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What material property decides how much will that material heat up when inside solenoid with alternating current applied to it?

I am trying to research what type of ceramic will absorb as little energy as possible inside the AC magnetic field so it stays cool.What is great mystery to me is,when you have a glass tube with gas and the whole thing is inside solenoid coil,why does the gas becomes plasma,while the glass doesnt melt?

I want to know how to calculate how much will certain ceramic material heat up by AC magnet so I can chose the right ceramic.Is it electrical conductivity? Permeability? Permitivity? Density? Or maybe certain freqency is transparent to glass but will heat gas? Is it becose gas atoms are free to move and heat up by collisions as they are accelerated and ceramic atoms cant move so cant heat up?

Gases and ceramics like fused silica are very similiar in the electrical properties,both are electrical insulators,both are non-magnetic,both have extremly low thermal conductivity,only thing really different is density,less amount of atoms requires less energy to turn it into plasma,but then it will only delay the melting of glass and the devices using induction coupled plasma technology operate continuously for long time.

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First of all, there are linear and nonlinear mechanisms of heating. That means that electric properties of materials and, therefore, heating efficiency, depend on the strength of the field. Each material has a breakdown threshold above which plasma may be formed. So at some field strength there is a discharge in gas, but not in glass. However, there will be a breakdown in glass at higher field strength. The breakdown threshold, say, in gas, depends, among other things, on density and frequency.

Linear mechanisms, in general, include electric and magnetic losses. Typically (in non-magnetic media), electric losses are more important and depend on the complex permittivity (https://en.wikipedia.org/wiki/Permittivity#Complex_permittivity), which depends on the frequency, among other things. You may find some formulas, say, at http://www.engr.sjsu.edu/rkwok/EE142/Lossy_Medium.pdf .

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  • $\begingroup$ I think you misunderstood me,I dont ask about electric field or even electromagnetic field,I ask about magnetic field.There is no breakdown threshold like with electric field.From your post I gained no answer to my question,the breakdown threshold at sufficient "field" strenght apply to electrodes with high voltage,my question is about magnetic coil,it uses low voltage like 3 volt and high current,there is no sudden breakdown like with high voltage,the ac magnet will just gradualy heat things up,its completly different thing $\endgroup$ Mar 3, 2017 at 10:21
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    $\begingroup$ @wavscientist: One of us may be mistaken. You were very clear that your question is about an AC electromagnet. That means that you have magnetic field varying with time. According to the Maxwell equations, such field necessarily generates varying electric field, and this field can cause breakdown. I think there is an easy way to check who is mistaken. You may try DC current in the coil instead of AC. I bet in this case there will be no plasma in the gas and, therefore, no visible radiation from the gas. $\endgroup$
    – akhmeteli
    Mar 3, 2017 at 10:39
  • $\begingroup$ I never claimed that DC current in coil can ionise gas.You are very right that alternating magnetic field will induce current,but thats for solid conductor like iron,not for electricaly insulating gas.I think the gas inside the glass tube is heated gradualy by colliding with other gas atoms when its accelerated by magnetic field,it then heats up to the point of plasma,but there is no electrical breakdown leading to that plasma,just gradualy increasing temperature till the electrons fall away from atom,its not like the magnetic field just rips the electrons away like with HV electrodes $\endgroup$ Mar 3, 2017 at 10:48
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    $\begingroup$ @wavscientist: Alternating magnetic field induces electric field, and this is also true for insulating media. This electric field can cause discharge in the media if it's strong enough. And how can atoms be accelerated by magnetic field? First, they are neutral, second, the Lorentz force caused by magnetic field is orthogonal to the velocity. What happens is an initial electron (which may appear in the gas accidentally) in gas can be accelerated by the (strong enough) electric field, ionize an atom, and thus start an avalanche. $\endgroup$
    – akhmeteli
    Mar 3, 2017 at 11:05
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    $\begingroup$ @wavscientist: Plasma in gas does not need to be thermal. Temperature of electrons in plasma can be much higher than that of ions and neutral atoms. $\endgroup$
    – akhmeteli
    Mar 3, 2017 at 11:06

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