Magboltz 11.12

From Steve:

I have attached an update for C3F8 which also includes some update for magboltz itself. The update removes the artificial ionisation x-section which was intended to improve the efficiency of calculation of attaching mixtures. Unfortunately it did not work as advertised so I have removed it and returned to version 10.n for the calculation of Townsends. I have also fixed two bugs:

1. I did a bad edit somewhere in version 10 or 11 and the magnetic field calculations were in error. The problem is now fixed
2. It was not possible to output the separate attachment collisions for the production of the different negative ions in eg SF6. I found the bug and the problem is now resolved.