DT Yield Research Articles

The Moderation and Tunneling Reaction of Recoil T Atoms in Solid Xenon–Hydrogen Mixtures at 77 K

Abstract Recoil T atom reactions were studied in Xe–H2–D2 mixtures at 77 K. The isotope effect on the T-atom reaction with H2 and D2 (k(T+H2→HT+H)/k(T+D2→DT+D)) was measured on the basis of the HT and DT yields. The isotope effect (k(T+H2)/k(T+D2)) is 1.1 in the range of hydrogen concentrations of 0.1–1.0 mol%. Since the small isotope effect (1.1)is similar to the isotope effect (1.0) for a hot T-atom reaction in the gas phase, recoil T atoms are not thermalized at these concentrations in solid xenon and form HT and DT by means of hot-atom reactions. At concentrations of hydrogen of less than 0.1 mol%, the recoil T atoms are thermalized before they encounter the solute hydrogen. The isotope effect increases with a decrease in the hydrogen concentration and amounts to 3.1 at a hydrogen concentration of 0.01 mol%. Since a large isotope effect is expected for the tunneling reaction of T atoms, the large isotope effect (3.1) at 0.01 mol% hydrogen was interpreted in terms of the tunneling reaction of thermalized T atoms. The present results in the solid xenon–hydrogen mixtures were compared with those in the gaseous xenon–hydrogen mixtures reported previously. It was concluded that hot T atoms in the solid xenon at 77 K are deactivated much less effectively than in the gas phase and that they migrate long distances with excess kinetic energies.

Non-thermal DT yield with (D)T ICRH heating in JET

Projections of the (D)T fusion yield expected during fundamental ICRH heating of D in JET tritium plasmas are presented. The highest fusion multiplication factor, Q( identical to Pfus/PRF), is achieved for a relatively high plasma density (ne0>5*1019 m-3) and minority concentration ratio nD/nT approximately=20-40% with dipole antenna (k/sub /// approximately=7 m-1). The latter reduces mode conversion and maximizes the RF power coupled to the minority ions. The authors have used ray-tracing and global wave ICRH codes to calculate power deposition profiles; 80% is cyclotron damped by deuterium and 17% is coupled directly to electrons via TTMP and Landau damping. With launched RF power PRF=12 MW deposited approximately=0.3 m off-axis, the authors predict fusion powers Pfus up to approximately=8 MW for a range of JET plasmas with achieved plasma pressure ne0Te0=6*1020 keV m-3 and Zeff=2. Projecting to PRF=25 MW, Pfus increases in 17 MW with Zeff=2.

Isotope effect on hydrogen atom abstraction reaction by recoil tritium atoms in xenon-ethane-perdeuteroethane mixtures at 77 K

Recoil T atom reactions have been studied in Xe-C/sub 2/H/sub 6/-C/sub 2/D/sub 6/ mixtures as 77 K. The ratio of the HT yield to the DT yield at 0.2 mol % ethane (C/sub 2/H/sub 6/+C/sub 2/D/sub 6/) is much higher than the C/sub 2/H/sub 6//C/sub 2/D/sub 6/ ratio. The H/D abstraction isotope effect for the T atom reaction with C/sub 2/H/sub 6/ and C/sub 2/D/sub 6/ is 3.5-6 at .02 mol % ethane, while the effect decreases with an increase of ethane concentration down to 1.4 at a concentration higher than 10 mol %. The remarkable isotope effect at the low concentration of ethane is much higher than the isotope effect (1.3) for the hot T atom reaction in the gas phase and is ascribed to a quantum-mechanical tunneling reaction by thermalized T atoms with ethane. The rate constant for the tunneling abstraction is calculated by using the unsymmetrical Eckart potential function and the effective mass in the linear triatomic system. It is concluded that T atoms can react with ethane by quantum-mechanical tunneling as easily as H atoms do.

Production of DT neutrons by means of TiT targets and analyzed atomic deuteron beams

The behaviour of TiT targets during irradiation with a pure beam of atomic deuteron ions was investigated. The dependence on time of the absolute DT neutron yield and the build-up of DD neutron intensity was determined at a constant current density of 0.3 mA/cm 2 for both a 2 Ci and 5 Ci/sq-inch TiT target. Half-lives of 12 mAh/cm 2 and 18 mAh/cm 2 for the DT neutron yield were observed in these two cases. These half-lives are more than an order of magnitude longer than those observed using TiT targets in low-energy accelerators with unanalyzed beams. The DD neutron intensity rises approximately proportional with the irradiation time and reaches a saturation value of about 0.3% of the initial DT yield or 30% of the yield of a TiD target at the end of one half-life. The results suggest that the effect of replacement of tritium by the implanted deuteron is less than hitherto assumed and most of the deuterons are capable of diffusing out of the target without interaction with the tritium. It appears that the short half-lives observed with the use of unanalyzed beams are mainly due to sputtering and radiation damage caused by heavy-ion contaminants always present in unanalyzed beams.