2017
DOI: 10.1088/1741-4326/aa8fb1
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Pre-ionization by AC Ohmic coil operation in the TST-2 spherical tokamak

Abstract: AC Ohmic coil operation experiments with frequencies up to 10 kHz were performed on the TST-2 spherical tokamak device, and the pre-ionization process was studied in detail. The minimum loop voltage for pre-ionization was 0.4 V, which corresponds to 0.5 V m −1 at the inboard limiter. Dependences of growth rate and saturation level of the process on various parameters were obtained, and they are compared with a time-dependent 0-dimensional model based on Townsend avalanche and loss along field lines. Most of th… Show more

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Cited by 4 publications
(24 citation statements)
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“…This is what we call an ambipolar diffusion state, and such a state was found in the experiments described in [7], and a similar phenomenon is reproduced by a two-dimensional (2D) PIC simulation [6]. In contrast, the AC Ohmic coil operation experiments showed exponential growths and instantaneous growth rates can be as fast as an ideal rate, implying the loss term should be negligible [5]. Thus, we need to find some mechanisms destroying or mitigating the ambipolar diffusion state.…”
Section: Introductionsupporting
confidence: 52%
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“…This is what we call an ambipolar diffusion state, and such a state was found in the experiments described in [7], and a similar phenomenon is reproduced by a two-dimensional (2D) PIC simulation [6]. In contrast, the AC Ohmic coil operation experiments showed exponential growths and instantaneous growth rates can be as fast as an ideal rate, implying the loss term should be negligible [5]. Thus, we need to find some mechanisms destroying or mitigating the ambipolar diffusion state.…”
Section: Introductionsupporting
confidence: 52%
“…The AC Ohmic coil operation is a good experimental system, in which quasi steady state conditions are achieved, and we can clearly observe the exponential growth of density during pre-ionization [4]. A time dependent zero-dimensional model, which is an extension of the previous models, has been developed, and the model can explain various experimental results qualitatively [5]. The differences between the predicted and experimental quantities, such as growth rates, are within an order of magnitude.…”
Section: Introductionmentioning
confidence: 82%
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