November 2003
In this month, test of hardware systems and conditioning operation have been carried out as an initial operation stage after the modification for the extension of pulse length from 15 s to 65 s and of heating duration from 10 s to 30 s.
(1) Test of hardware systems:
Interlock tests, sequence tests and tokamak power supply tests were performed to check modified systems for extended pulse length. Sustainment of flattop of toroidal field (BT) for 65 s and its control by the pre-programming were successfully achieved.
(2) Conditioning operation:
Wall conditioning was carried out by the combination of 300°C baking of vacuum vessel, TDC and GDC before the beginning of tokamak operation.
In the first week of conditioning operation, LH and EC conditioning, NBI port conditioning, and wall conditioning were carried out in 15 s discharges with the 300°C baking. Calibration of the diamagnetic loop, electron temperature measurement by using a new ECE system, and BT ramp-up test were also performed. The EC pulse length was extended up to 1 s on #1, #3 and #4 units (X-mode). The duration of NB injection was extended over 3 s for 4 units. The H/D (hydrogen/deuterium) ratio was decreased from 1~2 to ~0.4 in ~50 discharges.
In the second week, the discharge pulse length has been extended up to 47.8 s. NBI port conditioning has progressed significantly in long pulse mode operation. The vessel temperature was decreased to 150°C to allow longer NB pulse length, which was often restricted by increase in the tile temperature due to NBI shinethrough. As a result, the duration of NB injection was extended further to 9.5-12 s on 4 tangential units, and to 9-9.5 s on perpendicular units (except for one unit (#13), which was limited to 7 s). Long pulse NB heating up to 30 s was successfully demonstrated by injecting these units sequentially. The EC pulse length was extended up to 1 s on #1, 2 s on #2/#3, and 1.6 s on #4, respectively. The H/D ratio was decreased finally to ~0.2. Diagnostic systems such as diamag loop, MSE, Thomson scattering and so on, were also adjusted.