More news, please

[jamesr]

QuantumDot wrote: On the Wikipedia page about DPF it says that, the ones that are larger in the MJ, MA range have pinch’s that last milliseconds, but i didn’t see what experiment that it was referring to and if they do exist does that mean that somewhere the right equipment exists, do you or anyone know? with the improvements that have already been made so far the millisecond confinement time with megawatts of input power look very good.

“These critical phases last typically tens of nanoseconds for a small (kJ, 100 kA) focus to around a microsecond for a large (MJ, several MA) focus”
http://en.wikipedia.org/wiki/Dense_Plasma_Focus

Large devices like the PF-1000 in Poland have been operating for years. The image at http://www.intimal.edu.my/school/fas/UFLF/ show the scale of the machine. They do not achieve a very dense focus though compared to smaller devices, and so the triple product of density*temperature*confinement time needed for appreciable levels of fusion is not as high.

More details of the scaling from kJ to MJ devices based on the Sing Lee model can be found at http://www.plasmafocus.net/

The size of FoFu-1 was calculated to be near optimal. When they switch to the pB11 from deuterium the electrodes will need to be swapped out for even smaller ones as I understand it.

[Brian H]

jamesr wrote:
…
The size of FoFu-1 was calculated to be near optimal. When they switch to the pB11 from deuterium the electrodes will need to be swapped out for even smaller ones as I understand it.

Yes, that sounds right. When dealing with DPF, bigger is not better. It’s the intensity of “focus” which generates the necessary conditions for pB11 fusion long enough to produce an energetic collapse.

[Henning]

DPFs scale linearly with size, as opposed to Polywell or tokomaks, which get better the bigger they get.

[mchargue]

Henning wrote: DPFs scale linearly with size, as opposed to Polywell or tokomaks, which get better the bigger they get.

How are these two descriptions different?

Also, doesn’t the Polywell energy output scale as the square of the radius? (a function of ‘falling’ from a greater distance)

As for the tokomacs, from what I can see from the example of ITER, the only thing that scales on the tomomak is the price. Probably price as a cube of the radius. 😉

Pat

[QuantumDot]

Polywell’s are supposed to increase to the fifth power of the radius and the fourth power of the magnetic field.

[mchargue]

QuantumDot wrote: Polywell’s are supposed to increase to the fifth power of the radius and the fourth power of the magnetic field.

As in w = r^5 * B^4?

That’s a good bit!

[QuantumDot]

Does anyone know the current plasma density?

[Lerner]

Well, we, the experimental team don’t. We need more data. We need to either see clear evidence of neutrons from D reacting with tritium produced in the plasmoid or we need images to measure the radius of the plasmoid. We don’t have either yet, but we are working on it. Stay tuned!

[QuantumDot]

Could someone on the experiment team give a loose timeline of the future updates to the FoFu machine, like i have read that you expect to sometime by the end of the year switch to shorter electrodes and try for p-11B, so maybe say what the hope to do in the upcoming months like what new sensors you will add. or at less the next month if not for the whole year?

[jamesr]

Lerner wrote: Well, we, the experimental team don’t. We need more data. We need to either see clear evidence of neutrons from D reacting with tritium produced in the plasmoid or we need images to measure the radius of the plasmoid. We don’t have either yet, but we are working on it. Stay tuned!

So given 50% of the D-D reations produce a 2.45MeV neutron and the other 50% produce a triton which can then go on to produce a 14.1MeV neutron. Can you use the flight time data from both reactions to help recover the temperature of the plasmoid more accurately than with just the one peak.

Given D-T’s much higher cross section, would any confined tritium undergo enough scattering collisions to completely thermalise before undergoing fusion, or would a significant proportion fuse after only a few interactions and so the spread of the 14.1MeV peak would be too broad any not representative of the temperature.

If you assume tritium not only has time to thermalise, but also that any that does and remains confined will have a very high probability of fusing, can you use the ratio of D-D neutrons to D-T neutrons to gain some insight into the proportion of tritons (that would be produced with 1.01MeV) remained confined in the plasmoid. Could you then extrapolate the theory forward to get an estimate of how well confined the He produced in the pB11 reaction will be, and so how well the energy is recycled into the plasmoid to achieve ignition?

[Brian H]

jamesr wrote:

Well, we, the experimental team don’t. We need more data. We need to either see clear evidence of neutrons from D reacting with tritium produced in the plasmoid or we need images to measure the radius of the plasmoid. We don’t have either yet, but we are working on it. Stay tuned!

So given 50% of the D-D reations produce a 2.45MeV neutron and the other 50% produce a triton which can then go on to produce a 14.1MeV neutron. Can you use the flight time data from both reactions to help recover the temperature of the plasmoid more accurately than with just the one peak.

Given D-T’s much higher cross section, would any confined tritium undergo enough scattering collisions to completely thermalise before undergoing fusion, or would a significant proportion fuse after only a few interactions and so the spread of the 14.1MeV peak would be too broad any not representative of the temperature.

If you assume tritium not only has time to thermalise, but also that any that does and remains confined will have a very high probability of fusing, can you use the ratio of D-D neutrons to D-T neutrons to gain some insight into the proportion of tritons (that would be produced with 1.01MeV) remained confined in the plasmoid. Could you then extrapolate the theory forward to get an estimate of how well confined the He produced in the pB11 reaction will be, and so how well the energy is recycled into the plasmoid to achieve ignition?

james;
Since neither tritons nor neutrons will be involved in the pB11 cycle, is there a reason to expect such an extrapolation? And AFAIK, the He is not confined to the plasmoid at all, but exits as an alpha beam once the C12 disintegration occurs.

Signed,
Puzzled

[jamesr]

Brian,
As far as i knew the the a significant proportion of the He will be retained in the plasmoid (and needs to be if appreciable fusion is to occur). After >50ns (ie a long time), when hopefully most of the fuel as fused does the collapsing magnetic field create the strong axial electric field that accelerates the beam of ions and electrons.

If a triton or alpha is produced near the edge of the plasmoid then it might escape, but if it is generated somewhere such that the closed field lines of the plasmoid keep it trapped long enough to have the 20 or so collisions needed to deposit all its energy into the dense part of the plasma then that energy can make up for the huge losses due to bremsstrahlung radiation that is cooling the plasma.

By using all the information provided by these deuterium tests and understanding the processes going, I was suggesting that you could use the tritons to estimate how stable the plasmoid is to the production of fast ions, and so how much of their energy is transferred to the fuel ions to maintain the temperature high enough for them to fuse.

[Brian H]

jamesr wrote: Brian,
As far as i knew the the a significant proportion of the He will be retained in the plasmoid (and needs to be if appreciable fusion is to occur). After >50ns (ie a long time), when hopefully most of the fuel as fused does the collapsing magnetic field create the strong axial electric field that accelerates the beam of ions and electrons.

If a triton or alpha is produced near the edge of the plasmoid then it might escape, but if it is generated somewhere such that the closed field lines of the plasmoid keep it trapped long enough to have the 20 or so collisions needed to deposit all its energy into the dense part of the plasma then that energy can make up for the huge losses due to bremsstrahlung radiation that is cooling the plasma.

By using all the information provided by these deuterium tests and understanding the processes going, I was suggesting that you could use the tritons to estimate how stable the plasmoid is to the production of fast ions, and so how much of their energy is transferred to the fuel ions to maintain the temperature high enough for them to fuse.

The bremsstrahlung is minimized by the specific level of the mag field, IIRC, not by keeping the thermal energy high. As far as the field lines of the plasma containing the heavier nuclei, I assume that they are all ionized, and hence tightly contained.

[jamesr]

The bremsstrahlung is minimized by the specific level of the mag field, IIRC, not by keeping the thermal energy high. As far as the field lines of the plasma containing the heavier nuclei, I assume that they are all ionized, and hence tightly contained.

The quantum effect when the electron larmor radius due to a strong magnetic field is of the order of its de Broglie wavelength is a small (but key) factor, in that it may reduce bremsstrahlung from boron by a factor of 5 or so. Even with this effect the plasma would radiate its energy away and cool to well below the temperature needed for fusion in picoseconds rather than the nanoseconds needed to burn enough fuel to get nett energy gain. It is the recycling of energy from the helium to keep the hydrogen and boron hot enough for long enough that will make it viable.

At the magnetic field strengths involved, yes, the ions are well confined, and are bound to follow the field lines (gyrating around them). But no magnetic confinement is perfect, as collisions cause diffusion and transport of ions away from the dense core. Once an ion has scattered out to the last closed field line, or separatrix, of the plasmoid it will escape.

The question is – what is the probability for tritons or alphas that are created sufficiently close to the edge to have a chance of escaping before they have given up all their energy

[AaronB]

More news now posted on the LPP site.

[Author]

Posts