Conceptual design of data acquisition system for CALET on the ISS

We have been developing CALET (CALorimetric Electron Telescope) to make observations of high energy electrons, gamma-rays, and nuclei on the International Space Station (ISS). CALET consists of an imaging calorimeter (IMC), a total absorption calorimeter (TASC), a silicon array (SIA), and an anti coincidence detector (ACD). Triggers to start data acquisition of CAL are generated by combining information on tracks in IMC, partial shower energies in TASC, and traverse of charged particles through ACD. Three trigger conditions can be used simultaneously. The first one is for high energy cosmic rays over 10 GeV. The second one is for low energy electrons and protons affected by solar activities between 1 GeV and 10 GeV. The third one is for low energy gamma-rays from 20 MeV to 10 GeV. CALET can detect gamma-ray bursts (GRBs) in a wide energy range with a gamma-ray burst monitor (GBM) and CAL. Data of sum of energy deposit in TASC and event time are stored in ring memory for a certain period even if the low energy gamma-ray trigger is off.