Ultrafast relativistic electron probing of extreme magnetic fields

We investigate the suitability of using GeV laser wakefield accelerated electron beams to measure strong, B>0.1MT, magnetic fields. This method is explored as an alternative to proton deflectometry, which cannot be used for quantitative measurement using conventional analysis techniques at these extreme field strengths. Using such energetic electrons as a probe brings about several additional aspects for consideration, including beam divergence, detectors, and radiation reaction, which are considered here. Quantum radiation reaction on the probe is found to provide an additional measurement of the strength and length of fields, extending the standard deflectometry measurement that can only measure the path integrated fields. An experimental setup is proposed and measurement error is considered under near-term experimental conditions.