Tuesday, May 29, 2007

Polywell - Making The Well

I have come across some interesting research by Kiyoshi Yoshikawaa,of the Institute of Advanced Energy, Kyoto University, and others proving the formation of the Polywell.

For those of you who have not been following along here is how my understanding has been evolving.

Polywell As I Currently Understand It

Polywell - Adding Details

A schematic of the evolution of the Polywell design can be found in slides 8 and 11 in this Power Point slide show (link at bottom of page).

In the Hirsh/Farnsworth machine in slide 8 the reacting positive ions (like charged Deuterium particles for one kind of operation) are attracted to the center to collide and produce fusions.

In the Elmore/Tuck/Watson machine in slide 11 electrons are accelerated to the center of the machine where they form a grid sort of like what happens in a beam power tube. In the beam power tube the virtual grid is called a space charge. These negative electrons attract the positive fuel ions and fusion reactions take place. The advantage is that there is no grid near the reaction space so losses are reduced.

That is the theory any way. However, in any person's mind who has a little understanding of the physics involved the question is: is that really happening? Are we fooling ourselves? Which brings us back to the Yoshikawa paper. What is the evidence?

Yoshikawaa correctly states the central issue:

...it is essential to clarify the mechanism of potential well formation (see Fig. 5) predicted to develop in the central plasma core within the cathode, since potential well formation due to space charge associated with spherically converging ion beams plays a key and essential role in the beam-beam colliding fusion, i.e., the major mechanism of the IECF devices. Actually, this has been the central key issue for IECF researchers for the past 30 years, until the first successful direct measurement of the double-well potential profile in the IECF device through the laser- induced fluorescence (LIF) method at Kyoto University [6] in 1999 with an approximately 200 V dip at the center in the helium plasma core as will be described below.
So they have proved the formation of the Polywell. Outstanding!
Many theoretical results so far predicted strongly localized potential well formation, and actually for the past 30 years, many experiments were dedicated to clarify this mechanism using, such as, electron beam reflection method [7], spatially collimated neutron [4] or proton [8,9] profile measurements, or an emissive probe [10], as is seen in Table 2, but, neither seems to be perfectly conclusive in convincing that well does form.
He again hits the nail on the head. Lots of results that could have more than one interpretation. He then gives a list of past attempts at verification of the Polywell. Now let us get to how what he claims was the definitive experiment was done.
...we have adopted optical diagnostics by using the Stark effects, sensitive to the local electric fields, to the IECF device with a hollow cathode. Also to enhance S/N (signal to noise) ratio as well as to specify radial potential profile, we introduced the LIF method. Consequently, we could have finally measured the double-well potential profile (see Fig. 11) with an approximately 200 V dip at the center for the first time in the helium plasma core (Fig. 7) in the IECF device.
He goes on in even more technical detail. The end result? The dual (cathode and anode) potential well forms.

In any future experimental regimes such a measuring system should be used to verify machine operation and to provide machine diagnostics.

17 comments:

Anonymous said...

I do not see what this has anything to do with Polywell. Bussard is not mentioned, nor are polyhydron-shaped electron cages. One should send a link of Bussard's video to them though.

Tom Cuddihy said...

Well, it is related--a polywell is just functionally an elmore/tuck/watson machine with a magnetically protected inner grid. The real breakthrough for a Polywell is in finding a geometry for the inner grid that is able to conform to the magnetic field, and hence prevent electron loss.

I do agree that proving that is what is taking place in a Bussard polywell is very difficult. In fact, once you have a polywell, fusion itself is probably easier. However--with a WB-7 machine, producing neutrons from DD fusion at the level claimed by Bussard would clearly prove the method works--even if it doesn't by itself prove how the potential well forms.

Raelik said...

Yeah, this isn't a polywell. It's a standard IEC device (with a true grid). IECF has been a proven technology for a long time, just a dead-end as far as power is concerned. The Polywell may very well change that however.

M. Simon said...

Actually Polywell formation is the first step in Wiffle Ball formation.

I was never that confident of Polywell formation until I read this paper.

The formation of a spherical virtual grid always seemed iffy to me.

peter said...

I have a question that I haven't found answered in any of the reading or pdf files regarding building the polywell. The stainless steel hollow toroids that contain the copper windings in WB-6 appear to have been cut in half while the magnet coil windings were done then closed together and welded in place with short approx 2 inch welds spaced around the perimeter. At the welding temperatures required to weld stainless steel, would this not damage the windings? And as for the tubing that joined each stainless steel toroid to the four adjacent toroids, I wonder what the weld strength would need to be to cope with the 0.1Tesla field. And therefore what size tubing and what size welds. And for future high efficiency superconducting polywells fusing boron-11 plus Hydrogen or Lithum-6 fusion reactions wouldn't the cooling fluids for each toroid occupy a large amount of space in the tubing between each toroid? such that the stainless steel tubing joining each toroid would become large and thus impede electron recirculation and reduce efficiency. And increasing the size of the reactor may not help because the enormous increase in alpha radiation would require an enormous increase in volume for the cooling fluid.

M. Simon said...

Welding question:

Laser or electron beam welding should do the trick.

===

Each coil would need to be supported by wall connected standoffs each with its own fluid flow and current connections.

With the coils in parallel for fluid flow pumping pressure can be greatly reduced.

Water would also be used as a cooling fluid in the outer layers to handle the highest heat flux. In fact two lawyers of water. One at 300K and one at about 600K.

peter said...

That was a quick reply. You're really on the ball M. Simon. That is helpful about the two layers of water coolant.

M. Simon said...

We already know how to keep MRI magnets cool with very small heat losses when in a 300 K environment. I'm assuming using similar tricks.

So by having a 300 K layer we revert to mostly known technology.

peter said...

I've been working on a shopping list of the specifications and requirements of WB-6.

Most of the data comes from:
http://www.google.com.au/url?sa=t&ct=res&cd=1&url=http%3A%2F%2Fecow.engr.wisc.edu%2Fcgi-bin%2Fgetbig%2Fne%2F527%2Fanderson%2Fnotes%2Fbussard_wb6rpt080604fnl0107.pdf&ei=rBShR-i4C4n8pgS02sC0DQ&usg=AFQjCNHDUIpVKKl6Dvi_nvjdeLTssD8Tyg&sig2=72Tvp7YSnX4KQsKoG13C7w
http://www.emc2fusion.org/2006-9%20IAC%20Paper.pdf
http://video.google.com/videoplay?docid=1996321846673788606
Other bits are referenced.

If there are any mistakes or additions updates will be most welcome.

Polywell reactor specifications for a WB-6 equivalent reactor:

Vacuum chamber
• 2m diameter tank with a Faraday cage inside (WB-6 was 2m by 3.5 m) that can go down to 1*10^-9 Torr

Vacuum pump
• Able to pump (2m diameter chamber) down to less than 1*10^-9 Torr

Electron emitters
• Banks of headlight filaments
• Grounded
• Activated by fiber optically isolated Siemens switch
• Heating current of about 40 amps
• (Stainless steel?) poles to place them at a standoff distance approximately equal to the mean radius of the cusp face through which they are injected.
(to minimize electrostatic droop in the potential well at these corners)
• poles attached to the corners of the 'square' Faraday cage.

Microwave generator
• “microwaves at the ECR frequency corresponding to the magnetic field makes a death zone for neutral gas.” (What is the ECR freq in WB-6?)
Tom Ligon
http://www.fusor.net/board/download_forum.php

Magnetic field
• Preferably superconducting magnets (greatly reduces power requirements and magnet strength possible in a smaller space.)
• Otherwise 200 turns of approx 1000m of 0.15mm diameter copper magnet windings.
• Cross-sectional diameter of toroid about 3cm, inner diameter about 20cm and outer diameter about 30cm
• Linked in series with up to 2000A of current running through them for just over 20ms.
• Make sure no tight bends in the windings.

Magnetic Grid Shell
• Stainless steel tubing welded and then polished. (“Laser or electron beam welding should do the trick. –M Simon.” (so as not to damage the windings inside)
http://powerandcontrol.blogspot.com/2007/05/polywell-making-well.html
• Tightly conformal to the magnetic coils inside.
• Joined by small (approx 1cm long) tubing just outside the midplane of the magnetic field of the coils.
• Structural strength required to survive vacuum and force produced by six 0.2T magnets trying to separate from each other.
• No metal surface may penetrate the magnetic fields by more than 1*10^-4 of the total surface available to the recirculating electrons.

Structural support of Magnetic Grid
• Four support stands on the base toroid (or three or four on each with no (or slimmer) pipes joining the toroids.)
• (Stainless steel again?) encased and thus ‘hidden’ from electrons by tapered ceramic supports.
• Has current carrying conductors inside helping to protect it from electrons by magnetic shielding.
• Make sure no tight bends in power supplies through the legs or the joins.

Gas supply
• Supplied by a (or several) tubes of a known tiny finite
o volume (less than 5cm^3)
o and pressure (300mili Torr too high. Must be small enough that the resulting gas pressure in the chamber is less than 3*10^-6 Torr).
(This allows for the volume of gas in the reactor to be increased by tiny discrete intervals to ensure complete ionization and no flooding of the outer chamber with neutral gas.)
• Last section of tubing is glass to minimize electron losses.
• Gas input from tubes controlled by a fast acting (<1ms) solenoid valve
• Glass tube releases gas just inside the inner perimeter of the magnets. To one of the coil/coil spaced seam areas. The magnetic fields here are very strong and that reduces the likelihood of electron losses by electrons impacting the tube.

Sensors
• Sensitive Photomultiplier system
• Pressure sensors (sensitive down to 1*10^-9 Torr)
• Optical spectrometer
• Sensors for all currents and voltages on all supplies and lines and grounding cables.
• 3 neutron detectors at varying distances (of a type not affected by high voltage and able to give quick electronic output.)
• Cameras (They had two black and white ccd and 1 color camcorder) High speed color cameras operating at frame rates of much less than 0.1miliseconds would be best.
• "The earliest Polywell, HEPS, was also verified to make a potential well, I believe by using four 94 GHz microwave beams across the chamber to map electron density.
The more recent machines have used at least Langmuir Probe methods (stick a wire in the thing and see what happens). And generating DD fusion is fairly convincing evidence, as well."
Tom Ligon
http://www.fusor.net/board/download_forum.php

Power supplies
• Car batteries for the electron emitters
• 240 RV batteries connected via an IGBT switch
(able to safely produce at least 2000A)
• Twelve 225μF capacitors producing up to 15kV, 400kJ at 5A current (or 30kV at 2.5A) these can be discharged through the magnet windings.
• Fast acting pneumatic-driven copper block switch to connect capacitors.
• At least 1200W supply for microwave generator

Check
http://www.google.com.au/url?sa=t&ct=res&cd=1&url=http%3A%2F%2Fecow.engr.wisc.edu%2Fcgi-bin%2Fgetbig%2Fne%2F527%2Fanderson%2Fnotes%2Fbussard_wb6rpt080604fnl0107.pdf&ei=rBShR-i4C4n8pgS02sC0DQ&usg=AFQjCNHDUIpVKKl6Dvi_nvjdeLTssD8Tyg&sig2=72Tvp7YSnX4KQsKoG13C7w
for operating procedure.

peter said...

oh dear, the links didn't work.

they were the google video:

"should google go nuclear"

the in house paper from EMC2:

"EMC2 Inertial-Electrostatic Fusion (IEF) Development: Final Successful Tests of WB-6; October/November 2005"

and the 57th International Astronautical Congress paper:

"The Advent of Clean Nuclear Fusion: Superperformance Space Power and Propulsion"

peter said...

oops, another mistake.

the toroid diameters are from the blueprint photo and they're confusing. The cross-sectional diameter of the toroid is about 3cm and the outer diameter is about 30cm. that makes the inner diameter 27cm. best to look at the picture to be properly clear.

M. Simon said...

Peter,

Excellent list.

Here is how you make permalinks:

<a href="url">text to display</a>

replace url with:
http://powerandcontrol.blogspot.com/
leave the quote marks

replace text to display
with:
Power and Control

Power and Control

M. Simon said...

peter,

I'd like permission to repost your list. Nice bit of work.

Leave a note here or contact me by e-mail.

I want to give you proper credit.

peter said...

I pretty much just copied and condensed stuff out of those three links so it's not really my work. Feel free to use it however you like though only put my name on it if your copy is identical.

ok lets see how this permalink thing goes. Thanks M. Simon.

Tom Ligon's comments on a www.fusor.net forum
M. Simon's comment on welding the Magnetic Grid
EMC2 Inertial-Electrostatic Fusion (IEF) Development: Final Successful Tests of WB-6; October/November 2005
The Advent of Clean Nuclear Fusion: Super-performance Space Power and Propulsion
text to display

peter said...

Well some more mistakes. Here's a repair for the links that don't work:

Ignore the "text to display" link ;o)

Tom Ligon's comments on a www.fusor.net forum

peter said...

Well, just as expected, another mistake.

Here's the link to Tom's other comment on www.fusor.net

Tom's other comment about measuring the electron well

peter said...

I looked at your new post of the shopping list. It looks a lot nicer