Why is potassium often preferred over cesium as a seed material in MHD generators?

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magnetohydrodynamic power generator Comparison of the operating principles of (A) a turbogenerator and (B) an MHD generator.

In magnetohydrodynamic (MHD) power generators, a "seed" material—a readily ionizable alkali additive—is injected into hot gas to increase its electrical conductivity to levels necessary for efficient operation.1

While cesium is technically superior in terms of ionization potential, as it possesses the lowest ionizing potential at 3.894 electron volts, potassium is often preferred for practical applications because it is significantly less costly. Despite the small quantity of seed material required, economic considerations remain a critical factor in the design and operation of competitive MHD systems, necessitating a balance between performance and material expenses.1