Periodic Reporting for period 1 - PROTOCALC (PROTOCALC: a prototype for a polarized calibrator for CMB experiments)
Berichtszeitraum: 2021-04-01 bis 2023-03-31
Cosmic Microwave Background (CMB) polarization instruments need a very accurate control on the systematics introduced by absolute polarization orientation and polarized beam patterns, which limit the accuracy on multiple astrophysical signals such as the Inflationary Gravitational Waves and influences the reconstruction of the gravitational lensing effects on the CMB. Besides, an absolute calibration of the polarization angle of the CMB photons would enable the detection of signatures of parity-violating mechanisms in the early Universe, such as Cosmic Birefringence. CMB measurements are one of the best resources for testing cosmological models and fundamental physics. We have learned that the geometry of the Universe is flat and that its age is around 13.8 billion years. We have also determined that its energy content is dominated by non electromagnetic-interactive particles such as dark matter and dark energy. The signal emitted by the CMB is also linearly polarized. These polarized components, like the temperature, are not isotropic. As a result, they create patterns that are a combination of even-parity (E) and odd-parity (B) modes. Recent E-modes polarization measurements are consistent with the standard cosmological model. However, B-mode signals originated from the CMB have never been detected. They are approximately two order of magnitude lower that the E-modes and can be easily contaminated by other astrophysical signals, such as galactic dust. However, a detection of primordial B-modes can confirm the inflationary theory. It would also give an indication on the characteristics of the inflation, such as the epoch or the energy scale. An accurate study of the gravitational lensing can give more information about neutrinos, such as the number of species and their mass. Accurate measurements of B-modes can also give more information regarding Cosmic Birefringence which will help to understand and verify fundamental physics such as symmetry theories. Current and future CMB polarization experiments require orders of magnitude improvement in sensitivity, therefore instrumental systematic effects that until today were less important than statistical uncertainties are becoming one the most significant limitations. To overcome this limitation, my project, PROTOCALC, will build a prototype for a polarization angle and beam calibrator to be used with the most advanced CMB polarimeters, such as the Simons Observatory. This new instruments will allow a better calibration of CMB experiments improving their sensitivity.
The idea behind the project is to develop a new hardware design and then create a new calibrator source. This calibrator source will be flown on a drone giving the possibility to use for every telescope on the ground. The project uses commercially available components to develop this calibrator source. Given the accuracy that is required in the knowledge of the polarization angle of the source, PROTOCALC uses RTK to determine the position of the source and an inclinometer to estimate the roll and pitch angles. In addition to these sensors, PROTOCALC will also host a camera for photogrammetry. This last method is developed by some of our collaborators in the Simons Observatory. Given that PROTOCALC will be a calibrator for this experiment, we need to ensure the possibility to use the same method that will be used for other calibration sources.
The idea behind the project is to develop a new hardware design and then create a new calibrator source. This calibrator source will be flown on a drone giving the possibility to use for every telescope on the ground. The project uses commercially available components to develop this calibrator source. Given the accuracy that is required in the knowledge of the polarization angle of the source, PROTOCALC uses RTK to determine the position of the source and an inclinometer to estimate the roll and pitch angles. In addition to these sensors, PROTOCALC will also host a camera for photogrammetry. This last method is developed by some of our collaborators in the Simons Observatory. Given that PROTOCALC will be a calibrator for this experiment, we need to ensure the possibility to use the same method that will be used for other calibration sources.
Since the beginning of the project, we developed a calibrator source at 90GHz with a high degree of polarization. The source has been successfully flown thirty times during two different campaign at the Atacama Site. using a commercial drone above telescopes in Chile and in particular above the CLASS telescope. The first flights happened 1 year after the beginning of the project (april 2022), while the second ones in January 2023. We consider these two campaigns as preparatory for a full calibration campaign that will happen in the future, for calibrating both Simons Observatory and CLASS. The source itself has been designed in house using CAD software in the first 3 months and then it has been realized by the machine shop at the host institution. In parallel, we developed a fully autonomous software that control the source using a raspberry pi. The software uses cameras and attitude sensors, such as GPS and inclinometers, to estimate the position of the source within few centimeters and with an angle accuracy of ~0.1deg. Full analysis, of the last flight is still ongoing and the data collected will be used for calibrating the CLASS telescope. All the hardware has been characterized in the lab and on the field.
Finally, in parallel to this hardware related work, the project as also developed a simulator for a calibrator under the TOAST3 framework that is used within the Simons Observatory collaboration to design the calibration campaign.
Finally, in parallel to this hardware related work, the project as also developed a simulator for a calibrator under the TOAST3 framework that is used within the Simons Observatory collaboration to design the calibration campaign.
The project PROTOCALC had both scientific and technological impact. It advanced significantly the method for the calibration of the polarization angle in the field of the Cosmic Microwave Background observations, and in particular for the world-leading CMB polarimeters in the Atacama region. This will allow to control the systematic uncertainties on the discovery of the primordial gravitational waves and the Cosmic Birefringence. PROTOCALC is the first project that designed and shown the feasibility of a highly polarized source at 90GHz, flying above telescope sites at 5000 meters, with high accuracy (better than 0.1 degree) in the polarization angle determination, and which can be used for multiple telescopes due to its flexibility and portability. Moreover, this is the first non-fixed source that achieves all the requirements in terms of positioning required. Also the simulation capabilities that were developed for the project are unique in the field. For the first time, it is possible to simulate a full calibration campaign with an artificial source under the TOAST3 framework. We expect to reuse significantly this source also in the future for calibrating again CLASS but also additional telescopes like Simons Observatory.