An adaptive controller is proposed to replace the current conventional controller in the plasma density feedback system at Joint European Torus (JET). Changing plant dynamics calls for matching retuning of the controller to retain the required performance of the control system. This controller tuning must now be done manually. In the adaptive controller, the retuning process is automated and runs in parallel with the control function. The plant is analyzed, the components of the proposed controller are designed to suit prescribed performance, and the result is illustrated in simulations.