Longitudinal cooling of a strongly magnetized electron plasma

The optimal values of Q and (ω - Ω_r) for cooling a pure electron plasma with a microwave bath have been calculated. An electron plasma which has no internal degree of freedom, cannot be cooled down below a heat bath temperature. However, the longitudinal cooling can be achieved by energy transfer from the poorly cooled parallel degree of freedom to the well cooled (by synchrotron radiation) perpendicular degree of freedom. To do this, we introduce a microwave bath to the electron plasma. A microwave tuned to a frequency below the gyrofrequency of the electron forces an electron moving towards the microwave to absorb a photon and then to move up one in Landau state. The electron loses longitudinal momentum in this process, so that the longitudinal energy can be reduced. On the basis that most of the electrons are in the ground or first excited state, we set up a transition equation and develop a FEM code. With an appropriate condition for B-field and intensity of the microwave, the cooling times for several values of Q and (ω - Ω_r) are calculated and the optimal values are found. Applying the optimal values at appropriate times in a cooling process, the best cooling can be obtained. For an electron plasma magnetized with 10 T B-field, cooling to the solid state can occur within 2 hours. Without this optimization, times were always several hours, longer than the life time of the plasma in real system.