Sunday, December 13, 2009

Concise Questions & Answers about the Polywell (With Citations) (3-11-09)

Hello,

Wiki says P B11 produces 3 alphas and 8.7MeV. What form is the 8.7MeV, the speed of the alphas, x-rays? Is there a place to look up what happens when various things collide, sort of like a 3D periodic table?

What would happen if you put a target of B11 in front of a proton gun (particle accelerator)? As I remember a Fusor simulates high temperature by electrostatic acceleration. Generating a stream of protons at the optimum 500keV should be very easy, and eliminate the need for the magnetic or electrostatic containment?

On Wiki about Z-Pinch, it says the tungsten generates the plasma that carries the current, generates x-rays, and does the compression, but in the middle is D T fuel.

I was reading about N Li-6 today. I wouldn't think a Tocomak would use Li just to contain neutrons, other materials that are much better. But N + Li -> Tritium so I'd expect Li is used to convert stray neutrons into more fuel. Or am I showing my ignorance?

I usually write something, then get out Word, copy/paste it, then paste the corrections back. It'd be faster if I just composed in Word from the start.

Nice to visit with you.
Mark



Mark,

As far as I know, you are correct about the Z-machine. I forgot about the X-ray wrinkle. I want to state now, I am not an expert. My training is in chemical engineering, not theoretical physics. Therefore, you should check all the facts, and not necessarily trust the facts people tell you on Facebook. Also, I am a fusion enthusiast, a hobbyist. With regards to P-B11, I can quote what Thomas Ligon has said

“The really exciting fuel, is one that has been tantalizing fusion researchers since they started working through the possible reaction, and that is Proton Boron 11. There are also a number of Lithium reactions you can do. But, proton Boron 11 is sort of the holey grail of fusion. The nice thing about P B11, is almost all the energy in the reaction will come off in the form of charged particles, specifically alpha particles over a relatively limited range of energies, up in the 3 million electron volts per particle range.”

As I understand it, all the energy from that reaction comes off, contained within those hot alpha particles. This opens the possibility for direct conversion, again a quote from Thomas Ligon.

“If you have an alpha particle with 3 million electron volts and it has a charge of 2, if you decelerate it against a 1 ½ million volt electric field, it will slow down as it approaches that field, you know like charges repel, so your using a repelling field. You decelerate it against that field, it is essentially climbing a potential well, and then it will generate current at that voltage, when it kisses in it draws two electrons and generates electric current. And that is the scheme, in the simplistic way, for drawing power from charged particles”

1. As I understand it: P-B11 generates 2 alpha particles. These particles hit a surface of a metal and kick up two electrons, which generates a moving current. It generates current at the voltage it is at, in the field it decelerated through. This “direct conversion” idea would have a very, very high theoretical efficiency, ballpark 80% energy conversion. There are two companies attempting to use this for medical batteries (Alpha V inc and, Betta Batt inc). I have heard that P-B11 loses, ball park, a tenth of 1% of its energy through neutrons. This is through short lived side reactions. However there is evidence that if you design the reactor correctly, this won’t be a problem. D-D fusion “loses” about 40% of it’s energy in neutrons. DT fusion “loses” about 80% of its energy in neutrons.

Sources:
http://en.wikipedia.org/wiki/Aneutronic_fusion
http://alphav.com/
http://www.betabatt.com/
http://dspace.mit.edu/handle/1721.1/11412?show=full (Non-printable .pdf, page, page 24, 2nd paragraph)

2. I cannot speak to placing boron in the path of a proton stream. I will say that the method for measuring the cross section (the measure of fusibility of two things, measured in Barns) involves sending a stream of one particle at another fixed set of particles. An important equation to remember is the volumetric fusion rate:

Volumetric Fusion Rate = Density of fuel * cross section * Velocity of Particles.

That is key. When you’re talking fusion, everyone always talks about density and temperature. But really, temperature is only the means to drive the particle velocities to speeds where some of them can fuse. You always get the classic bell curve, or Boltzmann distribution of particle speeds, and only the tail of the curve contain particles with enough energy to fuse.

Sources:
http://www.fusor.net/newbie/files/Ligon-QED-IE.pdf


3. I cannot speak to N-Li6. I know there was talk about using lithium to surround the tokomak to recover all the neutrons coming off the fusion reactor. I know there was also a scheme to send the neutrons into spent fission fuel to recharge it. This was called LIFE.

Sources:
https://lasers.llnl.gov/missions/energy_for_the_future/life/


As I understand it: in terms of x-ray losses, most of it is generated by electrons colliding with other electrons and electrons colliding with other ions. You can imagine this would happen an awful lot with the polywell containing an estimated 2E12 ions and electrons in the center. I do not understand the mechanism. Tom Ligon described it as: the ions and electrons cause the other to make a tight turn around one another. Imagine a truck moving around a tight corner. The wheels squeal. This “squealing” is analogous to generating an X-ray, when an ion moves around an electron, or vice versa. There was some hint that they could minimize this by running the reactor electron rich. I really do not know allot about this.

Many credible, established physicists will tell you all non-thermodynamic equilibrium plasma devices will not work. Dr. Bussard hypothesized that this was because they were protecting their funding. (I have heard that the DOE fusion budget is 350 million a year). However, there has been one really in-depth study into non-thermodynamic equilibrium plasma devices: “Fundamental limitations on plasma fusion systems not in thermodynamic equilibrium” by Dr. Todd Rider, MIT, 1994. It appears to be the thing cited every time you bring up this topic. I think, someone needs to dig into Rider’s study and see if they can find holes in his science. If that can be shown, it would offer a really powerful argument for full scale funding of this research.

On the flipside, Dr. Nebel was quoted as say (at the end of the Livermore 10 month study): “we cannot find any reason why this will fail, that is very different from saying it will work”.

Riders thesis: http://dspace.mit.edu/handle/1721.1/11412?show=full
Nebels quote: http://cosmiclog.msnbc.msn.com/archive/2008/12/16/1718741.aspx

1 comment:

  1. http://www.physicsforums.com/showthread.php?t=178156

    A poster there mentions problems with using an accelerator for fusion.

    ReplyDelete