Dorganator

The  was a machine invented by the Javaman. He set it up on Volnex VI. It emitted theta-waves.

The Dorganator could project the Javaman's thoughts into another person. He used it to enslave the native Volnexians. He also used it to bring the TARDIS to Volnex. However, it had a side effect that he did not expect: it switched the Sixth Doctor and Peri Brown's minds into each others' bodies, a process known as corporelectroscopy.

The Javaman used the Dorganator to torture a Volnexian, trying to convince Peri (who he thought was the Doctor) to give him the secrets of time travel. The Dorganator was destroyed when the Doctor sabotaged it. (PROSE: Turnabout is Fair Play)