Heating Of Plasma And Bootstrap Current Of Fast Ions In Neutral Beam Injection

In order to reach ignition, the plasma must be very high temperature by heating. The auxiliary heat methods is needed in addition to the ohmic heating. Neutral beam injection heating is widely applied to the heating experiment, because this method of heating has a good power efficiency and its’ physical mechanism is clear. A large fraction of bootstrap current is expected in the steady-state operation of tokamaks.Many theoretical works have been done in deriving different model for the bootstrap current within different scenario. However, these researches are all focused on the bulk plasma.The additional bootstrap current is induced by the anisotropy of the pressure tensor distribution of the fast ions generated by neutral beam injection heating.What are the characteristics for these bootstrap current densitydistribution? how much is in the total plasma current? Which factors have impact on it? These problems are still need to be studied.The evolution of ion temperature is simulated by solved the one-dimensional Fokker-Planck equation with neutral beam injection heating. The results show that “the overshoot of the Maxwellian” that aroused for Fokker-Planck equation solved by traditional numerical method is eliminated. The ion distribution function tends to non-Maxwell distribution as the neutral beam injects, and the ion temperature rises rapidly and then reaches stability. It is investigated that the beam power and energy effect on the ion temperature, the results show that the ion temperature increase with the beam power and energy increasing. The change is more obvious by improving beam energy than power.The neutral beam deposition is investigated, the results show that the deposition of neutral beam mainly distribute on the outside of the plasma with small mean free paths relative to the plasma radius and the deposition of neutral beam will peak in the center of the plasma with 0? increasing. In addition, the deposition in the center will decreaseas 0?/ a ?2, because the beam transmission loss will arise. The peak central value of fast ion deposition increased as beam tangency radiustR approaches R0.The bootstrap current of fast ions is simulated with Taguchi’s physical model, and then the questions that neutral beam parameter and plasma parameter effect on the bootstrap current density are discussed. The results show that the value of the bootstrap current depends sensitively not only on the angle of the neutral beam injection but also on the ratio of the velocity of fast ions to the critical velocity: the value of bootstrap current is small for the neutral beam parallel injectionbut increases rapidlyfor perpendicular injection, and increases with beam energy increasing.the value of net current density increases with the temperature of plasma increasing and decreases with the density of plasmaincreasing. The value of net current density is weakly affected by the effective charge number, but the peak of net current density moves towards edge plasma with effective charge number increasing.In addition, it is taken into account that the beam cross section shape of finite beam is a circle with Gaussian current distribution. The peak of bootstrap current increased with increasing the 0?, and then the bootstrap current decrease with increasing the 0?, for 0?/ a ?2. The net current density increased with the beam tangency radius tR approaches R0.