A new 10 meter diameter telescope is being constructed for deployment
at the NSF South Pole research station. The telescope is designed for
conducting large-area millimeter and sub-millimeter wave surveys
of faint, low contrast emission, as required to map primary and secondary anisotropies in the cosmic microwave background. To achieve the required sensitivity and resolution, the telescope design employs an off-axis primary with a 10 meter diameter clear aperture. The full aperture and the associated optics will have a combined surface accuracy of better than 20 microns rms to allow precision operation in the submillimeter atmospheric windows. The telescope will be surrounded with a large reflecting ground screen to reduce sensitivity to thermal emission from the ground and local interference. The optics of the telescope will support a degree field of view at 2mm wavelength and will feed a new 1000-element micro-lithographed planar bolometric array with superconducting transition-edge sensors and frequency-multiplexed readouts. The first key project will be to conduct a survey over &dbigwig;4000 degrees for galaxy clusters using the Sunyaev-Zel'dovich Effect. This survey should find many thousands of clusters with a mass selection criteria that is remarkably uniform with redshift. Armed with redshifts obtained from optical and infrared follow-up observations, it is expected that the survey will enable significant constraints to be placed on the equation of state of the dark energy.
We describe the development of a frequency-domain multiplexer (MUX) to read out arrays of superconducting transition-edge sensors (TES). Fabrication of large-format arrays of these sensors is becoming practical; however, reading out each sensor in the array is a major instrumental challenge that is possibly solved by frequency-domain multiplexing. Each sensor is AC biased at a different frequency, ranging from 380 kHz to 1 MHz. The sensor signal amplitude-modulates its respective AC bias frequency. An LC filter associated with each sensor suppresses Johnson noise from the other sensors. The signals are combined at a current summing node and measured by a single superconducting quantum interference device (SQUID). The individual signals from each sensor are then lock-in detected by room temperature electronics. Test chips with fully lithographed LC filters for up to 32 channels have been designed and fabricated. The capacitance and inductance values have been measured and are close to the design goals. We discuss the basic principles of frequency-domain multiplexing, the design and testing of the test chips, and the implementation of a practical system.
We report on the development of arrays of Transition-Edge Sensor (TES) bolometers. We describe several architectures including planar-antenna-coupled, horn-coupled, and absorber-coupled devices. Antenna coupling can greatly simplify the fabrication of multi-frequency bolometer arrays compared to techniques in common use. Planar antennas are intrinsically polarization sensitive and are a promising technology for measurements of CMB polarization. We have designed a prototype device with a double-slot dipole antenna, integrated band-defining filters, and a membrane-suspended bolometer. A test chip has been constructed.
We are developing 300-1000 element arrays of horn-coupled TES bolometers with spider-web absorbers for galaxy cluster searches using the Sunyaev-Zel'dovich effect. Finally, we describe a filled absorber-coupled array design that is built using a single silicon wafer. Such arrays are well suited for far-infrared and sub-millimeter observations such as those from SOFIA and future orbital missions.