Abstract
Shot-integrated measurement of the triton burnup ratio has been performed in the Large Helical Device. It was reported that the triton burnup ratio, defined as total DT neutron yield divided by total DD neutron yield, increases significantly in inward shifted configurations. To understand the magnetic configuration dependence of the triton burnup ratio, the first orbit loss fraction of 1 MeV tritons is evaluated by means of the Lorentz orbit code for various magnetic configurations. The first orbit loss of 1 MeV tritons is seen at t of less than 10−5 s and loss points of the triton are concentrated on the side of the helical coil case where the magnetic field is relatively weak. The significant decrease of the first orbit loss fraction by 15% is obtained with the inward shift of the magnetic axis position from 3.90 to 3.55 m. It is found that the decrease of first orbit loss is due to the reduction of the first orbit loss of transition and helically trapped tritons.
Highlights
One of the key issues for sustaining fusion reactions in a burning plasma is how DT fusion born alpha particles are sufficiently confined
Most of the tritons are confined in the normal toroidal magnetic field strength (Bt > 2.5 T) condition in Rax of 3.6 m
In the half toroidal magnetic field strength condition (Bt = 1.375 T), most of the tritons are lost and the result is consistent with the low triton burnup ratio obtained in experiments
Summary
One of the key issues for sustaining fusion reactions in a burning plasma is how DT fusion born alpha particles are sufficiently confined. When we considered a classical confinement of tritons, the loss of tritons could be caused due to the collisionless issue which is a result of the lost orbit, the collisional issue which the particle reaches the loss cone due to the collision, and the charge exchange with neutral gas. In these experiments, typical electron temperature Te of 3 keV and typical electron density ne of 2×1019 m-3, it needs more than 2 seconds for 1 MeV triton to decrease its energy to 100 keV [13]. The first-orbit loss fraction of 1 MeV tritons is evaluated as a first step by means of the Lorentz orbit code in order to understand the magnetic configuration effect on the triton burnup ratio
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