[NF.6] Electron + Volt = ELECTRONVOLT

The the last NF article, about the recent EAST tokamak success, I skipped explanation of two important terms in the nuclear fusion: an electronvolt and "the triple product". Here I will deal with the former one, while leaving the latter one for Friday.

Before I start, I will repeat the guilty paragraph:

Remember this?

Before jumping to the graph, I would like to introduce an energy/temperature unit that plasma physicist use: ”electronvolt”, or short eV.

1 electronvolt corresponds to approximately 11 600 K or 11 300 ^oC.

Why would people use such random number will leave for another time. For now, you can see it as a more convenient way to write 10 000 ^oC only as 1 eV. Henceforth, 100 million ^oC will be about 10 000 eV or written even shorter: 10 keV (kiloelectronvolts).

Convinence

And really, one of the reasons is that it is more convenient to write and pronounce 10 keV than 100 000 000 K.

Intuition

Technically, electronvolt represents the energy that receives an electron that goes through the electric potential difference of 1 volt. In other words - for the layman, when you put 1 V at the end of some cable, electron that moved along that cable has energy larger for 1 electronvolt.

Value

But how much is this energy? Basic physics says: E [energy: joule] = q [charge: coulomb] * V [voltage: volt]. As charge of an electron is 1.6 * 10^-19 coulombs, we see that energy after passing electric potential of 1 V is 1.6 * 10^-19 joules.

Where is Temperature?

Have you noticed that I talk about energy all the time, without mentioning temperature? In reality, the temperature is just an averaged energy over all particles. In other words - the macroscopic effect of particle movements.

The connection in plasma physics is introduced with Boltzmann constant k_B that represent energy over temperature:

1 eV = 1.6 * 10^-19 J = k_B * T[K] = 1.38 * 10^-23 J/K * T[K]

obtaining:

T = 11 604.5 K

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I hope I did not border you with the equations, numbers and new terms. I will write soon about the famous triple product, and there will be even more new terms ;)

Please feel free to ask anything in the comments. I will either try to answer you in the comment or even make the new post.