Internal Surface Finishing of Additively Manufactured RF Components for Fusion Reactor Applications

Statement of the Problem: In a reactor environment, plasma material interaction (PMI) issues associated with radio frequency (RF) coupling structures are similar to those for the first wall and have been identified as a potential problem. A primary challenge is to obtain high power, breakdown resistant density couplers with low loss compatible with fusion plasmas. Advanced manufacturing techniques, i.e. additive manufacturing (AM), enable optimized RF structures to improve coupler performance; however, as-printed AM metal surfaces contain numerous surface and near-surface defects which can reduce performance and/or serve as failure points. A post-process surface finishing technique is required to facilitate successful AM implementation. General statement of how this problem is being addressed: REM proposes to address the PMI issues associated with RF coupling structures by utilizing additive manufacturing to maximize the benefits of AM specific alloys that, we believe, are optimized for these uses/environments. In order to fully realize the potential of the AM alloys, components must be surface finished. It is expected that the planarized and smoothed surfaces of the components will optimize the performance of the AM RF components, thus increasing the expected life and efficiency of the reactor, while potentially lowering its total lifecycle costs. What is to be done in Phase I? During Phase I, REM proposes to develop surface polishing processes for internal surfaces on applicable RF component geometries manufactured in GRCop-42 and molybdenum from wrought, AM, and/or plated forming techniques. Processes will be designed to produce <0.3 µm Ra roughnesses, be controllable to +/- 15 µm, and maintain critical geometries/part features. Samples will be produced utilizing the developed polishing processes. Preliminary testing of these samples will be performed at MIT to evaluate RF performance and demonstrate proof-of-concept. Commercial Applications and Other Benefits: As the plasma fusion market is as yet purely theoretical/academic in nature, exact market size for this specific application is difficult to define. It is understood that the endgame application for the SPARC and subsequently ARC fusion reactors is to supplant existing fossil-fuel driven power plants (steam turbines). As the global steam turbine market was valued at $24.1 billion in 2019, it would seem logical to suggest that the value of fusion technology-enabling RF component surface finishing processes could conservatively be in the $1 – 20 million range. [1] Primary customers would be fusion reactor producers. As no commercial producers currently exist, it would be assumed that traditional gas and steam turbine producers would step into this market: Siemens, GE, and Mitsuibishi. However, initial commercialization would be focused on government sponsored and/or university driven plasma fusion reactor projects such as SPARC, ITER, JET, and others. Looking beyond the plasma fusion market, GRCop alloys are being rapid adopted by the rocket propulsion industry (both public and private) for use in combustion chamber/combustion chamber liner applications. The rocket propulsion market was valued at $4.23 billion in 2018. [2] As LPBF combustion chambers can cost ~$35,000 – $50,000/each, and commercial rocket designs can contain 10 – 20 such components, it is reasonable to assume that an advanced GRCop alloy polishing process could produce >$150,000 per rocket. Primary customer targets who are known to be using or evaluating GRCop alloys include: Relativity Space, Sierra Nevada Corporation, Blue Origin, Virgin Orbit, and Launcher. It is expected that additional companies will adopt GRCop alloys as increased hot fire testing and other proof of performance data is made available. Additionally, non-plasma fusion waveguide applications for the GRCop alloys are broad, and include the satellite market, as well as medical devices, such as magnetic images devices. Companies such as Bridge12 and Swissto12 are actively producing waveguides and antennas via AM, and their end-use applications would be well suited to the GRCop alloys if they could be coupled with an adequate internal surface polishing process.