Optimization of electron beam irradiation at HELCZA experiment

Abstract

This paper deals with optimal electron beam heat distribution on the HELCZA experiment while calculating flatness of the heat input distribution and distribution of surface temperature for various samples. A new dedicated computer program has been developed for balancing the heat flux in the construction materials of the sample. The first boundary condition for this calculation were distribution functions describing the process of heat input from the electron beam. The beam power distribution is described via a beam shape Gaussian function and a screening pattern on the irradiated surface. The second boundary condition was cooling of the material by the refrigerant cooling ducts. While the heat input from the electron beam is relatively flat, the distribution of subsurface cooling channels and the design of individual elements of the sample leads to significant surface temperature distortions in the sample material. Depending on the method of scanning and relative beam position, a complex problem of heat conduction had to be solved numerically. The newly developed computer program solves the above problem and balances the given system of equations of heat conduction and it can then describe in detail the nature of the surface temperature of the sample as well as temperatures below its surface. The outputs are temperature profiles during heating, a comprehensive view of the temperature distribution in the sample and temperature profiles in selected areas below the surface of the sample. Due to good thermal conductivity of structural metal materials, low heat capacity and a sufficiently long time of irradiation the task was treated as stationary. As part of the solution the sample surfaces scanning pattern by electron beam was optimized.