Comparison of edge neutral effect on the condition of H-mode transition before and after the modified divertor in JT-60U

The JT-60U divertor geometry was recently modified to a W-shaped structure in order to reduce the back flow of neutrals from the divertor. The H-mode threshold power decreased subtly compared with the open divertor case. As regards density dependence, the exponent of density was 0.5 to 0.75. In addition, we found that the outflux from the outer baffle plate should be considered for the evaluation of neutrals.