The QUIJOTE Experiment (Q-U-I JOint TEnerife) is a combined operation of two telescopes and three instruments working in the microwave band to measure the polarization of the Cosmic Microwave Background (CMB) from the northern hemisphere, at medium and large angular scales. The experiment is located at the Teide Observatory in Tenerife, one of the seven Canary Islands (Spain). The project is a consortium maintained by several institutions: the Instituto de Astrofísica de Canarias (IAC), the Instituto de Física de Cantabria (IFCA), the Communications Engineering Department (DICOM) at Universidad de Cantabria, and the Universities of Manchester and Cambridge. The consortium is led by the IAC.
The QUIJOTE TGI instrument is currently being assembled and tested at the IAC in Spain. The TGI is a 31 pixel 26-36 GHz polarimeter array designed to be mounted at the focus of the second QUIJOTE telescope. This follows a first telescope and multi-frequency instrument that have now been observing almost 2 years. The polarimeter design is based on the QUIET polarimeter scheme but with the addition of an extra 90º phase switch which allows for quasiinstantaneous complete QUI measurements through each detector. The advantage of this solution is a reduction in the systematics associated with differencing two independent radiometer channels. The polarimeters are split into a cold front end and a warm back end. The back end is a highly integrated design by the engineers at DICOM. It is also sufficiently modular for testing purposes. In this presentation the high quality wide band components used in the optical design (also designed in DICOM) are presented as well as the novel cryogenic modular design. Each polarimeter chain is accessible individually and can be removed from the cryostat and replaced without having to move the remaining pixels. The optical components work over the complete Ka band showing excellent performance. Results from the sub unit measurements are presented and also a description of the novel calibration technique that allows for bandpass measurement and polar alignment. Terrestrial Calibration for this instrument is very important and will be carried out at three points in the commissioning phase: in the laboratory, at the telescope site and finally a reduced set of calibrations will be carried out on the telescope before measurements of extraterrestrial sources begin. The telescope pointing model is known to be more precise than the expected calibration precision so no further significant error will be added through the telescope optics. The integrated back-end components are presented showing the overall arrangement for mounting on the cryostat. Many of the microwave circuits are in-house designs with performances that go beyond commercially available products.
The QUIJOTE-CMB project has been described in previous publications. Here we present the current status of the
QUIJOTE multi-frequency instrument (MFI) with five separate polarimeters (providing 5 independent sky pixels): two
which operate at 10-14 GHz, two which operate at 16-20 GHz, and a central polarimeter at 30 GHz. The optical
arrangement includes 5 conical corrugated feedhorns staring into a dual reflector crossed-draconian system, which
provides optimal cross-polarization properties (designed to be < −35 dB) and symmetric beams. Each horn feeds a novel
cryogenic on-axis rotating polar modulator which can rotate at a speed of up to 1 Hz. The science driver for this first
instrument is the characterization of the galactic emission. The polarimeters use the polar modulator to derive linear
polar parameters Q, U and I and switch out various systematics. The detection system provides optimum sensitivity
through 2 correlated and 2 total power channels. The system is calibrated using bright polarized celestial sources and
through a secondary calibration source and antenna. The acquisition system, telescope control and housekeeping are all
linked through a real-time gigabit Ethernet network. All communication, power and helium gas are passed through a
central rotary joint. The time stamp is synchronized to a GPS time signal. The acquisition software is based on PLCs
written in Beckhoffs TwinCat and ethercat. The user interface is written in LABVIEW. The status of the QUIJOTE MFI
will be presented including pre-commissioning results and laboratory testing.
The QUIJOTE (Q-U-I JOint Tenerife) CMB Experiment will operate at the Teide Observatory with the aim
of characterizing the polarisation of the CMB and other processes of Galactic and extragalactic emission in the
frequency range of 10-40GHz and at large and medium angular scales. The first of the two QUIJOTE telescopes
and the first multi-frequency (10-30GHz) instrument are already built and have been tested in the laboratory.
QUIJOTE-CMB will be a valuable complement at low frequencies for the Planck mission, and will have the
required sensitivity to detect a primordial gravitational-wave component if the tensor-to-scalar ratio is larger
than r = 0.05.