TFTR natural diamond detectors based D–T neutron spectrometry system

Abstract

Three natural diamond detectors (NDD) based spectrometry systems have been developed and used on TFTR to perform D–T neutron spectrum and flux measurements. DT neutrons interact with the NDD through the 12C(n, alpha)9Be reaction to produce a narrow peak in the pulse height distribution which has 2%–3% energy resolution and is well isolated from other reactions by ∼2 MeV in energy. The NDD detector is also highly radiation resistant (5×1014 n/cm2) and compact in size (diameter ∼4 mm, thickness ∼0.2 mm). Three detectors have been installed near TFTR. One, installed in a central sight line of the neutron collimator views perpendicularly from below. Two other detectors placed inside radiation shields in the TFTR test cell have tangential and perpendicular cones of view. These three spectrometers provide spectrometry of D–T neutrons escaping the tokamak with angles with respect to plasma current in the ranges close to 90°, 110°–180°, and 60°–120° correspondingly. The fastest standard electronics have been used to reduce the influence of pulse pileup during spectrometry measurements at count rates up to 3×105 counts/s. Results of the first D–T neutron spectra and flux dynamics measurements made with the three NDD based spectrometers during TFTR high power neutral beam injection are presented.

Measurements of confined alphas and tritons in the MHD quiescent core of TFTR plasmas using the pellet charge exchange diagnostic

“…With the advent of D-T plasma operation on TFTR, a growing body of results from the PCX and other TFTR alpha particle diagnostics [25,26] is replacing prior speculation about alpha particle behavior. Using the PCX diagnostic, the first measurement of the alpha slowing down distribution up to the 3.5 MeV birth energy was obtained using boron pellet injection.…”

“…Unfortunately, the existing TRANSP code does not provide for modeling of the kinetic spreading of the alpha birth energy spectra, which must include precise information about beam energies species and injection angles, the computed thermonuclear beam-plasma and thermonuclear mix, and the ion temperature. In the FPPT code, a preliminary model of the "beam blip" data assumes simple thermonuclear Doppler broadening of the alpha particle birth energy, Ea, for which the full width at half maximum is given approximately by AE(keV) = 182(Teff)o.5 where Teff = 30 keV, the mean effective temperature of the deuterium and tritium ions, is based on measurement of the D-T neutron broadening in TFTR using a natural diamond spectrometer [25]. The thermonuclear formula used in FPPT is a first order approximation to illustrate the importance of the birth energy distribution for this data.…”

Proton recoil telescope based on diamond detectors for measurement of fusion neutrons

“…The use of a plastic converter makes the unfolding easier, thanks to the smoothness of the elastic scattering cross section of incoming neutron on hydrogen. The unfolding can be done also from the energy deposited by the neutron scattering on the carbon itself [4], but this task is complicated by various thresholds of inelastic channels and presence of resonances. The thicknesses of the two diamonds have to be optimized to allow 14 MeV protons to deposit enough energy in the first crystal and to stop completely in the second.…”

Time dependent 14MeV neutrons measurement using a polycrystalline chemical vapor deposited diamond detector at the JET tokamak

“…8,9 The main limitation in using NDD is their very scarce availability, the small size and the high cost. On the contrary, CVD diamond can be produced at low cost, with large surfaces and thickness ranging from a few microns up to more than 1 mm.…”