Archived - Fusor setup - Almost ready for first light!!

[benbartlett]

Hi everyone,

I've made so much progress these last few weeks - it's hard to believe that after all these months, first light could very well be this week. I made a gas feedthrough, as you can see attached the small 2.75" CFF. I basically drilled two small holes in the blank and cold-welded two UHV flex hoses to it. It saved me about $300 for a Conflat Gas feedthrough. I'm going to add a VCR valve to the end of one of the feedthroughs, and one will go through a calibrated leak, as you can see in one of the pictures.

People generally seem to really like viewports here, so I went a little overboard and got a 6" Conflat viewport. It looks awesome, but I will probably end up mowing a gazillion lawns to pay for it. =] I also added almost all of the needed blanks this week.

I double-grounded the chamber and positive supply through separate grounding rods. (A cable from both the positive supply and the chamber leading to each rod.) The transformer will carry a grounding wire to the Variac's grounding bolt, which will be grounded through the wall socket. Just for clarification - the positive supply and chamber will be grounded through two grounding rods; the transformer's grounding base, not the positive supply, will be grounded through the outlet along with the variac. I haven't insulated the accellerator grid stem yet, but I should probably get around to adding a quartz or ceramic insulation when I start using higher voltages. The current transformer I have connected to the apparatus will get it up to 15kV, not enough for large amounts fusion, but good for a start. The rectifier will handle up to 20kV@200ma, and the wires are rated for up to 40kV. I purposely made it expandable, so I could, if able, use higher voltage equipment without needing to replace a lot of parts. Transco, a neon sign company near us, has a neon sign "cleaner" - a powerful HV DC power supply used to, in their words "scrub the tubes with a powerful current". They said I could use some of their equipment while they're not using it. (Hello high voltage!) Hopefully I should be able to experiment with pulsing soon.

In case anyone saw the label (I took a piece of packaging tape and used a Sharpie on it) that says T.E.R.A.: Whenever I put a lot of work into something, like my reactor, I have a habit of giving it a name or acronym. T.E.R.A stands for Thermonuclear Electrostatic Reactor Apparatus. Any feedback/suggestions? I also kind of like the name, because my personal goal is to, before my senior year in high school, get my reactor to produce 1TeV per second. (TeV => TERA-electron volt -- get it?) Any and all feedback is appreciated. Hopefully first light by the end of the week.

By the way, how old is the youngest member of the plasma club? Would I be the youngest at 14? (DOB 10/20/94)

First light, plasma, and fusion to follow.... =]

Ben

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Also, because I was wondering about this but don't really want to start another thread right now, does anyone know where I can get a good bubble dosimeter? A URL or email address would be nice.

[Steven Sesselmann]

Ben,

That is a superb looking setup, you must be excited about powering up.

Richard will be the one to confirm the age record, but at 14 you have done well, and you are clearly miles ahead of your other class mates in physics.

Good luck..

Steven

[Carl Willis]

Hi Ben,

This is a fine-looking collection of vacuum hardware, suitable for a wide repertoire of projects including a fusor. Your efforts so far are top-notch...keep up the good work.

>I double-grounded the chamber and positive supply through separate grounding rods. (A cable from both the positive supply and the chamber leading to each rod.)

The chamber must be grounded for safety, and the positive supply lead should be connected to the vacuum chamber directly via a short, durable connection to provide a current return. It's unclear if you are relying on a current return path through the ground, but you shouldn't be... Keep in mind that your neon transformer is center-tapped and the tap is tied to the case. The positive end of the rectifier bridge is thus defined at a high positive potential with respect to ground. You CAN NOT tie this positive output to ground (well, you can, but you'd be shorting out your NST). It will have to be left floating in order to enable you to use the negative end of the bridge on the fusor grid.

>Transco, a neon sign company near us, has a neon sign "cleaner" - a powerful HV DC power supply used to, in their words "scrub the tubes with a powerful current"

This sounds like a bombarder unit. Like pole transformers, they're lethal on account of the enormous current available. Unfortunately for fusor use, the voltage available seldom exceeds what comes from a standard NST. You cannot have any errors in the wiring when you set up with such a supply. They will melt equipment, start footlong arcs, and of course kill you dead in a perfunctory manner. The mentorship of Transco people is a great thing, but note that their equipment may not be appropriate for advancing non-destructively toward a goal of fusion.

>T.E.R.A stands for Thermonuclear Electrostatic Reactor Apparatus.

Strictly speaking, "thermonuclear" has a meaning that is at odds with what typically happens in fusors. It implies that the fusion is occurring in a thermal plasma (e.g. the reactant particles are in thermal equilibrium, have a Maxwell distribution, and a high enough bulk temperature). IEC discharges don't meet the definition.

Good work, and you might check through your power supply scheme once more to be sure it will work and be safe.

-Carl

[benbartlett]

Hi Carl,

Okay, now I'm a little confused. (And worried that there might be an error in my reactor system.) When I first started this project a long long time ago in a garage far, far away, I based my design off of Richard Hull's fusor schematic. Maybe I am reading this wrong, but it looks like the positive supply is grounded along with the chamber. (See picture #1 below - Richard Hull's fusor schematic).

"The chamber must be grounded for safety, and the positive supply lead should be connected to the vacuum chamber directly via a short, durable connection to provide a current return. ......... You CAN NOT tie this positive output to ground (well, you can, but you'd be shorting out your NST). It will have to be left floating in order to enable you to use the negative end of the bridge on the fusor grid." ------ Won't the positive supply being connected to the chamber, which is grounded, in essence ground the positive supply, or is it basically forming an electrostatic potential difference to the negative supply? If I am understanding you right, is the correct schematic one of the following? (Either image #2 or #3) Could you correct me if I am wrong? Image #4 is my current fusor schematic.

About the Transco electrician: I didn't really know exactly what he was describing. I would, of course, look into further into its stats before connecting it to the reactor, but I had heard "high voltage" and counted it as a possibility for fusion voltages.

I kind of figured thermonuclear wasn't completely appropriate, but it was really all I could think of at the moment. (Better than deuterim electrostatic reactor apparatus - D.E.R.A ?!?) =]

I am really appreciative that someone has pointed out a potential error in my schematic. I am definitely going to hold off testing until I get this straightened out. (Just when I thought it was finished. =] )

Ben

P.S. If there is an error in my schematic (Image #4) could you please email me/post in this thread. A picture schematic would also be helpful.

-------------------------
Image #1: Richard Hull's fusor schematic
Image #2: First schematic, from what I understand, you could be suggesting.
Image #3: Second schematic, from what I understand, you could be suggesting.
Image #4: Simplified version of my current schematic. (Electrical system only.)
Image #5: The HV Rectifier I'm using

Sorry for the cheap MS Paint images; hopefully they're decipherable.

IMAGES REMOVED TO PREVENT POSSIBLE CONFUSION AT REQUEST OF MR. BRADLEY. -BEN

[Carl Willis]

Hi Ben,

Please recognize that Richard's schematic is generic. It's correct in that it depicts the positive side of the generic supply grounded. But in the specific case where you have a neon transformer with a rectifier bridge attached, the problem is that there are two positive outputs with respect to the HV negative output--the grounded center-tap of the secondary, and the positive HV output from the bridge. In this circumstance, the positive end of the supply that is grounded is already chosen for you by the transformer's construction. It is the center tap of the transformer.

My own MS Paint doodle is attached. In the doodle, I put a gray line around the physical contents of the NST box for clarity. I also show the positive side of the rectifier bridge in broken lines because these two rectifiers don't accomplish anything for you in the fusor circuit. (They do present you with a +HV output if you have other uses for positive high voltage and might be worth putting in, but you only NEED the two on the negative side). If you connect your +HV to ground, short-circuit current will flow through the transformer windings and back through the secondary center tap, preventing you from getting any voltage at the -HV. Your Image #3 is closest to correct. One implication of this is that if you have a 15 kV transformer, your useful DC high voltage between grounded center tap and -HV output is only 7.5 kV rms. Only half the secondary winding can be in play at any one time.

The discussion has been at the conceptual level--implications of the NST center tap, and what the rectifier bridge accomplishes. Now we come to the issue of how you wire this up in practice to effect safety and reliability. The safety issue is that if the connection between the chamber and ground potential is ever broken, the chamber may be dangerous to handle because it can rise to an arbitrary HV potential. So the chamber must be grounded robustly to a well-defined ground electrical point to ensure your safety. The other issue is that current must flow from the positive side of the supply (NST case, for you) to the chamber. You don't want to rely on flaky earth grounds or long ground paths through household wiring to furnish the current path. You want a short, direct wire connection in the interests of limiting RF radiation, noise, GFI tripouts, and "unexplained phenomena" around the house. So the chamber is grounded for safety, and the current return from power supply to chamber is a short, direct wire. It is also fine and appropriate to ground the variac case and the NST case to the household electrical ground as you show.

Making more sense?

-Carl

[Chris Bradley]

Ben Bartlett wrote:
> Okay, now I'm a little confused. (And worried that there might be an error in my reactor system.)
This should stand as a clear message to anyone using kV transformers in 'trial-and-error' set-ups.

If the HV+ had been tied to earth, as you planned, and if also you'd left the NST ground unearthed, as per your diagram #2, then you'd have pushed the NST case down by that kV amount, which would likely kill you dead if you got too close to it. Alternatively, the now-pushed-down NST centre-tap (and exterior) would've likely shorted across to your mains (as those parts of the NST aren't rated to hold that voltage off the mains inputs) and then you'd have made your whole house live to the tune of a few kV, at least for a moment until something gave out whilst that pulse ran its course back to the chamber, via the ground route and/or via somewhere-or-other.

Perhaps you could re-edit your images with a big red cross through them, to avoid anyone thinking those are how to do it. You can leave the 2nd one up, with an extra connection from the NST centre-tap earth to the chamber.

It has to be a recommendation to you that you do not power up until some 'sign-off' by someone with suitable competence. No matter how experienced or professional one's status, this is good advice in any freshly-wired-up kV situation anyway. Comments from a forum cannot be a substitute for someone overseeing the kit on-site.

[benbartlett]

Hi Carl,

Thank you again for your effort in helping me sort out these electrical issues. I attached some modified photos of my electrical schematic.

A few more questions:

"But in the specific case where you have a neon transformer with a rectifier bridge attached, the problem is that there are two positive outputs with respect to the HV negative output--the grounded center-tap of the secondary, and the positive HV output from the bridge." --- By center tap (see photo #1), do you mean the prong with the grounding label on it? And how is that a positive output? I thought that the prong grounded the NST's case.... And will that ground work with only a wall socket ground, or do you need a grounding rod ground? (Speaking of grounding rods, my dad has a 12' copper grounding rod. I know the American Electrical Agency, or whatever they're called, defines a ground as a rod driven 8 feet into moist ground. Is that really nessecary, or is 4 feet enough for a safe ground? We were going to split the rod in half to create a double ground for the chamber.) Also, could you clarify what you mean by "there are two positive outputs with respect to the HV negative output"? Are you defining a ground (neutral) as positive relative to the negative supply, such as the grounding prong (center tap?), or do you literally mean there are two points where positive voltage is emitted?

"The other issue is that current must flow from the positive side of the supply (NST case, for you) to the chamber." --- Do you mean that the chamber must be grounded through the NST case to a copper grounding rod -- earth ground? (See image #2)

"One implication of this is that if you have a 15 kV transformer, your useful DC high voltage between grounded center tap and -HV output is only 7.5 kV rms." --- Could you clarify this a little? And what does rms stand for and signify?

Thank you so much for your input.

Ben
-------------
Image #1: picture of the AC input (with one output visible in upper right) of the NST, with a grounding bolt with white and red label (grounding bolt assumed to be the center tap)
Image #2: Understood schematic of what you are describing
Image #3: Revised schematic of my fusor
Image #4: Close up of rectifier on my fusor

IMAGES REMOVED TO PREVENT POSSIBLE CONFUSION AT REQUEST OF MR. BRADLEY. -BEN

[benbartlett]

"It has to be a recommendation to you that you do not power up until some 'sign-off' by someone with suitable competence. No matter how experienced or professional one's status, this is good advice in any freshly-wired-up kV situation anyway. Comments from a forum cannot be a substitute for someone overseeing the kit on-site."

I agree. That's why I first was running the design through the forum, and will have someone (preferably an electrician) check the design first. I'll come back to this thread after first light and cross out the faulty designs and post my final schematic. I concur in not wanting anyone, such as myself, to misinterpret the schematic. However, I doubt that it would have killed/hurt me, because the only part I would be touching would be a plastic variac handle, having already backfilled and pumped down the chamber with the corresponding gas.

I do appreciate your concern and suggestions, however. Thank you.

Ben

[Chris Bradley]

Good. Glad to hear you'll get someone to check on it. It looks a supreme effort for a 14-yr-old so far, so don't let me put you off. Only, I would suggest it's not enough to *doubt* that you'll be killled, better that you know there is no reason that you will.

My parents left me to my own devices at that age - and I electrocuted myself with the mains more than once! If I'd been left with a kV transformer, maybe I'd be dead now!

Good luck with the experiment, but safety first.

[Carl Willis]

Hi Ben,

The center tap of the transformer means a wire that comes from the middle of the secondary winding, and goes to the transformer case. The ground terminal in the photo is the transformer case ground, so it is indeed electrically tied to the center tap.

If it were mine, I would run a piece of durable stranded wire from this lug directly to the fusor chamber and secure it via a ring terminal and one of the ConFlat bolts. You have already attached a three-conductor cord to the transformer. When the cord is plugged in, the case will be grounded to the home electrical system. I would be satisfied with that level of safety myself. For additional safety you could ground the chamber to a cold water pipe, the ground bus in an electrical distribution box, or a dedicated earth ground, but there's no need to carry it too far.

>"One implication of this is that if you have a 15 kV transformer, your useful DC high voltage between grounded center tap and -HV output is only 7.5 kV rms." --- Could you clarify this a little? And what does rms stand for and signify?

When you carefully examine the current path in the transformer-rectifier-fusor circuit at any instant, current is only flowing in half of the transformer secondary. It flows through one rectifier, through the fusor, and back to the center tap, completing the circuit. A half-cycle later, current will be flowing through the other half of the secondary and the other rectifier. But you only get to use half of the transformer at a time, cutting your available voltage in half. That's how the center tap punishes you.

The maximum voltage of your NST under very light loads across the ENTIRE secondary is 15 kVAC, rms (root-mean-square). This concept is very often used to define the voltages or currents in AC equipment. RMS voltage means that the average power delivered into a purely-resistive and ohmic load of resistance R--the time-averaged value of V^2 / R--is the same as if a DC voltage of 15 kV were applied to that R. Of course in an AC waveform the voltage has time-changing value. Some math can show that the peak voltage is equal to Vrms * SQRT(2). Divide this by 2 since you are using only half the secondary at a time. The maximum voltage your NST can supply to your fusor is thus 10,606 V. You would approach this maximum by adding filter capacitors on the output of the rectifier and drawing little or no current in your fusor. Any time you draw current from an NST the voltage drops precipitously. This phenomenon is discussed in the NST FAQ by Richard Hull.

I think you're getting there.

-Carl

[benbartlett]

Hi Carl,

Thank you so much for clarifying that. I'm excited about (sometime soon, once I have the schematic/circuits checked) running it, but I'm a little unnerved that there was this gap in my knowledge. I'm going to wait probably until next week to run it; I want to make sure the reactor is absolutely safe before running it.

I think I pretty much understand where I was going wrong, but I have a few more questions.

"You have already attached a three-conductor cord to the transformer. When the cord is plugged in, the case will be grounded to the home electrical system. I would be satisfied with that level of safety myself. For additional safety you could ground the chamber to a cold water pipe, the ground bus in an electrical distribution box, or a dedicated earth ground, but there's no need to carry it too far." ----- By this do you mean that the chamber will be safe to ground solely through an outlet? I had asked that question earlier, back when I first joined this site, and most responses were to always use a dedicated earth ground, and that grounding it only through an outlet would send a shock through the outlet and kill everything on the same AC line...... I don't quite understand their logic, but I would definitely like to play it safe nevertheless. Do you mean by this statement that it would be safe to ground only through a wall socket?

I always thought the root mean square was used primarily in mathematics and stats, not in electrical engineering! (Gives me something interesting to tell my math teacher! =] ) My Prob+Stats book had mentioned it briefly, but I had always thought it was relatively exclusive to math.

Finally, this is my current corrected schematic. Would you mind "proofreading" (for lack of a better word) it, and trying to spot any errors? I would truly appreciate it. Thanks. Could you also, if it's not too much trouble, post a doodle of your electrical schematic for your fusor?

Thanks everyone - you all have helped me so much with my project.

Ben

[Squidhat]

Cool! Pretty fancy setup. When are you gonna add the positron emitters and the helium (or possibly lack of helium) detectors?

[Tyler Christensen]

That schematic looks fine. It will definitely make plasma but I have my doubts about getting any neutrons out of it.

Also to save on rectifiers, you don't actually need the two leading to the positive float since they don't do anything except, well, float. This doesn't matter/apply if you have a single bridge rectifier containing all 4 diodes.

[benbartlett]

Ok, good to know.

I had already gotten a pack of 5 diodes, so I went ahead and put them all together, just in case I wanted to use it somehow; I had already had the pieces. Also, the first step before fusion is obviously plasma. I would like to achieve fusion before the end of the year, but I wasn't planning on using an NST for it. =]. Thanks for the tip, though.

Ben

[benbartlett]

Hi squidhat,

I sort of gave up on the positron project a few days after I posted it on the site. I was really just playing around with some spare parts I had, trying to see what I could come up with. Also, to save costs I'm only going to start with bubble dosimeters, then possibly move on to helium detectors.

Ben

[Richard Hull]

Coming very late to this discussion which should not have taken place here at all, but in the fusor power discussion forum.

Carl is right; my diagram was generic. Power connections related to ground should be short and only one single point actually grounded, and that is at the chamber only. This is a "star ground" system. One ground and all other grounding points radiate from it and it alone. This warrants minimal ground loop issues with instruments and other electronics provided the star or radial grounds are short, fat and secured to the same bolt on the chamber that your real, honest to God ground is attached.

Neon transformers and their respective hook ups can be a bear for neophytes to wrap their brains around, especially with the money saving,center tapped,case ground that all of them possess and the possible electrical issues and dangers it can create if not addressed properly. All of this has been addressed in some detail in past posts.

This past post is the circuit you might really use.

viewtopic.php?f=11&t=4405#p27243

Richard Hull

[Carl Willis]

Hi Ben,

Sorry to be late in responding. Once again, I've been on a trip where I had limited access to the Internet.

Your schematic looks good.

>do you mean that the chamber will be safe to ground solely through an outlet?

Yes. You can ground the chamber itself IN ADDITION to the connections shown on the diagram for added safety. This would not be a bad thing to do.

>grounding it only through an outlet would send a shock through the outlet and kill everything on the same AC line

I recall a number of discussions where the new experimenter apparently intended to actually complete the HV circuit through house wiring. I don't know if you came on board with that idea, or if I am mostly remembering others. There are problems with that approach: transients in the HV load (the fusor) will couple energy into the house wiring and perhaps sensitive appliances that are attached; the path is not guaranteed to be electrically short or have a low impedance; there could be lots of radiated or received noise; GFI interrupters in most new home wiring will trip out. I also remember someone's recent suggestion that the positive output from an x-ray supply be tied to the outlet ground! Like NSTs, x-ray trannies are center-tapped, so that particular suggestion would have caused current to flow and voltages to develop in house wiring.

Your plan looks good for now. Keep us updated.

-Carl

[Tyler Christensen]

Now I'm wondering about my x-ray setup... Is my attached schematic safe? The transformer has 2 independent secondaries that I linked together to make a center tap at the center of the transformer that I allow to float. Is there sufficient insulation at the center of the transformer to avoid an arc between the secondary's floating center tap and the primary? It's of course under oil. I've pushed it to about 35kv on the secondary so that was about 18kv on the center tap and didn't have any problems.

[Dustinit]

The centre tap will probably not be the breakdown point.
You neglect to say if you have tested with the bridge in circuit and ground connected to the bridge or it is open circuit secondary voltage.
The difference is that AC secondary voltage is +/- 18kv on the secondary open circuit ends of the secondary.
With the bridge and ground in circuit the secondary output is 0v -35kv. This is when it will breakdown secondary to primary if insulation is insufficient.
Also your diodes have to withstand 18kv reverse voltage.
You have not given enough information about the test or components to determine if breakdown may occur.
Dustin.

[Tyler Christensen]

I see what you mean, I have run it up to about 25,000 DC past rectification with the positive end grounded. It was in active use on my fusor so that should verify how it was configured. The 35,000 test was just plain old AC which you're right, wouldn't cause any breakdown. Would it be wise to rewire to use only one of the secondaries?

It seems to me, however, that I have it configured how it would be used in an actual x-ray power supply. They have only one HV power output which means one end is grounded at the transformer. Unless they float the center tap like I have, this means they "waste" half the secondary of voltage doesn't it?