From February the 17th to March the 3rd, I attended the IRFM Winter Event in CEA Cadarache as part of the second year programme of the European Master in Fusion Science and Engineering Physics. The event is organized jointly with the students of the French master in Plasma physics and consisted of two short projects in pairs.
For the first week, I worked on the backend of an Ion Cyclotron Resonance Heating (ICRH) antenna known as the Travelling Wave Antenna (TWA). The TWA is foreseen to heat the plasma ions directly, while handling mega-watts of electric power in a fail-safe and efficient manner! The TWA distributes the power distribution network along the toroidal direction, reducing the power accumulation at the launcher and thus lowering the risk of arcs, erosion and large reflected powers during plasma transients. In addition, the backend circuit is governed by a variable coupler: the association of two phase shifters with two 3db (hybrid) coupler. This simple configuration allows the recycling of the un-coupled power while simultaneously shielding the generator from the large reflections expected during edge-localized modes or disruptions. As a product of our investigations, we handed a report.
For the second week, I was involved in the testing of ITER and DEMO solid-tungsten plasma facing components (PFC) known as monoblocks. These PFC elements are 12cm x12cm x 4cm cuboids composed of layered armor (typically W), a coupling (typically Cu) and a structural (typically CuCrZr) materials, which will serve as the first line of defense against the million degree plasmas in ITER, DEMO and future fusion power plants (FPPs). Each block is traversed by a cooling channel, designed to deliver water between 100 and 150oC. While DEMO designs remain the subject of much R&D, the position of the coolant pipe is one of the last remaining issues for the ITER design: locate it too close to the surface and bubbles will form precluding an adequate heat removal, place it too far and the tungsten will melt. During this hands-on project, we studied the constraints of the monoblock thermos-mechanical design from a finite-element modelling and an experimental point of view, as we were given the opportunity to work with the SATIR validation facility at IRFM. The product of our work was a public defense on Friday afternoon, which concluded two weeks of hard work and exploration.
On the personal side I consider that this event has been a valuable experience as it allowed me to peruse the practical end of fusion science and better appreciate efforts that are often taken for granted by the community (design of RF networks and hydraulic systems).
- Alexis Devitre