The Ion particles are essential to complete the below Research nodes:
  • Interceptor Barrage (increases base damage of Interceptors)
  • Explorer Barrage (increases base damage of Explorers)
  • Battleship Barrage (increases base damage of Battleships)

Each of those researches requires one Ion particle to initiate. Due to their rarity, these particles have been scattered across the Galaxy. You can obtain the first one at Operations level 42 upon completing the mission "Familiar Face". The second one will be available at  Operations level 47 upon completing the mission "A Light in the Darkness". The last is the most elusive one and, based on witnesses, it can only be found in a few Special Event Stores.