The instruments of sFLASH experiment

We will report on the setup and calibration of the instrumentation for sFLASH. The sFLASH experiment is a measurement of the air fluorescence from ∼10$^{21}$ eV artificial air showers developed in an alumina target by an electron beam provided from End Station A of the Stanford Linear Accelerator Center (SLAC). sFLASH employs Photomultiplier tubes (PMTs) to detect the fluorescence photons and an Integrating Charge Transformer (ICT) to measure the beam current. The PMTs are positioned ~10m perpendicular to shower axis are used to measure the air fluorescence photons. The absolute gain of the PMTs was measured using CRAYS at the Institute of Cosmic-Ray Research, Japan. CRAYS is a PMT photo-gain calibration system consisting of a vessel containing nitrogen gas and a 14μJ nitrogen (337.1 nm) laser. The gain of each PMT was monitored during the course of the experiment using a YAP pulser (YAlO: Ce + $^{241}$Am) potted into an ultraviolet optical filter attached to the surface of the PMT window. We expect to achieve an overall experimental uncertainty of ~6%. The ICT (Bergoz) consists of 20 turns of coil to measure the beam current. In the sFLASH experiment we set it ~1 m away from beam exit to measure the beam current just prior to entering the target material. The ICT was calibrated with 2 ns pulse generator at Jet Propulsion Laboratory. The calibration uncertainty of the ICT is ~1%.