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posted by Jean-Francois Roussel at Feb 18, 2009 12:18 PM
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a known instability is for Debye length smaller than cells You can solve that by using the non linear Poisson Eq solver (linear = 0)

JFR

posted by Gregory Francisconi at Feb 18, 2009 12:39 AM
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Sorry about the list of variables syntax (second paragraph), let me try that again:

Te: 1.0 eV
Ne: varied from 1E6 to 1E9 equal to Ni m-3
Ti: 1.0 eV
Ni: varied from 1E6 to 1E9 equal to Ne m-3
Ion Type: H+
Run Time = 0.03sec
S/C Material = ITO
SCcap = 2.0E-10 F
Sphere (SC) Radius = 1 m
Comp Vol Radius = 10 m
elecDist = MaxwellBoltzmannVolDistrib

Hope that goes through ok

posted by Gregory Francisconi at Feb 18, 2009 12:24 AM
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Greetings,

Background: I am an Engineering Physics student with Embry Riddle University, in Florida, working on a research grant on space charging effects. I have been familiarizing myself with SPIS 3.6, and was running through your labwork1 simulations, duplicating your training course PDF. I have been varying one parameter at a time and pushing it to its upper and lower limits while holding everything else as a control the same as in labwork1, which are (aside from new project default values):

Te = 1.0 ! eV ! Ne = varied from 1E6 to 1E9 equal to Ni invalid link : m^-3(Illegal character in path at index 1: m^-3) Ti = 1.0 ! eV ! Ni = varied from 1E6 to 1E9 equal to Ne invalid link : m^-3(Illegal character in path at index 1: m^-3) Ion Type: H+ Run Time = 0.03! s ! S/C Material = ITO SCcap = 2.0E-10 ! F ! Sphere (SC) Radius = 1 ! m ! Comp Vol Radius = 10 ! m ! elecDist = MaxwellBoltzmannVolDistrib

So here comes my problem:

I need to work with densities up to 1E10 eventually. However, while running through the labwork1 simulation, changing the ion and electron densities equally, I find it behaves strangely with both Ne and Ni densities anywhere above 4.0E6. I get these strange drops in final plasma potential on the computation edges (in Cassandra 3D viewer), and eventually at higher densities what I can only describe as a strange swirl of high potential in a specific region. Scouring your forum posts, I saw a mention of instability at higher densities (wang ji Nov 9th 2007 post), although it wasnít any more specific than this.

Could you clarify what could be causing this? Why does this instability arise and what parts of the code do you think could be responsible? Is there any recommendations for a quick fix which would allow me to work at 1E10 densities?

I am new to PIC simulations, so I would like to understand what is happening. I want to start digging into the code to see if I can alleviate this, but donít really know where to start.

If you would like I can email a PowerPoint showing my 3D output during the density runs. It illustrates what I am seeing pretty clearly.

Any help or recommendations would be greatly appreciated. Thanks!

-Gregory Francisconi