An X-ray gas monitor for free-electron lasers.

Andrey A Sorokin,Ulf Fini Jastrow,Alexander Gottwald,Kai Tiedtke,Mathias Richter,Yilmaz Bican,Susanne Bonfigt,Markus Braune,Maciej Brachmanski,Hendrik Kaser

doi:10.1107/s1600577519005174

Abstract

A novel X-ray gas monitor (XGM) has been developed which allows the measurement of absolute photon pulse energy and photon beam position at all existing and upcoming free-electron lasers (FELs) over a broad spectral range covering vacuum ultraviolet (VUV), extreme ultraviolet (EUV) and soft and hard X-rays. The XGM covers a wide dynamic range from spontaneous undulator radiation to FEL radiation and provides a temporal resolution of better than 200 ns. The XGM consists of two X-ray gas-monitor detectors (XGMDs) and two huge-aperture open electron multipliers (HAMPs). The HAMP enhances the detection efficiency of the XGM for low-intensity radiation down to 105 photons per pulse and for FEL radiation in the hard X-ray spectral range, while the XGMD operates in higher-intensity regimes. The relative standard uncertainty for measurements of the absolute photon pulse energy is well below 10%, and down to 1% for measurements of relative pulse-to-pulse intensity on pulses with more than 1010 photons per pulse. The accuracy of beam-position monitoring in the vertical and horizontal directions is of the order of 10 µm.

Highlights

Characterization of free-electron laser (FEL) beam parameters such as the absolute photon flux is extremely important and a fundamental quantity for many user experiments, as well as for machine operators
A novel X-ray gas monitor (XGM) has been developed which allows the measurement of absolute photon pulse energy and photon beam position at all existing and upcoming free-electron lasers (FELs) over a broad spectral range covering vacuum ultraviolet (VUV), extreme ultraviolet (EUV) and soft and hard X-rays
The huge-aperture open electron multipliers (HAMPs) enhances the detection efficiency of the XGM for low-intensity radiation down to 105 photons per pulse and for FEL radiation in the hard X-ray spectral range, while the X-ray gas-monitor detectors (XGMDs) operates in higher-intensity regimes

Summary

Introduction

Characterization of free-electron laser (FEL) beam parameters such as the absolute photon flux is extremely important and a fundamental quantity for many user experiments, as well as for machine operators. The XGMDs have been calibrated in different measurement campaigns over a period of six years at the MLS using monochromatic synchrotron radiation in the VUV spectral range (photon energies from 20 to 100 eV), i.e. in the regime of single and/or double and triple ionization with xenon or krypton as the target gas.

Results

Conclusion