**Cavity Enhanced Cyclotron Cooling**

We cool our experiment to 10 K in the hope that the plasmas will also reach this temperature eventually. But the final temperature T_{f} of any cooled body also depends on the ratio of cooling rate Γ to heating power H:

_{f}= 10 + H / Γ

Γ is the rate of equilibration with the thermal bath at 10 K: it takes a time t = Γ^{-1} for the difference T - T_{f} to be reduced by 63%. Γ is about 0.24 s^{-1} for electrons in a 1 T magnetic field.

H is the amount of energy per unit time which the plasma absorbs due to radial expansion and RF noise on the electrodes. H is about 50 K s^{-1} but can be much larger for plasmas containing millions of electrons.

To reach the lowest plasma temperatures, we need to minimize H and maximize Γ. We have successfully increased Γ by over an order of magnitude by coupling the electron cyclotron motion to a microwave cavity.

The microwave cavity traps a set of electromagnetic modes, each with a characteristic frequency. When we tune the magnetic field B so that the electron cyclotron frequency eB/m matches the frequency of a cavity mode, the cavity can absorb cyclotron energy from the electrons, and the plasmas cool more quickly.