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Posted: Tue Dec 07, 2010 10:04 pm
Nop - I suggested the sparkgap to keep the cost down and provide a good workable system that can be built on a small budget. It will not allow you much control of pulse width - more the other circuit components and layout.
UHF or Microwave technics are required. Inductance will allow you to extend timing but usually the trick is to shorten it if possible.
As Richard says - it will give microsec timing but good work can be done at these speeds. A sparkgap and a good cap gets you started cheaply.
I use a Radar calibrator to get fast triggering but lose speed with switching loads
A simple sparkgap filled with D2 will get you a Neutron burst when discharged.
The quest continues but room for more workers using pulses.
Posted: Tue Dec 07, 2010 11:36 pm
Well, this is a subject that I am continually learning. I would love to try pulses for my next set of experiments!
Posted: Wed Dec 08, 2010 3:09 pm
I disaggree with Richard on this one - a 10Ghz Magnetron ( X band ) will give you 50 pico-sec pulses spaced at 50 pico-sec if halfwave rectifyed and shaped ( PFN ) and can be high-powered - well within amateur capabilty and access. - A nice cheap ( Ebay ) oscillator for 50 pico-sec work. Or a 2.4Ghz microwave oven magnetron giving about 200 pico-sec ( there abouts )
Posted: Wed Dec 08, 2010 4:07 pm
How would one go about shielding the EMF off of the Microwave oven magnetron? Especially from the now necessary camera.
Posted: Wed Dec 08, 2010 4:38 pm
Conrad - the need for shielding occurs when the power goes up - low power with low repartation rates generally are not a problem but standard RF shielding will work ok .
With all shielding issues, distance from the source is best.
A camera should not be a problem for low power and proper RF shielding- xray issues more so.
Posted: Wed Dec 08, 2010 8:18 pm
This discussion is starting to provoke some questions in my mind about its utility and direction. The original thread was about POPS, which is a specific plasma phenomenon excited by RF frequencies in the low-MHz range. Now we have a stream-of-consciousness exchange about all manner of stuff relating to pulses, to RF, most of it unquestionably distant from the original topic, some of which is of questionable legitimacy:
>A simple sparkgap filled with D2 will get you a Neutron burst when discharged.
Is this statement based on anyone's actual experience in this community? I don't doubt it as a theoretically-justified possibility of course, but unless I missed something big in the last ten years, NOBODY has done this kind of experiment and offered evidence of neutrons.
>a 10Ghz Magnetron ( X band ) will give you 50 pico-sec pulses spaced at 50 pico-sec if halfwave rectifyed and shaped ( PFN ) well within amateur capabilty and access. - A nice cheap ( Ebay ) oscillator for 50 pico-sec work.
A 10-GHz magnetron generates microwaves whose half-period is 50 ps. I challenge the idea that rectifying and "shaping" to produce trains of high-powered 50-ps pulses is at all an established (let alone cheap and easy) result. If it IS a real result, if the suggestion that this can be done IS a matter of someone's legitimate expertise, then let's hear about it in a new thread that is not about POPS (to which there is no relation).
>I work with pico-sec pulses at 4000+ joules
John, do you have any threads providing experimental details and data on whatever it is you purport to be doing with pulses? Picosecond pulses at 4000+ joules sounds like pure fantasy to me. This is the domain of bizarre terahertz radiation experiments, not conventional electricity running around on copper busbars.
Posted: Wed Dec 08, 2010 9:55 pm
I am with Carl on this. Much of the pulse discussion that he noted defies certain ideas in physics at first blush. There is a link between rep rate, extant devices, viable capacitances that can store large amounts of energy at high rep rates, etc.
I urge everyone to just stop and think physics and not blurt out fantastic figures that defy physical assembly at the amateur level. Just the simple electronic math, alone, throws much of this prior discussion into question.
State all the variables. It is truly easy to push 4 megawatts of peak pulse power in a pulse. But at what rep rate? At what voltage? What is your actual o'scoped pulse width? Peak current? Peak voltage? Peak power? Support this with images of a multitraced scope presentation and an image of your mechanical electronic assemblage. Then, we can start a real discussion.
My guess is the wideband measurement gear and multichannel scopes are not in the hands of those posting. I have done some of this stuff in the past and it ain't easy for the home experimenter.
You think you have a handle on the basic theory and the math and then there is the reality of all the gotchas that show their ugly faces. The gotchas are part of the more advanced theory and math, of course, but you don't even consider them until they bite you in the butt while assembling real stuff and operating it in the real world.
Never discuss pico-second high energy pulses until you can fully show the work and gear in a scientifically acceptable form. Critical to pico-second high energy pulsing is the rep rate statement.
If we don't challenge you, the physics of it all will.......After you have spent a lot of time and money having a tilt at the pulsed power windmill.
For pulse discussion to continue, someone might start a new thread, as Carl noted.
Posted: Thu Dec 09, 2010 12:07 am
I had posted all before and that I was working with high energy pulses - which is my main activity and the reason for a 3 meter deep pond in my back garden for several years now.
My main cap bank is 10 off 25MFD 20kv caps. ( I can't lift one ) I had posted photos of same and of the copper bar used for transfer and of both thyratrons and spark gaps used and of a high energy sparkgap project built in a ISO 160 nipple for which Doug Coulter had got me two 2" graphite discs. for terminals. I have posted photos of my 22kv pole pig I got from Colin Heath and other high power high voltage PSU's over the years.
I use clamping and crowbar technics to reduce pulsewidth - To be clear, I will state I have achived single figure nano-sec pulses for large power runs (not all 4000 joules final after processing the pulse as most of the energy is dumped when clamped) and sub-nano for lower power runs - current work not disclosed - I have posted photos of my naval mil radar PFN rated at 27kv and kilowatt power and capable of pico-sec shapping- I can trigger down to single figure pico-sec and have 7104 and 7934 scopes ( 500Mhz actual storage) with front end amps of 1 Ghz bandwidth and timebase of 20 pico-sec/cm on the x10 which I have posted photos off also.
A microwave diode will easly clamp the o/p from a magnetron to produce pico-sec pulses - I can post it sometime if you want.
I can't describe other experiments I have conducted using Tritium or D2 sparkgaps etc. for legal reason and have never claimed to have produced Neutrons for legal reasons (in the UK it is illegal to produce any radiation without a licence - I can't join the Neutron club ). but have communicated these to other members in private. I can't post all the detail of my expriment to measure the dia of the poissor at less than 1 micron - I used a high energy pulse to create th poissor and I measured something at less than a micron dia. Anyone can do these experiments if they wish and then call me out rather than from the armchair
I have looked for the photos posted but they have gone If you realy want I will try to dig some of them out from my archieve. There is no board specifically for pulse work.
Lastly I simply replied to a newbie in this forum to encouraged pulse work I did not intend to extend or breach discipline - sorry!
Posted: Thu Dec 09, 2010 12:37 am
Thanks! Sorry for reviving an old thread, I didn't realize that i would end up getting off topic. I will start a new thread here (viewtopic.php?f=6&t=3101#p12611
Posted: Thu Dec 09, 2010 5:00 am
John, here's the big problem, in your own words:
>current work not disclosed
>I can't post all the detail of my expriment
>I can't describe other experiments I have conducted using Tritium or D2 sparkgaps etc. for legal reason
The law isn't about what you can and cannot describe, it's about what you can and cannot DO. Think about it. Your plain admission here, as well as previously, is that you have conducted experiments with neutron-emitting D2 spark gaps. You're freely providing what looks like advice to a "newbie" about that subject, and some other subjects, so evidently, you think you get to provide advice, represent expertise, and assert achievements on those subjects, this law of yours notwithstanding. This purported legal barrier conveniently only prevents you from making scientific disclosures according to our prevailing standards. (Except maybe to certain unnamed people off the list, as you tell it.)
>Anyone can do these experiments if they wish and then call me out rather than from the armchair
How can anyone do "these experiments" when you aren't willing to publicly disclose methods and results? That's the central conundrum here. And by methods and results, I'm not talking about photos of surplus equipment in your possession, but details of how you make neutrons with a spark gap, how you generate 4-kJ (er, "not all 4000 joules after processing") picosecond (er, I mean "single figure nano-sec) pulses, and so forth.
You know my schtick...I'm just trying to keep this a reality-based community.