Thermal imaging of fusor grid / plasma
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Thermal imaging of fusor grid / plasma
I recently bought a microbolometer based thermal camera (160x120, 100mK resolution in 7-14um) and added a ZnSe macro lens(10" fl, 6" away from core center) view port on my fusor, allowing imaging of the inside of the vacuum chamber in the visible and far infrared. Posted are some preliminary pictures of a heated grid (~85F) in the infrared, demonstrating the transparency of the viewport in the 7-14um wavelength. For these pictures the grid cooling system was turned off and all liquid coolant was removed from the grid. Pressure was probably in the mTorr range, and the plasma was on for 10-15sec.
The final plan with the system is to measure the spacial distribution of ion bombardment on the grid surface vs elevation angle along the grid and spatial distribution of plasma density at the center of the grid.
The coolant flow through the grid will maintain the grid surface at a constant temperature, a copper ion collector array will be mounted on the grid surface; this will consist of an array of small copper segments mounted to the grid with a standoff of known thermal conductivity, the collector to grid temperature difference will them be proportional to the heat flux flowing through the standoff. Knowing grid surface temperature and collector temperature at different angles, the variation in ion flux to the grid vs position may be determined.
Plasma density distribution will be determined by back-illuminating the plasma with a pulsed CO2 laser genlocked to the thermal camera's vsync pulse in the NTSC video signal. The signal will also trigger an LC pulse forming network to pulse the plasma to high enough density to exceed the density cutoff of the laser beam (if possible) or diffuse the beam as it travels through the plasma density gradient, which will allow some determination of density contours in the plasma.
ZnSe viewport Viewport mounted Thermal Imager (L3 2500AS) Back glass viewport temperature grid insulator temperature Liquid cooled grid version 2 CO2 laser Andrew Seltzman
The final plan with the system is to measure the spacial distribution of ion bombardment on the grid surface vs elevation angle along the grid and spatial distribution of plasma density at the center of the grid.
The coolant flow through the grid will maintain the grid surface at a constant temperature, a copper ion collector array will be mounted on the grid surface; this will consist of an array of small copper segments mounted to the grid with a standoff of known thermal conductivity, the collector to grid temperature difference will them be proportional to the heat flux flowing through the standoff. Knowing grid surface temperature and collector temperature at different angles, the variation in ion flux to the grid vs position may be determined.
Plasma density distribution will be determined by back-illuminating the plasma with a pulsed CO2 laser genlocked to the thermal camera's vsync pulse in the NTSC video signal. The signal will also trigger an LC pulse forming network to pulse the plasma to high enough density to exceed the density cutoff of the laser beam (if possible) or diffuse the beam as it travels through the plasma density gradient, which will allow some determination of density contours in the plasma.
ZnSe viewport Viewport mounted Thermal Imager (L3 2500AS) Back glass viewport temperature grid insulator temperature Liquid cooled grid version 2 CO2 laser Andrew Seltzman
Andrew Seltzman
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- Mike Beauford
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Re: Thermal imaging of fusor grid / plasma
Now that is a really slick idea you have there. What kind of plasma densities are you expecting in your fusor?
Also, can you please post your results?
Mike Beauford
Also, can you please post your results?
Mike Beauford
Last edited by Mike Beauford on Thu Aug 08, 2013 6:21 pm, edited 1 time in total.
Mike Beauford
- Richard Hull
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Re: Thermal imaging of fusor grid / plasma
Nice bit of experiment. Keep us posted on this.
Richard Hull
Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
Retired now...Doing only what I want and not what I should...every day is a saturday.
Fusion is the energy of the future....and it always will be
Retired now...Doing only what I want and not what I should...every day is a saturday.
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Re: Thermal imaging of fusor grid / plasma
Here's some matlab code
%co2 laser plasma cutoff density
clear all
clc
e0=8.85E-12; %permitivity
e=1.6e-19; %electron charge
me=9.11e-31; %electron mass kg
lambda=10.6E-6; %co2 laser wavelength
c=3e8; %speed of light
f=c/lambda;
w=2*pi*f; %angular freq
nc=e0*me*w^2/e^2; %plasma density 1/m^3
disp(['plasma density= ',num2str(nc,3),' m^-3'])
disp(['plasma density= ',num2str(nc/100^3,3),' cm^-3'])
plasma density= 9.96e+024 m^-3
plasma density= 9.96e+018 cm^-3
So pretty high for cutoff(arc/shock tube/z-pinch density region), Probably out of the capabilities of a fusor even being driven by a PFN, unless there is some multiple well formation at the focal point. If a can't see any effects with cutoff, I'll try to observe any refraction effects from the density gradient. If that doesn't work, I'll try to rig up the laser as an interferometer to determine density.
Andrew
%co2 laser plasma cutoff density
clear all
clc
e0=8.85E-12; %permitivity
e=1.6e-19; %electron charge
me=9.11e-31; %electron mass kg
lambda=10.6E-6; %co2 laser wavelength
c=3e8; %speed of light
f=c/lambda;
w=2*pi*f; %angular freq
nc=e0*me*w^2/e^2; %plasma density 1/m^3
disp(['plasma density= ',num2str(nc,3),' m^-3'])
disp(['plasma density= ',num2str(nc/100^3,3),' cm^-3'])
plasma density= 9.96e+024 m^-3
plasma density= 9.96e+018 cm^-3
So pretty high for cutoff(arc/shock tube/z-pinch density region), Probably out of the capabilities of a fusor even being driven by a PFN, unless there is some multiple well formation at the focal point. If a can't see any effects with cutoff, I'll try to observe any refraction effects from the density gradient. If that doesn't work, I'll try to rig up the laser as an interferometer to determine density.
Andrew
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- Mike Beauford
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Re: Thermal imaging of fusor grid / plasma
I originally thought when I first looked at your setup you were doing laser interferometry. I'm pretty sure you might be the first on fusor net to actually do it this way. The only one I can think of that might have done it in the past is Carl.
Mike Beauford
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Re: Thermal imaging of fusor grid / plasma
Another interesting way of determining plasma density is to dope the deuterium plasma with a gas who's optical properties (strongly absorbs / reflects / transmits) at the 10.6um wavelength depend on its ionization state. Anyone know of such a gas(can be a single atomic species or a molecule, perhaps even a thermally evaporated metal atom beam)
Andrew
Andrew
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Re: Thermal imaging of fusor grid / plasma
You might look at CO2, I know it can be detected by IR, but thats at NIR, not sure what it does at thermal IR ranges.
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Re: Thermal imaging of fusor grid / plasma
Preliminary tests of thermal imaging of CO2 laser beam, the first step to a spatially resolved measurement of plasma density at the focal point of the fusor.
Laser, controller, and thermal imager Diverging lens More pictures of setup:
http://www.rtftechnologies.org/physics/ ... ometer.htm
Video of beam pulsing:
http://www.youtube.com/watch?v=SxVddPWnAQs
Laser, controller, and thermal imager Diverging lens More pictures of setup:
http://www.rtftechnologies.org/physics/ ... ometer.htm
Video of beam pulsing:
http://www.youtube.com/watch?v=SxVddPWnAQs
Andrew Seltzman
www.rtftechnologies.org
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Re: Thermal imaging of fusor grid / plasma
New updates on the laser density probe
Laser faceplate adapter to thorlabs optics cage system -0.5" FL diverging lens Thermal imager viewing diverging beam on wall 6x Beam expander Expanded beam viewed on thermal image plate Video of parallel beam on wall through 6x beam expander
http://youtu.be/gki9ab-8_7A
Cage system for mounting tuning mirror to direct beam through fusor more images at:
http://www.rtftechnologies.org/physics/ ... ometer.htm
Laser faceplate adapter to thorlabs optics cage system -0.5" FL diverging lens Thermal imager viewing diverging beam on wall 6x Beam expander Expanded beam viewed on thermal image plate Video of parallel beam on wall through 6x beam expander
http://youtu.be/gki9ab-8_7A
Cage system for mounting tuning mirror to direct beam through fusor more images at:
http://www.rtftechnologies.org/physics/ ... ometer.htm
Andrew Seltzman
www.rtftechnologies.org
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Re: Thermal imaging of fusor grid / plasma
Beam expander magnification increased to 9x for more uniform power distribution (top of gaussian of the beam)
Turning mirror
Mirror mounted on beam expander
Beam projected by turning mirror
Core input lens
Core output lens with mounting bracket
Andrew Seltzman
www.rtftechnologies.org
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