Plasma-surface interactions near the threshold energies for iter and demo reactors

Abstract

In the search for new energy sources for expanding needs over the globe, fusion is a promising alternative. Studies aiming to produce net energy by fusion are in progress in JointEuropean Thorus (JET), Axially Symmetric Divertor Experiment (ASDEX Upgrade), International Thermonuclear Experimental Reactor (ITER), and the following pre-commercial DEMOnstration Power Plants. The fuel used in a thermonuclear fusion reactor is Deuterium and Tritium. Hydrogen has a high abundance and relatively low-temperature levels to reach fusion conditions. Tungsten replaced the Carbon-Tungsten alloy on plasma-facing surfaces of ITER. Understanding the interactions between the plasma and the wall material is essential to maintaining the plasma fuel and the device's properties. Hydrogen isotope bombardment on wall material triggers physical and chemical processes. Collisions of deuterium with the reactor surface result in sputtering of target atoms, reflection, transmission, and structure manipulations on the target. This study simulated the interaction between the Tungsten layer and Deuterium ions with the Transmission of Ions in Matter (TRIM) program. Tungsten target with 600 Å is subjected to deuterium projectiles with energy from 500 to 1000 eV. A million shots are sent to the surface with varying angles with 5◦ intervals. Monte Carlo calculation results are investigated in terms of the number and the average energy of the sputtered W atoms and the number of backscattered deuterium atoms with average energies. The relation between ion penetration depth and incidence angle is inspected to determine the needed target depth to inhibit the transmission through the target. The number and the average energy of backscattered hydrogen ions increased with increasing projectile angle for all energy levels. Energy reflection coefficients are calculated, concluding that backscattered ions carry at least 50 energy. The rest of the ions are penetrated into the Tungsten layer. The depth profile of the implanted ions with constant incidence angles confirmed the direct relation with the projectile energy. Increasing angle for each projectile set shown the decreasing pattern in penetration depth values. Rate of sputtered tungsten atoms to incident particles is recorded. The sputtering yield had a maximum weight between 55-75 degrees for all projectile energies and decreased with increasing projectile angles. Compared with the experimental and simulated data by others, TRIM results have been systematically deflected from the fitting curves. Neglecting the change over the interaction potentials and inelastic energy losses due to ion/electron interactions, ready program TRIM with BCA approximation based on elastic collision calculations is not a preferable software within the investigated energy interval.