(EX/P3-11) Transport Barriers and H-mode in Regimes with Deuterium Pellets Injected into T-10 Plasma Heated by ECR

Abstract.  The confinement of energy and particles has been observed to improve in T-10 discharges when deuterium pellets are injected into the plasma heated by the ECR. The H factor found in the ITER scaling is equal to 1-1.4 in these regimes. Successive injections of deuterium pellets lead to corresponding increase in both the plasma energy and the energy confinement time. Moreover, the confinement time depends practically linearly on the averaged plasma density that increases after each pellet. In these regimes, the profile of the plasma density was observed to change abruptly. Namely, (i) a density pedestal, typical of an external transport barrier in the H mode, forms at the periphery of the plasma column; (ii) the power of auxiliary heating needed for transition to the H mode is several times less than that predicted by the ITER scaling; (iii) regions of steep density gradients, typical of internal transport barriers, form in the inner area of the plasma column. A change in the plasma temperature profile is also observed in the same regions. In addition, these regions are located near rational surfaces of low m and n values. The successive injection of deuterium pellets into the plasma has allowed the discharges with ELMs of type III to be obtained. In this case: (i) the plasma energy reduces when a packet of ELMs arises and restores when ELMs die out; (ii) a density pedestal at the plasma boundary is partially destroyed when an ELM train appears and forms again when ELMs decay; (iii) the rise of ELMs affects also the internal plasma area. The emergence of the ELM packet is accompanied by rapid decrease in ion temperature (about 15%) measured by a neutral particle analyzer, and a neutron flux decrease during an ELM train (in ∼1.5 times) and restores after ELMs damp. Such a behavior of ion temperature can be associated with the destruction and reconstruction of an ion transport barrier resulted from the pellet injection. An analysis of huge experimental data allows us to conclude that the injection of deuterium pellets forms the transport barriers (both external and internal ones) in the T-10 plasma heated by the ECR.

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