Neutral particle injection

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The neutral particle injection , engl. Neutral Beam Injection ( NBI ) is a process used to heat a magnetically confined plasma .

To do this, atoms are first completely ionized . After the ion source , they pass through an acceleration grid of a particle accelerator , in which they are accelerated with the help of an electric field of several thousand  volts . The level of the electrical voltage determines the speed and kinetic energy achieved . Before the particles hit the plasma, they are returned to the neutral state in the neutralizer by accumulating a corresponding number of electrons . Then they pass through a deflecting magnetic field that diverts the particles that have not yet been neutralized. These fly into an ion sump and do not get into the plasma. The entire process takes place under very low pressure, which is generated by a high-performance vacuum pump in the neutral particle injector . The neutral atoms penetrate the plasma, undisturbed by the strong magnetic field, and there transfer their kinetic energy to the particles of the plasma through collisions, which leads to the heating of the plasma.

The process is used with hydrogen ions (meaning all different isotopes ) in nuclear fusion test facilities of the tokamak type (e.g. JET , TEXTOR , ITER ) and is also intended for future power fusion reactors.

Special application in the TEXTOR system

In the TEXTOR test facility at the Jülich nuclear research facility , neutral particle injection is used not only for plasma heating but also to change the direction of rotation of the plasma. For this purpose, two neutral particle injectors are directed towards the plasma torus in opposite directions (with regard to the plasma rotation) . Therefore, a targeted change of rotation in both directions is possible.