The simplest method of heating a tokamak plasma, in which resistive dissipation of the plasma current raises the temperature — effective up to about 3 keV, after which plasma resistivity drops and auxiliary methods are needed.
ReviewedLast reviewed: 9 Aug 2026·Category: Glossary
Principle
In a tokamak, a large current (typically several megaamperes) flows through the plasma. Because plasma is not a perfect conductor, this current dissipates energy through resistive (ohmic) heating, analogous to a wire heating up when current flows through it.[1]
Temperature limit: Plasma resistivity scales as Te−3/2 (the Spitzer resistivity). As the plasma heats up, it becomes a better conductor and ohmic heating becomes less effective. Above ~3 keV (~35 million degrees), ohmic heating alone cannot reach fusion-relevant temperatures, and auxiliary heating methods are required.
Role in Tokamak Operations
Ohmic heating provides the initial temperature rise in every tokamak discharge. The central solenoid drives the plasma current inductively, and the resulting ohmic power heats the plasma from room temperature to several keV. Alcator C-Mod demonstrated ohmic H-mode access — reaching the high-confinement regime without any auxiliary heating.[2]
Limitations
To reach the 10–20 keV temperatures required for D–T fusion, tokamaks must supplement ohmic heating with neutral beam injection, radiofrequency heating (ECRH, ICRH), or alpha-particle self-heating in a burning plasma.[3]
Sources
Wesson, J. Tokamaks. 4th ed., Oxford University Press, 2011.
Greenwald, M. et al. "20 years of research on the Alcator C-Mod tokamak." Physics of Plasmas, 21(11), 110501, 2014.
Freidberg, J.P. Plasma Physics and Fusion Energy. Cambridge University Press, 2007.