Hello steemit! After becoming involved in the crypto world, I found this place and am excited to be here! I have read many great articles/posts on here already, and cannot wait to learn more! I will be bringing my extensive engineering and scientific experience to the community and would like to showcase one of my projects in my intro!
Figure 1. Plasma Torus contained in a low vacuum environment.
As you can see in the image, I have successfully contained a plasma torus within a permeable copper torus and the effect is a nice dense plasma ring! This effect is due to the fairly uniform electric field generated around the metal torus. This electric field was generated by a 15 kV high voltage power supply that I also built. The large copper tubing that you see in the background is connected to one output of the high voltage supply while the copper torus is connected to the other. They were both placed in a vacuum chamber (a large pickle jar in my case), and a moderate/low vacuum was pulled on the jar. This is when the magic starts!
Under normal pressures, high voltage electricity will simply arc between the points of high potential. This can be seen below from my 150kV power supply!
Figure 2. High voltage electricity arcing between two points.
These arcs are very hot, on the upward of 10,000 degrees (F), and the electron flow is concentrated to the wispy ionized air filaments. For those who not know what ionization is, the short verision is that atoms are stripped of their electrons and are no longer charge neutral. This causes them to flow to areas of negative potential(since atomic nuclei are positively charged) and allows conduction of electrical energy through thin air! These gas molecules are ionized when they randomly pass close to the metal charge carriers. The extreme electric field located at these points rips the electrons from the atoms, creating an avalanche of free electrons. These free electrons strike other neutral gas molecules and knock out some of it's electrons. This process repeats over and over in a chain reaction until an arc can form.
At atmospheric pressures, there are a large number of gas molecules in any given space. These molecules freely bounce around and collide with each other with various speeds and energies. These collisions happen frequently in air, since the molecules are moving quickly and the spacing between each molecule is on the order of nanometers (Extremely small). This means that the gas behaves like a fluid and it can be modeled as a fluid for many applications.
In a vacuum, things behave much differently than at normal atmospheric pressures. When the pressure gets into the high vacuum range, the flow becomes molecular, and the distance between gas molecules is on the order of centimeters. This means that when a gas molecule gets ionized, it can accelerate in one direction without getting knocked off course by other gas molecules. This also means that charged particles can be more readily controlled by electrostatic forces than at atmospheric conditions.
Figure 3. Same Torus as in Fig 1 except the voltage has been decreased to around 2kV.
The internal metal torus is positively charged while the exterior tubing is negatively charged. As you can see in Figure 3, there is a thin purple/pink glow surrounding the torus. Nitrogen molecules in this region have become ionized from the steady stream of electrons coming from the negatively charged outer copper structure. The now positively charged nitrogen molecules are strongly attracted to the negatively charged copper exterior and are not of much interest to us. Some of these molecules impact the copper metal and become electrically neutral and float off into the void until they are ionized by a stray electron again. Some of these electrons that are flying inward impact the metal torus and become part of the electric current. Other miss the grid entirely and enter the low potential space within. At this point, the structure can be modeled as a charged ring with electric fields as displayed in Figure 4.
Figure 4. A positively charged electric ring.
As you can see in the above figure, the charge density (orange) decreases as you approach the center of the ring. In fact, the theoretical net force in the center of a symmetric ring is 0! Those negatively charged electrons that miss the metal grid are now forced into this low potential energy area, and are effectively trapped within the structure. This trapping of electrons, although brief, allows for a much greater interaction time with stray gas molecules, thus increasing the chance of ionizing them. As time progresses, more neutral gas molecules within the metal torus region get struck by stray electrons and become positive ions. Since like forces repel(positive charge repels other positive charges), the new positive ions are pushed inward toward the low potential region. These ions quickly build up, forming the stable plasma ring you have witnessed above.
You may have notice that there are places around the ring where it looks like the plasma is leaking, and if you guessed that to be the case, you'd be right! Remember how I said that the Nitrogen molecules were positively charged? Well, as more and more molecules are ionized within the central region, their individual charges add collectively to give the previous zero potential region some positive charge. Eventually, enough molecules get crammed in this zone that it is effectively the same charge as the containing structure itself. At this point, the plasma is under fairly strong electrostatic pressures. These pressures force the ions to find weak field points in the structure, and allow them to be expelled outward. This is akin to squeezing a water bottle with a hole in it, and watching the water shoot out of the hole. The plasma then flows out of the internal structure at this critical charge balance point, and moves toward negative charge potential where it then becomes neutral on impact. This can also occur when the negatively charged structure is located close to the positive grid. This creates an artificial weak point in the electric field, allowing ions to escape. This is why there is such a large plume on the upper side of Figure 1.
I hope this explanation of my vacuum experiment was entertaining and informative. Please leave feedback on what you liked and also what you did not. That way I can improve my writing and explanations for my next project. This is the first of many more scientific projects to come!
I also would like to apologize for the low quality images. I had a bad camera when I originally did this experiment and these are the only images I have. I will redo the experiment in the future and capture much better images!
SOURCES:
Figure 4. source:
Mitchell (https://physics.stackexchange.com/users/138746/mitchell), Electric field at a point on axis of uniformly charged ring using Gauss law, URL (version: 2017-06-07): https://physics.stackexchange.com/q/337905