Operation method of negative ion neutral particle injection device

A negative ion neutron particle injection device is used for plasma heating and current driving for a thermonuclear device. Hydrogen negative ions are accelerated by a negative ion source. The intensity of the accelerated energy is determined by an acceleration voltage applied to the electrode of the negative ion source. The hydrogen negative ions are converted into neutral particles by passing through a hydrogen gas in a neutralization cell. A hydrogen gas is supplied to the neutralization cell by a flow rate control device. If the negative ion source acceleration voltage is determined, an optimum vacuum degree is determined by a control device, and flow rate is determined by a flow rate control device to change the vacuum degree in the neutralization cell to a maximum neutralization efficiency. In addition, if a vacuum degree in the neutralization cell is more than a limit thermal load of a positive ion beam damp, and negative ion beam damp corresponding to the negative ion source acceleration voltage, the acceleration of the beams is stopped. (I.N.)