Analysis of the DEMO-FNS magnetic field passive reduction and neutral beam injectors shielding methods

Abstract

Steady-state operation of a fusion neutron source (FNS) will require plasma heating and maintaining the current therein by fast atom beam injection. The DEMO-FNS project assumes the use of six injectors providing additional heating power up to 30 MW at an atomic energy of 500 keV. As a prototype for the DEMO-FNS injector, an injector developed in detail for the ITER project can be used. The overall injector layout may be retained, but changes in individual components will be required due to the difference in beam energy and power. Inside these components, there are very strict restrictions on the magnetic field magnitude: the flux density should be below a certain value along the path of ion movement and even lower in the neutralization region. To achieve these characteristics in an environment with a high scattered field due to the magnetic system of the facility – including the coils of the poloidal and toroidal fields, the central solenoid and the plasma itself – additional shielding of the injectors is required. At this stage, we expect that the proposed design will allow obtainment of the required magnetic field values using only passive shielding. The shield would be formed of a case made of ferromagnetic material with a high magnetic permeability index. An electromagnetic analysis of the effectiveness of such a screen was performed using 3D modeling using the ANSYS code. In addition, the BTR code was used to calculate power loads along the entire injection path length in the obtained magnetic fields conditions, taking into account reionization.