Youling Yue

THE FIVE-HUNDRED-METER APERTURE SPHERICAL RADIO TELESCOPE (FAST) PROJECT

The Five-hundred-meter Aperture Spherical radio Telescope (FAST) is a Chinese mega-science project funded by the National Development and Reform Commission (NDRC). The National Astronomical Observatories of China (NAOC) is in charge of its construction and the subsequent operation. Upon its expected completion in September of 2016, FAST will surpass the 300-meter Arecibo and the 100-meter GBT in terms of absolute sensitivity in the 70 MHz to 3 GHz bands. In this paper, we report the current status, the key science goals, and the aspiration of its early sciences. A special emphasis is paid to its innovative fatigue-resistant fibers, which are critical for the control and data acquisition under the unique FAST design.

Studying solutions for the fatigue of the FAST cable-net structure caused by the process of changing shape

The Five-hundred-meter Aperture Spherical Radio Telescope (FAST) is supported by a cable-net structure, whose change in shape leads to a stress range of approximately 500 MPa. This stress range is more than twice the standard recommended value. The cable-net structure is thus the most critical and fragile part of the FAST reflector system. In this study, we first search for a more appropriate deformation strategy that reduces the stress amplitude generated by the process of changing shape. Second, we roughly estimate the tracking trajectory of the telescope during its service life, and conduct an extensive numerical investigation to assess the requirements for fatigue resistance. Finally, we develop a new type of steel cable system that satisfies the cable requirements for construction of FAST.

FAST low frequency pulsar survey

The Five-hundred-meter Aperture Spherical radio Telescope (FAST) is under construction and will be commissioned in September 2016. A low frequency 7-beam receiver working around 400 MHz is proposed for FAST early science. It will be optimized for a whole FAST sky drift-scan pulsar survey. Simulations show that about 1500 new normal pulsars will be discovered, as while as about 200 millisecond pulsars.

EMC design for actuators in the FAST reflector

The active reflector is one of the three main innovations of the Five-hundred-meter Aperture Spherical radio Telescope (FAST). The deformation of such a huge spherically shaped reflector into different transient parabolic shapes is achieved by using 2225 hydraulic actuators which change the position of the 2225 nodes through the connected down tied cables. For each different tracking process of the telescope, more than 1/3 of these 2225 actuators must be in operation to tune the parabolic aperture accurately to meet the surface error restriction. It means that some of these actuators are inevitably located within the main beam of the receiver, and the Electromagnetic Interference (EMI) from the actuators must be mitigated to ensure the scientific output of the telescope. Based on the threshold level of interference detrimental to radio astronomy presented in ITU-R Recommendation RA.769 and EMI measurements, the shielding efficiency (SE) requirement of each actuator is set to be 80dB in the frequency range from 70MHz to 3GHz. Therefore, Electromagnetic Compatibility (EMC) was taken into account in the actuator design by measures such as power line filters, optical fibers, shielding enclosures and other structural measures. In 2015, all the actuators had been installed at the FAST site. Till now, no apparent EMI from the actuators has been detected by the receiver, which proves the effectiveness of these EMC measures.

Shielding effectiveness measurement for physically small enclosure in FAST telescope

Five-hundred-meter Aperture Spherical radio Telescope (FAST) is a Chinese mega-science project to build the largest single dish radio telescope in Guizhou province, Southwest China. The construction of FAST will involve many kinds of analog and digital electrical equipments. The electrical equipments are potential threat to radio observation due to its ElectroMagnetic Interference (EMI) emission. The EMI should be safely shielded when FAST telescope operates. The shielding effectiveness of large shielding enclosures can be tested with two log periodic antennas, signal generator and spectrum analyzer. It is not suitable to test small shielding enclosure for that is not possible to put big antenna and signal generator inside. In this paper, an effective shielding effectiveness measurement system for the small shielding enclosure is introduced. This measurement system uses a frequency synthesizer of Valon Technology as signal generator which can measure the shielding effectiveness no more than 100dB in a frequency range of 23–6000MHz. Some of measurement results of shielding effectiveness are also presented.

RFI mitigation on mobile base stations around FAST

After five and a half years construction, the main structure of Five-hundred-meter Aperture Spherical radio Telescope (FAST) has been completed in September 2016. Meanwhile, a Radio Quiet Zone (RQZ) with radius 30 km has also been established. In order to evaluate the Radio Frequency Interference (RFI) influence from the mobile base stations within radius 5 km (the restriction zone of RQZ) around FAST, several measurements have been carried out when these stations were closed temperately. Comparing the RFI measurement results before and after the closure of these stations, the interference has been decreased more than 30 dB. Since November 1 2016, all the mobile base station within the restriction zone of FAST RQZ have be closed permanently to avoid the risk of the receiver saturation due to the interference coming from these stations.

EMC design for FAST

Five-hundred-meter Aperture Spherical radio Telescope (FAST) is a Chinese mega-science project to build the largest single dish radio telescope in the world. The first light of FAST is expected in September 2016. Due to the high sensitivity of FAST, it is very sensitive to the radio frequency interference coming from the electrical and electronic equipments of telescope itself. In order to assure the realization of the scientific goals of the telescope, the electromagnetic compatibility (EMC) study on FAST at the design and construction stages, has been carried out to decrease the possibility of the interference from the telescope. Several examples, such as EMC designs and measurements for actuator and focus cabin, have been introduced briefly.

Wide-bandwidth drift-scan pulsar surveys of globular clusters: application to early science observations with FAST

The Five-hundred-meter Aperture Spherical Telescope (FAST) will begin its early-science operations during 2016. Drift-scan pulsar surveys will be carried out during this period using an ultra-wide-band receiver system (covering ~ 270 to 1620 MHz). We describe a method for accounting for the changes in the telescope beam shape and the pulsar parameters when searching for pulsars over such a wide bandwidth. We applied this method to simulated data sets of pulsars in globular clusters that are visible to FAST and found that a representative observation would have a sensitivity of ~40 μJy. Our results showed that a single drift-scan (lasting less than a minute) is likely to find at least one pulsar for observations of four globular clusters. Repeated observations will increase the likely number of detections. We found that pulsars in ~16 clusters are likely to be found if the data from 100 drift-scan observations of each cluster are incoherently combined.