Preliminary Report of the Waseda University Excavations at Dahshur North:Tenth Season,2004-2005

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増強されたECHアンテナシステムを用いたLHDにおけるECCD適用性の向上

The power injection system for electron cyclotron heating (ECH) and electron cyclotron current drive (ECCD) was modified and upgraded. An outside horizontal port 2-O on the Large Helical Device (LHD) was furnished with two antenna systems for the EC-waves of the frequencies of 77 and 154 GHz, respectively. In addition to them, two new antenna systems for 77 and 154 GHz waves were installed in the 2-O port. Each antenna in the 2-O port has wide range of EC-wave beam direction control so that these are suitable for ECCD which requires toroidally oblique EC-wave beam injection. In the LHD 18th experimental campaign in 2014-2015, an ECCD experiment with second harmonic resonance condition, on-axis magnetic field of 1.375 T for 77 GHz waves, was performed in which some combination patterns of two 77 GHz ECCDs were applied. The discharges of dual co- and dual counter-ECCDs showed remarkable plasma currents of ∼±26 kA in both of the co- and counter-directions, by 6 s pulse duration and injection powers of 366 and 365 kW. The new antenna has nearly the same capability for ECCD with that of the existing antenna. The improvement in the flexibility of the ways of applying plural ECCDs will offer a highly useful tool for investigations on the phenomena concerning with the plasma current such as magnetohydro-dynamics

Development and application of a ray-tracing code integrating with 3D equilibrium mapping in LHD ECH experiments

The central electron temperature has successfully reached up to 7.5 keV in large helical device(LHD) plasmas with a central high-ion temperature of 5 keV and a central electron density of1.3×1019 m−3. This result was obtained by heating with a newly-installed 154 GHz gyrotronand also the optimisation of injection geometry in electron cyclotron heating (ECH). Theoptimisation was carried out by using the ray-tracing code ‘LHDGauss’, which was upgradedto include the rapid post-processing three-dimensional (3D) equilibrium mapping obtainedfrom experiments. For ray-tracing calculations, LHDGauss can automatically read the relevantdata registered in the LHD database after a discharge, such as ECH injection settings (e.g.Gaussian beam parameters, target positions, polarisation and ECH power) and Thomsonscattering diagnostic data along with the 3D equilibrium mapping data. The equilibrium mapof the electron density and temperature profiles are then extrapolated into the region outsidethe last closed flux surface. Mode purity, or the ratio between the ordinary mode and theextraordinary mode, is obtained by calculating the 1D full-wave equation along the directionof the rays from the antenna to the absorption target point. Using the virtual magnetic fluxsurfaces, the effects of the modelled density profiles and the magnetic shear at the peripheralregion with a given polarisation are taken into account. Power deposition profiles calculatedfor each Thomson scattering measurement timing are registered in the LHD database. Theadjustment of the injection settings for the desired deposition profile from the feedbackprovided on a shot-by-shot basis resulted in an effective experimental procedure

Stable sustainment of plasmas with electron internal transport barrier by ECH in the LHD

The long pulse experiments in the Large Helical Device has made progress in sustainment of improved confinement states. It was found that steady-state sustainment of the plasmas with improved confinement at the core region, that is, electron internal transport barrier (e-ITB), was achieved with no significant difficulty. Sustainment of a plasma having e-ITB with the line average electron density ne_ave of 1.1 × 1019 m−3 and the central electron temperature Te0 of ∼3.5 keV for longer than 5 min only with 340 kW ECH power was successfully demonstrated

Progress of long pulse discharges by ECH in LHD

Using ion cyclotron heating and electron cyclotron heating (ECH), or solo ECH, trials of steady state plasma sustainment have been conducted in the superconducting helical/stellarator, large helical device (LHD) (Ida K et al 2015 Nucl. Fusion 55 104018). In recent years, the ECH system has been upgraded by applying newly developed 77 and 154 GHz gyrotrons. A new gas fueling system applied to the steady state operations in the LHD realized precise feedback control of the line average electron density even when the wall condition varied during long pulse discharges. Owing to these improvements in the ECH and the gas fueling systems, a stable 39 min discharge with a line average electron density ne_ave of 1.1  ×  1019 m−3, a central electron temperature Te0 of over 2.5 keV, and a central ion temperature Ti0 of 1.0 keV was successfully performed with ~350 kW EC-waves. The parameters are much improved from the previous 65 min discharge with ne_ave of 0.15  ×  1019 m−3 and Te0 of 1.7 keV, and the 30 min discharge with ne_ave of 0.7  ×  1019 m−3 and Te0 of 1.7 keV

King Khufu’s Second Boat: Scientific Identification of Wood Species for Deckhouse, Canopy, and Forecastle

Very little published information is available on the scientific identification of wood species used in the construction of boats in ancient Egypt. This paper deals with the scientific identification of wood species used in the construction of the deckhouse, canopy, and forecastle of King Khufu’s second wooden boat (4th Dynasty—Old Kingdom) in detail. This paper also discusses the principal technological characteristics of the identified woods, considering specifically their utilization for construction of the deckhouse, canopy, and forecastle. Almost all the woods used in the boat’s deckhouse, canopy, and forecastle were made of two imported species of wood (Cedrus libani A.Rich. and Juniperus sp.), with two native species (Ziziphus spina-christi (L.) Willd. and Vachellia sp.) also identified. The analysis most surprisingly revealed the presence of Ziziphus spina-christi (L.) Willd. in 25% of the analyzed forecastle samples, which was discovered for the first time for making cross beams in the construction of boats in ancient Egypt. Another intriguing aspect of the boat’s construction is the presence of Juniperus sp., which surprisingly showed that almost 85% of the analyzed samples were Juniperus sp., used in the deckhouse’s boards, frames, and cross beams. The data let us examine the specific employment of the wood species used in the parts of the boat, which evidenced that the identified woods were suitably used for the construction of the different parts of the deckhouse, canopy, and forecastle of the boat