Analysis of RE beams in COMPASS and JET using betatron equilibrium and radiation diagnostics

Runaway electrons (RE) still present a serious for the tokamak operation. Furthermore, the physics phenomenon itself is complicated and extrapolation to the large devices is difficult. In order to understand the RE phenomenon, it is necessary to optimise the diagnostics of the runaway electrons. Some of the properties of RE can be measured using the standard tokamak diagnostics directly (e.g. plasma or runaway current measurement by magnetic diagnostics). In some cases, it is necessary to improve the understanding of the effect of the RE on the diagnos- tics (e.g. electron cyclotron emission measurement by radiometer) by modelling and analytical approximations. However, often it is necessary to introduce a completely new diagnostics, that can be used specifically for RE (e.g. local loss measurement using a Cerenkov detector). In this contribution a new application of magnetic measurements for estimation of the RE energy is dis- cussed for two European machines with extensive RE experimental program.