Conceptual design of the Halo Machine

In 1996, when the danger of sideways forces was first recognised, the operational window of the JET tokamak was significantly restricted. Limits were placed on the maximum magnetic field and plasma current to prevent excessive stresses on the vacuum vessel. Despite three decades of research, predictions for the sideways force on the ITER wall remain highly uncertain, ranging from 2 to 60 MN with the upper estimate exceeding the design value of 48 MN, which would result in operational restrictions (operation with Ip < 15 MA potentially affecting ITER’s ultimate fusion performance). To address this issue, the ITPA community launched the dedicated joint experiment MDC-25 in 2018. While substantial progress has been made, recent findings highlight the need for complementary studies on a specialised linear device to investigate plasma–wall currents, key contributors to sideways forces. Here, we propose the first linear device specifically designed to investigate plasma–wall interactions in the presence of kink modes, with the aim of resolving uncertainties related to plasma–wall currents and associated sideways forces. It is expected that the findings obtained with the new device will guide the design of vacuum vessels and plasma facing components for future tokamaks.