Measurement of nanometer electron beam sizes with laser interference using Shintake Monitor

The Shintake Monitor is an essential beam tuning device installed at the interaction point (IP) of ATF2 [1], the final focus test beam line of the Accelerator Test Facility (ATF) to measure its nanometer order vertical e− beam sizes (σy⁎). The e− beam collides with a target of laser interference fringes, and σy⁎ is derived from the modulation depth of the resulting Compton signal photons measured by a downstream photon detector. By switching between several laser crossing angle modes, it is designed to accommodate a wide range of σy⁎ from 20 nm to a few micrometers with better than 10% accuracy. Owing to this ingenious technique, Shintake Monitor11 intake Monitor, invented by Dr. T. Shintake, had first been put into practical usage at the FFTB experiment at SLAC [4]. is the only existing device capable of measuring σy⁎<100 nm, and is crucial for verifying ATF2ʹs Goal 1 of focusing σy⁎ down to the design value of 37 nm. Shintake Monitor has demonstrated stable σy⁎ measurement with 5–10% stability. Major improvements in hardware and measurement schemes contributed to the suppression of error sources. This paper describes the design concepts and beam time performance of Shintake Monitor, as well as an extensive study of systematic errors with the aim of precisely extracting σy⁎ from the measured modulation.