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Hot core and preheating for fusion

  1. Mar 21, 2014 #1
    If I was going to build a fusion device for energy production I would build a cylinder filled with fusion fuel and the fusion would happened in the center. First it would be hard to start the fusion with relatively cold fuel. After a while of heating, the surrounding fuel would be hotter even if the fuel in the center wouldn't fuse. With rising temperature and focusing the plasma in the center, fusion would happen.

    Removing reactant from the center and adding fuel from the outside, the fuel just outside the center would fall in to the center and react and so on. After a while the fuel just outside the center would be very hot to. Almost reaction hot, sort of speaking. The further away from the center the cooler it gets. The heat waste from the fusion is not waste then. It's preheating the fuel, making fusion lot easier.

    Is it possible? To confine the plasma in a cylinder is possible and quite easy.
    To concentrate plasma in a string or thread is possible.
    But what I don't know is: Does the heat transfer from the hot plasma to the not so hot plasma. I suppose it's most radiation and that works well between two bodies with different temperatures, but does it work between layers of plasma. Plasma is a funny thing sometimes and I don't know what to think. Is it totally transparent? Gas can absorb radiation, maybe not so much, but plasma is't just a gas, so I don't know, do you?
     
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  3. Mar 21, 2014 #2

    mfb

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    Where "cold" is everything below millions of K.
    Nano- to microseconds?
    Why does the temperature rise, how is plasma focussed?
    How?
    And after a few microseconds, everything explodes due to the incredible pressure?
    Why would it be waste. In most setups, it is the way the released fusion energy gets extracted.

    With low temperatures or low densities, it is easy. But then you don't get fusion with relevant rates.
    Yes it does.
    Plasma has free charges, so it is much less transparent than gases of the same density.
     
  4. Mar 21, 2014 #3
    Yes cold means plasma but definitely less then million K

    After a while means seconds, steady state. The more volume the better, but then steady state take longer. About an cubic meter would be a good compromise.

    There are many way of heating. As long as the heating is in the center and of coarse sufficient it's ok. Sorry I will not reveal everything.

    Moving ions forward can be done electrostatic for example. When you move the center ions after they have react, most of them should be reactants, shouldn't they? D-T reaction produce a lot of neutrons and they seem to just escape anything, but outside the confinement their heat must be gathered. Fresh gas will be fed from outside the cylinder.

    You say the fusion will cause explosive pressure immediately. Yes but but ions is possible to hold together rather tight. I will not tell how yet, but I have found a method. I hope it can hold the ions together hard enough. I want the central plasma to stay, so you can gather it after reaction and to heat the nearest surrounding. Think about the reaction volume as a very hot string. The plasma around the "string" is heated. Mostly very near the "string" less further away. When the reaction in the "string"is finished, well everything will never react, but most of it, that volume will be pushed out and what's just around, the next hottest volume will takes its place. What was the next next hottest volume becomes now the next hottest volume and so on. This will be repeated over and over again. New fuel is added from outside, so it can goes on forever almost.

    Maybe waste isn't the right world. Losses is probably more accurate. You may know that well working fusion devices exist, but they don't give energy excess. They are used to get neutrons. For example a fuser works but just consume power. The losses are to big. In the JET Tokamak the losses is also to big. In a real huge volume they think it's going to give excess heat. Se ITER. They believe it will almost burn the fuel by itself. My idea is to get an almost burn because the fuel that react is already almost hot enough and most of that heat is from the reaction itself and the losses. The losses is not a big problem anymore. As I mentioned the neutrons carry most of the energy, and mostly that is what you can use for generating electricity. In the best of worlds you would use H + boron 11 for fusion and get much excess heat, and very little neutrons, and a lot of the reactants He that is, could be used for generating electricity. Just a small amount would be needed to preheat the fuel. But it's very difficult to fuse. Maybe tomorrow.

    The confinement is a problem. But it's easier in a cylinder than a Tokamak. As I mentioned it's necessary to keep the ions in the center close together, so there will be better concentration in the reaction volume of that reason to.

    Well I'm glad to hear that heat from hot plasma can be transferred to cooler plasma. The cooler the plasma get the thicker it gets. The pressure is the same overall, but the concentration then depends on the temperature.
     
  5. Mar 21, 2014 #4

    mfb

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    That is very small for a fusion plasma and very large for inertial fusion concepts.
    You do not "reveal" anything, so it is hard to guess what you think of. Answering questions is close to impossible like that.

    It is easy to get fusion reactions. Even a table-top electrostatic accelerator can do that. The hard thing is to get enough to use them as an energy source.

    Then publish it, get a patent, make a product out of it, or do whatever you like. But don't ask questions that require detailed knowledge of your setup, if you are not willing to even tell the most basic things about it.

    It always is, as you have some (at least radiative) contact between fusion region, arbitrary things in between and the environment. You can just improve the volume to surface ratio, which is the way ITER is going.
     
  6. Mar 22, 2014 #5
    me After a while means seconds, steady state. The more volume the better, but then steady state take longer. About an cubic meter would be a good compromise.

    Mentor That is very small for a fusion plasma and very large for inertial fusion concepts.

    me It's a fusion plasma with a pinch in the middle you could say. It's not unique, focus fusion se focusfusion.org and z-pinch use it. You wondered how I would keep the reaction in the core, with current as they do. Current in the middle, pull the ions together, that is why the reaction happens most in the core. Now that detail is revealed. But you can read it in most physics book anyway.

    me My idea is to get an almost burn because the fuel that react is already almost hot enough and most of that heat is from the reaction itself and the losses. The losses is not a big problem anymore.

    Mentor It always is, as you have some (at least radiative) contact between fusion region, arbitrary things in between and the environment. You can just improve the volume to surface ratio, which is the way ITER is going.

    me The environment around the reaction core, in this case is mostly fuel. The fuel collect more and more of the heat from the losses, therefor it will be of some use, not just a problem. Even if not everything will be used it's much better. The fuel nearest the walls are hot, but not at all so hot as the plasma in the Tokamak. Therefore less losses to the outside environment.

    Mentor Then publish it, get a patent, make a product out of it, or do whatever you like. But don't ask questions that require detailed knowledge of your setup, if you are not willing to even tell the most basic things about it.

    me I would really like to tell everything about it, but I'm very insecure how much I should tell. Anyone on a forum can get use of my work and ideas and just steal the concept. On the other hand I don't know everything I need to know. I would like to here about how some important details work, so I can judge if this is even possible ever.

    In the next step, if there are any more steps, I can't do on my own and it's not enough just to ask single questions. Sorry if I'm not so generous with details, but I'm afraid that other would take credit for this idea.
     
  7. Mar 22, 2014 #6

    etudiant

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    Earl,
    There is clearly a need for a breakthrough idea before fusion becomes a practical reality.
    The current approach of 'lets make it bigger' because that way the obvious problems from surface losses become relatively smaller just underscores that need.
    So if you think you have a good idea, throw it out there!
    Its value is nil unless it gets used and the details of the implementation are certainly going to take huge effort to master, no matter how good the initial idea is. Do remember that the radiation compression idea for the hydrogen bomb was Ulams, even though Teller got most of the credit. Yet neither one got rich from it, largely because making it work cost billions, when that was real money, so the idea itself was only the first step. Peer recognition and prestige was their primary reward, something neither Ulam nor Teller much cared about.
     
  8. Mar 22, 2014 #7

    mheslep

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    I've wondered why the chemical explosive lens concept, invented at Los Alamos, could not be extended to inertial fusion ignition. If I recall chemical implosion in weapons achieves something like 500,000 atm, sufficient to compress and make the Pu mass in a weapon critical, yet some 20 million atm is required to ignite DT. Could not the 40X improvement be achieved by building a lens with large magnification (or reducing the size of the fuel ball)? I'm guessing some instability gets in the way?

    I suppose the additional requirement is that chemical implosion must *only* work at the scale of tiny fuel pellets (if at all), i.e. something like the 2mm* pellets used at NIF, otherwise a thermonuclear weapon might be realizable without exceedingly difficult to obtain materials (Pu-239, U-235)

    *Theoretic peak release ~240 MJ/pellet over 1ns, ~200 GW. Thus no more than ~15 kg of explosive lens per pellet is required, else the process is not net energy positive.
     
    Last edited: Mar 22, 2014
  9. Mar 22, 2014 #8
    Explosive lens concept is new to me so I can't figure out if and how you can improve the effect. A few month ago I thought about using chemical explosive to compress, but I didn't find anything like lenses, so I abounded the idea. It seem a bit messy with a big blast and everything. Do you have any idea how to harvest the heat?

    But I'm sure it's easier and cheaper than laser inertial fusion. I suppose that's your argument for this concept.
     
  10. Mar 23, 2014 #9

    mheslep

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    If it works, the chemical detonation would be minor compared to the nuclear burn. This 1982 reference by Wintergbeg might be useful. Discusses chemical explosion ignition, kinetic impact, magnetic implosion.

    Walls with density sufficient to stop neutrons, in contact with some kind of heat exchanger. As is the case with all the fusion efforts, ITER, NIF, having the wall survive long term neutron damage is the problem.
     
  11. Mar 23, 2014 #10

    etudiant

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    I believe that this was studied extensively by the US nuclear weapons community in its 1980s search for a fusion device that would function without a fission initiator. Presumably the effort was abandoned, because the subject has gone entirely quiet, afaik.
     
  12. Mar 23, 2014 #11

    berkeman

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    Welcome to the PF.

    It's very important for you to learn a lot more physics before you spend a lot of time on a dead-end idea. At the very least you should take a few introductory physics courses, and do some reading about plasma physics, and about existing fusion schemes.

    What level are you in school right now?
     
  13. Mar 23, 2014 #12

    mheslep

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    If such a chemically imploded fusion device was actually feasible with weapon scale energy release it would be extremely dangerous with respect to proliferation as, given the design instructions and the explosives, one could be made in a basement. Yes, I expect that realization, if such is the case, would quiet any work on the subject.

    That's unfortunate if similar technology could produce electric power via commercial fusion (or spacecraft propulsion). It would mean that fusion power, whenever it arrives, would come only and forever via colossal facilities containing large volumes of low density plasma. Such has always been one of the major critiques of ITER: power density inevitably less than the worst nuclear fission reactor, so why would any utility ever buy one.
     
  14. Mar 23, 2014 #13

    mheslep

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    Hmm. Somebody was paid to study exactly this problem in '98. Jones and von Hipple at Princeton.
    The Question of Pure Fusion Explosions Under the CTBT


     
    Last edited: Mar 23, 2014
  15. Mar 24, 2014 #14
    I'm an engineer, working with building construction and energy, so I know a lot about physics. At least when it comes to mechanics and also quite a lot about electricity and energy sources. Plasma however is new to me and it would be a good idea to learn more about that.

    I don't think this is an dead end idea. If it's not possible to do practically, then it's a dead end idea. Heating the fuel is very inefficient today, so it is imortant to improve the heating process. What could be better the le losses heat the fuel
     
  16. Mar 25, 2014 #15
    While I'm in this thread I ask s few questions about plasma and fusion.

    How intransparent is plasma. Do I need meters or kilometers of plasma to absorb at least half of radiation from losses. Bremmstrahlung and other losses that goes away from very hot plasma.

    Have I got this right. 100 milj K means 10 ekV, when D-T react it will be helium with 3,5 MeV. So if I use thousends of amp to pull a string of plasma together, to get higher concentration it works until it react. The particles that react will be impossible to keep in the current string and flew away with a tremendous speed. More than 10 times greater than the average speed of the 100 milj K plasma it recently was.

    Answer to that could make me understand how this work.
     
  17. Mar 26, 2014 #16

    mfb

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    The relevant temperatures are so far above everything used in engineering that the plasma behaves completely different.

    All hot fusion concepts (=all promising concepts) use fusion energy to heat more material. If that is your main idea, it is nothing new.
     
  18. Mar 26, 2014 #17
    I suppose you think about the Tokamak. It does use the fusion reaction to heat the fuel and ITER is supposed the do it so much that the fuel will burn by itself. But how efficient and economical is that preheating process?

    All the fuel get mixed and the extreme temperature are almost the same in the whole volume. The bremsstrahlung must be enormous. It is enormous they admit.

    I don't care so much if the concept is so much different, if it's good I'm glad. But I think there are differences. I don't mean to heat all fuel to same temperature. Heat as little volume as possible. That minimize the bremsstrahlung and the bremsstrahlung that do occur will come to use, because there are cooler fuel around that need to be heated.

    How much of the fusion reacted fuel that get used for heating I don't know. I have find out more about that, but I think it will mostly fly out of the confinement because of that particles enormous energy. What is enough confinement for the hot plasma is not for these reacted helium particles I believe. Neutrons they absolutely fly away.

    There are a few doubts although. What is the relation between the losses as bremsstrahlung for example and fuel temperature. The losses must drop more than the volume increase for lower temperatures. Otherwise the losses just increase as further out from the center you get. Power from heat radiation increase power to four with the temperature, but is it that connection?

    You don't know if it works before you test it. Even if you calculate and consider everything mankind know, there can still be a lot of surprises.
     
  19. Mar 27, 2014 #18

    mheslep

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    Not just Tokamaks but all the serious attempts via magnetic confinement (tokamaks, speromaks, pinches, mirrors, stellarator) and inertial confinement (laser, and I suppose pinches again). All of these rely on the energy generated by fusion events to burn more fuel, as stated by MFB.

    Yes, the escape of large portions of the energy via forms that don't heat the plasma is a problem. Bremmstrahlung for instance is a major impediment to higher Z fuels (higher atomic number), i.e. the x-rays from the large increase in electrons.
     
  20. Mar 27, 2014 #19
    Yes there have been, and are several attempt to make fusion. Speromaks was new to me. Fast inertial confinement like laser, does it use the reaction to heat. I thought it was just the enormous pressure and eventually heat from the lasers that make it happened? It seems so quick to me that the reaction heat comes when it's over. Another serious attempt to get fusion is the Farnsworth fuser. The original one makes a lot of fusion or neutrons but not excess heat. It also suffer from bremsstrahlung losses. Let's see if the Polywell can work. It's a variant of the fusor idea.

    I don't have so much more to say about this now. I have bought a book about plasma and fusion and I will try to investigate more about plasma behavior and do some calculations to see what it can lead to.

    The thread has been interesting and at least give me a lot of knew knowledge about fusion and plasma. Thanks a lot folks.
     
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