Comparison of Heating Efficiency Between Co and Counter Neutral Beam injection in Large Helical Device
Abstract
In the Large Helical Device, tangential neutral beam injection (NBI) is adopted in order to avoid that the fast ions are directly trapped in helical ripples. Then effective heating is realized by negative ion based high energy tangential NBI systems in Large Helical Device, two beam lines ware arranged counter -injection and the other one was arranged co-injection. However, it is predicted that the absorption efficiency of a NBI heating is also influenced by troidal drift motion of injected beam particle in weak magnetic field (Bt < 1T) operations such as high beta experiment. And also plasmas must be build up by using tangential NBI heating alone from the magnetic field strength Bt 0.5T to 1.5T, since heating by electron cyclotron heating can not be performed. So, the efficiency of co and counter NBI heating is an important issue for generating high beta plasma. According to experiment results, either of co and counter NBI was able to heat plasma efficiently in Bt=0.75T. Enhancement factors of energy confinement time without considering direct drift loss is almost the same in these plasmas. However, there is a difference in build up time of plasma by co and counter. There are no big difference in an electron temperature profile of co and counter heating as low as Bt=0.75 although the beam absorption profile may be different between co and counter injection.
- Publication:
-
APS Division of Plasma Physics Meeting Abstracts
- Pub Date:
- October 2001
- Bibcode:
- 2001APS..DPPCP1060I