Fusor Forums

About two and a half months ago I decided to build a fusion reactor for the fun of it and as something to do over the summer before college. I've designed the reactor to be relatively portable and so that it can be remotely operated and monitored from up to 100ft away (although the deuterium line, pumps, and vacuum gauging have to be setup at the reactor beforehand). This is just the beginning but here is my progress so far:

Vacuum Chamber
The main chamber is MDC 8" CF, with 2.75" CF ports connecting the feedthrough, gauges, deuterium line, pump line, etc. The main 4-way cross has an 8" window and an 8" chamber door. Once I install the deuterium line and build a steel structure around it I will integrate the electronics and secondary systems to make it one portable unit (2-3 guys could pick it up, it'll probably need wheels). Vacuum Pump Line
Pfeiffer TPH60 60 l/s turbopump with TPG121 controller. Seems to be in great condition although I don't know the bearing condition (the blades do spin freely) or oil levels. The backing pump is a 3cfm two-stage, nothing special but it should get the job done. EDIT: "nothing special" is a bit of an understatement so I'll be upgrading it to a Pfeiffer Duo 016 B

Control Center
Variac to control input to the x-ray transformer, e stop button, neutron count monitoring, and multi-feed camera viewing. Neutron Detection
I'm using a soviet He3 detector tube connected to a pc digital oscilloscope and corresponding software. I'm getting average background counts of 5-7.5 cpm on average, and gamma rejection seems to be working well. Grid
I've been planning to test a variety of different grid designs, so I'm building a "hotswappable" mounting system where grid designs can be changed in seconds, also thanks to the 8" door. Vacuum Monitoring/
A pfeiffer balzers PKR251 compact full range gauge (cc + pirani) relays to a pfeiffer singlegauge controller. At atmospheric it always reads around 20 torr. Could the gauge be malfunctioning? ... it has a small dent on the magnet housing. Power Supply
I still have to build a power supply out of the xray transformer. While my wiring and connectors are rated to 75kV the chamber feedthrough is a standard 30kV. Is it possible to modify it to take 60kV?
EDIT: Deuterium Line
The deuterium line includes an electrolysis unit of Andrew Seltzman's design, a drierite stage, a micron filter, a 1 liter storage tank (might also add a 500cc tank) and two needle valves to regulate flow. And here are some construction pics:

Wow. That's an amazing collection of professional-level parts, especially for a high school student. Not sure if you pulled that off with amazing scrounging, piles of money, or good connections with the right people.

Although rectifiers aren't very complicated electronics, it seems you haven't quite figured that out yet. Your proposed schematic is a bad mishmash of two different kinds of full wave circuit. What you have drawn is a full-wave short. You only want the two diodes on the left side of the diamond pattern you have drawn. The right-side two should be deleted. Although each of those two remaining diodes may need to be a series string of diodes to tolerate the full voltage (I think it was probably 120 kv from your earlier posts).

Good luck on your process. You'd probably do well to get some mentor guidance on the HV supply.

First and foremost, read the FAQ's related to powering a fusor and read some basic electrical theory on diodes and how they work. Not understanding now to create a diode bridge demonstrates you need to study these topics more closely with the goal of understanding what and why these circuits work the way they do. A very high voltage and current rated fusor grade supply is absolutely deadly - no second chance - one error and that supply will kill.

Looks like you do have a lot of very high quality components and will be looking for a power supply soon. To get a correct supply, both read the FAQ's on that topic and do ask questions here. Looks like you have the makings of a successful system. But one needs a successful approach which means getting both knowledge and experience. Best of luck!

Thanks guys, and I've updated the XRT schematic.

A minor point: In the diagram, that "V" for the meter should be an "A" since that will be your current measurement device for the x-former (Yes, the 'V' could be a voltmeter in current mode.) Just being clear so you know that is not how the x-former's voltage is read. That requires a voltage divider on the high voltage side unless the x-former is one that offers a low voltage following circuit.

If you have resources, consider a high end leak valve for the deuterium gas line inlet to the fusor - mine works great and allows me to set micron steps in deuterium pressure in the fusor (of course, my gate valve opening has a big impact on that as well.) The larger valves you show will not offer enough fine control to easily control the pressure.

Also, remember that copper sealing rings can generally only be used once so keep extras on hand.

Yeah, I'm using an extra multimeter for the current.

That type of valve is great, but won't these needle valves offer similar precision? About the gaskets, I may have used some multiple times, although the flanges weren't torqued down fully. If this causes a leak I'll know about it soon.

>> In the diagram, that "V" for the meter should be an "A" since that will be your current measurement device for the x-former ...

I respectfully disagree with Dennis here. Schematic shows a 100 ohm current sensing resistor (a.k.a. ammeter shunt) in series with the HV circuit. We measure the voltage drop across that resistor with a voltmeter, which ideally carries no current. It's correctly rendered with a V-meter symbol. The associated label on the equipment front panel, or printed meter scale, belongs in the schematic as a note. Should not affect the choice of an electrical component symbol.

Josh _could_ use a panel milliammeter, or a multimeter in mA mode, connected in parallel with that 100 ohm resistor. In fact it would read more accurately if it simply replaced the 100 ohm resistor. Speaking from experience, I bet the meter would be damaged or destroyed when the first unplanned spark or arc happens elsewhere in HV circuit.

Consider the analogous case of this milliammeter, when applied as a kilovolts indicator. In schematic diagram it's an A-meter, with value "1 mA FS". Schematic will also show the multi-megohm resistors that set the scale. For the A component, schematic can show its part number, and/or a note that says it's the kilovolts indicator. Sadly, there are newbies who have bought things like this on ebay and connected them to kilovolt sources.

Josh _could_ use a panel milliammeter, or a multimeter in mA mode, connected in parallel with that 100 ohm resistor. In fact it would read more accurately if it simply replaced the 100 ohm resistor. Speaking from experience, I bet the meter would be damaged or destroyed when the first unplanned spark or arc happens elsewhere in HV circuit.

Not only would the meter be destroyed, it would put the whole system in a very hazardous condition, as the ground return to the power supply would now be open. This is why a 10 or 100 ohm 10 watt resistor should be used for the current sample. During normal operation it won't be dissipating that much power, but during a fault condition, such as a chamber arc over, sizable current will be passing through it during the arc.

The valve you picture does not appear to offer very precise control; a high end valve will have a rotary knob and vertical scale and look very much like a micrometer (it has a very fine needle valve control.)

I concur with the posts that a voltmeter can be used; however, I use a protected milli-amp meter and shunt it - however, that can be tricky (to design) but on the other-hand, it gives me direct readings on my current. I use a 10 Mega-ohm (6-inch long and under oil) resistor before the meter/shunt (ground side of one of the HV x-former outputs) to prevent having to deal with any dangerous high voltage. If either the meter or shunt fails, no real issue. But the shunt is very high wattage so that isn't likely (the meter is easy to replace but even with massive swings of my plasma, the meter has been fine.)

A fine point......All d' Arsonval meters are current meters only as they deflect by magnetic action and this demands a specific current flow to make the meter needle deflect full range. We usually refer to the meter based on is manufactured printed scaling, voltmeter, ammeter, wattmeter, etc. All good meter manufacturers, regardless of printed face scaling, will usually place the meter's full scale, (FS), "current value" down low, out of direct view, just below the glass base level. Look for it by peering down on the lower left or right side of the printed scale through the glass. It might look like..... FS 50ua or FS 1ma, etc.

Once armed with this key info you can make the meter into most anything you wish. A voltmeter is made by adding a series resistor and an ammeter is made by adding a paralleled resistor. The values are determined mathematically using very simple math.

If you are smart, you can use the existing scale provided you figure the resistor to match the printed deflection range. (A 0-100ua meter can easily be made into a 0-100 volt voltmeter or a 0-100ma current meter.)
Of, course you can go through the tedium of making up a nice new scale by opening the meter and printing your own scale, then gluing it over the old scale. (A possible, but usually terrible, idea.)

Richard Hull

A lot of good info there.

I've got college starting now so my free time will be limited, but whenever you hear from me next I'll probably have some fusion tests to show. There's still plenty to do, namely new kit coming in and a minor chamber redesign.

Joshua Turbyfill