Reply To: Military Effects

[asymmetric_implosion]

The most common example of this approach is so-called planar wire arrays. Rather than arrange a group of wires in concentric cylindrical shells, they are arranged in two straight planes or other planar geometries. The JxB force drives the wires to some central axis. The problem appears to be that the wires arrive at different times. Rather than getting all the mass arriving on the axis at the same time which leads to a dense pinch, you have waves of mass arriving. You can’t compress the plasma as tightly leading to a cold pinch which is bad for the application of wire arrays (soft x-ray production). Planar wire arrays are one of the fads of the Z-pinch community right now so the literature is filled with tomes on the subject.

One might argue that a planar sheet of gas is different. My concern is that when the sheet breaks up into a few pinches, you are splitting the current between each pinch. Say you get an equal division of current in two pinches. The radiation yield (neutrons, alphas, x-ray) scales with the current to some power (Yield=a*Current^n). In the equation, n tends to vary from 3-6 for fusion and a is all over the place (1E-4 to 0.1). The typical value of n is around 4. You divide the current into two equal pinches sharing half the current. Thus, each pinch is emitting ~6% of the radiation a single pinch with all the current. You have two pinches so you get a total of ~12% of the radiation yield from a single pinch in a concentric geometry if a is the same. The exact value of a is not easy to get. My feeling, but not proven, is a will drop for the parallel pinch case because you are dividing the pinch inductance into a parallel paths reducing what is commonly referred to as the current bite. Small current bite tends to correlate with small a. The problem is far more complicated but you need to read the published literature for a more complete description.

If you argue you can drive more current per shot, you might have a hope of increasing the yield by increasing the number of pinches. However, you can drive more current in a cylinder than you can a set of parallel plates for the same gap between anode and cathode due to inductance.