MAGIC simulation of ion extraction - ~25 mA

Below is shown a simulation of ion extraction performed by the MAGIC particle-in-cell code.

Details

0.25 A of both Pb25+ and electrons is emitted from the surface at the left of the simulation, which is biased at +80 kV. This plasma (which has a high directional velocity) drifts to the source outlet aperture in the centre. The next electrode is biased at -10 kV. The elctrons are held back by the fields and the ions are extracted.

As the extraction hole is 1.5 cm in radius and the emitter electrode is 5.0 cm in radius, around 25 mA should be extracted.

Results

In this case the plasma is very underdense for the applied voltage and therefore the meniscus is pushed deep into the plasma.

As the plasma does not penetrate close to the gap, the focusing fields are very strong and the beam is quickly brought to a waist. The lack of any transverse space-charge force allows the beam particles to cross-over. As the beam is very small in the defocusing field region of the gap it sees little force and emerges as a highly divergent beam.

This case shows the lowest aberrations (phase-space diagram below the animation) strongly suggesting that space-charge is the major force for aberrations in the other higher density cases.

Animation of extraction
Go to 500 mA and 130 mA animations.

Phase space diagram
Go to 500 mA and 130 mA phase-space.

back to home... prepared by Richard Scrivens 23rd January 1998