Generation, transformation and transport of sub-microsecond low energy high power ion beams

The paper reports on results of formation and transport of sub-microsecond low energy high power ion beams (HPIB) combined with their transformation to quazi parallel geometry from initial converging along the transport length of ~ 1 m. Experiments were done on 2 pulsed rep-rate accelerators HIB-1 and HIB-2. The first includes a linear transformer (LTR) with a primary circuit, which consists of 7 formation lines built on discrete LC-elements. LTR has impedance of 12.4 Ohm and provides a round of 5 pulses of 600 ns duration that follow with f = 25 Hz with a variable output voltage in the range of U₁ ~ 100-270 keV. Accelerator HIB-2 includes Marx generator and intermediate fast capacitor between the Marx and the output diode. HIB-2 provides a variable output voltage in the range of U₂ ~ 100-160 keV, with Z₂ = 3-5 Ohm, τ₂ ~ 800 ns, round of 5 pulses with f = 25 Hz. Both accelerators feature the same type of the plasma filled ion diode with ballistic focusing and anode ion emission source of large annular area (~470 cm²) organized by inductive breakdown of diverging H₂ gas puff flow provided by a circular Laval nozzle. Ion diode includes toroidal B-lens of B ~ 1/r type in post cathode space, and RF plasma source to enhance HPIB space charge neutralization. Tests of HIB-1 and HIB-2 in matched regimes at the voltage levels of 100 - 150 kV gave ion current amplitudes in the range of 5-7 kA and 10-15 kA respectively. The average efficiency of HPIB generation was ~ 60%. The report provides comparative analysis of various modes of transport and transformation of low energy HPIB with the different particle density in vacuum, plasma and gas.