I am building a small plasma nitriding unit and need a temperature measurement recommendation. Inside my bell jar, I have a small cathode biased by V and I want to measure the temperature of metal samples mounted to the cathode I don't want to use IR temperature sensors at this point, I want a direct measurement on the samples.
I can imbed the end of a thermocouple probe in the cathode or sample, and bring the probe wires out through a thermocouple feedthrough, but I'm not sure whether typical thermocouples will prevent shorting of the cathode to ground through the thermocouple sheath. Can you make any recommendations? I don't think I can make recommendations.
I'll list what I think are the likely problems you face. If I presume you can only "see" one side of the target surface, won't you have trouble inserting a thermocouple without it too being affected by the plasma? If you can see both sides depending on the temperature you expect the target to reach you might consider using one of those stick-on tapes that change color with temperature. You will have to find a battery operated unit that can be well insulated and floated to VDC.
I apologize for not being more positive and helpful but I think you face a challenge that is typically solve with IR thermometry. What do you think about this approach: Use a dual-disconnect switch for the thermocouple e. Briefly turn off the V bias, close the switch for the thermocouple, and take the temperature reading.
Open the thermocouple switch, then re-apply the V bias. The plasma will be off during the temperature measurement, so EMI shouldn't be a problem. Any thoughts or comments? Regarding IR thermometry: Accurate measurements require that you know the surface emissivity. Even the very expensive two-color and laser-correcting systems are prone to error. I'm hoping to use the thermocouple setup to calibrate an IR system for specific conditions.
If I were going to do this I'd modify your approach a little. Of course, there's a risk that someone will leave it connected and fry the read-out device, or will try to connect while the target voltage is still around and fry themselves.
However, I see another potentially major problem I missed in my last 'Cautious Granny' email. A sputter source is designed using magnets and dark space shields to limit the plasma to the front surface of the target. Some source designs have biased bolts at the back surface.
And occasionally a plasma forms around them. Yes, you're right IR thermometry has it problems. But for this project, I think it is the lesser of two evils.
I was trying to measure the temperature of a magnetron argon plasma by a K type thermocouple. As soon as I ignite the plasma the pico log attached to the thermocouple cannot give any reading except room temperature. But after shutting off the plasma the thermocouple gives reading. There is target Ti target plate when plasma is ignited Ti atom is sputtered as well. Is that causing the problem. Any help in this regard will be worth appreciated.
I am no expert in plasma thermometry but I can think of many reasons why attempting to measure this way will not work:. Plasma temperature is a measure of particle atoms, molecules, ions, electrons velocity not the heat content as in a piece of steel. So even if a measurement could be made, it would be meaningless. Remember the right hand rule for motion of electrons in crossed magnetic and electric fields. Regrettably, I couldn't get the diagrams to load.
We have a KJLC chamber for an e-beam application. Originally it was meant to be water-cooled through its cooling jacket. I am investigating if I could cool it with liquid nitrogen LN instead of water. I am not talking about a continuous flow but a filling of the cooling jacket with LN.
For filling and during usage both inlet and outlet would be open to atmosphere. This should also prevent an overpressure in the cooling jacket. Do you see any reasons why I should not do this like overpressure, stress of weld seams, etc. I also consider another option were I would switch between normal cooling water and LN.
If you manage to pump all the air out of a steel can, for example, you will have a vacuum in there, but there will be photons constantly radiated off of the walls and re-absorbed by them.
This soup of photons will be in thermal equilibrium with the walls, and therefore will have a defined "temperature". In fact, even the deepest of deep space outside the galaxy, for example , is in a radiation bath of temperature 3K, left over from the Big Bang.
There may be other stuff, like the neutrinos, for example, which are not in thermal equilibrium with the 3K radiation because they don't interact with it, and so space may have two or more "temperatures".
But we said a vacuum is a region of space with nothing in it, and that means those photons have to go. Cooling the walls down to as close to absolute zero as you can get and the limit here is that photons of energies that would be radiated by a wall of a cold temperature would have wavelengths longer than the size of the can -- that'll let you freeze out all of the photons will give you a vacuum.
You have to also shield it from outside sources of energy. There's little you can do about the neutrinos and dark matter -- they penetrate ordinary matter, but also don't really interact with it so to a good approximation you can neglect them. Tom p. So the answer really depends on what you mean by vacuum.
If you mean what's left when all the atoms etc. If you want, though, you could choose to only call that a vacuum if the temperature is zero. By the way, the third law of thermodynamics says nothing can ever get to zero temperature, so by that definition there wouldn't be any vacuums. Mike W. If you want to insist that a vacuum have no electromagnetic radiation in it, then its temperature is 0 K. However, no such thing exists. If you want a vacuum that at least is empty of more conventional particles, then its temperature must be well under that needed to excite particle-hole pairs.
To be free of electron-positron pairs, that means T would be much less than 5x10 9 K. To be free of neutrinos in equilibrium would require a lower temperature. Since the neutrino masses aren't known, I can't give much of a clear figure.
In principle some neutrinos might be around in equilibrium at room temperature. However, neutrinos interact so slowly with ordinary matter that they won't reach equilibrium for an extremely long time.
The neutrinos interact so weakly with everything else that they don't reach thermal equilibrium. The gluons don't form for reasons that I don't understand connected with how chromodynamics works. So it's really just the photons, until things get hot enough to start making some electron-positron pairs and so forth. No, definitely not. It's been understood since before that the thermal energy in the electromagnetic field goes as T 4.
Another puzzling thing is when photon is confined btw two very closely-placed walls, only extremely short wavelength can fit inside them. Why is this? The effect of the spacing between, for example, conducting plates on the zero-temperature photon modes does exert a force on the plates. It's called the Casimir effect and it's been measured.
Certainly you can get things very hot in vacuum chambers. That's routinely done in thermal evaporation systems to make, for example, metal films. The energy from an incandescent light bulb comes out both as electromagnetic radiation and as heating up of the nearby air. The radiation is similar to thermal radiation, but not necessarily with exactly a thermal spectrum. The air near the bulb gets heated largely by conduction through the glass. Once the air gets hot, the heat probably spreads more by convection than by simple conduction.
If you count photons as particles as we ordinarily do then there are indeed particles in any otherwise perfect vacuum. This is a bit different from the situation you might be picturing, in which temperature is a property of some fixed collection of particles. The temperature here accounts for the existence of the particles.
Cooling things down would leave fewer photons in the space. The jar may cool down a bit as you pump on it but after sitting a while trading heat with the room it should end up back at room temperature. The water will start to boil when the pressure gets low enough. That will cool the water down until the boiling stops. If the pump is good it will get the pressure low enough for the remaining water to freeze before boiling stops.
The water will continue to evaporate until it's all gone, with the pump sucking the water vapor out. When the water is all gone, the temperature will drift back up to room temperature.
The junction of the thermocouple extends past the heating elements, the distance being determined by hot zone design. However, when running furnace surveys, the average temperature of the survey thermocouples can be increased by pulling the control thermocouple out, closer to the plane of the heating elements. The average temperature decreases if the control thermocouple is pushed farther into the hot zone.
Flexible work thermocouples are generally placed in the load but masked from seeing the direct radiation of the heating elements. Direct radiation tends to make the work thermocouples read incorrectly. The thermocouples are usually placed inside slugs or scrap parts with holes drilled in them to provide shielding. Keep in mind that when using thermocouples with twisted junctions, the measuring junction is not at the extreme end of the thermocouple, but is at the last twist before the wires go into the insulating material.
This area must be shielded to get good readings. Work thermocouples are frequently provided with quick-connects that plug into a jack panel located just outside of the hot zone Fig. This makes it very convenient to place the thermocouples in the load before it is put into the furnace and then plugging the thermocouples into the jack panel after the furnace is loaded.
The one negative aspect to this approach is that the jack panel is usually located in an area where temperatures can range from to F to C during operation. The jack panel selected must be rated for high-temperature operation. In addition, one must be careful to have no dissimilar metal junctions in this area, because the introduction of a secondary junction will create an error in the thermocouple reading.
In applications where contaminants are out-gassing from the load, the jack panel connection is subject to contamination, which can introduce errors into the measurement. In this case, the logical choice is to terminate the thermocouple outside the furnace through vacuum-tight fittings. For platinum-type thermocouples, use of a jack panel within the furnace becomes more complicated. For most thermocouple types, jack panel sockets are made of the same material as the thermocouple being used; for example, chromel and alumel for a type K thermocouple.
However, in the case of platinum type thermocouples B, S and R , because of the softness and price of the material, sockets are made of copper instead of platinum. Copper works well and introduces only a small error into the reading as long as the temperature difference is less than F C. However, as mentioned above, in most furnaces the jack panel can see temperatures in excess of F. Therefore, the jack panels must be located in an area where the temperature does not exceed F if they are to be used to interface with platinum type thermocouples.
Two alternatives are to bring the platinum wire through vacuum tight glands or to use rigid type platinum thermocouples as shown in Fig. With proper thermocouple selection and application, the user can obtain more accurate temperature measurements and more repeatable results in their processes.
They simply cannot exist. This is not just because it is not possible to 'pump' all the matter out of a region of space, it is a consequenceof the fact that all the time, particle-antiparticle pairs are being created from nothing and annihilating each other.
There are always particles in any given region of space. Sign in Register. News Guardian. Recent queries. Send a query. Lucky dip. Any answers? Nooks and crannies. Semantic enigmas. The body beautiful.
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