抄録
The recent dramatic progress in the study of helical systems related to achieving high beta plasmas is reviewed.Discharges with over 3% beta plasmas have been achieved in LHD and W7-AS experiments. Although MHD instabilities affect pressure gradients as a local effect, high beta plasmas have been achieved in a fairly stable region according to ideal MHD stability analysis. Heating power and/or radiation phenomena were shown to still limit the experimental beta values. Magnetic surfaces with good quality are considered to exit even in over 3% beta plasmas. The issues involved in achieving more than 5% beta plasmas are summarized.
