Another (Preliminary) Report on Anisotropy

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Liam David
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Re: Another (Preliminary) Report on Anisotropy

Post by Liam David »

Progress report. I now have a measurement plan and have been working on the analysis tools for when the data exist. I've downloaded a spherical harmonics library for MATLAB that can use least-squares regression on a coarse (measurement) grid to estimate the spherical harmonic Y_l^m coefficients. For those unfamiliar, you can express any "suitably nice" function defined on the surface of a sphere as a linear combination of spherical harmonics. Finding these coefficients from a limited set of points allows you to reconstruct what the overall distribution may look like. To validate the method and code, I created some theoretical measurements for different scenarios (including some random error). The results are in the following images (higher res when you click on them). I'm assuming symmetry between all octants.

Dual beam-on-target, 2.5" distance, 20" measurement radius - flux
Dual beam-on-target, 2.5" distance, 20" measurement radius - flux

Isotropic 5" beam, 20" measurement radius - flux
Isotropic 5" beam, 20" measurement radius - flux

Anisotropic 5" beam, 20" measurement radius - flux
Anisotropic 5" beam, 20" measurement radius - flux

Same scenarios, equatorial flux
Same scenarios, equatorial flux


The reconstruction errors are of the same order as the measurement uncertainties. When removed, the reconstructions are accurate within ~1e-7, meaning the math works. Next step is to spend quite a few hours collecting data.
Last edited by Liam David on Fri Feb 12, 2021 1:49 am, edited 1 time in total.
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Richard Hull
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Re: Another (Preliminary) Report on Anisotropy

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Great work! I love the spiked porcupine balls related to hot emission areas!

Precision computed anisotropy reminds me of a one teraohm 10% resistor being a warranted open circuit to within +/- 100 gigohms of said warranted open. In general, D-D fusion wants isotropy, but in the end it can be steered and directed to the same order as herding cats. In the end, it is what it is actually measured to be, regardless of computational efforts. This is especially true within the amateur effort.

Still, it is fun to plug in values in the most complicated string of computations and then turn the crank, push the go button and to watch the fun begin based on one's musings amongst the supplied variables.

I often wondered, (I wonder a lot!),that should there be a God or omniscient presence, if we and the universe are just a running complex amusement, a wonderful and fascinating complex of self-assembling ever more complex, self-conscious, thinking organisms, scattered over trillions of worlds juxtaposed to a constantly running down clockwork of entropic death of all that is or ever will be in this one universe. What a gloriously wonderful universe! Such an entity could have multiple universes running at the same time! Just monkey with a few hundred key variables and spin her up! Never a dull day, right? Plus, absolutely no need to intervene lest the original startup be soiled and fouled to its original purpose. (Seeing where it goes if left undisturbed)

Sorry for the musings.....got wound up on our thinking we can figure it all out. I find it great that we try and will never stop trying. We have to think we are the "little engine that can" or there is nothing left to keep the train moving forward. Progress, science, engineering, art...Call it what you will....It moves and inspires those who think deeply.

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
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
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Liam David
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Re: Another (Preliminary) Report on Anisotropy

Post by Liam David »

I now have some pretty good data on neutron anisotropy in the fusor "equatorial plane." Each run was ~5 minutes long at ~35kV, 8.56mA, 6-7e5n/s. The small 1.5" detector was 43cm from the center of the chamber and the output was monitored by my larger tube on the opposite side of the fusor. Count rates were ~50kcpm on the main tube and ~300cpm on the smaller detector. I measured at 8 angles between 0 and 90 degrees, with 0 corresponding to the beamline.


anisotropy.png


The ratio on/90 off axis is 1.34:1 and tapers off smoothly. The results are repeatable, and I conducted a few extra runs at various angles to check.

The endcaps are 6.35cm from the chamber center, so 6.35/43=0.15<<1 meaning it's in the far-field. Fusion in the beamline seems anisotropic.


Last two BOT curves have anisotropic source functions. Note that theta in the title is not the plot coordinate, but the relative angle between the measurement point and source. This distribution function is based on the Leslie Kicka paper on anisotropy, a rough estimate from the plots.
Last two BOT curves have anisotropic source functions. Note that theta in the title is not the plot coordinate, but the relative angle between the measurement point and source. This distribution function is based on the Leslie Kicka paper on anisotropy, a rough estimate from the plots.
Last edited by Liam David on Sat Feb 27, 2021 8:47 pm, edited 1 time in total.
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Richard Hull
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Re: Another (Preliminary) Report on Anisotropy

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I was in sympathy with Liam as I have thought a lot about this. Table space is an issue in quarters of limited size and fixed gear in this study at the amateur level. To serve the ideal, one would want an empty 20X20 room with the fusor device on a table or platform about 1 foot above any materials on that table. A roll-around cart with a good neutron detector system could then be positioned all about the fusion device at any number of ranges that would seem reasonable. This arrangement should rule out significant neutron scatter that might tend to confuse and confound results.

20X20 open spaces are rare outside of research and certain college labs. Out buildings on private property might not make a good lab, but if the right size, might be emptied and roll-around or portable fusors and measuring carts could be placed there in a temporary arrangements.

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
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
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