Measurements of source divergence angle of pulsed nitrogen ion beams

Singly or doubly ionized nitrogen beams, including a small part of oxygen ion beams, were extracted from a cryogenic diode with N2O ice on the anode surface. The nominal diode voltage was 100–360 kV, and the peak ion current was 300 A. With a one-dimensional arrayed pinhole camera with 5 pinholes, very small divergence angle at the beam source was measured. Although, we used a very rough apparatus (not being as sophisticated as the modern version), the absolute value (measured) of the divergence angle was 5–6 mrad. This value was small enough for us to recommend this beam as one of the candidates for the future ICF or IFE driver. With the same apparatus, we observed a rather large angle of 25–60 mrad for the proton beam in our former experiment. These results indicated that this kind of medium-mass ion beam must be investigated in more detail to make clear the potential of the beam. We also developed a Thomson ion spectometer with a CCD detector, which could be applicable to the above ion beams. The energy spectrum of a proton beam was measured as the early stage preparation of the spectometer development.