RF Central Solenoid Operation for Plasma Production and Current Drive in TST-2

Ejiri, A.; Takase, Y.; Tsujii, N.; Shinya, Takahiro; Yajima, S.; Sonehara, Makoto; Furui, H.; Togashi, H.; Homma, H.; Nakamura, Kenta; Takeuchi, Takamasa; Yoshida, Yusuke; Takahashi, Wataru; Toida, K.; Yamazaki, H.

doi:10.1585/pfr.11.1202004

Cited by 4 publications

(11 citation statements)

References 9 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Hence, we can apply AC loop voltage indefinitely with a very small flux swing. The method has been applied to the TST-2 spherical tokamak device, and preionization and generation of plasma current with a DC component were demonstrated [2].…”

Section: Introductionmentioning

confidence: 99%

Pre-ionization by AC Ohmic coil operation in the TST-2 spherical tokamak

et al. 2017

View full text Add to dashboard Cite

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 the dependences are reproduced qualitatively by the model, and quantitative differences are within a factor of several. However, the external vertical field dependence of the appearance time, which is defined as the time to observe a plasma, and the isotope effect cannot be reproduced by the model. An ambipolar diffusion state which is predicted theoretically but mitigated experimentally is discussed. It was found that secondary electron emission at the limiter surfaces is a candidate mechanism to mitigate the state.

show abstract

Section: Introductionmentioning

confidence: 99%

Pre-ionization by AC Ohmic coil operation in the TST-2 spherical tokamak

et al. 2017

View full text Add to dashboard Cite

show abstract

“…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].…”

Section: Introductionmentioning

confidence: 92%

“…One of the main targets of this study is the theoretical interpretation of the results of the AC Ohmic coil operation, in which thin cylindrical plasma is generated on the inboard side [4,5]. The toroidal field strength B t was much higher than the vertical and the radial field strengths B z and B R .…”

Section: Configuration and Fluid Equationsmentioning

confidence: 99%

“…where n i and n e are the deuterium (or hydrogen) ion and electron densities, and E z denotes the parallel component of the vertical electrostatic field E z . We used the axisymmetry condition ∂/∂y = 0 and the relationship E z ≈ bE z to derive equation (4). Note that there is no toroidal electrostatic field due to the toroidal symmetry.…”

Section: Configuration and Fluid Equationsmentioning

confidence: 99%

“…AC Ohmic coil operation is used for pre-ionization or heating in toroidal devices [4,16,17]. Since the flux swing of an Ohmic coil is a product of the inductive voltage and the duration, the maximum flux swing is proportional to the period of AC and it is quite small.…”

Section: Effects Of Ac Fieldmentioning

confidence: 99%

See 2 more Smart Citations

Theoretical study of pre-ionization by inductive field in tokamaks

et al. 2020

View full text Add to dashboard Cite

A one-dimensional fluid model is developed for a numerical study of pre-ionization in a tokamak device under a given external inductive field. The calculation space is a magnetic field line connecting the bottom and the top limiters, and the spatial profiles of ion and electron densities and their time evolutions are calculated, assuming density growth by the Townsend avalanche. It was found that at a low initial density, electrons are evacuated and exponential growth can be stopped (i.e. stagnation phase), and at a high density, formation of an ambipolar diffusion state may suppress further avalanche by compensating the external inductive field. The numerical study revealed that these two obstacles for pre-ionization can be avoided or mitigated under a certain condition. A high ion impact secondary electron emission efficiency at the limiter, a long field line length and a large Townsend’s coefficient are preferable to avoid the stagnation phase or to resume growth from the stagnation phase. The ambipolar diffusion state can be mitigated or avoided using the following four mechanisms: drift induced diffusion, and curvature drifts, a high ion impact secondary electron emission efficiency and AC inductive field. Among them, only the first is practically useful in weak inductive field large devices. Various analytical expressions describing these behaviors and the conditions for a successful pre-ionization are obtained.

show abstract

Overview of spherical tokamak research in Japan

et al. 2017

View full text Add to dashboard Cite

Nationally coordinated research on spherical tokamak is being conducted in Japan. Recent achievements include: (i) plasma current start-up and ramp-up without the use of the central solenoid by RF waves (in electron cyclotron and lower hybrid frequency ranges), (ii) plasma current start-up by AC Ohmic operation and by coaxial helicity injection, (iii) development of an advanced fuelling technique by compact toroid injection, (iv) ultra-long-pulse operation and particle control using a high temperature metal wall, (v) access to the ultra-high-β regime by high-power reconnection heating, and (vi) improvement of spherical tokamak plasma stability by externally applied helical field.

show abstract

RF Central Solenoid Operation for Plasma Production and Current Drive in TST-2

Cited by 4 publications

References 9 publications

Pre-ionization by AC Ohmic coil operation in the TST-2 spherical tokamak

Pre-ionization by AC Ohmic coil operation in the TST-2 spherical tokamak

Theoretical study of pre-ionization by inductive field in tokamaks

Overview of spherical tokamak research in Japan

Contact Info

Product

Resources

About