Improvements in Firing and Instruments
(20) CommentsFrom LPP’s March 31 report: “Improvements in Firing and Instruments Combine to Produce Encouraging Results”:
Right now, our most important instruments are the Time-Of-Flight (TOF) detectors that measure both neutrons and X-rays emitted by the plasmoid. These detectors look at narrow beams of radiation that pass through the experimental room’s walls through 1” tubes. Previously, alignment problems prevented us from seeing both signals clearly. This month, we found that the detectors’ view of the plasmoid was partially blocked, making us think we were producing fewer neutrons and less X-rays than we were. We’ve now fixed the alignment and expect to improve it still further in the next month after the arrival of a surveyor’s transit, a type of telescope ideally suited for alignments.
This realignment brought the TOF’s measurements of neutron flux into closer agreement with the measurements of total neutrons performed by the silver activation detector. This agreement gives us more confidence in both measurements.
Using this new improvement in instrumentation, the LPP team has found that so far, over the range of currents from 500-800 kA, the neutron yield is following an I6 power scaling, exactly what our theory has predicted and considerably better than the I4 scaling obtained by most other researchers.
Equally important, the two TOFs working together have produced more evidence that we are already duplicating the high ion energies achieved with higher currents in the Texas experiments. As the neutrons travel to the detector, they spread out, due to their different energies, which reflect the energies of the ions whose collisions produced the neutrons. The more they spread out, the greater the ion energies. Our measurements show that in our best shots, ion energies are in the range of 40-60 keV (the equivalent of 0.4-0.6 billion degrees K). An example shot, 032510-07, is shown in the figure.
Comparing how much X-ray energy is received at the two TOFs can give a measure of the average electron energy. For relatively low energy X-rays, the air between the plasmoid and the detector filters them, so the ratio at each instant of the X-ray signal at the two detectors can be a measure of average X-ray energy. This measurement is a bit more complicated, but indicates that peak electron energies are around 30 keV.
A third major new observation comes from a more low-tech measurement device—a depth gauge. Accurate measurements of the depth of the hole in the central electrode, the anode, show that on average, the electron beam from each pinch vaporizes about 18 microns of copper. This may not seem like a lot, but to do this, the electron beam must carry about 0.5 kJ of energy and the plasmoid must have about 1 kJ of energy, nearly half that stored in the magnetic field of the device. So, this is evidence that a substantial part of the total energy available is being concentrated in the plasmoids and transferred to the beams.
More Reliable Firing at Greater Current
More on Magnetic Fields
Comments
For a more in depth discussion, start a thread in the forums.if this electron beam carries so much energy, wouldn’t it make sense to recuperate its energy to reach fusion break-even more rapidly?
My idea is you only have to make the DPF anode a hollow tube, and add a rogowski coil device at the open end, similar to the one you plan to capture the ion beam that exits at the forward end. After these electrons gave up most of their energy, they are collected on a simple, positively charged plate anode.
40 years ago, vacuum electronics was mainstream engineering, now its almost a forgotten science. Maybe find yourself a retired vac tube engineer before they’re all deceased…
belbear;
My understanding is that the beta beam energy is used/needed to reheat the plasma. I may be wrong or oversimplifying, of course!
I don’t doubt that this heating is indeed occuring inside the plasmoid. But not all electron energy will be spent this way.
What escapes out of the tiny plasma ball is now useless for the plasma, but can be converted to useful power by decelerating the electrons. Or wasted by letting these energetic electrons slam into a solid surface where all their remaining energy is converted to hard EM radiation, heat and material destruction. (= the 18 microns of copper vaporized)
Fortunately, the 25 keV beam of a CRT color TV doesn’t “eat” into the screen surface, so there must be a pretty intense beam involved in FF-1.
Now imagine how much more powerful a beam will escape out of an ignited p-B11 plasma instead of a marginally fusing deuterium plasma.
Recycling an electron beam’s energy is actually just the opposite to what happens in a picture tube’s electron gun, and conversion from beam energy to electricity by deceleration can be made straightforward and efficient. After all, moving electrons that’s exactly what electricity is.
Indeed, i’m an electronics engineer and not a physicist.
I think the alpha beam (He ions) is going to be the source of such recovery; it’s probably impossible to tap both alpha and beta beams that way. The alpha beam recharges the capacitors; the beta beam reheats the plasma; the X-rays generate about a 40% “profit” through the photoelectric process in the onion-shell.
Don’t shoot me if i’m wrong, but what I had in mind is the “residual” beta beam, that what escapes the plasma into the quasi-vacuum of the reaction vessel, hits the anode and erodes it, as observed in FF-1. An escaped beam can no longer heat the plasma, just like a bullet can no longer be accelerated after leaving the gun barrel.
If all the electrons would heat the plasma, no beta beam would originate and no anode erosion would be observed, is it?
However, IF an electron beam escapes the plasma, it’s useless for plasma heating anyway and its energy surely can be recovered. You only have to give it a way to avoid hitting the anode, by making it a hollow tube and then apply the reverse-electron-gun principle.
If there is no electron beam at all escaping the plasma, there is of course no need to recycle one.
And by the way, I think that the photoelectric “onion shell” will prove to be much harder to make into a durable X-ray-to-electricity converter than anticipated.
Hard X-rays have a nasty side effect when they hit solid matter: They not only knock off electrons, they also break down chemical bonds and crystal lattices, which is eating away at the very structure that is meant to convert them.
It would be a sad thing to discover that such an expensive “onion shell” shorts out and stops functioning after only as much as a million X-ray pulses, which is hardly more than one hour of operation for a 220 pulses/sec DPF unit. Lets hope i’m wrong.
To Eric L. or Rezwan: Can you please post a picture of that eroded anode? I’d like to see how it looks like.
I believe you misunderstand the point—that “quasi-vacuum” IS the plasma. It is composed of decaborane gas in the final design, or deuterium-enriched hydrogen at the moment.
Electrons that are vaporizing the anode are obviously not heating a plasma.
I thought that only the very dense plasma inside the superstrong, but micron-sized magnetic field of the plasmoid really matters for generating fusion.
If you look at the “dpf animation” on the ff homepage: What I mean is the red beam that shows on 1’:10” of the video. When this happens, the fusion process should essentially be finished.
Heating plasma outside that plasmoid, AFTER it collapsed, would only be a waste of power and most of the electrons from the emitted beam will not interact at all but continue until they hit the anode.
If that animation, of course is really showing what happens.
Very unlike a machine like a tokamak, where the field from the huge magnetic coils confines the electrons inside the fusing plasma all the time.
After a shot comes another shot. The plasma must be energized in advance. The beta beam does that. Or so I’ve always understood.
I am not clear on the geometry of the final design, and how it will be dispersed.
What belbear is saying, I think, is that in the process of fusion in the shrinking plasmoid, two beams eject from it at opposite directions, along the axis of the anode. One is carrying positively-charged He ions and the other is negatively-charged electrons. Currently, the electron beam fires into the back of the anode and its energy is wasted, and is causing the vaporization of the copper anode. I assume the reason for doing this at the moment is analytical; they want to measure the energy ejected, and are using the amount of erosion to gauge the plasmoid’s efficiency.
I would hope that a final design would capture the energy of this beam and feed it back into the capacitors for the next firing, lowering the energy cost of operating the device and making it much more efficient. Belbear’s idea about using a “reverse electron gun” to capture that energy addresses this very issue.
I think what you are saying, Brian, makes it sound like you believe that the electron beam should be fed back into the plasmoid to increase the temperature thus increasing the fusion reactions inside it. I don’t think this is possible given the nature of the device’s design. Power is fed into the system with a single burst of electricity that travels up the anode as plasma “lightning” via the surrounding cathodes. Once at the top of the anode, the plasma currents then curl into each other and shrink, forming the plasmoid. (This curling is helped by the innovation of using magnets around the chamber to add additional angular momentum, as you can read about in a previous post.)
When the plasmoid gets to its critical size, the temperatures, the pressures, and the magnetic field effect hopefully will be all that is needed to fuse the fuel. It is after the fusion has occurred, and the plasmoid finally decays, that the two beams are emitted. There is basically no plasmoid left to feed energy back into it. The best plan is to capture as much “waste” energy as possible, and feed it back into the next shot.
After re-reading your posts, I think what you are saying is that the beam should be fed into the decaborane gas surrounding the device to “charge the plasma” for the next shot. Pardon my confusion.
I’m not sure that is the way to go either. You want to carefully control what is electrically charged in the chamber. You want everything to be pretty neutral prior to firing the shot, or you might have arcing in the chamber from where negatively-charged gas connects to the positively charged cathodes. Plasma is not the gas in the chamber, it is the “lightning” arcs created from the central anode to the surrounding cathodes. (I explain plasma to people this way. Remember in Young Frankenstein where they had those weird devices with the two wires in a V-shape that had the electric arc going up it? The arc is plasma.) Since plasmas have inherent instabilities, the FF-1 seeks to use these natural instabilities to make several arcs curl up into a shrinking, hot ball. That is the beauty of its design and why I think it will work where tokamaks fail. But to get the arcs to form properly, the decaborane gas needs to be neutral, and uncharged prior to a shot.
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