A portable electron linear accelerator for absolute energy calibration of ultra-high energy cosmic ray telescope

Telescope Array experiment (TA) which observes ultra-high energy cosmic ray was started from 2008 at Utah State in U.S. We will calibrate the absolute energy scale of fluorescence detector with a portable electron linear accelerator (ELS) of beam intensity is 40 MeV × 109 e- per pulse. The ELS was developed in KEK, Japan, and was installed at the TA site in March 2009. In September 2010, we began operation of ELS, and FD observed the fluorescence photons from the air shower which was generated by the electron beam. In this article, we will report about the status of ELS operation, and data analysis. (author)