Masatada Ogasawara

Basic Requirements for a 1000-MW(electric) Class Tokamak Fusion-Fission Hybrid Reactor and Its Blanket Concept

AbstractPlasma size and other basic performance parameters for 1000-MW (electric) power production are calculated with the blanket energy multiplication factor, the M value, as a parameter. The calculational model is based on the International Thermonuclear Experimental Reactor (ITER) physics design guidelines and includes overall plant power flow. Plasma size decreases as the M value increases. However, the improvement in the plasma compactness and other basic performance parameters, such as the total plant power efficiency, becomes saturated above the M = 5 to 7 range. Thus, a value in the M = 5 to 7 range is a reasonable choice for 1000-MW (electric) hybrids. Typical plasma parameters for 1000-MW (electric) hybrids with a value of M = 7 are a major radius of R = 5.2 m, minor radius of a = 1.7 m, plasma current of Ip = 15 MA, and toroidal field on the axis of B0 = 5 T. The concept of a thermal fission blanket that uses light water as a coolant is selected as an attractive candidate for electricity-produ...

Estimate of cusp loss width in multicusp negative ion source

Expression of cusp loss width derived by Bosch and Merlino is applied to JAERI’s Kamaboko source. The width is related to the ambipolar diffusion coefficient across the cusp magnetic field. Electron–ion collision is found 1.2–7.4 times larger as compared with electron-neutral collision. Averaged cusp magnetic field in the diffusion coefficient is taken as a parameter in the simulation code for Kamaboko source. When the averaged magnetic field is 48 G, simulation results agree well with JAERI’s experiment in a wide range of pressure and arc power variation. The value of 48 G is reasonable from the consideration of confining the equation of ion source plasma. The obtained width is about 10 times the value evaluated by two times ion Larmor radius on the surface of cusp magnet.

Numerical analysis of negative ion temperature in a negative ion source

To understand the origin of the two energy groups of volume produced H− ions observed in the multicusp, hybrid-type H− ion source (Camembert III), numerical analysis by the three-dimensional Monte Carlo simulation code has been done. Realistic multicusp geometry and the electric field near the filament are taken into account in the model. The energy relaxation process by Coulomb collision is also included in the model by the Monte Carlo method. Under the typical low-pressure condition of Camembert III, high-energy H− ions are clearly observed in the central region. The origin of these high-energy H− ions is possibly explained by the combined effects of (1) acceleration by electric field near the filament and (2) relatively large energy-loss time of these high-energy H− ions. However, the low energy group is not clearly observed in the simulation. The low energy H− ions with original energy (∼0.05 eV) have enough time to relax their energy towards the relatively high temperature of the background H+ ions, ...

Onset condition of thermoelectric instability in divertor tokamaks

The onset condition of a thermoelectric instability in divertor tokamaks has been studied analytically and numerically by using a five point model based on SOL and divertor plasmas. The SOL current due to the thermoelectric effect causes the thermoelectric instability and destabilizes the symmetric equilibrium of the SOL and divertor plasmas below a critical divertor plasma temperature. The critical temperature of the thermoelectric instability is equal to or higher than that of the thermal instability due to the divertor radiation, and depends on the midplane SOL plasma temperature and the divertor radiation loss. Below the critical temperature, stable asymmetric equilibria are obtained. As the degree of the asymmetry in the divertor plasma temperature increases, the SOL current has no effect on the instability, or even stabilizes the equilibrium. The SOL current generates spontaneously the divertor asymmetry through the thermoelectric instability.

Magnetic Field Generating Thermal Instability Including the Nernst Effect

Nernst effect is taken into account in the analysis of the magnetic field generating thermal instability. Instability condition and the growth rate γ are obtained. The Nernst effect as well as the hydrodynamic effect induces the instability in the region of ∇ n 0 ·∇ T 0 <0 and it increases the magnitude of the magnetic field especially in the overdense region.

Theoretical investigation of electron temperature variation across magnetic filter in a negative ion source

Electron temperature variation over the magnetic filter region and the extraction region is investigated theoretically. We assume qx/{(5/2)TΓx}=β between heat flux qx and electron flux Γx, where β is a ratio of the heat flux to the enthalpy flux and T is the electron temperature. Terms of diamagnetic drift in the expressions of the flux and heat flux are important in obtaining temperature T(x) that agrees with Haas et al.’s experimental results. Electron loss along the magnetic field is important in determining the exponential dependence of the electron number density and temperature on y. Flux inversion is attributed to the negative flux due to the electric field.

Numerical simulation of a hybrid negative ion source

Abstract Cesiated volume sources which we call hybrid sources have been reported recently to show improved results for H− production. Here we present results of numerical simulation, in particular the dependence on arc current, pressure and surface to volume ratio of H− production in the hybrid source. The results agree well with experiments.

Numerical simulation of the effect of Cs volume reaction in an H− ion source

Effects of cesium related reactions are investigated using a simulation code for H− ion sources. Effects begin to appear when cesium density is 1011 cm−3, but are still small and become large when the cesium density is greater than 1012 cm−3. The H− density decreases due to electron detachment. Decreasing the plasma potential by cesium seeding results in 12% smaller H− density. The minimum of the plasma potential shown experimentally by Bacal is found to correspond to a cesium coverage of 50% with the use of Langmuir adsorption isotherm. Surface production is effective only when the cesium density is around 1011 cm−3. For cesium density greater than 1012 cm−3, the effect of the cesium related volume reaction becomes larger.

Numerical analysis of thermoelectric instability in tokamak divertor

Abstract The thermoelectric instability in tokamak divertor has been studied numerically by using a five-point model. When the divertor plasma temperature Tdiv decreases below a critical temperature, this instability arises in a symmetric equilibrium of scrape-off layer (SOL) and divertor plasmas, and stable asymmetric equilibria are found. The SOL current causes spontaneously the divertor asymmetry at the onset of the thermoelectric instability. In an asymmetric equilibrium, the SOL current flows from the higher-Tdiv side to the lower-Tdiv side. The heat flux flowing into the divertor plate of the higher-Tdiv side becomes larger than that of the lower-Tdiv side. The heat flux asymmetry is larger for cases of high recycling and low heating power.

Estimation of the cusp loss width in negative-ion sources

To estimate loss width in the cusp magnetic field in multicusp negative-ion sources, diffusion of plasma across magnetic field is investigated analytically. The transport process of plasma depends on various plasma conditions. Diffusion coefficients are classified by degrees of plasma ionization. In weakly ionized plasma, where a case of electron-neutral particle collision is dominant as compared with electron-ion collision, there is a possibility that ambipolar diffusion or electron short circuit occurs in plasma. This strongly depends on the conditions of the plasma, the system length, and the wall material. On the other hand, in fully ionized plasma, only ambipolar diffusion occurs automatically due to momentum conservation of electron and ion. In not fully but strongly ionized plasma, plasma diffusion depends on electron-neutral particle collision, ion-neutral particle collision, and electron-ion collision. Being based on the classification of the diffusion coefficients, we derive expressions of loss ...