-
Author(s):
K.Yamazaki, N.Ohyabu, M.Okamoto, T.Amano, J.Todoroki, Y.Ogawa, N.Nakajima, H.Akao, M.Asao, J.Fujita, Y.Hamada, T.Hayashi, T.Kamimura, H.Kaneko, T.Kuroda, S.Morimoto, N.Noda, T.Obiki, H.Sanuki, T.Sato, T.Satow, M.Wakatani, T.Watanabe, J.Yamamoto, O.Motojima, M.Fujiwara, A.Iiyoshi and LHD Design Group
-
Title:
Physics Studies on Helical Confinement Configurations with l=2 Continuous Coil Systems
Date of publication:
Sep. 1990
-
Key words:
Iarge helical device, physics design optimization, MHD beta limit, particle loss, neoclassical transport, anomalous transport, drift wave turbulence, bootstrap current, Ohkawa current, helical divertor
-
Abstract:
The physics studies have been carried out to optimize l=2 heliotron/torsatron configurations having continuous coil system for the Large Helical Device (LHD), focusing on beta-orbit-divertor compatibility requirement, neoclassical & anomalous transports, bootstrap & Ohkawa currents, and divertor layer analysis. The optimal m number is found ~ 10 for the LHD system based on three physics criteria: MHD stability (beta is greater than or equal to 5%), particle orbit confinement (loss-cone-free radius gamma_L is greater than or equal to1/3a_p (plasma minor radius)) and clean divertor layer (divertor-wall clearance Delta_dw is greater than or equal to 3cm). The pitch parameter of helical coil gamma_c is determined mainly from the beta-divertor condition. For the detailed prediction of LHD plasma parameters, 2.5-dimensional equilibrium-transport simulations including empirical or drift wave turbulence models are carried out, which reveal that the global confinement time is sensitive to the edge electron anomalous transport although ripple loss through the ion channel is dominant in the plasma core. When ripple-transport-optimized configurations are adopted, the bootstrap current is increased; however, the Ohkawa current may be utilized cancel this current. The divertor layer study clarifies peculiar magnetic properties of thin curved divertor layers and suggests the effectiveness of helical divertors. From these physics considerations within the related engineering constraints, a final standard LHD configuration (m=10, gamma_c=1.25, alpha^ast=0.1, where m, gamma_c and alpha^ast are toroidal mode, pitch and pitch modulation parameters of the helical coil, respectively) is determined.
-
|
