Fabrication of NBI Ion Source Back Plate and its High Heat Flux Experiment

Abstract

The back plate is an important component of the ion source because of its multiple roles including heat load removal during beam operation. The main components of the back plate are (1) a Type 304L stainless steel (SS304L) magnet positioning plate that holds samarium cobalt permanent magnets required for the confinement of ion source plasma, (2) an oxygen-free electronic copper cooling plate with 35 inner and 8 outer cooling channel grooves (each of which is 4 × 1.8 mm²) that is vacuum brazed with a SS304L magnet positioning plate, and (3) a SS304L magnet cover plate. In this paper, the back plate is successfully fabricated, and a high heat flux experiment is done at the High Heat Flux Test Facility Center with an electron beam power of 200 kW for 458 s. The uniform incident heat flux is 2.5 MW/m². Demineralized water at 34°C is supplied at the rate of 1 kg/s to the cooling plate at inlet pressure of 8.2 bars to remove the high heat load. The surface temperature of the copper plate is measured by an infrared camera, and three temperature regions are observed. The measured average surface temperature of the cooling plate is ~152°C. The bulk water temperature rise ΔT_w is ~39.42°C. The estimated absorbed heat flux is ~2.04 MW/m², and the heat absorption coefficient is 81.6%. The measured leak rate after the heat flux test is 1.6 × 10⁻⁸ mbars∙L/s. These High Heat Flux Test experimental results will be useful to study the thermomechanical performance of the back plate and to understand the effect of increasing the beam pulse length.

Keywords:

• Ion source
• positive neutral beam injection
• back plate
• High Heat Flux Test
• surface temperature
• cooling channels

Acknowledgments

The authors would like to acknowledge Vishnu Prajapati for the design of 3D CAD models of the back plate. The authors also acknowledge S. Rambabu, colleagues of the PNBI group, and the Institute for Plasma Research workshop for the various help received. The authors are thankful to Tejendra Patel for providing CFD analysis data. The authors are also thankful to Mainak Bandyopadhyay for his comments, which were helpful to improve the quality of the manuscript. Finally, the authors are very much thankful to the three reviewers for their valuable comments to improve the quality of the paper.

Disclosure Statement

No potential conflict of interest was reported by the author(s).