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Report No.
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Experimental investigation and validation of neutral beam current drive for ITER through ITPA joint experiments

Suzuki, Takahiro; Akers, R.*; Gates, D. A.*; G$"u$nter, S.*; Heidbrink, W. W.*; Hobirk, J.*; Luce, T. C.*; Murakami, Masanori*; Park, J. M.*; Turnyanskiy, M.*; ITPA Integrated Operation Scenarios Topical Group*

Joint experiments investigating the off-axis neutral beam current drive (NBCD) capability to be utilized for advanced operation scenario development in ITER was conducted in 5 tokamaks (AUG, DIII-D, JT-60U, MAST and NSTX) through the ITPA. We discuss results obtained in the joint experiments, where the toroidal field, $$B$$$$_{rm t}$$, covered 0.3-3.7 T, the plasma current, $$I$$$$_{rm p}$$, 0.6-1.2 MA, and the beam energy, Eb, 67-350 keV. A current profile broadened by off-axis NBCD was observed in MAST. In DIII-D, good agreement between the measured and calculated NB driven current profile was observed. In JT-60U, agreement between measured and calculated NBCD location was obtained, when the NBCD location (0.3-0.6 in $$r$$/$$a$$), heating power (6-13 MW), triangularity $$d$$ (0.25-0.45), and $$E$$$$_{b}$$ (85 and 350 keV) were widely scanned. In AUG (at low $$delta$$$$ sim$$ 0.2) and DIII-D, introduction of a fast ion diffusion coefficient of $$D$$$$_{rm b}$$ 0.3-0.5 m$$^2$$/s in the calculation gave better agreement at high heating power (5 and 7.2 MW), suggesting anomalous transport of fast ions by turbulence. It was found through these ITPA joint experiments that NBCD related physics quantities reasonably agree with calculations (with $$D$$$$_{rm b}$$ = 0-0.5 m$$^2$$/s) in all devices when there is no MHD activity except ELMs. Proximity of measured off-axis beam driven current to the corresponding calculation with $$D$$$$_{rm b}$$ = 0 has been discussed for ITER in terms of a theoretically predicted scaling of fast-ion diffusion that depends on $$E$$$$_{rm b}$$/$$T$$$$_{rm e}$$ for electrostatic turbulence or $$beta$$$$_{rm t}$$ for electromagnetic turbulence.

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