量研学術機関リポジトリ「QST-Repository」は、国立研究開発法人 量子科学技術研究開発機構に所属する職員等が生み出した学術成果（学会誌発表論文、学会発表、研究開発報告書、特許等）を集積しインターネット上で広く公開するサービスです。 Welcome to QST-Repository where we accumulates and discloses the academic research results(Journal Publications, Conference presentation, Research and Development Report, Patent, etc.) of the members of National Institutes for Quantum Science and Technology.
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The mission of the future tokamak device JT-60SA, currently under construction at Naka, is to produce steady-state scenarios at high beta and density in support of the ITER and DEMO steady-state program. The development of such fully non-inductive plasmas both at high normalized (βN) and poloidal (βp) beta is a crucial challenge for the steady-state operation of a tokamak reactor due to a significant number of exigent physics requirements. One of the key elements that can alleviate such difficulties is performing previous validated modelling with the aim of preparing the target scenarios and find possible solutions. However, validated models in conditions relevant for JT-60SA or the future reactor, i.e. with significant NBI and ECRH current drive, bootstrap current and fast ion fraction for several current diffusion times, is difficult due to the limited number of such plasmas available.
In order to assess the difficulties found on those scenarios, steady-state regimes have been explored at TCV using the newly available 1MW Neutral Beam Injection (NBI) system [1]. Compared to the past, when fully non-inductive plasmas were sustained using Electron Cylotron (EC) waves only [2,3], the operating space has been now extended towards plasma conditions compatible with co-Ip NBI heating, i.e. plasma current (Ip=[130, 150]kA) and density (ne,0≈[2,3]e19m-3) with a combination of on-axis and off-axis heating schemes.
βN values up to 1.4 and 1.7 have been reached in fully non-inductive plasmas (Vloop~0) in L-mode and H-mode respectively, both occurring with central EC and NB deposition and H/CD in the co-Ip direction. For comparison, note that βN<0.4 and Vloop>0.7V are typically obtained in similar Ohmic plasmas. Fully non-inductive operation could not be achieved with NBI alone (Vloop>0.5V). Adding NBI results in an increase or decrease of Vloop depending on other plasma parameters. For instance, NBI can significantly increase the density which in turn reduces the ECCD efficiency.
One of the routes explored has been the creation of Internal Transport Barriers (ITB) in order to maximize the bootstrap current fraction. This turned out to be a challenge as they were not formed in either the electron or the ion channel in the plasmas explored up to date in spite of the fact of a significant increasing of the toroidal rotation and fast ion (FI) fraction with NBI, which are known to reduce turbulence [4]. The possibility that these plasmas are Trapped Electron Mode (TEM) turbulence dominated, which is less susceptible to such stabilizations [5], is being analysed in dedicated turbulence analyses. Additionally, excessive on-axis NBI current obtained prevented the onset of strong ITB’s as previously shown in modelling [6].
Optimization of high beta steady-state scenarios at TCV in support of JT-60SA
