Reply To: Repowering the electric utility industry

[asymmetric_implosion]

Most of the anode material loss seems to come from the e-beam damage on the bottom of the anode. The outer anode walls tend not to erode and in some cases they will actually increase in diameter as cathode material will deposit on the anode faster than the anode material erodes. I’ve done tests with copper anodes and stainless steel cathode rods. The anode looked like stainless steel in less than 1000 shots on the outer diameter at 140 kA. The cathode erosion is probably more substantial on the inner diameter but there is plenty of cathode material to burn so it is a minor problem. I’ve burned up plenty of anodes and still use the same cathode rods.

Beryllium should do well compared to copper on a per unit mass basis by comparing the heat of vaporization. However, copper and beryllium are very similar on a per mol basis.

One could make the anode central hole very deep so it enters into a secondary vacuum chamber to manage the e-beam by spreading it out so that it cannot vaporize the beam dump area. The key problems to date have been the small expansion of the e-beam (~3 deg half angle) so if you let the beam grow naturally, it could take meters before you get to a point where the beam cannot vaporize the beam dump. Most experiments don’t have that kind of space. The alternative to is allow the beam into a small vacuum region well away from the anode and use magnetic fields and electric fields to spread out the beam. The key concern is to keep these fields far from the pinch region so it doesn’t screw up the PF dynamics. It is possible to do the second on most experiments but few groups have serious problems with anode erosion because they fire so few shots before changing the anode.

The plasmoids ability to contain the e-beam needs to be demonstrated before one can seriously speculate about the reduction in damage. It is probably prudent to plan for the non-plasmoid e-beam dose and know that a reduced beam is easier to handle.