MAGIC simulation of ion extraction - ~130 mA

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

Details

1.3 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 130 mA should be extracted.

Results

This shows something close to a matched extraction system. The electrons are stopped before the output aperture and produce a concave surface.

The extracted ion beam is then pricipally focused by the gap fields (not the plasma meniscus) and then the transverse space-charge and the defocusing field of the second half of the gap produce reduce the beams angles, but without causing a space-charge explosion.

The resulting beam has a low total divergence and is therefore the closest to the matched case for this extraction geometry and voltages.

Below the animation is shown the resulting phase-space. Even though these conidtions give the lowest divergence we can see a large amount of aberration in the resulting emittance. This aberration is the spherical aberration of the electrostatic lens, but this may then couple into the beam due to the space-charge field to further disrupt the beam.

Animation of extraction
Go to 500 mA and 25 mA animations.

Phase space diagram
Go to 500 mA and 25 mA phase-space.

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