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Urano, Hajime
no journal, ,
The effects of argon seeding on H-mode plasmas have been investigated in JT-60U. While energy confinement degrades with density in conventional H-mode plasmas, it was improved at high density by argon seeding. At high density, higher core and pedestal temperatures were obtained with argon gas puffing. While the density profiles became flatter with increasing density in conventional H-mode plasmas, peaked density profiles were kept even at high density in argon seeded plasmas. Reduction in ELM frequency with argon seeding might be able to be explained by the reduction in the power across the separatrix with the increased radiation loss power. Higher pedestal temperature was obtained with the lower pedestal density which was given by the peaked density profile. The pedestal pressure increases only slightly with argon seeding.
Aiba, Nobuyuki; Saarelma, S.*; Urano, Hajime; Beurskens, M.*
no journal, ,
In JET with ITER-like wall (ILW), edge localized mode sometimes appears even when the pedestal pressure is below the stability boundary determined with numerical analysis, though such a numerical analysis predicted the stability boundary successfully in JET with carbon wall. To identify the reason of this discrepancy in JET ILW plasma, we analyze the pedestal MHD stability whose toroidal mode number, n, is up to 100 with MARG2D code. The numerical results showed that the pedestal stability of JET-ILW plasma is sometimes determined by the stability of n 
50 MHD mode, though that of JET with carbon wall was usually determined by the stability of n 
30 mode. Such a high-n mode stability remains important even when several non-ideal effects are taken into account in MHD stability analysis.