The Academy of Sciences of the Czech rebublic - ASCR

Additional heating – Neutral Beam Injection system


The COMPASS tokamak is equipped with a new Neutral Beam Injection (NBI) system for additional heating and current drive applications. The design is optimized for specific properties of COMPASS. It is a compact tokamak for which, due to short trajectory of interaction between neutrals and plasma, the NBI power, energy and geometry is chosen carefully.


NBI provides a flexible heating and current drive system, consists of two injectors with particle energy 40 keV and 400 kW output power, delivering 800 kW of total power to the plasma. The basic configuration shown in Fig.1a is optimized for plasma heating. The parameters of the COMPASS NBI system are summarized in Table 1. The tangential injection is also optimal for absorption due to the longest passage through the plasma achievable on COMPASS.

For balanced injection both injectors will be located at the same port, aiming in co- and counter-current directions as shown in Fig. 1b. With proper power modulation to compensate different orbit losses for co- and counter- beams, one can obtain NBI heating scenario with minimum momentum input.






Fig. 1: Top view on the NBI system layout. a) co-injection, b) balanced injection.


Number of injectors 2
Energy of the beam 40 keV
Total ion current 2 x 12.5 A
Total power in neutrals 2 x 400 kW
Pulse length 300 ms
Beam diameter < 5 cm
Input voltage 3 x 400 V
Total input power ~ 1.5 MW

Table 1: Main parameters of the NBI system designed for COMPASS tokamak.