[Debaser]

Every time i've fought this fight, i've found that having some fighters go right in and start smashing the raksashas is the best approach, magic not really being too effective on them. in your situation, though, that really isn't an option.
this fight must be really hard for a solo magic-user...for such a situation, you might want to just come back and finish the druid grove when your sorcerer is a little higher than 12th level...