The next step
Posted: Wed Jul 03, 2019 10:53 am
OK, so I've finally seen what kinda looks like bunching, and some sort of transit-time measurements on the big machine at a couple sets of speeds and feeds. BUT!
After normalizing the faraday probes to c - in other words, calibrating out the time delay on the capacity coupling from the speed of light - I measured times that "don't make sense".
They are way slower than c, but way, way, faster than anything in there should be going with a mere 50kv or so energy on it. The signals are far louder than the capacity coupling, so that's not shifting the phase of what I see much. (Note to self, go back and get the numbers...and put them here, but I've already analyzed them in speed-volt code...).
I'm having to assume that rather than ballistics - we are seeing some sort of polarization wave in the mix of ions and neutrals in there. And it's a mix containing largely neutrals, as I proved another way - by really ionizing the bulk of the tank with RF feed, the conductivity of the result is such that you'd see around 500 ohms to ground on the main grid. For reference, when acting as a normal fusor, ion source or not - it's around 750,000 ohms load. That's not a small percentage change...
I theorized that since ion traps / quadrupole mass spectrometers are run just outside the predicted region of stability to provide narrow spectral lines (even rejecting some of what you were tuned for - aperture is the word they overload for that) - we could perhaps move toward the area in the middle of a stability region the math predicts.
Should be obvious that with a bunch of neutrals and collisions, things won't work like that. Add in some more ions (and we have both charges of them, a couple e/m ratios, and that's not even counting the electrons) and at some point things are going to smear out so badly they can't be controlled at all with varying field gradients we can actually produce - and certainly it's not going to be easy to predict. But there is still hope that we can find a set of conditions that will work.
The trouble is, that set of conditions may not even be on the plot of the Mathieu stability overlap regions...it may be shifted and broadened so much that the prediction of that math is just plain "not on the real paper" for us. And jumping from the limit of where that math does work - say something a little under 1e-4 mbar (optimistically! Really it's getting crappy at 1/10th that) directly to the normal fusor type operating conditions, for a decent center value - 2e-2 millibar, or 200 times where a mass spec fails...was a "well, why not try it" but it seems, doomed to failure - it's just too large a leap.
Well then, I've done enough of this and that to know that when this kind of thing happens, you drop back to baby steps - they are sometimes the quickest way, and really do beat "running of in all directions" when the going gets tough.
So, it's time to get down in the mud, temporarily forget about neutrons etc, and just map out the turf - what shifts, and how much, as a function of pressure and how much percentage of what's there is ionized (and what mixed flavor of them we have). So, being somewhat a creature of logic and actually wanting to solve this one...here we go down another road that right now looks more promising.
My earliest work was with a smaller pumping station, and I'd built up a fair amount of stuff to hang on it. Rather than disturb the main setup, which otherwise is good, no obvious flaws, by taking it down repeatedly and losing purity - out-gassing is a bear - I'm going to move to the smaller one again, and have been cleaning up and getting it operational again. I've had a couple of different chambers on it, and right now am figuring out what's going to be the best test mule for this set of experimentation and learning. The little 2,75" cross is what I have a ton of parts for, the there's this "ship in a bottle" aspect of working with it much, as well as the tank walls being close in are going to affect the fields I want to apply, so it's not cast in stone yet.
But at least so far, I have large parts of the bench visible, and after 24 hours or so of outgassing just the blanked-off pumping station and gage, it's back to normal (for it) at around 6e-7 millibar, which will be plenty good enough if I can hold it under a few e-6 as a baseline. As any vacuum experienced person knows, surface area is the enemy fortification, and water is the enemy. We'll see what I can get - half of this was QF and that "leaks" water a bit....
Anyway, it looks like this now -
Everyone needs real tube type opamps, shelves full of exotic materials, and a feather boa in their lab, right?
Guess I'm going to have to spin up some more and somewhat different data aq and control stuff, but with all the experience and spares from the other setup, shouldn't be any sort of roadblock to do.
Now we want to measure some different stuff, so a new setup is called for - the old hardware is so tied into the other system there'd be no point trying to move it anyway. Here I don't expect quite the possible electromagnetic violence that forced the other setup to need fiber optic isolation either. Even wifi from a newer pi might do...The database server is already setup elsewhere (and in a safer spot) on the network here, and works great - adding another database is not a big deal.
At least I have a plan now. The pause in fusor operations and posting to play with other stuff was to let a plan form on one of my internal back burners....it's a good technique when you can't just force it because of that whole tree-forest and inside/outside the box stuff. As Paul DiLascia used to say on MSJ - when I run into a wall programming, I just go mow the lawn, and the answer comes to me.
After normalizing the faraday probes to c - in other words, calibrating out the time delay on the capacity coupling from the speed of light - I measured times that "don't make sense".
They are way slower than c, but way, way, faster than anything in there should be going with a mere 50kv or so energy on it. The signals are far louder than the capacity coupling, so that's not shifting the phase of what I see much. (Note to self, go back and get the numbers...and put them here, but I've already analyzed them in speed-volt code...).
I'm having to assume that rather than ballistics - we are seeing some sort of polarization wave in the mix of ions and neutrals in there. And it's a mix containing largely neutrals, as I proved another way - by really ionizing the bulk of the tank with RF feed, the conductivity of the result is such that you'd see around 500 ohms to ground on the main grid. For reference, when acting as a normal fusor, ion source or not - it's around 750,000 ohms load. That's not a small percentage change...
I theorized that since ion traps / quadrupole mass spectrometers are run just outside the predicted region of stability to provide narrow spectral lines (even rejecting some of what you were tuned for - aperture is the word they overload for that) - we could perhaps move toward the area in the middle of a stability region the math predicts.
Should be obvious that with a bunch of neutrals and collisions, things won't work like that. Add in some more ions (and we have both charges of them, a couple e/m ratios, and that's not even counting the electrons) and at some point things are going to smear out so badly they can't be controlled at all with varying field gradients we can actually produce - and certainly it's not going to be easy to predict. But there is still hope that we can find a set of conditions that will work.
The trouble is, that set of conditions may not even be on the plot of the Mathieu stability overlap regions...it may be shifted and broadened so much that the prediction of that math is just plain "not on the real paper" for us. And jumping from the limit of where that math does work - say something a little under 1e-4 mbar (optimistically! Really it's getting crappy at 1/10th that) directly to the normal fusor type operating conditions, for a decent center value - 2e-2 millibar, or 200 times where a mass spec fails...was a "well, why not try it" but it seems, doomed to failure - it's just too large a leap.
Well then, I've done enough of this and that to know that when this kind of thing happens, you drop back to baby steps - they are sometimes the quickest way, and really do beat "running of in all directions" when the going gets tough.
So, it's time to get down in the mud, temporarily forget about neutrons etc, and just map out the turf - what shifts, and how much, as a function of pressure and how much percentage of what's there is ionized (and what mixed flavor of them we have). So, being somewhat a creature of logic and actually wanting to solve this one...here we go down another road that right now looks more promising.
My earliest work was with a smaller pumping station, and I'd built up a fair amount of stuff to hang on it. Rather than disturb the main setup, which otherwise is good, no obvious flaws, by taking it down repeatedly and losing purity - out-gassing is a bear - I'm going to move to the smaller one again, and have been cleaning up and getting it operational again. I've had a couple of different chambers on it, and right now am figuring out what's going to be the best test mule for this set of experimentation and learning. The little 2,75" cross is what I have a ton of parts for, the there's this "ship in a bottle" aspect of working with it much, as well as the tank walls being close in are going to affect the fields I want to apply, so it's not cast in stone yet.
But at least so far, I have large parts of the bench visible, and after 24 hours or so of outgassing just the blanked-off pumping station and gage, it's back to normal (for it) at around 6e-7 millibar, which will be plenty good enough if I can hold it under a few e-6 as a baseline. As any vacuum experienced person knows, surface area is the enemy fortification, and water is the enemy. We'll see what I can get - half of this was QF and that "leaks" water a bit....
Anyway, it looks like this now -
Everyone needs real tube type opamps, shelves full of exotic materials, and a feather boa in their lab, right?
Guess I'm going to have to spin up some more and somewhat different data aq and control stuff, but with all the experience and spares from the other setup, shouldn't be any sort of roadblock to do.
Now we want to measure some different stuff, so a new setup is called for - the old hardware is so tied into the other system there'd be no point trying to move it anyway. Here I don't expect quite the possible electromagnetic violence that forced the other setup to need fiber optic isolation either. Even wifi from a newer pi might do...The database server is already setup elsewhere (and in a safer spot) on the network here, and works great - adding another database is not a big deal.
At least I have a plan now. The pause in fusor operations and posting to play with other stuff was to let a plan form on one of my internal back burners....it's a good technique when you can't just force it because of that whole tree-forest and inside/outside the box stuff. As Paul DiLascia used to say on MSJ - when I run into a wall programming, I just go mow the lawn, and the answer comes to me.