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Kunihiko Okano, Shin Yamamoto, Masayoshi Sugihara, Noboru Fujisawa
Fusion Science and Technology | Volume 16 | Number 1 | August 1989 | Pages 73-95
Technical Paper | Plasma Engineering | doi.org/10.13182/FST89-A29098
Articles are hosted by Taylor and Francis Online.
The current drive potential by the negative-ion-based neutral beam injector is investigated for International Tokamak Reactor (INTOR) benchmark test parameters. To estimate the current drive profile, the beam current drive efficiency, and the various parameter dependences, a beam current drive analysis code is used. The code is composed of the two-dimensional Fokker-Planck and the three-dimensional beam power/momentum deposition calculations. In most cases, the 500-keV injection energy is assumed except for the beam energy scanning, and the 500-keV beam feasibility in the INTOR design is clarified. The current drive profile depends on the beamline orientation. Using these characteristics, current profile tailoring is possible. By using the vertically arranged multibeam-lines, in which each beam power is controlled to take into account the power profile variation, a very flexible current profile is realized. The very flat current profile and even the hollow profile can be driven by such controlled beam injections, as well as the parabolic current profile. The magnitude of the 500-keV beam current drive efficiency is acceptable f or INTOR-size tokamaks, and it would be nearly the same magnitude in comparison with other radio-frequency current drivers. The beam current drive potential is also discussed for transformer recharging in quasi-steady-state operations. An energy balance equation is combined with the beam current drive analysis code to study the stational operation conditions in the transformer recharging period. It is shown that the same beam system can be used in strict steady-state operations and in transformer recharging. The additional plasma pressure due to circulating fast ions is investigated in both the strict steady state and the transformer recharge phase. Fast alpha-particle pressures are discussed, taking into account the beam-plasma direct deuterium-tritium reaction. All fast ion pressures and the fusion power (including the beam direct reactions) are developed in simple formulas. Combining these formulas with the Troyon-type beta scaling, the required beam power and the current drive, consistent with the beta limit condition, are approximately determined. The toroidal beta increment Δβ due to these fast ions can attain magnitude comparable to the thermal beta, making it a critical factor in reactor design.
