The E and B Experiment (EBEX) will measure the cosmic microwave background radiation of a part of the sky during two sub-orbital (high altitude) balloon flights. It is an experiment to make large, high-fidelity images of the CMB polarization anisotropies. By using a telescope which flies at over 42,000 metres high, it is possible to reduce the atmospheric absorption of microwaves to a minimum. This allows massive cost reduction compared to a satellite probe, though only a small part of the sky can be scanned and for shorter duration than a typical satellite mission such as WMAP.
The first flight was a test flight over North America in 2009. In the subsequent flight in 2011, the balloon will be launched at the McMurdo Station in the Antarctic. It will use the Polar vortex winds to circle around the South Pole, returning after two weeks.
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EBEX consists of a 1.5 m Dragone-type telescope that provides a resolution of 8 arcminutes in frequency bands centered around 150, 250, and 410 GHz. Polarimetry is achieved with a continuously-rotating achromatic half-wave plate supported by a superconducting magnetic bearing and a fixed wire grid polarizer. The wire grid is mounted at 45 degrees to the incoming light beam and transmits one polarization state while reflecting the other. Each polarization state is subsequently detected by its own focal plane with a 6 degree instantaneous field-of-view on the sky.
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