Determining the fuel ion ratio for D(T) and T(D) plasmas at JET using neutron time-of-flight spectrometry

Abstract

The fusion fuel ion ratio, nT/nD, is an important plasma parameter that needs to be tuned to maximize the power of a tokamak type fusion reactor. It is recognized as a parameter required for optimizing several ITER operating scenarios, and will likely be continuously monitored in future high-performance fusion devices such as DEMO. Tritium was recently introduced in the Joint European Torus (JET) plasma for the first time since the 1997 DTE1 and 2003 TTE campaigns, enabling the possibility to investigate fuel ion ratios. We present a method for measuring nT/nD using neutron time-of-flight (TOF) spectrometry. By fitting the measured neutron spectral features, the relative reaction rate intensities between different ion species can be inferred, from which the fuel ion ratio can be extracted for a corresponding modeled reactivity. Unlike previous measurements of nT/nD using neutron spectrometry, we utilize the neutron energy continuum produced in the three-body TT reaction to determine the fuel ion ratio for plasmas with large concentrations of tritium. Further, the use of neutron TOF spectrometry has never previously been demonstrated for evaluating nT/nD. The method is applied to TOF spectra acquired with TOFOR (JET name KM11) and shown to be consistent with the optical JET diagnostic KT5P which uses optical spectroscopy of a modified Penning gauge plasma to measure tritium and deuterium concentrations in the divertor exhaust gas.

Fusion product diagnostics based on commercially available chemical vapor deposition diamond detector in large helical device

“…Figure 4a shows the 𝑄 total spectra obtained by the diamond detector (B120033). The peak at approximately 7000 channels corresponded to a 12 C(n,𝛼) 9 Be reaction. The position of the 12 C(n,𝛼) 9 Be reaction peak shift and broadness of the peak change depended on the detector angle, due to the D-T neutron spectrum at the detector position.…”

“…The peak at approximately 7000 channels corresponded to a 12 C(n,𝛼) 9 Be reaction. The position of the 12 C(n,𝛼) 9 Be reaction peak shift and broadness of the peak change depended on the detector angle, due to the D-T neutron spectrum at the detector position. The full width at a half maximum of the 12 C(n,𝛼) 9 Be reaction peaks were 4.6%, 3.8%, 3.1%, and 2.1% in 0-, 27-, 48-, and 81-degree cases, respectively.…”

“…The position of the 12 C(n,𝛼) 9 Be reaction peak shift and broadness of the peak change depended on the detector angle, due to the D-T neutron spectrum at the detector position. The full width at a half maximum of the 12 C(n,𝛼) 9 Be reaction peaks were 4.6%, 3.8%, 3.1%, and 2.1% in 0-, 27-, 48-, and 81-degree cases, respectively. The main reason for the broadening of the 𝑄 total peak might habe been the broadening of the D-T neutron spectrum caused by the beam deuteron energy spectrum inside the thick tritium target.…”

“…In fusion-burning plasmas, neutron energy reflects fuel ion velocity distributions. Therefore, neutron energy spectrum measurements in thermal plasma can provide the fuel ion temperature [4][5][6], fuel ratio [7][8][9], and plasma rotation [10]. Moreover, neutron diagnostics provide information on energetic ion confinement in currently functioning neutral-beam-heated or ion-cyclotron-range-of-frequencyheated plasmas [11,12].…”

“…This is feasible due to its relatively wide band gap of 5.5 eV, which is wider than that of silicon 1.14 eV. Fusion plasma diagnostics based on a diamond detector, such as a neutral particle analyzer [15][16][17][18][19][20], a recoiled proton detector [21,22], and a deuterium-tritium (D-T) neutron detector [23] based on 12 C(n,𝛼) 9 Be reactions [24] have been developed. To measure the ion temperature of 9 keV through D-T neutron energy spectrum broadening [25], the energy resolution of the detector to the D-T neutron should be less than 4% [26].…”