Improved Thermo-Mechanical Design of the VASIMR RF Coupler

The proposed work on Phase II involves the design, manufacture, and test of a full-scale embedded RF Coupler for the plasma ldquo;heaterrdquo; stage of the VX-200SStrade; VASIMRreg; rocket core. The RF Coupler is a critical power component of the engine and, specifically, the heater stage RF Coupler delivers the largest fraction of the power to the VASIMRreg; plasma.In 2021, an earlier innovation to the design of the RF Coupler-GCT assembly, called the ldquo;Trapped Coupler,rdquo; enabled the VASIMRreg; VX-200SStrade; test article to reach thermal steady-state at a company record of 80 kW. With the ldquo;Embedded Couplerrdquo; design, the proposed innovation in Phase II of this SBIR, and the knowledge obtained from Phase I, the Ad Astra team looks to increase that power to ge;100 kW, an objective relevant to the Phase I Solicitation Subtopic, High-Power Electric Propulsion Thrusters for Mars-Class Missions.In a ldquo;Trapped Coupler,rdquo; all heat coming from the ceramic must pass through its inner diameter surface. In contrast, the Embedded Coupler uses its walls as two additional surface heat pathways. Theoretical estimates conducted by the Ad Astra team show that the heat transfer area in the embedded design increases by roughly a factor of 3 and results in a lower steady-state temperature for the GCT.To accomplish this, the RF Coupler will be machined-in-place in a high-purity copper vein pattern cast on a ceramic GCT host. The coolant within the coupler flows along two stacked counter-flowing channels, a feature required by the current RF electrical circuit. Other potential designs for this channel structure are possible and being explored outside of this SBIR but, in all cases, the manufacture requires a high-precision welding technique that Ad Astra has developed in-house and successfully demonstrated in the Trapped Coupler configuration.