re-qual detectors, AC ion source, DC main

[Doug Coulter]

I thought it would be good to requalify some of my detectors, which turned out to be a good idea, as the one I mainly listen to for my safety had some issues.
So I went back to DC drives to do that. "While I was there" I decided to try the 42khz ion grid supply I'd repaired earlier (it had arced and burned), since, well, it was there too.
I noted that at reasonable inputs (for this thing) it was harder to get the fusor ion grid to "light off" than with say 10kv DC, but once lit, I could hold that state quite a bit lower than usual. This was taking on the order of 3+ e-2 mbar to start, but would hold to around 6e-3 mbar and allow me to run down there.

Well, the old trend continues to hold, more or less - lower gas pressure means more ideal behavior in the sense of ballistic ion travel and less scattering far from focus - and when we're at or near focus, it doesn't matter that much. I did some running at around 1e-2 mbar, which is about half what we could normally do, and it appears (no good numbers were taken, really) that we do around 2x as good there - at only 40kv or so - as we did at 53 kv and 1.9e-2 mbar. With the AC ion source it seems there are more ions per mbar here - it takes more current for a given gas pressure to get up to volts on the main grid, which was part of the reason I ran down there in the first place, as I didn't want a lot of heat but did want enough neutrons to test-activate our silver and indium targets to back-check the electronic sensors, which, after fixing an obvious insect nest and humidity problem in one, are all fine again, and everything agrees as it should.

This run, at the top power of 12 ma and 40kv, gave us a new record on silver activation of slightly greater than 2k cpm on our coupon, backed up by the indium at around 1/10th that - but in only 90 seconds compared to our usual standard 5 min (300 seconds) run time. So, not too shabby, I'll have to work this further once I get the data taking gear, which also had a glitch, going correctly again.

I've improved the gridcam a heck of a lot, using longer exposures (it's not like taking a sports picture, after all) and getting many times the light sensitivity than it used to have. The first frame in this animated gig might as well have been totally black to the naked eye...nope, nothing was glowing red hot there either.
These are at 5, 7, and 12 ma. The lower currents went with somewhat lower voltages too - we were current limited (@ around 30kv) till the last one.

animation at 3 power levels (here I have to click the pic to get the animation)

An interesting effect is that the ion grid doesn't show the usual poisser here - it's just a blob of plasma, or so it appears. Further, the faraday probe nearest the main grid showed a sine wave (capacitive coupling) till things lit off - then clipped at ground with only positive pulses once it did light off - the drive is simply directly connected to a transformer secondary which is driven around 42 khz. Not only that - note that it moves with varying main grid power (no other changes...).

Normally if we have even one DC driven grid in the tank, that's it, all the faraday probes see a large negative net charge. Here, the opposite is true, the faraday I was looking at (the left one in the pic) went to ground, but never negative at all...

One of my other counters is a little flakey, but I'm sure that when it takes data at all, it's correct (tested with a cal source) - no rest for me for a bit, I'll have to chase down why that locks up sometimes, but I got a couple of pix as screenshots...

Whole screens shot. Fusor control wasn't taking data this time (I didn't try).

Then I restarted it after it locked up, but put on the indium. Our normal background is ~~ 80 cpm on this counter.

I think you can see where I put the indium on and took it back off in this.

More when I get more - I now have some things to look into further...interesting. And a real big 1700 khz RF source coming online....

[Bob Reite]

And a real big 1700 khz RF source coming online....

Good thing you are way out in the country where all that RF at the top end of the "expanded" standard broadcast band shouldn't bother anyone.

[Doug Coulter]

I hope I don't radiate too much...it's not that easy to radiate a LOT in this range, but yeah, what gets out can go far.
I'm not sure this is where I'm going to wind up, but it's a SWAG based on measured transit times, and how fast I have to change the potential
to keep from bashing deuterons against the tank walls before I bring them back towards focus, using some 10's of kv drive. More drive needs higher F and
so forth. This seems to pan out with recent measurements, I should be able to go around 40kv (enough to prove the point) at around this frequency.
I would then need around 60x this frequency to do the same for the electrons, but one step at a time (and the result wouldn't be two pure sines mixed,
but close enough for now).
According to the allocation charts, I'll either be jamming a pretty unused part of the AM band, or, oops, a little slice dedicated to other uses. I should be able to stay out of the 160 meter ham band...
This isn't AM band heaven, as you say, I'm out in "noplace" and what few stations there are in the daytime are in the middle of the band..night is another issue, but I won't be running at night - or for that matter, very long at a time. I'd hate to be trying to DF me....

United_States_Frequency_Allocations_Chart_2016_-_The_Radio_Spectrum.pdf

I should probably link this in the data section too.

(952.2 KiB) Downloaded 212 times

I could have posted an image of the above, but you can barely even read this one, even magnified...

[Bob Reite]

I suppose the next thing to do is build a faraday cage around the whole setup. I remember SCE having to do that around part of the Sylmar converter station, because of the hash and harmonics that extended into the BC band from the DC to AC converter. But hopefully it will be awhile before you have to do that, if you even get noticed.