LHD first plasma operation
The LHD cryostat and plasma vacuum vessel were evacuated to confirm their leak tightness. This evacuation process and leak test were conducted from Jan. 20 to Feb. 14,1998. Subsequently, the first cool down process was started on Feb. 23. Both helical and poloidal coils became superconducting on Mar. 17 and the LHD cryogenic system reached steady-state operation on schedule.Finally, the superconducting coils successfully generated a 1.5 Tesla magnetic field at the center of the plasma vacuum vessel was begun on Mar. 28 to prepare for the first plasma experiment.
Description of the first cycle of experiments
The creation of the first high-temperature plasma took place on Mar. 31, 1998. The device perfomance is being improved by increased heating power and discharge cleaning of the plasma vessel. During the first cycle of operation, the plasma had a major radius 3.7-3.9 m, minor radius 0.65m, electron density 1.3X 1019m-3and temperature 15,000,000 Celsius with 350kW of electron cyclotron resonance heating. The duration of energy confinement was more than 250 msec,which breaks the record of conventional helicaltype fusion experimental apparatus. Measurements of the magnetic surfaces created by the superconducting coils confirmed the validity of the design and the proper construction of the LHD.
Data from plasma experiments
Discharge cleaning of plasma vacuum vessel
We keep the cacuum vessel clean for our plasma.
The plasma performance is significantly sffected by the surface condition of the plasma vacuum vessel. To attain highplasma temperature and density the vacuum vessel walls must be maintained with no more than a low level of impurities. Discharge cleaning of LHD can be performed using 2.54GHz electron cyclotron resonance heating.Pictures on the left and the graph show improvement of the plasma performance during the first cycle of operation.