In this space, visitors are invited to post any comments, questions, or skeptical observations about Philo T. Farnsworth's contributions to the field of Nuclear Fusion research.
Subject: What you should see!
Date: Sep 23, 09:35 am
Poster: Richard Hull
On Sep 23, 09:35 am, Richard Hull wrote:
I feel that we should discuss what to expect from the fusor visually, especially with Joshuas nice photos and attendant questions.
I have recommended a demo fusor be constructed first in order that the neophyte become familiar with the optical phenomena associated with ionized gases. Joshua has done just that. The great thing is that if you plan well, you can use the demo unit as the actual deuterium fusor without having to remake the system.
Most of us start off with really crappy vacuum systems because that is what we cobble up quickly. This is captured on my fusor video as you see me slap that first system together only 2 weeks after I see my first fusor. I lament the fact that my vacuum is only 50-100 microns and hail the attainment of 40 microns as a big event! Yes, Joshua is there now. it is important to sequester yourself in the darkened room and sit and stare at the central ball of ionized plasma as you run the full range of peressures and voltages. If you are half a scientist, you will run out and get at least two good books on ionized gases. (One of the best is Ionized Gases by Von engels - American Vacuum Society "classics" series.)
The eyeballing of a process and the absorption of delicate optical changes will teach volumes especially when bounced off of the reading material. (remember labs)
I have several gauges and I can now tell more about the vacuum and what is going on by looking at the plasma than reading the sluggish TC (thermocouple) gauge.
Joshua is looking at things and seeing losses in polar jets. Most of what he is seeing is just hot ions and electrons escaping the intense temperature of the core and colliding with other gas atoms in the still dense gas at 100 microns.
This will happen far less vividly once he pumps out about 1 more order of gas molecules (10 microns).
The visual part:
The central plasma at 1mm (1000 microns)is just a simple glow discharge and is pure purple. With higher current a ionized gas shell can be seen just around the inner grid with delicate but noticeable jets exiting from every opening in the grid of very short length.
At 500 microns the image is still pretty purple but the outer shell may expand outward into the inter-grid region. At the same time, the ball in the inner grid begins to collapse and intensify.
As 100 microns is attained, the jets intensify and lengthen slightly and the plasma ball starts getting blue or blue white. The bugle jets are ions and the central core is an electron stream. There may be several beams hopping around looking for electrostatically fortuitous paths out of the central plasma ball.
As pressure is lowered towards 50 microns, the bugle jets begin to optically disappear. The electron beam narrows and lengthens as the mean free path starts to really step out. At lower currents the E beams can be seen to focus and vary most dleicately along the shaft. As small as a 3-5 micron pressure change can start to radically affect the beam at certain fixed currents.
This is the old "discharge tube" idea which used to be so common on early vacuum systems. The old vacuum heads of yesteryear could monitor their vacuums just by viewing this attached tube! It took lots of experience to visually gauge a vacuum by discharge, but I have seen it done!
Below about 30 microns in the fusor, the beams can approach the full radius of the chamber and will focus to needle like conical beams around 20 microns. These E beams can strike the walls of the chamber heating it to very high temperatures.
Glass chambered systems must be of pyrex or Kimax (borosilicate) to withstand the heat and it should be monitored carefully even with pyrex! I often take a magnet and set it near the beam impact point to deflect the beam to a long arc in the chamber allowing in to spend its energy in the gas where we want it.
Normally, at these lower pressures there is only one single preferred beam path. The central plasma is now very hot (usually white hot in color). This is where star mode can begin provided the water vapor and oil vapors are cleared from the system with a foreline trap or are buried by magnetic pumping with Neodymium-Iron-Boron magnets as in an ion pump.
All of these effects are seen on the fusor video tape. In star mode, all the electron/ion beams shine out of the inner grid and are now paths of recirculation to a greater or lesser degree. This was a key discovery of Bob Hirsch of the Farnsworth team. The complicated and expensive ion guns were not needed to just do simple fusion. They were needed to do intense fusion.
As the pressure is dropped further, the glow in the ball of plasma decreases unless the current is kept high through increased voltage across the fusor. This is where, with a chamber back filled to 5 microns with deuterium, you can do fusion!
We are still discussing the different regimes within the system at different pressures. It is a real mixed and turgid bag of stuff which is at a percipitous edge of operation, though fusion can occur over a vast range of voltages and pressures. Finding the sweet spot is a matter of experiment.
The eyes can often deceive, but they are our only windows to physical reality as well as self-deception.
Use them wisely.
- Re: What you should see! - Stephen Coley Sep 23, 12:53 pm