199 research outputs found
Toward inertial confinement fusion energy based on heavy ion beam
Heavy ion inertial fusion (HIF) energy would be one of promising energy
resources securing our future energy in order to sustain our human life for
centuries and beyond. The heavy ion beam (HIB) has remarkable preferable
features to release the fusion energy in inertial confinement fusion: in
particle accelerators HIBs are generated with a high driver efficiency of ~
30-40%, and the HIB ions deposit their energy inside of materials. Therefore, a
requirement for the fusion target energy gain is relatively low, that would be
~50-70 to operate a HIF fusion reactor with the standard energy output of 1GW
of electricity. The HIF reactor operation frequency would be ~10~15 Hz or so.
Several-MJ HIBs illuminate a fusion fuel target, and the fuel target is
imploded to about a thousand times of the solid density. Then the DT fuel is
ignited and burned. The HIB ion deposition range would be ~0.5-1 mm or so
depending on the material. Therefore, a relatively large density-scale length
appears in the fuel target material. The large density-gradient-scale length
helps to reduce the Rayleigh-Taylor (R-T) growth rate. The key merits in HIF
physics are presented in the article toward our bright future energy resource.Comment: 17 pages. arXiv admin note: substantial text overlap with
arXiv:1511.06508, arXiv:1608.0106
Absence of Hybridization Gap in Heavy Electron Systems and Analysis of YbAl3 in terms of Nearly Free Electron Conduction Band
In the analysis of the heavy electron systems, theoretical models with c-f
hybridization gap are often used. We point out that such a gap does not exist
and the simple picture with the hybridization gap is misleading in the metallic
systems, and present a correct picture by explicitly constructing an effective
band model of YbAl_3. Hamiltonian consists of a nearly free electron model for
conduction bands which hybridize with localized f-electrons, and includes only
a few parameters. Density of states, Sommerfeld coefficient, f-electron number
and optical conductivity are calculated and compared with the band calculations
and the experiments.Comment: 9 pages, 9 figures, submitted to J. Phys. Soc. Jp
Formation Mechanism of Hybridization Gap in Kondo Insulators based on a Realistic Band Model and Application to YbB
A new LDA+U band calculation is performed on the Kondo insulator material
YbB and an energy gap of about 0.001Ryd is obtained. Based on this, a
simple tight-binding model with 5d and 4f orbitals on Yb
atoms and the nearest neighbor -bonds between them is constructed with
a good agreement to the above the LDA+U calculation near the gap. The density
of states is also calculated and the shape is found to be very asymmetric with
respect to the gap. A formation mechanism of the gap is clarified for the first
time in a realistic situation with the orbital degeneracies in both conduction
bands and the f states. This model can be a useful starting point for
incorporating the strong correlation effect, and for understanding all the
thermal, thermoelectric, transport and magnetic properties of YbB.Comment: 15 pages, 15 figures, to appear in J. Phys. Soc. Jpn. Vol. 72 No. 5
(2003
Determination of the Gamow-Teller Quenching Factor from Charge Exchange Reactions on 90Zr
Double differential cross sections between 0-12 degrees were measured for the
90Zr(n,p) reaction at 293 MeV over a wide excitation energy range of 0-70 MeV.
A multipole decomposition technique was applied to the present data as well as
the previously obtained 90Zr(p,n) data to extract the Gamow-Teller (GT)
component from the continuum. The GT quenching factor Q was derived by using
the obtained total GT strengths. The result is Q=0.88+/-0.06 not including an
overall normalization uncertainty in the GT unit cross section of 16%.Comment: 11 papes, 4 figures, submitted to Physics Letters B (accepted),
gzipped tar file, changed content
Thermal transport barrier in heliotron-type devices (Large Helical Device and Compact Helical System)
In the discharges of the Large Helical Device [O. Motojima et al., Proceedings of the 16th Conference on Fusion Energy, Montreal, 1996 (International Atomic Energy Agency, Vienna, 1997), Vol. 3, p. 437], a significant enhancement of the energy confinement has been achieved with an edge thermal transport barrier, which exhibits a sharp gradient at the edge. Key features associated with the barrier are quite different from those seen in tokamaks (i) almost no change in particle (including impurity) transport, (ii) a gradual formation of the barrier, (iii) a very high ratio of the edge temperature to the average temperature, (iv) no edge relaxation phenomenon. In the electron cyclotron heating (ECH) heated discharges in the Compact Helical System [K. Matsuoka et al., in Proceedings of the 12th International Conference on Plasma Physics and Controlled Nuclear Fusion Research, Nice, France, 1988 (International Atomic Energy Agency, Vienna, 1989), Vol. 2, p. 411], the internal electron transport barrier has been observed, which enhances the central electron temperature significantly. High shear of the radial electric field appears to suppress the turbulence in the core region and enhance the electron confinement there
ヨウリョクタイガタ フェレドキシン ノ コウゾウ カイセキ 2.8Å ブンカイノウ
Remarkable progress in the physical parameters of net-current free plasmas has been made in the Large Helical Device (LHD) since the last Fusion Energy Conference in Chengdu, 2006 (O.Motojima et al., Nucl. Fusion 47 (2007) S668). The beta value reached 5 % and a high beta state beyond 4.5% from the diamagnetic measurement has been maintained for longer than 100 times the energy confinement time. The density and temperature regimes also have been extended. The central density has exceeded 1.0 x 10^21 m^-3 due to the formation of an Internal Diffusion Barrier (IDB). The ion temperature has reached 6.8 keV at the density of 2 x 10^19m^-3, which is associated with the suppression of ion heat conduction loss. Although these parameters have been obtained in separated discharges, each fusion-reactor relevant parameter has elucidated the potential of net-current free heliotron plasmas. Diversified studies in recent LHD experiments are reviewed in this paper
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