Microwave Plasma Jet for Surface Treatment of Solar Mirror Assemblies

     Be aware that there is at this time absolutely no evidence that this will work or do what I want it to do. But I feel that I need to try it anyway and see if anything workable can come out of it. When I was looking for DC and AC air and vacuum arc plasma guns, I happened across an article that identified that a plasma could be generated in air using the standard microwave oven frequency of 2450MHz. The setup identified in the article "Efficient Modular Microwave Plasma torch for Thermal Treatment" by Kamal Hadidi and Paul Woskov of the Plasma Science and Fusion Center MIT showed that two microwave sources, one 1.5kW the other 2.5kW could be successfully coupled together to generate enough heat to melt a coke bottle.

    Outside of all of the problems that will arise trying to set up an experimental version of one of these things, there is a plethora of ongoing research in the field relating to real time control of atmospheric microwave plasmas, and other related items of interest. If you want to check out the IEEE transactions on plasma science, you can find many articles on the subject. Initially I can see only three basic problems at this point. The first is the requirement to have a circulator at the requisite power levels to divert the reflected microwaves away from the driving element. This requires a special magnet and ferrite combination to work at the specified frequency of 2450MHz. I have not found the design parameters yet to be able to build one, and obviously I can't afford to purchase one outright. I guess I'll check with the Army Surplus and see if they might have any laying around somewhere stored from the cold war. The second problem is the real time control. As material is fed through the plasma field, in our case tiny glass particles, variations in density alter the impedance of the output. Therefore either the density / feed rate must be precisely controlled, and / or a feed back control circuit setup to drive the tuning elements so that maximum power is delivered to the spray and not reflected back at the element. The third problem, which is hopefully minor, will be the heat affected zone and shape of the plasma flame. I have no idea at this time how to describe it, specify it, analyze it or predict it. I do know that there is software available based on antennae theory that will allow someone who knows how, to determine the electrical microwave field gradients around the tip of the flow head. I suspect that the shape and position of the flow head will affect the flame shape,  and that the shape and position of the exit hole will have an effect, and I think that it might be important to be able accurately describe this field ahead of time. Some people are generating a very fine and thin heat affected zone adequate for cutting thin plates. I suspect that we might want a spray that is more spread out like that one that is depicted in the article above.

    This project stands like the mirror / dish assembly. I need to wait until school starts to gain access to the machine room so that I can fabricate the torch assembly. Also I have asked some of the people in the IEEE club for some assistance with the field analysis. So far there have not been any takers, but I'll check out the first couple of meetings, and chase down a few instructors for advice in this regard.

    So far I have a couple tons of carbon graphite suitable as a thermal heat shield, and also as a sink for the dummy load required to absorb the reflected energy away from the driving element. I purchased one 2.4kW microwave oven from the Salvation Army for $25.00. Now I need to determine how much power is really going to be required, and see if I need to buy more kW, and if so, how much more. And then again we can always just wing it and see what happens with what we already have.