A device for collecting electrically charged particles comprising a first shell and a second shell disposed concentrically around the first shell is provided. Each of the shells is divided respectively into a first half-shell and a second half-shell. A first switch is disposed between the first half-shell of the first shell and the second half-shell of the first shell. A second switch is disposed between the second half-shell of the first shell and the first half-shell of the second shell. The first half-shell of the second shell has a through opening.