Measuring the Phase Portrait of an Ion Beam in a Tandem Accelerator with Vacuum Insulation

One of the charged-particle accelerators with relatively low energy and relatively high current is the vacuum-insulated tandem accelerator proposed for boron neutron capture therapy and planned for use in a number of other applications requiring a more remote location of the neutron-generating target from the accelerator. In this work, the phase portrait of the ion beam and its dependence on the ion beam current and the strength of the magnetic lens focusing the beam of negative hydrogen ions on the input of the accelerator are measured. It is shown that the modernization of the magnetic lens contributed to the reduction of the spherical aberration of the lens and improved the quality of the negative ion beam. It has been established that the ion beam emittance increases with increasing current, and the space charge affects the phase portrait of the ion beam in the low energy transport path. To compensate for the action of the space charge on the phase portrait of the proton beam, the strength of the magnetic lens is changed. The obtained experimental data indicate that the proton beam can be transported to the site of the planned location of the neutron-generating target without adding focusing elements.