A Cold Focal Plane Chopper for the PACS Instrument of the FIRST satellite - Tests of an Advanced Prototype

摘要

The imaging photometer and spectroscopic camera PACS, one of the three scientific instruments aboard the European 3.5 m infrared space telescope FIRST, will apply a tilting mirror mechanism for optical beam switching. The development of this focal plane chopper, capable of operation under cryovacuum conditions, is reported here. In order to meet the stringent requirements with respect to power dissipation and positional accuracy, special drive coils and a new position sensor had to be develoepd. A simulation model including electromagnetic analysis by the 3D code MAFIA, verified by extensive cold testing of the prototype hardware, was used for the optimization of the system and led to the advanced prototype of the chopper. Closed loop control of the mirror deflection allows square wave modulation in the frequency range 0-15 Hz (80 percent duty cycle) with amplitudes of +/- 9 deg with high positional accuracy of less than 30". The power dissipation at operating temperature of 4 K is below 500 muW.