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Study of a closed divertor with strong gas puffing on JFT-2M

In order to improve the particle control capability of the divertor and to demonstrate the possibility of a dense and cold divertor with high confinement plasmas, a closed divertor study has been carried out on the JFT-2M tokamak. When a strong gas puff is applied into the divertor chamber, a baffling effect is revealed by enhanced radiation localization and high neutral pressure in the divertor chamber, low core fuelling and sustainment of core confinement quality. The baffling effect is further enhanced with E × B flow and/or current in the scrape-off layer by applying divertor biasing. A dense and cold divertor state (nediv ≈ 4 × 1019m-3 and Tediv ≈ 4 eV), together with the improved confinement modes, can be obtained by strong gas puffing. Furthermore, the improved core confinement is not affected significantly in the high density region (n̄e/neG < 0.7). The UEDA code simulation reproduces the baffling effect and a dense and cold divertor plasma with a closed divertor structure.