Investigation of remaining tritium in the LHD vacuum vessel after the first deuterium experimental campaign

Abstract

To reveal the triton transport and the tritium migration in a deuterium plasma experiment in the Large Helical Device (LHD), the distribution of the remaining tritium in divertor tiles made of graphite after the first deuterium plasma experimental campaign in 2017 was investigated. In this study, tritium contents in divertor tiles have been measured by using a full-combustion method. The asymmetric tritium retention in divertor tiles located at symmetric positions, which was found in the previous study by the surface tritium measurement using an imaging plate technique, has been confirmed by the results of the full-combustion method. The asymmetry is considered to be attributed to the asymmetric distribution of lost-points of energetic tritons in divertor. A depth profile of remaining tritium in a divertor tile estimated by using a combination of the imaging plate technique and a sputtering treatment shows that the peak of the profile locates at several micro-meters from the surface. This result suggests that the majority of the remaining tritium impinged upon the divertor tile as energetic tritons. In this study, a distribution of lost-points of energetic tritons has been calculated by using a Lorentz orbit following code (LORBIT) with taking into account divertor components. The obtained distribution has been compared with measured tritium distributions on divertor tiles. The measured and calculated distributions are similar to each other, but they are not the same. The difference between them can be attributed to plasma exposures during and after the deuterium plasma campaign.

Progress on Integrated Neutron Diagnostics for Deuterium Plasma Experiments and Energetic Particle Confinement Studies in the Large Helical Device During the Campaigns from FY2017 to FY2019

“…It was observed that the confinement of tritons having helically-trapped and transition orbits improved with the inward shift of the magnetic axis. Additionally, the loss points of triton measured by applying a tritium imaging plate technique were compared with the first orbit loss results [111]. The LORBIT code demonstrated that the loss point of triton changes based on the direction of the toroidal magnetic field.…”

Estimation of the Tritium Yields in Deuterium Fusion Plasmas Considering the Fast-Ion Velocity Distribution Function

“…Because the fusion cross-section of the D(d,p)T reaction becomes less than the fusion cross-section of the D(d,n) 3 He reaction, as the relative kinetic energy increases, the tritium yields Y t should be less than the neutron yields Y n in the LHD deuterium experiment. Although it was reported that approximately 6.4 GBq of tritium was yielded and approximately 4.3 GBq of tritium remained in the vacuum vessel [10,11] in the 19th LHD experiment campaign, the value of the remaining tritium should be less than 4.3 GBq by considering the fast-ion velocity distribution function. Therefore in this work, the ratio of the tritium yields to the neutron yields, Y t /Y n , during the 22nd LHD experiment campaign is numerically estimated for 4650 discharges by using integrated simulation code TASK3D-a.…”

“…removal system, etc. Also in the LHD, an investigation of exhausted tritium [10] and remaining tritium in a vacuum vessel [11] have been performed.…”

Tritium Balance in Large Helical Device during and after the First Deuterium Plasma Experiment Campaign

“…The tritium analysis in the plasma-facing materials has just started. The initial results of tritium distribution on the surface by using the Imaging Plate (IP) technique have been reported [26]. A relatively large amount of tritium was observed on the surfaces of the baffle part tile.…”