I know that the big hype is pB11 or possibly DD, but does anybody know if WB-7 was tested with DT?
Would it be possible to have net power production, (theoretical), with a WB-7 size machine if you were using DT?
Does anybody know if WB-7 was tested with DT
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Barry Kirk
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Barry Kirk
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I doubt they had any tritium.
Anyways, in an IEC reactor the energy/temperature level isn't the major obstacle the way it is in tokamaks.
I think Nebel put it something like "In tokamaks, confinement is easy and temperature is hard. In IEC, temperature is easy and confinement is hard."
Absolutely not. You're looking at maybe a milliwatt of power output, and that for only a quarter-millisecond. The slightly lower energy requirement for D-T is not going to be anywhere close to making up r^7.Would it be possible to have net power production, (theoretical), with a WB-7 size machine if you were using DT?
...
I'm wondering if DT could make up that difference.
Anyways, in an IEC reactor the energy/temperature level isn't the major obstacle the way it is in tokamaks.
I think Nebel put it something like "In tokamaks, confinement is easy and temperature is hard. In IEC, temperature is easy and confinement is hard."
n*kBolt*Te = B**2/(2*mu0) and B^.25 loss scaling? Or not so much? Hopefully we'll know soon...
I'm relatively sure they did not use tritium, just because the licensing alone would have driven them nuts. DD is good enough, and way safer to handle.
IIRC, around the parameters of hobby fusors and the WB machines, DT gives you something like a boost of 30-50. That's meaningful if you can just get a reaction going, but with an IEC or IEF machine you can generally just jack the voltage up a bit and get the same effect. If the scaling laws are right, the difference in size between a DD and DT machine at the same reaction rate is hardly worth worrying about.
Hirsch used DT on some of the old Farnsworth work, pushing to 150 kV. I looked at the crossection curves and concluded he may actually have been hitting so hard he was past peak reactivity. Later work has gotten about the same reaction rate on DD at 120 kV. That's the rate (large fraction of 1e9 fusions/sec) Dr. Bussard thinks he hit with WB6 at a well depth of 10 kV, with a reaction volume which should have been within a factor of two or so of a typical fusor.
IIRC, around the parameters of hobby fusors and the WB machines, DT gives you something like a boost of 30-50. That's meaningful if you can just get a reaction going, but with an IEC or IEF machine you can generally just jack the voltage up a bit and get the same effect. If the scaling laws are right, the difference in size between a DD and DT machine at the same reaction rate is hardly worth worrying about.
Hirsch used DT on some of the old Farnsworth work, pushing to 150 kV. I looked at the crossection curves and concluded he may actually have been hitting so hard he was past peak reactivity. Later work has gotten about the same reaction rate on DD at 120 kV. That's the rate (large fraction of 1e9 fusions/sec) Dr. Bussard thinks he hit with WB6 at a well depth of 10 kV, with a reaction volume which should have been within a factor of two or so of a typical fusor.
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Barry Kirk
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More or less.
p-B11 is essentially impossible for toks because they'll never get the temp high enough (and even then the thermal tail would create a lot of problems with side reactions). But if you could get wiffleball confinement with an IEC, you might be able to get aneutronic power from p-b11.
Art Carslon illustrated the difference when he commented that if you're burning p-B11 you could be getting something like 2000x more power from D-D. In a tok, this would make no sense, but in an IEC you might be willing to make that trade to eliminate the neutronicity (beacuse temp is easy).
p-B11 is essentially impossible for toks because they'll never get the temp high enough (and even then the thermal tail would create a lot of problems with side reactions). But if you could get wiffleball confinement with an IEC, you might be able to get aneutronic power from p-b11.
Art Carslon illustrated the difference when he commented that if you're burning p-B11 you could be getting something like 2000x more power from D-D. In a tok, this would make no sense, but in an IEC you might be willing to make that trade to eliminate the neutronicity (beacuse temp is easy).
n*kBolt*Te = B**2/(2*mu0) and B^.25 loss scaling? Or not so much? Hopefully we'll know soon...
In both the DD and DT cases, they are isotopes of hydrogen and the ions will have a charge of +1. All the isotopes pick up the same KE in a given potential well.
In the case of boron, the charge can be up to +5, so you get that factor of voltage reduction available for the potential well depth to get the borons to the desired KE.
The difference in size for the same power output between DD and p-B11 seems to correlate nicely with a bremsstrahlung-reduction strategy pointed out in a paper in the early 90's. I'd have to look it up to be sure which was which, but one factor was raising the p density relative to B11 by about a factor of 6-8. The other was controlling virtual anode height to about 15% of the maximum possible. I remember thinking that second trick would reduce the reaction rate significantly, then calculated and found the change from 1.5 to 2 meters would just make up for it.
The p-B11 case is not a perfect analog to the other two, but you still play size against other effects to make up for reaction rate problems. With D and T you have the option to go to higher voltage with no serious problems. With p-B11, the bremsstrahlung losses probably become significantly worse as you boost voltage, so your better strategy is boosting reaction rate with B and R.
In the case of boron, the charge can be up to +5, so you get that factor of voltage reduction available for the potential well depth to get the borons to the desired KE.
The difference in size for the same power output between DD and p-B11 seems to correlate nicely with a bremsstrahlung-reduction strategy pointed out in a paper in the early 90's. I'd have to look it up to be sure which was which, but one factor was raising the p density relative to B11 by about a factor of 6-8. The other was controlling virtual anode height to about 15% of the maximum possible. I remember thinking that second trick would reduce the reaction rate significantly, then calculated and found the change from 1.5 to 2 meters would just make up for it.
The p-B11 case is not a perfect analog to the other two, but you still play size against other effects to make up for reaction rate problems. With D and T you have the option to go to higher voltage with no serious problems. With p-B11, the bremsstrahlung losses probably become significantly worse as you boost voltage, so your better strategy is boosting reaction rate with B and R.
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Barry Kirk
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I'm going to assume that the overwhelming majority of brem loses are experienced by electrons since they have a much higher acceleration.
Is most of the electron acceleration due to travelling through a potential gradient?
Would the potential gradient be lower for a bigger machine? Or at least spread out over a larger distance which would lower accel.
I'm trying to understand if brem loses can be reduced by going to a larger machine.
Is most of the electron acceleration due to travelling through a potential gradient?
Would the potential gradient be lower for a bigger machine? Or at least spread out over a larger distance which would lower accel.
I'm trying to understand if brem loses can be reduced by going to a larger machine.
In the absence of ions, at the center of the machine the electron KE should be low, so there would be little brem. Basically, the potential well depth is defined by the electron kinetic energy, assuming they are relatively monoenergetic in the vicinity of the magrid. By definition, at the center of a fully-populated potential well, they would have no KE left.
Adding ions makes them want to converge in the center. If allowed to do so liberally, they make central positively-charged zone (Dr. Bussard's papers show a sharp spike in the center ... likely it is not really this well-defined). This zone acts as a virtual anode, and allows the electrons to retain some kinetic energy at the center. High electron KE is the source of brem.
Increasing the potential well depth by increasing electron KE would presumably boost reaction rate, but it would likely also boost the height of the virtual anode, making brem losses worse. To lower the virtual anode height requires lowering ion density, which lowers the reaction rate.
The reason I think a larger machine allows you to have lower brem losses is it lets you work at the lowest practical voltage. Instead of boosting voltage to get a higher rate, you rely on B^4R^3 scaling. If that scaling really holds, it is so strong it can overcome problems easier than just about anything you can manipulate. I think.
Adding ions makes them want to converge in the center. If allowed to do so liberally, they make central positively-charged zone (Dr. Bussard's papers show a sharp spike in the center ... likely it is not really this well-defined). This zone acts as a virtual anode, and allows the electrons to retain some kinetic energy at the center. High electron KE is the source of brem.
Increasing the potential well depth by increasing electron KE would presumably boost reaction rate, but it would likely also boost the height of the virtual anode, making brem losses worse. To lower the virtual anode height requires lowering ion density, which lowers the reaction rate.
The reason I think a larger machine allows you to have lower brem losses is it lets you work at the lowest practical voltage. Instead of boosting voltage to get a higher rate, you rely on B^4R^3 scaling. If that scaling really holds, it is so strong it can overcome problems easier than just about anything you can manipulate. I think.
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Barry Kirk
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