Magnetic field calibration and instrumental response for Project 8 Phase II apparatus with a Kr-83m source

The Project 8 collaboration developed the Cyclotron Radiation Emission Spectroscopy (CRES) technique, aiming to directly measure the absolute neutrino mass with the tritium beta-decay electron energy spectrum endpoint method. Given the convenience of its K-conversion line at 17.8 keV near the tritium endpoint at 18.6 keV, we use $^{83m}$Kr as an electron source for magnetic field calibration and instrumental response measurement. In this poster, we present our fitting of the spectrum of the $^{83m}$Kr 17.8 keV line measured by the Project 8 Phase II apparatus. Based on the fitting, we find our instrumental resolution can be as small as $\sim$2 eV in a shallow magnetic trap. We also present the linearity performance of the instrumental response.