FPN13-11

Progress of high-temperature experiments in LHD

February 25, 2013

Realization of high-temperature plasmas is one of the most important issues in helical plasmas, which have an advantage over tokamak plasmas for steady-state operation and no disruptions. In the Large Helical Device (LHD), a stellarator in Japan, the heating capability has been upgraded year by year and the high-temperature regime has been successfully extended.

In the LHD, three negative-ion-based neutral beam injectors (NBs) produce hydrogen neutral beams with a beam energy of 180 keV and a total port-through power of 16 MW. These negative NBs are tangentially injected to the LHD plasma. A positive-ion-based NB with a "low" energy of 40 keV was perpendicularly injected for ion heating. Since 2010, a second 40-keV perpendicular NB has been operational in LHD and the total port-through power for perpendicular NBI has thus increased from 6 MW to 12 MW. An electron cyclotron resonance heating (ECRH) system with eight gyrotrons has been operated for preionization and plasma heating. Enhancement of the output power per gyrotron has been planned in LHD and the replacement of the existing gyrotrons with higher-power tubes is in progress. At present,three 77-GHz gyrotrons with output power of more than 1 MW each, are operational for plasma experiments. LHD now has 28 MW of NB power and 3.7 MW of ECRH power available for experiments. Peak electron temperatures of 20 keV and peak ion temperatures above 5 keV are obtained.

Details of the experiments can be seen in the latest issue of Stellarator News at http://www.ornl.gov/sci/fed/stelnews/pdf/sn139.pdf