1. A method of generating a control program for a plasma process, the method comprising: a) obtaining predetermined process data defining, in a series of time steps, changes in at least one control parameter for the plasma process during the said process, wherein the at least one control parameter is constant within each said time step; b) generating control data from the process data, the control data defining the at least one control parameter at a plurality of discrete times within each said time step of the series; c) presenting the control data graphically to a user, using an interactive display device after step (b); and d) modifying the control data in response to the operation by the user of the interactive display device, so as to generate the control program.