Development and characterization of the readout system for POLARBEAR-2

Polarbear-2 is a next-generation receiver for precision measurements of the polarization of the cosmic mi-crowave background (Cosmic Microwave Background (CMB)). Scheduled to deploy in early 2015, it will observealongside the existing Polarbear-1 receiver, on a new telescope in the Simons Arrayon Cerro Toco in theAtacama desert of Chile. For increased sensitivity, it will feature a larger area focal plane, with a total of 7,588 polarization sensitive antenna-coupled Transition Edge Sensor (TES) bolometers, with a design sensitivity of 4.1 μKs. The focal plane will be cooled to 250 milliKelvin, and the bolometers will be read-out with 40 × frequency domain multiplexing, with 36 optical bolometers on a single SQUID amplier, along with 2 dark bolometers and 2 calibration resistors. To increase the multiplexing factor from 8 × for Polarbear-1 to 40 × for Polarbear-2 requires additional bandwidth for SQUID readout and well-dened frequency channel spacing. Extending to these higher frequencies requires new components and design for the LC lters which dene channel spacing. The LC lters are cold resonant circuits with an inductor and capacitor in series with each bolometer, and stray inductance in the wiring and equivalent series resistance from the capacitors can aect bolometer operation. We present results from characterizing these new readout components. Integration of the readout system is being done rst on a small scale, to ensure that the readout system does not aect bolometer sensitivity or stability, and to validate the overall system before expansion into the full receiver. We present the status of readout integration, and the initial results and status of components for the full array.