PM HELICON THRUSTERS

    The 8-tube Medusa 2 machine had to be scrapped when the larger room of the laboratory was given over to Prof. Joshi's project on plasma wakefield accelerators.  With student Davide Curreli, a single-tube permanent-magnet helicon source was built in the smaller room for the purpose of developing compact ambipolar plasma thrusters.  Computations using Arnush's HELIC code for helicons showed that the small 2-inch tubes would work better at 27.12 MHz than at 13.56.  A new machine was built for that frequency.  Here is a picture of the source.

Two 5-inch OD ring magnets produce 300 G at the antenna position.  The plasma is ejected into a large chamber below it.  The B-field diverges slowly, since it is the reverse field below the stagnation point of the magnets. as shown here:

Here is a picture of the source in operation: