The Large Helical Device (LHD) helical divertor

Ohyabu, N.; Watanabe, Toshiya; Ji, H.; Akao, H.; Ono, Tetsu; Kawamura, T.; Yamazaki, K.; Akaishi, K.; Inoue, Noriyuki; Komori, A.; Kubota, Yūsuke; Noda, N.; Sagara, A.; Suzuki, H.; Motojima, O.; Fujiwara, Masami; Iiyoshi, A.

doi:10.1088/0029-5515/34/3/i07

Cited by 187 publications

(167 citation statements)

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“…One of the major goals of the LHD program is the demonstration of a reactor-relevant, diverted helical plasma. Two different divertor systems are available in LHD: the Helical Divertor (HD) [7] and the Local Island Divertor (LID) [8][9][10]. The HD is an intrinsic helical double-null divertor with an open divertor geometry, essentially like a helically twisting double-null tokamak poloidal divertor.…”

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confidence: 99%

Observation of Stable Superdense Core Plasmas in the Large Helical Device

et al. 2006

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In reduced recycling discharges in the Large Helical Device, a super dense core plasma develops when a series of pellets are injected. A core region with density as high as 4:5 10 20 m ÿ3 and temperature of 0.85 keV is maintained by an internal diffusion barrier with very high-density gradient. These results may extrapolate to a scenario for fusion ignition at very high density and relatively low temperature in helical devices. DOI: 10.1103/PhysRevLett.97.055002 PACS numbers: 52.55.HcImprovement of plasma particle and energy confinement is a major challenge for toroidal magnetic fusion research, and will be important in igniting burning plasmas in ITER [1]. Various confinement improvement modes have been discovered including edge transport barriers (ETBs, or H mode) [2] and internal transport barriers (ITBs) [3][4][5]. In this Letter, we describe improved confinement in super dense core (SDC) plasmas, in diverted discharges in the Large Helical Device (LHD), a heliotron configuration in which the rotational transform is provided by external magnetic coils. This operational regime may extrapolate to a high-density, relatively low temperature ignition scenario for these devices.LHD has an external helical field with poloidal winding number l 2 and M 10 toroidal field periods. The major radius of the magnetic axis, R ax 3:5-3:9 m, average plasma minor radius a 0:6 m, and toroidal magnetic field B 3:0 T [6]. Depending on the relative currents in the helical and auxiliary poloidal coils, the rotational transform on axis, 0 =2 0:3-0:6 and the edge transform, a =2 1-1:5. One of the major goals of the LHD program is the demonstration of a reactor-relevant, diverted helical plasma. Two different divertor systems are available in LHD: the Helical Divertor (HD) [7] and the Local Island Divertor (LID) [8][9][10]. The HD is an intrinsic helical double-null divertor with an open divertor geometry, essentially like a helically twisting double-null tokamak poloidal divertor. The LID uses an m 1, n 1 resonant magnetic island (poloidal and toroidal mode numbers m and n, respectively) to guide particle and heat fluxes to divertor plates.A SDC plasma develops spontaneously in LHD as a highly peaked density profile is created by injection of multiple pellets from the outside midplane as illustrated in Fig. 1(a). The density and temperature profiles are depicted for the standard (R ax 3:75 m, B 2:64 T, P 10 MW) discharge diverted by the LID in Fig. 1(b). These profiles are measured using a Thomson scattering diagnostic along R horiz , the major radius in the poloidal plane where the plasma is horizontally elongated [ Fig. 1(a)]. A core region with electron density 4:5 10 20 m ÿ3 and temperatures 0:85 keV is maintained by an internal diffusion barrier (IDB) located at normalized minor radius 0:5. The radial width of the IDB is 0:10 m ( 0:2). The density gradient at the IDB is extremely high (rn 2:5 10 21 m ÿ4 ). Inside the SDC region, the density and temperature gradients are nearly zero. The density gradient outside the IDB is we...

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Observation of Stable Superdense Core Plasmas in the Large Helical Device

et al. 2006

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“…1 with the vacuum vessel and divertor traces of the lines of force. The small pitch modulation of α c = 0.1 was determined by considering the gap distance between the first wall and the last closed flux surface (LCFS) and the confinement properties of the high-energy particles [1].…”

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confidence: 99%

Reduced-Size LHD-Type Fusion Reactor with D-Shaped Magnetic Surface

Watanabe

2012

Plasma and Fusion Research

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A new winding law for the continuous helical coils is proposed for Large Helical Device (LHD) type fusion reactors to satisfy the requirements for a wide blanket space and large plasma volume. Helical coils wound along the geodesic line of a torus with an elongated cross section can produce a magnetic configuration having a D-shaped magnetic surface with a magnetic well in the core region and high magnetic shear in the peripheral regions. The DT alpha particle confinement performance is greatly improved by increasing the elongation factor κ of the cross section of the winding frame for the helical coils. The results suggest that a smaller LHD-type fusion reactor can be realized.

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“…The Large Helical Device (LHD) [1] is a heliotron/tersatron type device with helical divertors. A poloidal cross section is illustrated in Fig.…”

Section: Introductionmentioning

confidence: 99%

1D Modeling of LHD Divertor Plasma and Hydrogen Recycling

Kawamura

Tomita

Kobayashi

et al. 2010

Plasma and Fusion Research

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One dimensional plasma and neutral model of the divertor plasma in Large Helical Device is presented. The plasma is described by stationary fluid equations for electron and ion. The atomic processes such as dissociation of hydrogen molecules released from the divertor plate, ionization of hydrogen atoms, charge exchange and recombination are included in equations of neutrals. This model is intended to be employed in an integrated simulation where an equilibrium of the upstream plasma and plasma-surface interactions at the divertor plate are solved in different numerical codes separately. From the computational point of view, the numerical code for the divertor plasma is developed for 1D flux tube where the boundary conditions of both ends are specified. The calculation time is less than one second and reasonably short to use in future integrated simulations. In the results, interactions between plasma and neutrals and dependence of the energy loss on the plasma density are studied. In low density case, the energy is lost through ionization and charge exchange but the total amount of the loss is small and the impurity loss is negligibly small. In high density case, the ionization loss and impurity cooling become much larger than the charge exchange loss and causes a drop of the heat flux.

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The Large Helical Device (LHD) helical divertor

Cited by 187 publications

References 16 publications

Observation of Stable Superdense Core Plasmas in the Large Helical Device

Observation of Stable Superdense Core Plasmas in the Large Helical Device

Reduced-Size LHD-Type Fusion Reactor with D-Shaped Magnetic Surface

1D Modeling of LHD Divertor Plasma and Hydrogen Recycling

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