Abstract
A laserwire transverse electron beam size measurement system has been developed and operated at the Accelerator Test Facility 2 (ATF2) at KEK. Special electron beam optics were developed to create an approximately 1 x 100 {\mu}m (vertical x horizontal) electron beam at the laserwire location, which was profiled using a 150 mJ, 71 ps laser pulse with a wavelength of 532 nm. The precise characterisation of the laser propagation allows the non-Gaussian transverse profiles of the electron beam caused by the laser divergence to be deconvolved. A minimum vertical electron beam size of 1.07 ${\pm}$ 0.06 (stat.) ${\pm}$ 0.05 (sys.) {\mu}m was measured. A vertically focussing quadrupole just before the laserwire was varied whilst making laserwire measurements and the projected vertical emittance was measured to be 82.56 ${\pm}$ 3.04 pm rad.
Highlights
For future linear electron-positron colliders such as the Compact Linear Collider (CLIC) [1] and the International Linear Collider (ILC) [2], measurement of the particle beam emittance is essential for achieving and maintaining the required nanometer level final focus beam sizes if their target luminosity is to be reached
The laser system consists of a Q-switched neodymiumdoped yttrium aluminium garnet (Nd:YAG) amplifier seeded by a 357 MHz mode-locked oscillator
The laserwire detector is placed after the BH5X dipole magnet in the ATF2 lattice, which is the first bend after the laserwire interaction point (LWIP) and constitutes a bend of 2.927°
Summary
For future linear electron-positron colliders such as the Compact Linear Collider (CLIC) [1] and the International Linear Collider (ILC) [2], measurement of the particle beam emittance is essential for achieving and maintaining the required nanometer level final focus beam sizes if their target luminosity is to be reached. Two commonly used methods at electron accelerators to measure the transverse beam profile are optical transition radiation (OTR) screens that image the beam directly [3] and wire scanners [4]. Transmissive focusing optics allow direct access to the laser focus for measurement and laserwire calibration It affords a greater scanning range and allows the laser pulse energy to be measured after the interaction point for normalization. This paper presents results from the upgraded ATF laserwire system that aims to achieve micrometer sized transverse profiles using a visible wavelength laser system. An overview of the various subsystems and their upgrades from the laserwire installation at the ATF are described
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