Abstract
We present recent achievements in the application of optical diffraction radiation (ODR) to the measurement of the transverse beam size of a 1.3 GeV micrometer-size electron beam performed with an instrument installed in the extended extraction line of the KEK Accelerator Test Facility. ODR is a recent technique for the measurement of the transverse size and emittance of highly relativistic particle beams. ODR has the advantage of being a noninvasive and relatively inexpensive technique and is a candidate for the operation of linear particle accelerators, where no simple alternatives (e.g., synchrotron radiation) are available. In an effort to improve the resolution and performance, we establish an alternative target microfabrication technology, adopt solutions to improve the signal-to-noise ratio, and perform an experiment in the UV spectrum at 250 nm. With such a configuration, a transverse beam size as low as $3\phantom{\rule{0.2em}{0ex}}\ensuremath{\mu}\mathrm{m}$ is measured, drastically improving on past measurements reported in the literature. In light of these results, ODR, when combined with a high-resolution optical-transition-radiation monitor, represents a credible diagnostics solution for low-emittance high-intensity particle beams.
Highlights
In particle accelerators, the measurement of the particle beam’s transverse profile is a key diagnostic for the assessment of the beam emittance and for safe operation of the machine [1,2]
We present recent achievements in the application of optical diffraction radiation (ODR) to the measurement of the transverse beam size of a 1.3 GeV micrometer-size electron beam performed with an instrument installed in the extended extraction line of the KEK Accelerator Test Facility
We restrict our attention to a method, perhaps one of the most widespread ones, that relies on the use of optical transition radiation (OTR), an effect discovered by Ginzburg and Frank
Summary
The measurement of the particle beam’s transverse profile is a key diagnostic for the assessment of the beam emittance and for safe operation of the machine [1,2]. The state of the art in noninvasive (i.e., techniques that do not perturbing the particle beam to be measured, or do so minimally) transverse-beam-profile and emittance diagnostics for ultrarelativistic electron and positron beams is based on the so-called laser-wire technique [11,12,13], where a thin laser beam is scanned across a particle beam and inverse-scattered photons are registered downstream This technique requires an expensive laser, sophisticated final focus optics, and a team of experts to operate the system. The best reported sensitivity to beam size (14 μm) was achieved in the optical wavelength range, a very promising result for a noninvasive technique but not sufficient for future linear colliders, where a resolution smaller than 10 μm is required Despite these advantages, ODR is still an “expert” technique and, to the knowledge of the authors, is not used in the operation of any collider or light source where either tolerance to high intensity or noninvasive techniques are needed. The paper summarizes all technical challenges met during the experimental work, the solutions found, and the main achievements demonstrating the performance of the instrument
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