Helical Configuration with Low Ripple and High beta Stability

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For general discussions on the collaboration Prof.Motojima and Mr.R.Pavlichenko (graduate student of The Graduate University for Advanced Studies) visited Kiev and Kharkov in June. Mr.Pavlichenko brought a lot of materials on the design study of Uragan-2M torsatron (U-2M). U-2M is characterized with its low helical ripple, and combination of toroidal field ripple and helical ripple makes the effective ripple small. Although its experimental results will give us an important guide-line on the effect of helical ripple on the plasma confinemnt, its operation has not started yet because of bad economical conditions in Ukraine.Dr.Fedyanin presented his new idea of a diamagnetic loop, which gives us a high temporal resolution in measuring the plasma stored energy. He showed experimental results from L-2M stellarator. The prompt loss of energetic electrons which are accelerated in the electron cyclotron resonance heating (ECH) plays an important role in determining the power deposition. Usual … More ly the power deposition is estimated by the electron temperature change (with ECE measurement) after the turn-off of the heating power. However the accuracy of this ECE method is inversely proportional to the temporal resolution. The diamagnetic loop with high temporal resolution will be a powerful tool for the transport analysis of ECH plasma. Prof.O.Pavlichenko discussed with CHS group to promote a remote participation in CHS and LHD experiments, which will be an important subject in a worldwide fusion society. Dr.Marushchenko discussed the velocity distribution of electrons of a ECH plasma in CHS.The distribution is sensitive to the helical ripple which induces the loss of perpendicularly accelerated electrons. He is developing the Fokker-Planck computer code for this estimate with CHS experimentalists. Dr.Pustovitov is a great specialist in the MHD theory of helical plasma. He has made a lot of contributions to the theory in Japan since his first visit (1992). This year he found a simple and clear relation between magnetic coordinates (Hamada-and Boozer-coordinates). It is easily understood that coordinate usually used in tokamak is similar to the Boozer coordinate. The magnetic coordinates are essential to the optimization of helical nagnetic configuration. Based on these discussions we are designing a quasi-toroidally symmetric stellarator, which is the optimized configuration with essentially no helical ripple. Less