Long story short: Graphite is a mediocre electrical conductor full of pollutants. It tends to explode at high current and hydrogen likes carbon. Worst case option is the boron carbides with the surface and well… pretty bad conductor. Carbon is good for x-ray transmission but bad for high current.
Tungsten is important in the initial testing to reduce impurities and determine the optimal conditions. Tungsten is the material of choice for DPF electrodes for low rep rate devices. It might not be good in the long haul but it is an important step. Beryllium may or may not pan out for a number of reasons.
