FAQ - Pressure needed in a fusor
Posted: Tue Feb 25, 2014 2:41 pm
There is no such thing as a pure vacuum only varying degrees of pressure. We need a special vacuum pumping system for fusor operation as fusion occurs in the fusor at a greatly reduced pressure. That pressure must be one of deuterium gas only! We must remove as much of the atmosphere, (air), in the fusor vessel as is possible and back fill to a fusion pressure with deuterium gas only.
Fusion, in a fusor, operates in a delicate and narrow range of pressures where a glow discharge can be established and maintained. This range is between 1 and 20 microns or, 1X10-3 torr and 2X10-2 torr. The best and most successful run pressures are between 5 and 20 microns in a common 6 inch to 8 inch spherical fusor.
There is a critical balance between achieving a pressure where the fusor can actually operate and the values of applied voltage and current demanded to do fusion to advantage.
Too much pressure and the voltage can't be raised into a decent fusion range without drawing too much current and melting the grid. If using too little pressure, almost no voltage that the amateur can supply will operate the fusor in glow mode.
At the bottom end of fusion pressures, in glow mode, (about 4-5 microns), you can get a glow at some very high voltages, but the current might be limited and reduced fusion will be seen, in spite of superb cross section in the process, as the fusor is starved for fuel (deuterium). At the higher, easier end of glow mode, (15 microns or more), the fusor and current must be "conditioned-in" by a skilled operator over a period of time ,(1/2 hour to 1 hour) in order to achieve amazing results where both the voltage and current are allowing the greatest possible fusion to occur.
Only true operation by the amateur can show and refine this process. This is why the demo fusor is a good idea as it trains the person in the dynamics of glow mode fusion via hands-on experience.
related FAQs on the voltage and current needed to do fusion are found at:
viewtopic.php?f=29&t=9171&p=62349#p62349
viewtopic.php?f=29&t=4843
Pressure units - A discussion
I have given my thoughts in the past regarding pressure units solely for use by fusioneers using the fusor. We are not highly technical or the types to write papers for Nature. We are forced into two worlds in our quest for vacuum. One of technical vacuums and the other the scientific vacuum.
For our purposes and for the sake of most reading, we might encounter, the micron and the torr. These are all we need concern ourselves with.
All fusors run solely in a technical vacuum.....Above 1 micron. All fusion pressures can be expressed in microns. Why?.... The cheapest and most used gauges found surplus are TC, (thermocouple gauges). Virtually all of these are in microns. Thus, we work, do fusion and talk mostly in microns in a technical vacuum.
However, most of us strive with diffusion and turbo pumps to achieve some sort of scientific vacuum level in our chambers before introducing the fusion fuel, (deuterium). As this is the case, we might resort to the time honored Torr found in the bulk of classic literature on vacuum. Thus, we might speak of achieving 10e-5 or 10e-6 torr as a base pressure for those advanced enough to speak in scientific notation using torr-speak. This is proper when discussing deeper vacuums than fusor operational pressures.
The beauty of the micron is that when operating a fusor we can use whole numbers. (5, 12, 25 microns). We have an intimate grasp of these pressures due to the base level of most fore-pumps and inexpensive vacuum gauges which we deal with every day. We know that we must be well below 50 microns before starting our diffusion or Turbo pumps and that regardless of where they may take us in the "torr" range, we must add deuterium to at least 5 microns before attempting fusion.
Likewise, there is little sense in using .03 microns. If we are going to use fractional units, use torr as the whole point of using microns was to escape fractional units in fusion operating pressures, preferring whole number units.
Richard Hull
Fusion, in a fusor, operates in a delicate and narrow range of pressures where a glow discharge can be established and maintained. This range is between 1 and 20 microns or, 1X10-3 torr and 2X10-2 torr. The best and most successful run pressures are between 5 and 20 microns in a common 6 inch to 8 inch spherical fusor.
There is a critical balance between achieving a pressure where the fusor can actually operate and the values of applied voltage and current demanded to do fusion to advantage.
Too much pressure and the voltage can't be raised into a decent fusion range without drawing too much current and melting the grid. If using too little pressure, almost no voltage that the amateur can supply will operate the fusor in glow mode.
At the bottom end of fusion pressures, in glow mode, (about 4-5 microns), you can get a glow at some very high voltages, but the current might be limited and reduced fusion will be seen, in spite of superb cross section in the process, as the fusor is starved for fuel (deuterium). At the higher, easier end of glow mode, (15 microns or more), the fusor and current must be "conditioned-in" by a skilled operator over a period of time ,(1/2 hour to 1 hour) in order to achieve amazing results where both the voltage and current are allowing the greatest possible fusion to occur.
Only true operation by the amateur can show and refine this process. This is why the demo fusor is a good idea as it trains the person in the dynamics of glow mode fusion via hands-on experience.
related FAQs on the voltage and current needed to do fusion are found at:
viewtopic.php?f=29&t=9171&p=62349#p62349
viewtopic.php?f=29&t=4843
Pressure units - A discussion
I have given my thoughts in the past regarding pressure units solely for use by fusioneers using the fusor. We are not highly technical or the types to write papers for Nature. We are forced into two worlds in our quest for vacuum. One of technical vacuums and the other the scientific vacuum.
For our purposes and for the sake of most reading, we might encounter, the micron and the torr. These are all we need concern ourselves with.
All fusors run solely in a technical vacuum.....Above 1 micron. All fusion pressures can be expressed in microns. Why?.... The cheapest and most used gauges found surplus are TC, (thermocouple gauges). Virtually all of these are in microns. Thus, we work, do fusion and talk mostly in microns in a technical vacuum.
However, most of us strive with diffusion and turbo pumps to achieve some sort of scientific vacuum level in our chambers before introducing the fusion fuel, (deuterium). As this is the case, we might resort to the time honored Torr found in the bulk of classic literature on vacuum. Thus, we might speak of achieving 10e-5 or 10e-6 torr as a base pressure for those advanced enough to speak in scientific notation using torr-speak. This is proper when discussing deeper vacuums than fusor operational pressures.
The beauty of the micron is that when operating a fusor we can use whole numbers. (5, 12, 25 microns). We have an intimate grasp of these pressures due to the base level of most fore-pumps and inexpensive vacuum gauges which we deal with every day. We know that we must be well below 50 microns before starting our diffusion or Turbo pumps and that regardless of where they may take us in the "torr" range, we must add deuterium to at least 5 microns before attempting fusion.
Likewise, there is little sense in using .03 microns. If we are going to use fractional units, use torr as the whole point of using microns was to escape fractional units in fusion operating pressures, preferring whole number units.
Richard Hull