How are temperatures of 100 million degrees attained?
The plasma temperature needed for ignition is produced by external heating. Powerful methods were developed for this purpose:
- Heating with current
- Heating by injection of fast particles
- Heating by high-frequency waves, i.e. radio-frequency or microwaves
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These methods produce temperatures of 100 million degrees centigrade in present-day fusion devices, almost at the push of a button.
The hot plasma is at the same time of extremely low density, just 1020 particles to a cubic metre. Technically speaking, this is almost high vacuum. The thermal energy of the plasma is correspondingly low, despite the high temperature. The hot plasma of a future fusion power plant, with a volume of 1,000 cubic metres and a temperature of 100 million degrees, therefore contains just 200 megajoules of thermal energy, this being equivalent to the combustion value of about 100 bars of chocolate.