A collaboration between the two EUROfusion Research Units, KIT and CEA, just saw its efficient outcome. Scientists in Karlsruhe delivered 70 Langmuir probes to the French tokamak WEST. Producing those tiny diagnostics was difficult, but not impossible, thanks to KIT’s experience in Tungsten Powder Injection Moulding and its expert industrial partners.

Langmuir probes, named after the US-American chemist and physicist Irving Langmuir, determine the temperature, density and electric potential of a fusion plasma. These diagnostics must be capable of withstanding harsh conditions inside tokamaks. They are therefore made from the refractory metal tungsten. Due to the brittleness of tungsten, manufacturing by way of mechanical machining is time-consuming and the fabrication costs are high.

Langmuir, determine the temperature, density and electric potential of a fusion plasma. These diagnostics must be capable of withstanding harsh conditions inside tokamaks. They are therefore made from the refractory metal tungsten. Due to the brittleness of tungsten, manufacturing by way of mechanical machining is time-consuming and the fabrication costs are high.

Injecting tungsten powder

Jamie Gunn, plasma physicist from CEA. Picture: private

Jamie Gunn, plasma
physicist from CEA.
Picture: private

Steffen Antusch, powder metallurgy scientist from KIT’s Institute for Applied Materials. Picture: Antusch

Steffen Antusch, powder
metallurgy scientist from KIT’s
Institute for Applied Materials.
Picture: Antusch

Two years ago, the WEST researchers were scratching their heads to find a technical solution which would enable them to design tiny Langmuir probes. These diagnostics needed to survive high power and steady state particle bombardment, without being a risk for machine operation in the event of damage. Discussions with EUROfusion colleagues from KIT (Karlsruhe Institute for Technology) convinced the French team that Tungsten Powder Injection Moulding (W-PIM) could be the solution to producing tungsten components with a complex shape. The Institute for Applied Materials (IAM) in Karlsruhe specialises in W-PIM, a cost-efficient method which is used to fabricate extremely tiny, but precise, metal parts.

Compliance with strict tolerances

Each of the 70 Langmuir probes is 25 mm long, 17mm tall and only 2 mm thick, similar in size to a paperclip. “It was tricky to comply with the strict tolerances of such diagnostics and, moreover, to deliver in time”, says Steffen Antusch, powder metallurgy scientist from the IAM. His laboratory took advantage of their well-established relationship with two industrial partners: the Rodinger Kunststoff-Technik GmbH produced the tools for the powder injection and the green tungsten compacts. Plansee, SE, which specialises in processing high-performance materials, finalised the components for WEST.

Tiny pieces for a big approach

As WEST is intended to become one of EUROfusion’s test benches for tungsten components under ITER-like conditions, the French Research Unit CEA (Commissariat à l‘énergie atomique et aux énergies alternatives) is happy to receive the pieces from Germany: “We are grateful for their in-kind contribution, impressed with their timely delivery, and now eagerly await the first plasma in WEST to test the probes”, says Jamie Gunn, plasma physicist from CEA. Not only will the diagnostics provide essential data, the use of tungsten Langmuir probes bolted onto an actively cooled divertor target is considered to be a technical solution suitable for the ITER divertor probe system. Consequently, feedback from the Langmuir probes in WEST will provide input into the ITER design decision.

Read more about it in the article “New manufacturing technique for DEMO divertor components” Fusion in Europe II/2014 https://www.euro-fusion.org/?p=32596