Pellets and Supersonic Gas Jet

1. Gas puff Li injection is switched off effect Pellets and Supersonic Gas Jet S.V. Krylov2, L.N. Khimchenko2, and T-10 team2 St. Petersburg, Russia Center “Kurchatov Institute”, Moscow, Russia ECE profiles behavior 1. Ablation features of carbon pellets Pellet diagnostic system Experimental results Normalized Te signals illustrating the appearance of the cooling fronts with velocities Vcool that are significantly higher than Vpel in the ceartain regions. The distance between the observation points ri+1-ri = 1.8 cm. In the figure (t6–t5), (t2–t1) are significantly lower than (t5–t4), (t4–t3), (t3–t2) ones => fast cooling fronts are forming in vicinity of r1 = 26 cm and r6 = 16 cm. The enhanced pellet ablation have the threshold versus the injected pellet diameter: in the cases of Dpel > 0.3 mm probability of enhanced ablation zones becomes 100%, otherwise it is < 30% NGS model modification Section 1 summary Simulation results • Calculations are based on Neutral Gas Shielding (NGS) model • Unperturbed ne(r) and Te(r) profiles were taken for ablation rate calculations before pellet reaches q = 2.5 • Assumption: tearing mode islands withw = 3-4 cm are forming instantly (forming time ~1 s corresponds to pellet displacement ≤ 0.4 mm) • Reconnection forms new ne(r) and Te(r) profiles in front of the pellet at the w/2distance. The ablation rate after the reconnection event is simulated using these new profiles • When pellet reaches the q = 1 magnetic surface we use the Kadomtsev’s reconnection model and modified ne and Te profiles • Beyond the plasma center profiles are calculated accounting the pellet material ablated prior the magnetic axis. Reconnections were not taken into account. • The dthr 0.3 mm carbon pellet diameter threshold of an appearance of the enhanced pellet ablation rate is experimentally observed • The possible explanation of the observed phenomena is based on the assumption that the pellet excites recon-nections due to the plasma conductivity decrease in x-points • Predictions of the improved NGS model by taking into account the reconnection events can reasonably describe radial profiles of the measured ablation rate for large carbon pellets • The observed MHD processes ensure the deeper penetration of the pellet itself as well as ablated material into the plasma The model with reconnections reasonably describes the experimentally observed ablation rate behavior. The modeled ablation rate behavior inside the q = 1 surface with the Kadomtsev reconnection event is reasonably agree with experimental one as well. Deuterium puffing Evolution of plasma parameters in the reference shots before (#42312), with Li pellet (#42317) and after (#42319) a sequence of Li injection Density behavior in reference shots Injection moment Gas valve signal Total deuterium puff amount AXUVD, a.u. (peripheral chord) Gas(t) ND • Plasma response has disturbance just after Li injection and relaxation to a quasi steady-state level • No obvious effects of the discharge conditioning (improving the plasma purity) takes place Dalfa Line emission, a.u. Time, ms Time, ms CIII Line emission, a.u. • ND increases after the first Li pellet injection in #42313 to keep the same programmed plasma density • It reveals a decrease of the deuterium recycling from the wall Lower particle flux from the wall in subsequent shots after Li injection was observed  Time, ms Penetration depth of He jet Temperature during saw-tooth Temperature profile evolution #42683 #42683 #42683 Ø He jet penetrates approximately 12 cm deep which corresponds to 0.6 r/a penetration depth (18 cm in the case of limiter position aL=30 cm) ΔTebefore the gas jet time, ms ΔTeduring the gas jet time, ms Injection direction Plasma center minor radius, cm minor radius, cm 10 cm Saw-tooth oscillations conceal the temperature effect during the gas jet injection! The injection experiments into configurations with q up to 5 without saw-tooth is necessary Ø Improvements of diagnostics are planned To obtain the PDF version of this poster please write your e-mail address here 1. 2. 3. 4. 5.