2025 – Plasma Exposure of Ceramic and Pre-Irradiated Materials in DiMES

Plasma Exposure of Ceramic and Pre-Irradiated Materials in DiMES

2025 Research Campaign, Thrust: FPP Candidate Wall Materials

Purpose of Experiment

Novel and/or advanced plasma-facing materials must be investigated for use in next-generation fusion devices. This experiment in DIII-D aims to characterize the plasma-material interaction (PMI) response of fusion pilot-plant relevant material candidates by exposing them to tokamak plasma using the Divertor Materials Evaluation System (DiMES) test-stand. Materials to-be exposed are silicon carbide fiber composites (SiCf/SiC), pristine and neutron irradiated monolithic silicon carbide (SiC), boron carbide (B4C), silicon nitride (Si3N4), pristine and neutron irradiated titanium diboride (TiB2), pristine and neutron irradiated titanium carbide (TiC), pristine and neutron irradiated tungsten (W), and pristine and neutron irradiated tungsten doped with potassium ions (K-doped W). SiCf/SiC, B4C, Si3N4, and SiC samples will be exposed to H-mode plasma with a strike point swept across and back the DiMES surface. H-mode plasma exposures will induce intense steady-state and transient heat and particle fluxes on the materials; by comparing post-exposure material surface morphology and erosion, conclusions can be made on material suitability for fusion plasma-facing applications. TiB2, TiC, W, and K-doped W samples will be exposed to L-mode plasma in order to characterize how neutron damage influences plasma-induced defect evolution and deuterium capture and retention behavior in the materials. This experiment includes first-of-its-kind DIII-D plasma exposures to samples pre-irradiated with neutrons and is highly relevant for both near-term ITER-like devices as well as fusion pilot-plant type facilities where neutron degradation is unavoidable.

Experimental Approach

Step 1: Establish H-mode reference shot (#2000083) (2-4 shots) Experiment starts by reproducing the H-mode plasma reference shot from the FPP candidate materials development session. The objective is to ensure that the inter- and intra-ELM heat flux deposited on DiMES is approximate to what is anticipated for the sample exposures. It is also necessary to capture near DiMES background spectroscopy data for post-experiment processing and normalization. Step 2: Expose first DiMES cap with SiC/SiC buttons to H-mode plasma (~5 shots) We will repeat the discharge established in Step 1 on the samples. The strike point will be swept over the sample with 5 out-and-back sweeps done per shot. Repeat discharges will be done to capture spectroscopic documentation of the Si and C eroded elements. Step 3: Expose second DiMES cap with SiC, B4C, and Si3N4 buttons to H-mode plasma (~5 shots) Again, the discharge established in Step 1 will be repeated on this set of samples, also with a similarly swept strike point. This cap contains several elements that must be captured spectroscopy through the repeated discharges. Step 4: Expose third DiMES cap with TiB2 and TiC buttons to L-mode plasma (6-7 shots) These samples will be exposed to L-mode plasma. In order to achieve this, first the L-reference discharge (200682) will be re-established while the DiMES head sits recessed in the tokamak. Once the reference shot is re-established, the DiMES head will be raised and the samples will be exposed to 5 repeat discharges to build up deuterium fluences on the samples. Step 5: Expose fourth DiMES cap with W and K-doped W buttons to L-mode plasma (5 shots) The discharge established in Step 3 will be repeated on these samples, again 5 discharges are desired to build up sufficient deuterium fluence.

Interested in a behind-the-scenes look at DIII-D? Join us for a virtual tour during Fusion Energy Week (tour times: May 7 at 10am PDT, May 8 at 4pm PDT)! Sign up for a tour here.

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