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To maximize the tritium breeding ratio and protect the chamber wall from neutron damage and x-ray erosion, a large blanket is desirable. For example, a radial thickness of approximately 2.15 meters of Yb:FliBe is required to capture 99.99% of the neutrons.
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Yields from ICF targets increase super-linearly with the amount of driver energy. Ideally, to maximize gain, the reactor should operate at the highest yield it can tolerate, even if that means a lower repetition rate. For instance, Sandia National Laboratories proposed 20 GJ targets in their 2005 annual report for a cylindrical Z-IFE chamber (6 m radius, 8 m height) running at 0.1 Hz to produce 2000 MW. Their reasoning: “The economics of scale will favor having a single chamber with the largest acceptable yield.” A lower repetition rate also simplifies pumping the hot blanket material between pulses.
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A more massive target requires more ignition energy, so the total laser medium must scale accordingly. NIF uses 11.8 m³ of Nd:glass to produce 4 MJ of laser light. If BSF targets are 10x larger than NIF’s ~0.24 mg, they might require ~20 MJ for ignition. Assuming Yb:FliBe can match Nd:glass in energy density, the reactor would need ~60 m³ (a sphere with ~2.4 m radius) of Yb:FliBe.