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 U 1 ∼ 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 U 2 ∼ 100–160 keV, with Z 2 = 3–5 Ohm, τ 2 ∼ 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 cm 2 ) organized by inductive breakdown of diverging H 2 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.