Cartridge-Type 800 GHz Receiver for the Atacama Submillimeter Telescope Experiment (ASTE)

We have developed a cartridge-type 800 GHz receiver for the ASTE telescope in Atacama, Chile. The receiver has been assembled with a cooled receiver optics, a Nb-based SIS mixer, a local oscillator (LO) optics, and IF components in a 170 mm diameter column-type cartridge. The cooled optics is composed of a single ellipsoidal mirror to couple between the feed horn and the subreflector of the antenna, and an LO coupler with 10% efficiency. Owing to its cartridge and cryostat structure, the mechanical vibrations of the GM cryocooler are significantly reduced, and therefore the receiver is highly stable on the telescope. The receiver noise temperature, using a Nb-based SIS mixer and a 4–8 GHz HEMT amplifier, was attained to 1300 K in DSB at an LO frequency of 815 GHz. The system noise temperature, $T_{\mathrm{sys}}$ , was typically 4000–8000 K in DSB at an LO frequency of 812 GHz during operations, which depended on the atmospheric opacity. The typical zenith opacity at an LO frequency of 812 GHz was $\sim 1$ . The half-power beam width (HPBW) of the main beam was measured by total power scanning across the Moon, and was consistent with the diffraction limit. A spectrum of the CO $J=7 \hbox{--} 6$ line (806.6518 GHz) toward Orion KL was successfully detected.