Hey all,
I've been scrounging for demo fusor parts for the past month, and all I need now is a proper power supply. I have a neon sign transformer (the microwave diodes are in transit), but I still have some questions. I know from the forums that the fusor needs a DC power supply, but why? Would someone mind providing me with a physical explanation of why an AC current isn't sufficient? I'm a physics major who's taken some E&M and quantum, so I don't mind a technical explanation. I'm simply curious.
My second question: why does the power supply need to be variable for a fusor? Would someone mind providing me with a physical explanation for that question as well?
Thanks so much for your time,
Joe
P.S. I have a 10,000 Volt/30 mA AC power supply that I'm going to rectify.
Physical explanations for demo fusor power supply
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Joe Strehlow
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Carl Willis
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Re: Physical explanations for demo fusor power supply
Hi Joe,
A DC power supply is specified because by maintaining the grid at a negative potential with respect to the shell, it will attract ions that can collide near or within it at high velocities and fuse there. The conventional theory of fusor operation holds that energetic ions will be trapped in orbit around or through the grid until collision occurs. On the other hand, if you use an AC power supply, ions will be attracted to the grid in one half-cycle, while electrons will be attracted to it in the other. Presumably this positive half-cycle is useless at causing fusion, although ions born in the center in this mode will reach the wall with high velocity and the presumption may be inaccurate, depending on wall material, geometry, and gas pressure. Bottom line: there is no hard and fast rule against running AC, or against running DC with the grid positive, but conventional wisdom suggests that these modes are inefficient. When running AC, you are also likely to see asymmetric current flowing--higher in either the positive or the negative half-cycle.
Being able to control the output power or voltage of the HV supply is crucial to fine-tuning a fusor for good performance. An NST can be controlled inexpensively with a variable transformer (e.g. "Variac"). Resistive and inductive ballasts are also commonly discussed. Magnetic amplifiers and semiconductor phase controllers are some less-frequent options. Output control improves safety for both the operator and the equipment--you'll be able to vary operating power smoothly, beginning at zero, and as you increase power you can get a sense of what parts are heating up, what the radiation situation is like, etc.
Hope this is helpful.
Carl
A DC power supply is specified because by maintaining the grid at a negative potential with respect to the shell, it will attract ions that can collide near or within it at high velocities and fuse there. The conventional theory of fusor operation holds that energetic ions will be trapped in orbit around or through the grid until collision occurs. On the other hand, if you use an AC power supply, ions will be attracted to the grid in one half-cycle, while electrons will be attracted to it in the other. Presumably this positive half-cycle is useless at causing fusion, although ions born in the center in this mode will reach the wall with high velocity and the presumption may be inaccurate, depending on wall material, geometry, and gas pressure. Bottom line: there is no hard and fast rule against running AC, or against running DC with the grid positive, but conventional wisdom suggests that these modes are inefficient. When running AC, you are also likely to see asymmetric current flowing--higher in either the positive or the negative half-cycle.
Being able to control the output power or voltage of the HV supply is crucial to fine-tuning a fusor for good performance. An NST can be controlled inexpensively with a variable transformer (e.g. "Variac"). Resistive and inductive ballasts are also commonly discussed. Magnetic amplifiers and semiconductor phase controllers are some less-frequent options. Output control improves safety for both the operator and the equipment--you'll be able to vary operating power smoothly, beginning at zero, and as you increase power you can get a sense of what parts are heating up, what the radiation situation is like, etc.
Hope this is helpful.
Carl
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Richard Hull
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Re: Physical explanations for demo fusor power supply
Joe,
As you note, you are gathering parts for your demo fusor. All will be made menifest with the "hands-on" and the doing. Once you get your demo device going, you can experiment and see for yourself the issues with both operation of a fusor and learn a bit of real, hands-on, plasma characteristics. Such self study would demand a fully instrumented demo fusor where the input voltage and current could be closely monitored. As Carl notes, there is no law against using AC or reversed DC. As a matter of fact, no one has ever made a serious run at real fusion here with either of these seemingly bizzare suggestions.
Like Carl, I would doubt that you would approach the fusion results, if there is fusion at all, using these alternate methods than that which is seen in the conventionally biased fusor in normal use here. The obvious physics is against such alternate operational schemes and the science falls in line with the way we operate our fusors and has been proven highly successful in amateur hands.
If you ever get as far as doing real fusion with a device you fabricate at some future date, you might choose to be the first to experiment and report to us on the other two approaches.
All the best of luck in your efforts.
Richard Hull
As you note, you are gathering parts for your demo fusor. All will be made menifest with the "hands-on" and the doing. Once you get your demo device going, you can experiment and see for yourself the issues with both operation of a fusor and learn a bit of real, hands-on, plasma characteristics. Such self study would demand a fully instrumented demo fusor where the input voltage and current could be closely monitored. As Carl notes, there is no law against using AC or reversed DC. As a matter of fact, no one has ever made a serious run at real fusion here with either of these seemingly bizzare suggestions.
Like Carl, I would doubt that you would approach the fusion results, if there is fusion at all, using these alternate methods than that which is seen in the conventionally biased fusor in normal use here. The obvious physics is against such alternate operational schemes and the science falls in line with the way we operate our fusors and has been proven highly successful in amateur hands.
If you ever get as far as doing real fusion with a device you fabricate at some future date, you might choose to be the first to experiment and report to us on the other two approaches.
All the best of luck in your efforts.
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
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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Joe Strehlow
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- Real name: Joe Strehlow
Re: Physical explanations for demo fusor power supply
Carl, thank you so much for your explanation; it was most informative. And Richard, thank you for your input, and I do plan on producing a full fusor once I understand the intricacies of my demo device. Once I get my demo fusor up and running (hopefully within a week), I'll conduct some experiments with both AC and DC current. I'll post an update on these forums once my demo fusor is complete.
Best,
Joe Strehlow
Best,
Joe Strehlow
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Richard Hull
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- Real name: Richard Hull
Re: Physical explanations for demo fusor power supply
Of course, you realize that a demo fusor will tell you little about what current and polarity method is best for fusion. On AC you will see a rather diffuse and worthless glow. With DC current applied as normal with a negative central grid and positive, grounded outer grid you will see the central plasma ball characteristic of ion centralized collision. All this is assuming you can drag the demo fusor down to about 25 microns or lower.
Richard Hull
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
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