Talk-Polywell.org

Getting information from these CSI videos is difficult. We know that they can depressurize a vacuum chamber and load it with Model 1. Model 1 is a diamond shaped wire, with current and a coolant loop inside it. Great.

Once Model One is turned on, they drive electrons towards it using a voltage. This is the “drive voltage”. They tested:

1,000 volts
1,500 volts
10,000 volts

We do not have an internal picture of the chamber. I would assume that the magnets are held at ground and the “sides” are held at -1,000 volts. They’re description suggests that the electrons are coming in from the cusps (the corners of the diamond?). The type, strength or details about injectors are almost never mentioned. The talks suggest that they work continuously throughout the run. We know that CSI also wants to heat these electrons using “wave-heating” or “RF heating” or “induction heating”. However, they said: “The wave-heating is very much in its early stages, so we are not going to share our mechanism for that, now.”

There are a couple of options for generating electrons. A simple one is heating a lightbulb wire. This would be using thermionic emission: you heat a wire, electrons fly off. Once they leave they hit this “injection voltage” and fall towards model 1. At some point, the magnetic part of the Lorentz force overtakes the electric part and the electron starts corkscrewing. It (hopefully) enters the field and gets reflected and trapped. The plasma would look like this:



They are using a Langmuir probe to measure the electron cloud. In fact, at 10,000 volts they melted their probe. CSI wants to know how long they can maintain this electron cloud. “Long-term” is the term that gets thrown around, but it is unclear how long this is: microseconds? Seconds? Minutes? This is the extent of the testing they have done. There is a bombshell in their executive summary, stating that: “Model 1. Completed in January 2012, with which we achieved the first-ever generation of an indefinitely stable, steady state, magnetically stabilized virtual cathode…”

http://convsci.com/sites/default/files/ ... ummary.pdf

Indefinite? Steady state? I am curious to know how long they actually tested. It would be a big deal. If you can hold a stable electron cloud for say 20 minutes, while pumping electrons into the center – you have got something really worthwhile. WB6 only ran for 400 microseconds, tokamaks’ world record is something like 30 seconds. (Are there any other examples of this today? Maybe a magnetron?) Even if this machine is crappy, or the cloud is small, or the magnetic field is weak, long term stability would be the direction I would follow.

Without clear discriptions from them it is dificult to pin down their methods. But some generalities from my understanding. The electron emmiters could be at low voltage or high voltage. Bussard described two methods of accelerating electrons into the magrid. One is low voltage and high current on the electron guns- headlight fillament. The magrid is at high positive voltage and accelerates the electons inward. Alternatly the e- guns can be at high negative voltage and the magrid at near ground, or any combination in between. With an exposed copper(?) tube acting as the magnetic field current carrying magrid., it is unlikely to be at high voltage. Probably at a few dozen volts. I doubt that the vacuum vessel shll would be at anything other than ground.

As for electron lifetimes, like Bussard, steady state is used because the confinement time is much longer than much of the dynamic action of the electrons. Much of the electron dynamics occur over time periods of a few microseconds at most, so a few hundred microseconds is essentially steady state from this perspective. At 10 KeV the electrons are moving at ~ 10,000,000 M/s so transit the machine in well under a microsecond, they are reflected and repeat, and repeat, and repeat, etc. This is the described steady state. In some of the early work, a burst of electrons were injected, a modest potential well was formed, and a few microseconds later the potential well decayed. Prolonging or delaying this decay was an indication of better confinement. Dozens of microseconds means fair confinement (perhaps 50-60 passes). This is described as cusp confinement. Confinement (potential well persistance) for up to several hundred microseconds represents thousands of passes and is consistant with further Wiffleball confinement.
In WB6 I believe test duration was up to several milliseconds and was limited by the build up of gas outside of the magrid with resultant Pashin arc breakdown. Admittedly though the claimed steady state conditions persisted for ~ 0.25 seconds. Beyond that time arcing started to distort the results. Keep in mind though that other configurations were tested by EMC2. The one most consistent with this test may have been the very early MPG1,2 machines.

http://www.google.com/url?sa=t&rct=j&q= ... 8465,d.cGU

Dan Tibbets

Dan,

CSI said the run was at most 35 seconds. If they had the cash, this could go much longer.

It is easy to run prolonged tests at mild conditions. A thin copper tube, even with vigorous water coolant flow will tolerate only a limited current. Perhaps a few dozen to at most a few hundred amps. Any more and the copper would melt. With only one turn the amp turns would be ~ 100 or less. Compared to WB6 this would result in a magnetic field ~ 1/1000th, or ~ a few Gauss. As for arc breakdown, so long as the chamber pressure could be maintained at ~ 0.000001 atmospheres, a potential well might be maintained. Neither of these conditions allow for much latitude in testing., especially when outgassing is considered. If they are very clever they might get some Lagmieu prob data, though the signal to noise ratios are formidable. Nebel pointed out that testing at scales smaller than WB6 made practical tests worthless, at least for them .

I have produced glow discharge plasmas for many seconds using permanent magnets and e-guns, or various wire grids; as has many fusioners. The problem is that these easy to achieve glow discharges are not very useful for measuring parameters applicable to the Polywell.

As Beta is dependent on current, voltage, and B field proportions. It would seem even small numbers would create Beta = 1 and Wiffleball formation conditions. But, at these levels, if they have achieved this they have achieved instrumentation performance that is astounding.

In the picture, I note a relatively bright glow. This comes primarily from recombination reactions (produce visable light) and this is not consistent with Polywell operating conditions. As with the picture of WB7, the glow seen with this condition can show the magnetic confinement grossly, but beyond that little can be obtained. Note that I do not see any plasma separation from the surface of the wires so the magnetic field is trivial, if it is even turned on.

A simple glow discharge can be maintained indefinitely until the electrode is finally eroded by the plasma impacts. I don't know what experiments they have run, but the picture presented is meaningless, as is maintaining such a plasma for weeks. After all, that is what a fluorescent (more accurately a neon) light does.

Dan Tibbets

Dan,

That image is of a fusor/polywell hybrid at 10,000 volts drive. They stuck a wire cage inside.



The light blocks the cage, in the left image.

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Here is a draft on a CSI write up. Feedback appreciated.

Part 1: Experimental Work:

Overview:

Between October 22nd and December 17th CSI did a number of web talks. Discerning the real tests from the plans was hard. Moreover, CSI did not want to give the details outright. Specific dimensions were the hardest to get. Sizes were extracted from photos and emails. But, the same parameters likely changed between individual tests. Hence, this analysis is not going to be perfect. To circumvent this, ranges are often used. This research is still in the early phases. Early on, it is important to get something that works. This allows you to troubleshoot everything else. The team has not done fusion. They have trapped electrons long-term inside model 1. Long-term is subjective. The world record for a tokamak is six and a half minutes [6]. WB6 ran for less than a second [8]. Model one was a low power, low cost and simple device. Despite these limitations, it held in plasma for twenty seconds [1]. The run was limited by the cooling system. If the team had the cash, they could run much longer. Long term trapping is the direction to go in.

Experimental Setup:

The team is testing model 1. This is a single copper wire bent into a diamond shape. Attached to it, is a cooling system, power supply and voltage source. This is placed inside a cylindrical vacuum chamber, about the size of a trash bin [6]. Four electron emitters sit around model one [1]. They may align with the device’s corners. There is also a Langmuir probe. The probe may be a simple wire, or a fancy tool with software. The probe is critical. It proves the concept. If everything works correctly, it should measure a negative voltage. The chamber is also connected to a pump and a gas supply. One possible chamber configuration is shown below.



We have seen this experiment before. The 2010 Khachan paper is very similar [9]. You spray electrons from an emitter. They enter a device. You see if they can be trapped. If CSI can prove trapping; then it validates Khachans published work.

Vacuum Chamber:

The vacuum chamber is filled with nitrogen or helium gas [6, 22]. This is common in vacuums. Nitrogen blocks water vapor from entering the chamber [42]. Helium is used to check for leaks [42]. From here, they pump down the chamber. It reaches pressures between 1.3 and 0.04 Pascals [22]. This is still thousands of times higher than the WB6 system [6]. There is still gas inside. This background gas, will impact performance. It can create fast moving neutral atoms. It can also be a source of unwanted of positive ions. Both can hurt performance.

Model One:

Inside the chamber is model one. It is the most unique device in the chamber. It is shaped like a diamond, and it has three subsystems. The first system: is one long copper wire. This is used to make the magnetic field. The team tried to re-snake this many times – but ran into cooling problems [1]. With only one pass, a lot of current will be needed. At full power, 1,500 amps flow through this wire; creating a 1,000 gauss field at the corners [22]. This current, heats up the wire [7]. A hot wire creates problems, like arching. Moreover, this problem grows as the device runs “long-term”. The second subsystem is a chilling system. This is a coolant which is pumped inside wire center. The coolant is Fluorinert, a liquid, often used to cool electronics. The fluid does not conduct; lowering its negative impacts [1]. The fluid moves in a closed loop: from the pump, through the device, and into a heat exchanger. The exchanger moves heat into a second water and glycol loop. This flows into a giant open tank. A sketch and model of the cooling system is shown below [7].



This coolant system can pull about six kilowatts of heat from model one [5]. Estimates (using joule heating) show that this is probably twice what they need. The team also tried to flow the coolant around the outside of the wire – but this behaved poorly. The last subsystem is the drive voltage. Model one needs to attract, affect and trap electrons. Negative electrons are attracted to a positive object. Model one must be biased positive. The team used a transformer to put it at a positive 500 volts [1]. When everything is turned on, model one makes a web of electric and magnetic fields. These are shown below.



Electron Emitters:

CSI examined three ways to make electrons [1]. The first is field emission. Electrons can spontaneously leave metals in a vacuum. This can happen at room temperature and may have happen inside CSI’s chamber [2]. However this can easily avoided by engineering. The effect amplifies as the temperature rises. This is known thermionic emission. If you heat the wire, more electrons will leave. CSI purposely used four heated nichrome wires to do this. Nichrome is a common emitter [3]. In addition, these wires can be part of a proper electron gun. This was CSI third method [1]. Their guns were simple: a heated wire next to a positive disc, with a hole in it. The disc focuses the electrons in a beam [4]. All the tests used at least four emitters [1]. They had a voltage placed on them. Using a transformer, the team could make the emitters a negative 9,500 volts. The combined positive model one and negative emitters - made a hill for the electrons to roll down. They fell into model one. Their flow was constant; emitters ran throughout the runs [5].

Operating Procedure:

CSI ran experiments from January to late summer 2012 [5]. Many tests were done. These included: several geometries, various emitters and even a fusor/polywell hybrid. Tests meant several steps. First, the vacuum chamber was prepared. The chamber was filled with helium, to check for leaks. To seal off the leaks, they coated the chamber in copper. This was done using electroplating [5, XX]. Once sealed, nitrogen was pumped in. Next, they pumped down the chamber. It reached pressures between 1.3 and 0.04 Pascals [22]. The next step is turning on the coolant system. This makes the chamber, low pressure and cool. Next, the voltages are applied. From here the test can start. The device and emitters are turned on. Runs typically lasted for 35 seconds [1]. CSI states that for 20 of those seconds, it measured a steady, constant voltage drop.

Here are copies of the emails CSI sent me.


Email from 1-16-2014:

I hate to sound like a broken record, but the answer to these questions is again "many configurations were tested".

Multiple turn designs were tried, but cooling was problematic, as the pressure drop across the system became larger due to the longer tube length, and coolant flow was adversely effected. Keep in mind we're not cooling this for fractions of a second; the Model 1 was designed to test plasma stability on true steady-state time scales-- not ion-bounce time scales. That said, even the shortest turn length tried (single turn octahedron) was only able to be run for 35 seconds before too much heat built up in the first cooling loop. With a better pump and heat exchange system this could have been overcome, but the Model 1 was built on a shoestring budget, and the vacuum system was the limiting factor for plasma duration anyhow, heating and bombardment of the internal surfaces desorbed water and other contaminants rapidly.This limited plasma duration to around 20 seconds maximum (but only truly good well depth for a quarter as long).

Electron emitters varied in design, including field emission, hollow cathode and thermionic (nichrome filament) designs. Some simple wehnelt (lens) designs were tested in all cases. All tests included at least 4 electron sources, though note that the projected design for Model 2 only includes a single gun.

The magnetic coil of the Model 1 could be biased +/- 500V from ground. The cooling system is fully dielectric in the first loop, only the current source needed to be biased via an isolation transformer. The transformer we had was only rated to 800V, and exhibited issues above 500V, so it was never pushed very far. The smaller isolation transformer used for electron guns is rated to 50kV, so generally in EXL the magnet was biased positively a few hundred volts and the electron emitters biased negatively up to the desired voltage offset (500 to 9500 V). It is possible to run with the magnet at ground and electron emitters biased negative (with a biased Faraday cage around the emitters), but parasitic discharge to the chamber walls limited indicated well depth and plasma density in that case. Lacking electron emitters in most tests, in hybrid mode the magnet was generally left at ground.

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I sent a draft of the work (above) and this was the reply:
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Email from 1-20-2014:

The only corrections that I'll mention are,

1) that the "Electroplating" statement was something of a joke, not a method for sealing the chamber. One of the first immersed grid (hybrid) tests used a water/glycerol cooled inner electrode grid, made of small diameter copper pipe. On our first high power test it melted very rapidly (less than 2 seconds), and the high voltage auto-off system didn't trip. So molten copper got splashed all over the inside of the chamber, as well as blasted onto the walls by interaction with the fields and plasma. The coolant mixed with this, and made all sorts of various copper oxide deposits inside of the chamber. It took forever to get it cleaned down enough to obtain a hard vacuum after that (lots of scrubbing). Luckily the safety system on the turbomolecular pump was working and the isolation valve slammed shut, otherwise the pump could well have been damaged. Similarly the auto-off on the magnet worked as designed, so when a chunk of the melted grid fell onto the magnet, shorting two sections of it, the power automatically shut down.

The "failure at high power" image from the Applications talk is a picture of this test; the streaks reaching downward are a mixture of molten copper and vaporized coolant. After that incident we changed to tungsten or rhodium inner grids, which were much more resistant to heating (as you'd expect). None of the W or Rh grids were actively cooled, however (though one was conductively cooled by a large copper support rod).

2) The three methods of electron injection were field emission, thermionic emission (I include gun designs with lenses in this category, as they still have a thermionic source), and the hollow cathode. The hollow cathode is a variation of that suggested by Scott Cornish at the 2011 IEC Conference (http://www.physics.usyd.edu.au/~khachan ... poster.pdf), though the layout of our system was somewhat different the physics were the same.

Hey All,

This poster has details about the emitters used at the U of Sydney which I had not seen before.