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5 EX/P3-37 3.1 Evaluation of CT Performance on the Test stand
On the test stand, the CTs pass through the drift tube and then penetrate into transverse magnetic field with the profile of vacuum magnetic field before CT injection as shown in FIG. 5 (a) [8]. The penetration depth and velocity are measured by the time-of-flight method from time evolution of magnetic signals as shown in FIG. 5 (b). The dashed lines tracing initial peaks of magnetic field waveform. Penetration speed of CT evaluated by this measurement is approximately 100km/s. The typical position of separatrix rs of C-2U FRC is about 40 cm from the entrance end of grass tube as depicted with pink line on FIG.5 (a) This speed is consistent with the one obtained on the drift tube.
(a) (b)
FIG. 5. (a) Vacuum field profile before CT injection. (b) Time evolution of magnetic probe signals obtained by the upper array (red) and the lower array (blue). The dashed lines tracing initial peaks of waveforms.
3.2 CT injection into C-2U FRC
To avoid disruptive perturbation on the FRC, the CT injectors have been operated at the lower limit of particle inventory. Figure 6 shows the time evolution of line integrated electron density that was measured by a CO2 interferometer at the midplane. Approximately 30% of increment in line-integrated density was observed by single CT injection at t = 2.0 ms (FIG. 6 (a)). This is approximately 60% of particle inventory of injected CTs [6].
Multi-pulsed injection with frequency of 0.5kHz has also been performed with two injectors.
It also demonstrated successful fueling as shown in FIG. 6 (b). Injected CTs have spheromak-
(a) (b)
like magnetic configuration and they temporarily tear flux surfaces when entering the FRC. Also the temperature of the injected CT is about 10% of the target plasma. This leads to some fast particle loss and cooling of plasma. However, any disruptive effect on the FRC has not been observed.