FAQ - Operation - Visual analysis, qualitative

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Richard Hull
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FAQ - Operation - Visual analysis, qualitative

Post by Richard Hull »

Virtually every fusor made, from demo fusors to neutron producing fusors, have some sort of view port. This allows visual examination of the central grid region and the de-excitation plasma glow zone during, startup and operation.

For the demo fusor, which is often used as a school science project, the view port allows judges and others to observe, first hand, the workings of the device.

Novice fusor builders can also learn a lot related to pressure-vacuum-voltage regimes by observing their first light plasma regions.

Fusioneers actually doing fusion, can also tell when the prime situation exists for fusion as well as monitor relative grid temperatures. This will help stave off possible catastrophic grid failure, etc.

The following will help catagorize the various visual perceptions observered.

Beginners:

The beginner fusor builder classically suffers from poor or uncalibrated, first pass, vacuum gauges. As such, they often report low readings on the gauge while the images supplied show obvious much higher pressures.

At pressures from 50torr down to 1 torr, the entire inner grid wire system is glowing and often enveloped in a dim hazy glow. NOTE: It is common for brand new grids to sputter off trash, grease and small nicked areas. This appears as an early fireworks show in the virgin demo fusor. We see bright sparks and small flashes all over the grid through the view port. This interesting display subsides rather quickly never to return.

As you dip below one torr and especially below 500 microns, the grid glow decreases and, ultimately, goes away. A large central glowing purple-violet-blue ball is formed.

At just below 100 microns, the ball starts to shrink in size and a single jet will come out of the side of the ball and once outside the grid, will fan out broadly. This is referred to as a "bugle jet".

As the pressure get to 50 microns and below, a lot more voltage is needed to sustain the discharge. The bugle jet starts to lose the short,wide fanning bell and become more slender and get longer but still fans out slightly.

As more voltage is added and the pressure drops to 25 microns or below, the now very narrow jet impacts the edges of the fusor. New additional jets may start to become visible and even dance around the central plasma ball through various grid openings. more voltage is needed and some mild red glow of the grid wires can be seen as it starts to heat.

Below 15 microns, most fusors will start to enter what is call star mode. Multiple, stable, fine rays will be seen to issue, one from each grid opening, as a rule.

For demo fusors, this is the ultimate and final point, showing that the vacuum is clean and the pressure from the mechanical pump is just about as low as it can go. If more voltage is added, the visual image of the star gets more vivid and brighter, but the grid starts to heat considerably and can glow almost white hot in extreme cases. Usually, before white heat begins, electron runaway, (runaway ionization), occurs forcing an immediate reduction in voltage to avoid melting the inner grid. Working in this mode with a very hot grid, but just short of runaway is a prelude mode to real fusion and is referred to as glow cleaning mode. In a demo fusor it may act to lower the pressure a few more microns, if continued.

It is very rare, and I have never seen it happen, but a new, high conductance mechanical pump with a zeolite type trap may lower the pressure enough to cause glow extinction in a demo system that is running with a limited, upper end high voltage supply. This can happen at 4-5 microns, (5X10e-3 torr), in air based demo systems.

Advanced Fusioneers:

Folks going beyond the demo stage have already dealt with the above in most cases and have used the above visual data to "glow clean" their fusors after maintenance or takeapart, for whatever reason.

Thus, they know that once star mode is achieved around 10 microns and the glow is stable, it is now time to turn on the diffusion or turbo-molecular, secondary vacuum pump.

They also know that once they valve open the secondary pump, the glow will immediately extinguish and all visible trace of anything will go away as the pump empties the chamber down to 10-5 to 10e-7 torr. This is "gauge country" and you really need a deeper reading gauge here. Once down at your base pressure, it is time to let in D2 back up to glow mode again. This usually begins at about 6-8 microns with flowing D2 gas, but in a recently re-sealed or new system it might begin at 4-5 microns until some current at high voltage has cleaned and buried a bit of that flowing D2. For systems that are used frequently and that have remained sealed well. the D2 may not even glow until 35kv is applied and the pressure is above 12 microns!

D2 gives off a ruby red glow to the eye and is quite different from the air glow seen in a demo system.

As the fusion regime begins, and until you are in the region of 25kv and above, the fusion star might have a large central ball of about what might seem to be 1/8 to 1/4-inch in diameter. Red star rays will be seen and the grid may be uniformly heated and glowing quite hot all over the wire.

As things settle down, the pressure and voltage can be slowly raised to whatever operating regime you desire. If an audible neutron counter is at hand the clicking will increase noticably and especially if the central star has a "pinpoint", micro centeral dot or even no real dot at all. At this point, in the 14 micron range and with voltage above 30 KV, the grid will actually cool except near the ray streamlines where they penetrate the wire grid openings.

This is the point where the real fusioneer has "arrived" and is limited solely by his power supply and the ability of his system to withstand more voltage and current! More power and more pressure will just increase fusion, but the grid may start to show more uniform heating as you go over 45-60kv.

A word of caution:

It is most important that direct viewing with the human eye, looking directly into the port should NOT be undertaken.

Above 10kv there is a possibilty of x-rays being emitted from the port through the glass. At 20 kv a geiger counter is roaring at the glass. Above 20kv neutrons are also deeply in the mix.

The eye is the most sensitive organ of the body to radiation! Do not risk your eyesight!

Use a mirror at 45 degrees and view with a small telescope from a safe distance. Better still, purchase a small color video camera, (<70.00) and view remotely from a video monitor.

Images of all of these modes may be appended to this post in future.

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
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