A New Capacitive / Resistive Probe Method for Studying Magnetic Surfaces

Kitajima, S.; Takayama, M.; Zama, Tatsuya; Takaya, Kazuhiro; Takeuchi, Nobunao; Watanabe, Hiroshige

doi:10.1143/jjap.30.2606

Cited by 22 publications

(9 citation statements)

References 7 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…1 (a). Three capacitor banks, consisting of two-stage pulse forming networks, separately supplied coil currents of 10 ms flat top [11]. The target plasma for external perturbation fields was He plasma produced by low-frequency joule heating ( f = 18.8 kHz, P out ∼ 35 kW).…”

Section: Tu-heliacmentioning

confidence: 99%

Effects of Rotating Magnetic Islands Driven by External Perturbation Fields in the TU-Heliac

Kitajima

Umetsu

Sasao

et al. 2008

Plasma and Fusion Research

Self Cite

View full text Add to dashboard Cite

A new method for rotating magnetic islands by external perturbation fields is proposed. In the experiments, perturbation fields were produced using four pairs of cusp field coil, in which alternating currents having a π/2 phase shift flowed. A phase shifter for the coil currents was designed and constructed. The phase difference in the floating potential signals measured using two Langmuir probes confirmed that the magnetic islands rotated in the counterclockwise direction (c/cw). The clockwise (cw) rotation was also observed in the plasma biased by the hot cathode electrode. These experimental results suggest the ability of producing plasma poloidal rotation driven by rotating islands. InroductionA study on the effects of magnetic islands on transport in helical devices is important, because it leads to the advanced control method for a plasma periphery in a helical fusion reactor. The magnetic island effects on transport have been surveyed widely in the Large Helical Device (LHD) [1][2][3][4][5][6]. For the research on the island effects on the confinement modes, the Tohoku University Heliac (TU-Heliac) has advantages that (1) the position of a rational surface is changeable by selecting the ratio of coil currents, (2) the island formation can be controlled by external perturbation field coils, and (3) a radial electric field and particle transport can be controlled by electrode biasing. In the TU-Heliac, the improved mode transition was triggered by electrode biasing using a hot cathode composed of LaB 6 . The driving force J × B for the plasma poloidal rotation was externally controlled, and the poloidal viscosity was successfully estimated from the external driving force [7][8][9]. In recent experiments, the ion viscosity in the biased plasma with islands was roughly estimated. It suggested that the ion viscosity increased with the magnetic island width [10]. Therefore, it is expected that the plasma poloidal rotation will be driven by the poloidal rotation of the island. The purposes of this experiment are to propose the new method of rotating islands by the external perturbation fields, survey the ability of the plasma poloidal rotaauthor's e-mail: sumio.kitajima@qse.tohoku.ac.jp tion driven by rotating islands, and study the rotating island effects on confinement modes in TU-Heliac. Experimental Setup TU-HeliacThe TU-Heliac is a four-period heliac (major radius, 0.48 m; average plasma radius, 0.07 m). The heliac configurations were produced using three sets of magnetic field coils; 32 toroidal field coils, a center conductor coil, and one pair of vertical field coils, as shown in Fig. 1 (a). Three capacitor banks, consisting of two-stage pulse forming networks, separately supplied coil currents of 10 ms flat top [11]. The target plasma for external perturbation fields was He plasma produced by low-frequency joule heating ( f = 18.8 kHz, P out ∼ 35 kW). The joule heating power was supplied to one pair of the poloidal coils wound outside the toroidal coils [12]. The vacuum vessel was filled with fueling n...

show abstract

Section: Tu-heliacmentioning

confidence: 99%

Effects of Rotating Magnetic Islands Driven by External Perturbation Fields in the TU-Heliac

Kitajima

Umetsu

Sasao

et al. 2008

Plasma and Fusion Research

Self Cite

View full text Add to dashboard Cite

show abstract

“…A similar presentation (the RC method), i.e. the introduction of equivalent capacitance and resistance between the electron cloud on the CMS and the vacuum wall, has already been applied to study the electron transport in a stellarator [11] (see section 2). However, the consideration of the TSD discharge behaviour admits the following analogues: discharges at a low working-gas pressure with the thermionic cathode, a cylindrical diode in the magnetic field, Penning discharges, magnetrons and discharges in the magnetic field with a rotating plasma.…”

Section: Discussion Of the Discharge Patternmentioning

confidence: 99%

“…The measurements gave a number of scalings: I em ∝ B −0.67 to I em ∝ B −2.23 . Using the "RC method" [11] (the TSD version with an additional anode as a grid around the thermionic emitter that excludes the influence of the electron space charge in the vicinity of the thermionic cathode), the researchers at the Tohoku University Heliac stellarator with a helical magnetic axis have determined the coefficient of electron diffusion due to elastic electron-neutral-atom collisions, D ∝ B −1.5 (D ∝ I em ) [18], in the range of magnetic fields B = 0.03 − 0.308 T under pulsed conditions. In [18], it was asserted that the dependence obtained is similar to that predicted on the basis of the neoclassical transport theory for the tokamak.…”

Section: Present-day Ideas Of the Toroidal Stellarator Diode And Physmentioning

confidence: 99%

Toroidal stellarator diode: discharge features and electron transport

Lesnyakov

Волков

2006

Plasma Devices and Operations

View full text Add to dashboard Cite

The radial dependences of the emission current I em of a small thermionic emitter at different anode voltages, as well as the current-voltage characteristics (CVCs) and the dependence of I em on the magnetic field B were measured to investigate the relationship between the electron transport and the E × B electric and magnetic fields in the toroidal stellarator diode system in stellarator-type magnetic traps (Uragan-3M and Uragan-2M torsatrons). It is demonstrated that the electron transport in the discharge is controlled to a large measure by an applied radial electric field, while the current jump (nonlinear dynamic behaviour) in the discharge is due to the attainment of the critical value by the radial electric field and to the occurrence of the ionization process. A phenomenological description of the CVCs showing a hysteresis behaviour is presented. A large variety of electron transport scalings (I em -B dependences) were obtained in two different torsatrons.

show abstract

“…The heliac configurations were produced by three sets of magnetic field coils: 32 toroidal field coils, a centre conductor coil and one pair of vertical field coils. Three capacitor banks consisting of two-stage pulse forming networks separately supplied coil currents of 10 ms flat top [28]. The target plasma for biasing was an He plasma produced by low frequency joule heating (f = 18.8 kHz, P out ∼ 35 kW).…”

Section: Experimental Set-up In Tu-heliacmentioning

confidence: 99%

Study of ion viscosity by spontaneous L–H transitions under marginal hot cathode biasing in the Tohoku University Heliac

Kitajima¹,

Takahashi²,

Takeda³

et al. 2008

Nucl. Fusion

View full text Add to dashboard Cite

Using the spontaneous transition condition under marginal hot cathode biasing, the ion viscosity at the L–H transition was estimated in various magnetic configurations in the Tohoku University Heliac. The critical viscosity, which is the viscosity at the transition point, was experimentally estimated from the J × B driving force. The critical viscosities in different magnetic configurations were in agreement with the neoclassical predictions within a factor of 2 and were compared with the viscosities obtained in the externally forced biasing experiments. Although the transition points were spread over a wide range, poloidal Mach numbers at the transition point were concentrated near the viscosity maxima predicted by the theory.

show abstract

A New Capacitive / Resistive Probe Method for Studying Magnetic Surfaces

Cited by 22 publications

References 7 publications

Effects of Rotating Magnetic Islands Driven by External Perturbation Fields in the TU-Heliac

Effects of Rotating Magnetic Islands Driven by External Perturbation Fields in the TU-Heliac

Toroidal stellarator diode: discharge features and electron transport

Study of ion viscosity by spontaneous L–H transitions under marginal hot cathode biasing in the Tohoku University Heliac

Contact Info

Product

Resources

About