sim needs faraday cage?

Discuss how polywell fusion works; share theoretical questions and answers.

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happyjack27
Posts: 1439
Joined: Wed Jul 14, 2010 5:27 pm

Post by happyjack27 »

kiteman is on the right track. i think the confusion here is we are talking electrodynamics where you are talking electrostatics. we are both correct.

electrostatically, the charges in the conductor will move so as to neutralize any voltage gradients, thus moving so as to make themselves invisible to anything on the inside.

however, we are keeping the outer sphere at ground, and the inner sphere at a constant positive voltage relative to ground. as just mentioned, the charges will move so as to neutralize the voltage gradient. this means electrons will move from the outer sphere to the inner sphere. thus, we will not have this charge differential for very long. to get it back we have to move electrons from the inner sphere back to the outer sphere. when we say we are holding the inner and outer spheres at constant charge, that implies that we are doing precisely this.

so you see, while gauss' law (of course) accurately tells us what the system will be like when it reaches equillibrium, we are actively keeping the system _out_ of equilibrium by applying a current between the inner and outer spheres. this current constantly recharges the voltage gradient that the electrons are constantly neutralizing. if we turn the power off -- if we either unground the outer sphere or stop pumping electrons out of the inner sphere -- the electrons will quickly succeed in neutralizing the voltage gradient and we'd come to the situation described by you; by gauss's law. which means we would no longer have a charge differential between the two spheres (well, at least not one that can't be maintained electrostaticaly for very long). and the situation ipso facto would no longer be that which we seek to analyze.

KitemanSA
Posts: 6179
Joined: Sun Sep 28, 2008 3:05 pm
Location: OlyPen WA

Post by KitemanSA »

Code: Select all

 Property	              Scaling Law 	    Property           Scaling Law 
 Voltage	                   L	           Magnetic Fields	 L
 Electric Resistance	       1/L	         Magnetic Force	  LLLL
 Electric Current	          LL	          Magnetic Energy	 LLLLL
 Electric Current Density     1	           Mag ERG Density	 LL
 Electric Capacitance	      L	
Given these scaling factors, if the inner image coils are 1/2 as big then the current thru them is 1/4 AmpTurns relative to the main coil. I think. Worth a try!

happyjack27
Posts: 1439
Joined: Wed Jul 14, 2010 5:27 pm

Post by happyjack27 »

the goal of the grounded faraday cage is to go from a voltage gradient something like this:

no grounded cage:
v =
{magrid_radius < observation_radius : 1/(observation_radius-magrid_radius)^2
{obervation_radius < magrid_radius : 1

to one something like this:

grounded cage:
v =
{cage_radius < obervation_radius : 0
{magrid_radius < obervation_radius < cage_radius : (cage_radius-observation_radius)/(cage_radius-magrid_radius)
{obervation_radius < magrid_radius : 1

thus making the PE reach its extrema while the observation radius is still finite.

(i'd rather just draw a picture, but that's not so easy to do w/this medium!)

KitemanSA
Posts: 6179
Joined: Sun Sep 28, 2008 3:05 pm
Location: OlyPen WA

Post by KitemanSA »

No Cage:

Code: Select all

    *
    |*
    | *
    |  *
    |    *
    |        *
    |              *
    |                                  *
With Cage:

Code: Select all

    *
    |*
    | *
    |  *    |
    |   *   |
    |    *  |
    |     * |
    |      *|
Yah?

happyjack27
Posts: 1439
Joined: Wed Jul 14, 2010 5:27 pm

Post by happyjack27 »

KitemanSA wrote:No Cage:

Code: Select all

    *
    |*
    | *
    |  *
    |    *
    |        *
    |              *
    |                                  *
With Cage:

Code: Select all

    *
    |*
    | *
    |  *    |
    |   *   |
    |    *  |
    |     * |
    |      *|
Yah?

YEP! Exactly! Thank you!

happyjack27
Posts: 1439
Joined: Wed Jul 14, 2010 5:27 pm

Post by happyjack27 »

isn't that something bussard said?; "the devil is in the details." details, such as, oh, whether or not the vaccuum chamber is grounded? i'm on to you, dr. bussard! ;)

KitemanSA
Posts: 6179
Joined: Sun Sep 28, 2008 3:05 pm
Location: OlyPen WA

Post by KitemanSA »

hj27 wrote:{x_start, y_start, z_start, x_end, y_end, z_end, current_multiplier, charge_multiplier}
So, given these items: Image magnet, MaGrid, Chamber... and if the MaGrid current and charge factors are both 1, then with a 0.5 scale image magnet, the two values should be -.25 and 0 while the Chamber with a size scale factor of 2 would have the two values 0 and -1.

How do I get this run?

happyjack27
Posts: 1439
Joined: Wed Jul 14, 2010 5:27 pm

Post by happyjack27 »

i've moved on. im all about my swarm wars game now.

i can picture it in my head w/the grounded chamber to improve recirculation and it works. nothing more to do on sims, imo. just have to wait until building and testing is all done. it works and we'll have a commercial reactor in the future. just have to wait a few years. which, of course, isn't the fun part.

if you can handle it and you've got an nvidia geforce 8800 or later, you can download the code and compile it yourself and run whatever you like (google sourceforge em-nbody for the code, you can download and run "eclipse" for the compiler, and you'll have to also install the sdk from nvidia and set up the compile chain. so it's not for the weak of heart. but sorry to disappoint but i don't feel like running it anymore.)

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