Classes of metrology defined

[Doug Coulter]

This can be a touchy subject, and I look forward to being corrected and amplified upon for this one. So I will merely toss out a straw-man here and hope to get the ball rolling.

1: Measuring a specific thing
A: relative
B: absolute measurement

2: Looking for the unexpected
A: known unknowns
B: unknown unknowns

Which should get things going. Ya'll chime in.

For a lot of things, 1-A gets you there. Let's say I have a fusor, and want relative neutron outputs, mainly so I can tell if this change made things better or not. All you need for that is stable relative measurements at least until you start wanting to compare your results with those of others. For that, you need 1-B, and you hope that others who think they have achieved that really have and haven't missed something important. But to have a clue at all if one of the other of you did, you have to get to where the numbers mean something (you think) and if you can't get them to agree with otherwise identical conditions, well, that should be a spur to all to find out why the discrepancy exists. There have been far too many times in science where people fudged their results to agree with some "authority" that later have been blown because some new guy insisted on getting them to agree without fudging, and found some missed assumption the authority made....which resulted in better numbers, after all too long a delay that wasted a lot of time for others working in the same field. We'd rather shuck the egos and just make faster progress here.

These are both very-extremely important for development (ie refinement), but less so for raw discovery unless you got lucky and measured the correct thing that allows the discovery. So things under class 2 are a lot more diverse and interesting, the main difficulty being "how do I set myself up for discovery of things I don't expect". After all, it's easy to say "be prepared" or "expect the unexpected" but not so easy to really do, and not blind yourself to the idea that something not in your personal theory might be happening despite what you think (or if you're intellectually honest, what you thought up till you saw the new thing).

Since I don't myself know how to tell you to actually expect the unexpected as a philosophical issue, truly and fully, a couple of examples may help here.

Let's say I have a neutron counter working in class 1-A here -- it counts neutrons per second, and is stable between experiments. That will tell me if this one is making more neutrons per second than the last one.
But since a count is a count from one of these, I can't tell if I'm getting multiple hits in bursts inside one detector response time window -- I tossed that information out the window when I thresholded the signal and just counted how many of them there were. So there will be a certain tendency for that to lose information, and only tell me what I expect it to. However, if I also send that same signal, raw, to an oscilloscope or an audio amplifier, I might take advantage of my superior in-brain processing to see things that a counter cannot report -- some pulses are wider, or taller, indicating multiple hits that the counter would have reported as just one count. The counter wouldn't notice if the counts were coming at say, a 60hz rate, which might be due either to simple EMI getting into the system, or the fact that I may have a 60hz component in what I'm driving the experiment with, that is affecting it's success -- most of the neutrons may come out during some phase of the ripple of my HV for example, and that would sure be nice to know, but a counter won't tell you things like that, or let you separate them from simple hum on the wiring either.

Here's another one:
Let's suppose (truly) that sometimes I don't have a clue where the charged particles are moving from and in what directions in my fusor. And I'm interested because I've not yet heard anyone else with a theory of why the thing doesn't simply degenerate into a static equilibrium with very little fusion, that doesn't need "armwaving" or "then a miracle occurs" at some point. So I build a pinhole camera I can move around in there and look, and I get a picture somewhat different than what I see with the naked eye, and as I move it, it changes -- obviously I've got some things entering it in straight lines (like X ray photons) and some things that seem to be coming in in beams so they get brighter or darker relatively as I move the camera around, compared to isotropic X ray emission. Well then, the obvious thing to do is fit that camera with some electromagnets so I can move the charged particles around vs the X rays, then I can learn something I couldn't learn from the thing as unmodified. If I actuate the magnets, the X ray picture won't move, but the charged particle one will, and different polarities of particle will move in opposite directions. So I began with a known unknown -- where's the radiation coming from, and discovered that there is more than one type -- an unknown unknown, then hammered that one down. I might then chase this one down by putting in a movable Faraday or Langmuir probe to learn more, but at that point, I'm back in "known unknown" and trying to nail it down -- the basic discovery has been made already.

Wash, rinse repeat -- the basics of science!

I am drawing from actuality in these examples. I thought I could calibrate my 3He neutron counter against say BTI bubble detectors and/or silver activations. Then I discovered that there was divergence between the ratios of the raw numbers there produced from run to run when there were other changes -- for example a run that didn't make the 3He make exciting counts, did make silver and one but not all of the BTI's fill with a larger amount of bubbles that would be indicated from other cross-calibrations, made before. Once I hooked up the tube raw (pre threshold) output to an audio amp the reason became obvious. The run that produced the low counts, but high readings on the other detectors was bursting in its output, so hitting into the tube dead-time -- something I've since been looking into here.

So I guess I should add a little philosophy too -- for one thing, measure everything you can more than one way, and keep track of when they track, or don't -- it could be broken tools, but it might not be.

The other thing, exemplified by Fleming, is if something unexpected, maybe even negative, happens, do go ahead and try to find out why it did and what it means -- had he tossed that contaminated petri dish in the trash, we'd not have penicillin. And most "big science" outfits would do just that -- toss it and tell the lab assistant to get it right next time, instead of making that discovery. Sad but mostly true. This is where we "small science" people have a real advantage....and we need all we can get!

[troy]

We've all heard the expression, "expect the unexpected" or perhaps "keep an eye out for anything out of the ordinary".

To offer another example, I'll say "keep your nose to the air" or "use *all* your senses." Anecdotally, I recall a time just munging around trying to breath some new life into an old PC. Everything looked correct; and, according to my mental checklist, I'd covered all my bases. And so it came time to fire the thing up. Things looked ok. POST was dutifully counting memory and proceeded to report on the drives installed, etc. About 30sec in, I noticed "the smell". I thought to myself, "I shouldn't be smelling ozone at this particular point in my life" and immediately flipped the machine off. Puzzled, I checked all my connections -- looks good. By this time, the smell was gone; so, I thought I'd have another go. Again, "the smell". Upon further inspection (with the machine off, of course) a power cable had dipped low-enough to block the CPU fan from spinning. DOH! Not a big deal to fix, but it could've been expensive to correct had it not been detected.

The point, here, is that you often don't know what you're looking for. However, if you engage all of your "tools" (in this case, my "smelling" tool), one can often discover a facet of something that had gone, heretofore, undetected. I s'pose my story falls under Doug's 2-B, but it may perhaps be a story with which many can indentify.

So, the take-away from this is, "Use every metric you can, because you never know what you're gonna smell."

[Doug Coulter]

To second Troy on this one -- here's an example of something that after you've seen it a few times with a gage, you don't need the gage so badly to know what is going on.
Use ALL your senses. With a little practice you can also tell gas purity by color after having seen it with various contaminations. Cameras don't tend to get the spectra
right, this has to be a Mark I eyeball thing. Keep your nose high!

http://www.youtube.com/user/DCFusor#p/u/7/3ltD6GM77bI is what I see logged into my channel, dunno how to make the normal trick work with this url, but I'll figure it out at some point.
Anyone? I had to just go search to find the "watch" URL.



In this video I started out at fairly high pressure, then allowed the pumps to take it out while running with a current limit on the power supply of 6.7 ma. At the start, the voltage is pretty low, but it comes up as the gas goes out, up to the 52 or so kV it was set for. For what it's worth, in recent runs in this setup, we get best fusion at about 1.6 to 1.9 e-2 millibar when you can't see the rays much at all, just a dot at focus. The ray pictures most show seem to the be photogenic, but not best operating point mode. The numbers given above are for a 1" grid in a 6" ID tube, and will differ depending on those sizes -- we run much less pressure with a grid out in the 14" diameter main tank for example -- Paschen's law. Also, note my gage itself reads high on D and higher yet on already-ionized D, which is what that bright dot at the left is -- the tank entrance for pre-ionized D+.

[Bill Fain]

Hi, Things are kinda slow at the start of the year so I thought I'd throw this out there to maybe get some conservation flowing.
I have attempted to list what I think we can measure or calculate in a Fusor. I know I have left out something. Also, I casually list these quantities, but I don't necessarily know how to measure them all and some are probably a real tough to do. Feel free to add or subtract from this list and tell me why they can't be measured easily, if they can't or why a particular measurement may be useless. Some items may be the same as others only stated differently; please tell me this as well. I hope this will bring out discussion like: "We used to measure roller bearing life from their acoustic profile etc. or has anybody thought of measuring....?" Thanks. -bill

heat
light spectra intensity/any frequency components
gas inlet flow
atom quantity
pressure ratio
ion current
ion speed
pressure
electrostatic field/charge?
neutron count
neutron energy
gamma count gamma energy
grid voltage, current, wave shape, frequency
resonance, capacitance, reactance
acoustic properties
magnetic properties
exhaust flow rate
reaction components i.e
helium tritium
neutrals ?
x-ray energy/count
Q

[Doug Coulter]

A decent list, Bill. Some of these would be time and place dependent. Some can be derived from others, and some are hard (but maybe important to measure. I'll look at this closer and have more to say in an edit.

[Bill Fain]

Hi, I was thinking about what we can measure in a fusor again last night (while I was trying to sleep as usual). I realized that we need a standard nomenclature for fusor specifications to see if we're on the same page. Doug has already talked about this for neutron/gamma counting. Specifications and measurements sometimes blurr the line and may be considered the same thing. Stuff like:
gas purity
number and type of ion sources
chamber volume
grid volume
grid material
grid construction wire vane perforated etc.
fusor form factor: spherical, cylindrical, cylinder withing cylinder beam on target etc.
horizontal grid vertical grid etc.
ratio of virtual grid volume to chamber volume
we've also noticed something like transition loses/gains (or changes) in fluid (ion/plasma) flow in the fusor; when we go inside from the small chamber to the larger one.
Does anybody have any ideas on how to organize all of this into a standard for everybody to go by? Thanks. -bill

[chrismb]

There are a large number of plasma properties that can also be measured, which would be different for each region. So these, and some of the ones mentioned above, would have to be done in a big table for; the central plasmoid, the beams, the background, the vicinity where the beams meet the wall. For various values in the beam, you'd also need to do another table for properties of the beam versus distance from centre.

[Bill Fain]

Chris, Hi. That doesn't sound like something for the uninitiated or faint of heart. Are quantities like that measured visually or with ion probes and or some sort of Kelvin temperature devices ,or something else. Thanks. -bill

[Doug Coulter]

Lasers, microwaves, interferometers, and a bunch of other stuff. There's a few papers in our library and elsewhere that speak to all that. Some of it is not so hard to do that we won't try it here. Main issue is like at CERN -- OK, here's a zillion bits of data -- now write it all down and find a way to make some sense of it in an organized way. I'm already working that one with the data aq stuff we have!