neutron emission spectroscopy (YNES) measurements. The YNES method is discussed in comparison to conventional methods to determine the total neutron yield rates and related plasma fusion power relying on uncollimated flux measurements and a different calibration base for the flux-yield relationship. The results have a special bearing for tokamaks operating with both deuterium and deuterium-tritium plasmas and future high power machines such as for ITER, DEMO, and IGNITOR.

Simulation of neutron emission spectra from neutral beam-heated plasmas in the EAST tokamak

“…The LOS effect on the neutron spectrum was evaluated by calculating the collimated brightness B(p) along a given chord λ(p) [24]. The collimated brightness B(p), which is proportional to the neutron flux impinging on the detector, is defined as…”

Diagnosing NB plasmas on the EAST tokamak with new time-of-flight neutron spectrometer

“…In this context it is interesting to note that, with a NES diagnostic, one could also provide support in the determination of the absolute value of the neutron yield rate of the EAST plasmas, i.e. the calibration of neutron flux monitors [25].…”

A generalized Abel inversion method for gamma-ray imaging of thermonuclear plasmas

“…In the following, we shall further adopt the notation of [25] and use y γ (s) to denote the local gamma-ray emissivity. This will be a function of a radial coordinate s in the poloidal plane and gives the number of gamma-rays/second/cm 3 born at each plasma position.…”

“…where y 0 is the peak emissivity, typically occurring on the magnetic axis, and ν is the peaking factor. The latter is related to the half width w of the profile by [25]…”