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- An excellent resource on concepts in electricity and electrical engineering - Spinning Numbers
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Introduction- Become familiar with the most important electrical quantities: charge, current, and voltage.
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The voltage and current relationship when a spark gap's gap is increased is as follows:
Voltage: The voltage required to initiate a spark across the gap increases as the gap widens. This is because the air in the gap has to be ionized before a spark can occur, and it takes more voltage to ionize the air as the gap widens.
Current: The current that flows through the spark gap after it has initiated is relatively constant, regardless of the gap width. This is because the resistance of the ionized air is very low, so a large current can flow even with a small voltage difference.
For example, spark gaps are used in spark-ignition engines to ignite the fuel-air mixture. The spark plug in a spark-ignition engine has a gap of about 0.020 inches, and the voltage required to initiate a spark across this gap is about 20,000 volts. However, once the spark has initiated, the current that flows through the spark plug can be as high as 20 amperes.
The relationship between voltage and current in a spark gap is not linear. As the gap widens, the voltage required to initiate a spark increases exponentially. This means that a small increase in the gap width can result in a large increase in the voltage required to initiate a spark.
The voltage and current relationship in a spark gap is also affected by the type of gas that is present in the gap. Air is the most common gas used in spark gaps, but other gases such as argon and helium can also be used. The breakdown voltage of a gas is the voltage required to ionize the gas, and it is different for different gases. This means that the voltage required to initiate a spark in a spark gap will be different depending on the type of gas that is present in the gap.
- #1 rule, It is not deterministic.
- Every spark gap is unique at some level. There is a distribution curve that can be exploited, in terms of multiple sampling and ratiometric sampling.
- Both amplitude and time can be exploited.
- the uniqueness can be measured, but not anticipated prior to the event.
- and you can have more than one spark gap as well, but one current coupling them all together, i think this would have a tighter bell curve via synchronous, similarity induced averaging. the hot spark get damped by the colder ones, and the cold ones get sped up by the hot ones (think faster)
The discharge concept becomes simpler if instead of thinking about the electric field between the electrodes which is the driver for the discharge process. Of course the shape and distance between electrodes determine the electric field, but the the electrons are only driven by the electric field. Putting in the geometry at this point only confuses the issues.
Consider this, a free electron will travel along the electric field from the negative electrode to the positive electrode and gather energy in the process.
If there is neutral gas along the path, the electron can bounce off of a gas molecule while transferring some of its energy to the molecule.
If the electron has an energy less than the ionization energy of the gas molecule, that is all that happens (e + i --> e+ i). If the electron has more than the ionization energy of the gas molecule, then the electron will give up some of its energy to the molecule causing an electron from the molecule to be ejected. The result of this is e + i --> 2e + i. We then have can have an avalanche process producing huge number of electrons which will result in a high current between the electrodes.
What determines the probability of an electron colliding with a neutral molecule and ionizing it?
- the electron has to have energy greater than the ionization potential of the particular type of gas molecule
- The probability of a electron-molecule collision. This probability is very roughly the area of the molecule (cross-section) and the number density of the molecule in the gas times the path length between the electrodes. Pc ~ A x Nd x L. More commonly this is expressed as a distance = mean free path (MFP) for the electron molecule problem. If the MFP is shorter than the distance between electrode there should be a ionizing collision. If the MFP is much smaller than the inter-electrode spacing there will be many collisions.
Now, if the energy acquired while traveling one MFP is greater than the ionization potential of the gas, then the electrons ejected from the ionized gas can, themselves can gain enough energy to ionized even more gas molecules. In other words, we have self-sustaining discharge highly dependent on the inter-electrode voltage, the gas pressure and the gas type.
How do we get the first electron that we need to trigger the discharge? It can come from a cosmic ray, a radioactive element in the chamber, a UV light source. Also, a high enough voltage across the electrodes (producing a high electric field) can cause:
- electrons to be torn directly from the molecules or
- electrons can be torn away from the metal electrodes (field emission).
This is the qualitative basics. Real world is a bit more complicated, but these concepts might give you a qualitative understanding of the principles involved. Certainly, look at the Paschens Law information.
BTW If an electrode has a sharp point, like a needle, that geometry results if a high electric field near the point. That's how field emission electron sources are made. If you heat the electrode hot enough, the electrons in the metal can get hot enough to be ejected from the metal; i.e., thermionic electron sources.
via the [LT Spice] Group Chat:
Gas Tube Quench Circuit
It seems to be common knowledge that a NE-2 or similar neon lamp can be pressed into service as radiation (x-ray) detector. But can a simple lamp serve as a low-level detector, possibly replacing a Geiger tube?
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