Homepage Forums Innovative Confinement Concepts (ICC) and others Magnetized inertial fusion (MIF)

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  • #11681
    Avatarzapkitty
    Member

    asymmetric_implosion wrote: I hope the photovoltaics work as described. Is there test data to support the 80% efficiency or are these theoretical calculations?

    The FF onion uses the photoelectric effect, not the photovoltaic effect. Although the effects are related, and it’s an error that I’ve made myself in referring to FF, the photoelectric effect is different from the photovoltaic effect.

    In simple terms, the photovoltaic effect encourages conduction of electrons between different bands in an atomic structure while the photoelectric effect knocks electrons loose from the surface of a material. Higher energy photons means more efficient transfer.

    The effect is well understood but no one has needed to harvest x-rays for power before… that is, before FF 🙂

    asymmetric_implosion wrote: If they do work why aren’t they deployed on every nuclear power plant? Tons of gamma rays are produced and could be converted to useful electrons.

    Why did you switch up to gamma rays? That’s not something an FF unit would produce much of.

    The FF x-rays are high energy photons but they can be stopped by a few thousand layers of metal foil: the “onion”

    The gamma rays that are a copious byproduct of fission reactions are much more penetrating than FF’s x-rays and are thus much, much harder to convert.

    And there are currently no commercial or natural x-ray sources worth trying to harvest for energy. Instead, people use electricity to generate x-rays that they need.

    And that brings us to one of the FF spinoff techs: use as an efficient, almost self-powering portable x-ray generator. Add a partial “onion” and it becomes self-powering. Great for bridge inspections etc etc etc etc (lots of uses)

    asymmetric_implosion wrote: I hadn’t considered using the heat for buildings and such. The loss seems significant but probably better than a turbine. The Russians have some data on this since they used fission plants to heat towns.

    I guess the big question is will a power conversion cycle be needed at all?

    The FF unit beam conversion is currently estimated to be not quite sufficient to recover the electrical energy needed for the next shot. Thus the “onion.”

    #11683
    AvatarFrancisl
    Participant

    Could a small onion type device be constructed now and placed close to the DPF to catch some x-rays to test the concept and do some preliminary engineering?

    #11684
    Avatarzapkitty
    Member

    Francisl wrote: Could a small onion type device be constructed now and placed close to the DPF to catch some x-rays to test the concept and do some preliminary engineering?

    Well, it depends on what you want to test and what LPP could afford to spare in terms of time, effort and money.

    But just showing that x-rays hitting carefully arranged layers of metal foil results in a certain amount electrical power would be nothing remarkable. The photoelectric effect is not all that mysterious… except, perhaps, when people confuse it with the relatively inefficient photovoltaic effect 🙂

    If you would want to test an assembly more akin to what would go into an actual “onion” in a functional generator… then that will take time, effort and money that should instead be going to proving pB11 fusion.

    First things first: proving the theory.

    The “onion” will no doubt hold its own engineering surprises along the way but it’s not on the same level or the same scale as the reach for aneutronic fusion.

    Now, if someone would want to build and donate a test panel of “onion” structure to LPP then perhaps something could be done that way?

    #11685
    Avatarjamesr
    Member

    zapkitty wrote:

    Now, if someone would want to build and donate a test panel of “onion” structure to LPP then perhaps something could be done that way?

    Seems the sensible way to go.

    Similar to the way diagnostics and other equipment is added to tokamaks & other experiments. Get a collaboration with some university then some PhD student can build & test the device, with LPP specifying the physical constraints of size and where it could be mounted. Once built & tested in their home University they can bring it along and mount it and spend a few weeks gathering data (working around LPP’s main campaign)

    Obviously the tricky bit is getting the funding/collaboration sponsor for it. Maybe good for one of these new crowd-sourced funding projects.

    #11686

    Photoelectric effect is used all over the place to detect radiation but never in a power conversion configuration. It seems like a daunting problem considering the plasma interacting with the first wall of the onion leading to eddy currents and other electrical noise that will screw up the collection of photo electrons. The onion seems easy enough to test now. In fact, it seems that it should be tested before the PF. If LPP shows a viable means to convert x-rays/gamma rays (more layers in the onion is all you need unless you are worried about Compton scatter), it could be implemented in nuclear fission plants. That would provide a revenue stream in licensing or sales that could support the PF development while improving efficiency of the electrical production in the near term. It seems the whole idea was approached backwards. Use money from the easy thing to support the hard thing, if the onion is as simple as producing photo electrons and gathering them.

    #11688
    AvatarBrian H
    Member

    zapkitty wrote:

    Needlessly? Who would do that? No one here, that’s for sure 🙂

    Industry uses vast amounts of heat for a vast number of processes and some processes need cooling as well. Buildings and, indeed, entire communities need heating and cooling.

    Locally distributed FF units can provide both heating and cooling (via heat-powered absorption chiller systems.)

    Simply substituting FF units for fossil power sources [em]lowers[/em] total industrial and habitation waste heat.

    That’s the key concept I’ve tried to emphasize on many threads. The net heat-efficiency of FF is so far beyond any alternate source that there is only negative gain in tacking on any ancilliary equipment, etc. The vented heat, even just “dumped”, is less than the losses from any competing power source.

    #11689
    AvatarBrian H
    Member

    asymmetric_implosion wrote:

    If LPP shows a viable means to convert x-rays/gamma rays (more layers in the onion is all you need unless you are worried about Compton scatter), it could be implemented in nuclear fission plants.

    That’s their concern; IMO, IIRC, there’s not enough stray gamma from the FF to make it worthwhile. Gamma can be very penetrating; the “just a few more layers” might mean double or triple!

    #11690
    Avatarjamesr
    Member

    asymmetric_implosion wrote: It seems like a daunting problem considering the plasma interacting with the first wall of the onion leading to eddy currents and other electrical noise that will screw up the collection of photo electrons.

    I was assuming it was outside the vacuum chamber. OK the chamber wall itself will absorb most of the softer xrays, so a final one would want the minimum obstruction before it. However, for the harder (10-200keV) xrays, you could test the concept.

    useful tables and graphs of X-ray absorption can be found at
    http://www.nist.gov/pml/data/xraycoef/index.cfm

    #11692

    More than double or tripe, probably like 10X, but who cares. The onion is described as a low cost, easy to build solution. If you can convert the photons from fission at 80% to electricity you gain another 3-5% efficiency on a fission plant. That is game changing in the power industry and probably worth more than $100M. That would build a nice PF test facility and demo reactor.

    Jamesr: thanks for the ref, NIST XCOM is my standard data base for these calculations. For a standard SS304 vacuum wall, you lose sensitivity below 40 keV. For a pinch, mean x-ray energy is near the pinch voltage. For a 2 MA PF, the maximum pinch voltage is around 500 kV so you can expect many x-rays around 500 keV. If you do a better job of pinching as expected from LPP you could get up to 1 MV as the mean energy. Go up in current and the pinch voltage increases along with the mean energy of the x-rays. Consider the anode converts most of the runaway electrons to x-rays in existing PF devices. If the anode is Be, your electron energy is likely lost to heat. If the plasmoid is the dominant converter it will be B doing most of the converting to x-rays. There is a reason bremms x-rays sources use high Z converters. One might argue that less x-rays is a good thing. According to Zapkitty these x-rays are supposed to push you over the top to Q>1. It seems pretty convoluted to me.

    As I already stated above, fission produced 700 keV photons nominally. It seems that the two system are in the same ball park. The x-ray spectrum is a bremmsstrahlung spectrum and it favors lower energy but it is not stretch that LPP will be producing x-ray that are already produced on operating systems that would make excellent test beds for the “onion”.

    #11693
    Avatardennisp
    Member

    How efficient does the onion have to be to give us practical net power?

    If 40% is ok, then if the onion turns out slow to develop, a turbine would work. Pressurized water reactors run at only about 315 deg C:
    http://hyperphysics.phy-astr.gsu.edu/hbase/nucene/reactor.html

    If water coolant doesn’t absorb X-rays well enough, maybe we could borrow from certain fast reactors and use lead, which melts at 327C and definitely isn’t transparent to X-rays. Molten salt and sodium are other options, though I have no idea how suitable they’d be.

    Ideal Carnot efficiency at 600C on a warm day is around 65% according to this calculator:
    http://hyperphysics.phy-astr.gsu.edu/hbase/thermo/carnot.html#c1

    Of course you have to keep the lead above its freeze temp, which takes you down to 28% or so. But you could have a secondary loop of water coolant to take you from >327C to outside temp, with about the efficiency of PWR turbines, getting us in the neighborhood of 50% total. Now you’re approaching the complexity of the PWR power loop, but at least you don’t have a containment dome and a bunch of complicated safety systems. You can probably get in the neighborhood of coal power cost, especially given the relative lack of fuel expense, or of the regulatory and political delays that plague fission reactors.

    It might not be the ultra-cheap power source we’re hoping for, but a zero-waste, zero-pollution, reasonably-cheap, perfectly safe power source is still good enough to go to production, and kick off a lot of investment in developing better options.

    #11694
    Avatarjamesr
    Member

    Given that the bulk plasma in the device should not cool between each pulse below ~800C or so, you could just extend the helium gas cooling needed for the anode to the rest of the walls (making them out of something like tungsten), and run it through a brayton cycle turbine.

    But as has been said before it would be much better to avoid having to use a thermal cycle and just extract even just 10-15% directly from the xrays to push over the Q=1 and dump the rest as waste heat.

    asymmetric_implosion: The 500kV pinch voltage does not relate to the energy of the x-rays. The x-ray energy peak from bremsstrahlung is a function of electron temperature (http://en.wikipedia.org/wiki/File:Bremsstrahlung_power2.svg ). If the electrons are at ~150keV then the bremsstrahlung peak will be around a quarter of this – so around 30-40keV.

    #11695

    jamesr wrote: Given that the bulk plasma in the device should not cool between each pulse below ~800C or so, you could just extend the helium gas cooling needed for the anode to the rest of the walls (making them out of something like tungsten), and run it through a brayton cycle turbine.

    But as has been said before it would be much better to avoid having to use a thermal cycle and just extract even just 10-15% directly from the xrays to push over the Q=1 and dump the rest as waste heat.

    asymmetric_implosion: The 500kV pinch voltage does not relate to the energy of the x-rays. The x-ray energy peak from bremsstrahlung is a function of electron temperature (http://en.wikipedia.org/wiki/File:Bremsstrahlung_power2.svg ). If the electrons are at ~150keV then the bremsstrahlung peak will be around a quarter of this – so around 30-40keV.

    Brems in the plasma might agree with a thermal spectrum if the electrons remain confined in the plasmoid but brems from the electron beam will not obey a thermal spectrum. The run away electron beam that impacts the anode is much higher energy. It hast to be to escape the B-field. Literature from as early as 1977 (Krompholz et al Appl Phys 13, 29-35, 1977) has verified this. The mean e-beam energy is near the pinch voltage with electron energies up to 1 MeV in ~100 kA machines. It gets worse as you go up in pinch current. If the electron beam remains the dominant x-ray sources the brems spectrum will be harder than the thermal spectrum prediction requiring a thicker onion. I’ve been fighting this particularly vexing problem of the hard x-ray spectrum for a couple years because it complicates my application for the plasma focus.

    If the x-ray emission is dominated by the plasmoid emission, most of the x-rays will be lost in the vacuum spool before the onion if they are separate pieces. Based upon LPP’s recent release of copious x-ray above 100 keV it seems that the beam is still king as 30-40 keV x-ray would have been significantly attenuated by the copper filters. It seems pretty reasonable for a 1 MA pinch that the mean x-ray energy is near 250 keV (typical pinch impedance is 0.25 Ohm with ~ 1MA so 250 kV). To my knowledge LPP doesn’t measure the voltage during the pulse outside vacuum. Pinch voltage is hard to back out without both the current and voltage outside vacuum. Published techniques exist to calculate the pinch voltage if the data is taken. You can use models to estimate the pinch voltage if you wish but I’ve always preferred a maximum data, minimum model approach.

    #11696
    Avatarzapkitty
    Member

    asymmetric_implosion wrote:

    asymmetric_implosion: The 500kV pinch voltage does not relate to the energy of the x-rays. The x-ray energy peak from bremsstrahlung is a function of electron temperature (http://en.wikipedia.org/wiki/File:Bremsstrahlung_power2.svg ). If the electrons are at ~150keV then the bremsstrahlung peak will be around a quarter of this – so around 30-40keV.

    Brems in the plasma might agree with a thermal spectrum if the electrons remain confined in the plasmoid but brems from the electron beam will not obey a thermal spectrum. The run away electron beam that impacts the anode is much higher energy.

    Per Lerner-haklase: In an all-up FF pB11 device the electron beam doesn’t make it out of the plasmoid. Instead the electron beam contributes to further heating of the plasmoid and thus an increased fusion rate.

    #11697

    E-beam does not need to be born in the plasmoid. Any region of strong electric fields near the pinch region can generate runaway electrons. Most observations suggest that the runaway electrons are generated in low density regions outside what LPP calls the plasmoid region. If this observation remains true, you still have a runaway e-beam problem and the x-rays that go with it. This assumes that a plasmoid can confine all the electrons as the theory under test describes. Again, LPPs recent results suggest that the plasmoid has yet to confine electrons as the x-ray spectrum was very hard; much harder than a 140 keV thermal spectrum suggests. I can’t speak to the theory in detail but the experiment seems to disagree with the theory up to this point.

    #11698
    AvatarLerner
    Participant

    Assymetric, what makes the x-ray data so striking is that it can’t come from the beam hitting the anode. There is 4 inches of lead between the point where the beam hits the anode and the NTF or the FTF. Either the first x-ray peak comes from beam elctrons that are trapped in the plasmoid or from the heated electrons in the plasmoid itself. I’m still analysing the last several months’ data on this. the second x-ray peak, which is also pretty hot, comes well after the beam.

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