Lanqiang Zhang

Optical monitoring of three gamma ray-Loud Bl Lacertae objects in 1999-2002

We present the results of optical photometric (BVRI) monitoring of three gamma-ray - loud BL Lac objects (3C 66A, PKS 0735+ 178, and BL Lacertae) in 1999 - 2002. During our observations, these objects showed significant rapid variations: 3C 66A and PKS 0735+ 178 exhibit short-timescale ( similar to 1 hr) variability in the B band, and BL Lac exhibits intraday variability in B and V. We find that there is a strong correlation between brightness and color for 3C 66A and BL Lac. We have analyzed the relationship between optical variability and gamma-ray variability and discuss theoretical models for gamma-ray - loud BL Lac emission. We have found shorter time variability for 3C 66A and PKS 0735+ 178 compared with previous reports.

The modification of the nonlinear guiding center theory

We modify the NonLinear Guiding Center theory for perpendicular diffusion by replacing the spectral amplitude of the two-component model of magnetic turbulence with that of the two-dimensional model (following Shalchi), and replacing the constant a(2), which indicates the degree particles following the magnetic field line, with the variable a(2) as a function of the magnetic turbulence. We combine the modified model with the NonLinear PArallel diffusion theory to solve perpendicular and parallel diffusion coefficients simultaneously. It is shown that the new model agrees better with simulations. Furthermore, we fit the numerical results of the new model with polynomials, so that the parallel and perpendicular diffusion coefficients can be calculated directly without iteration of integrations, and many numerical calculations can be reduced.

Application of high temperature superconducting quantum interference devices in transient electromagnetic method for magnetotelluric soundings

Abstract We have explored the application of high temperature superconducting interference devices (SQUIDs) in the artificial source magnetotelluric sounding. Field experiments were performed to test the high T c SQUID in transient electromagnetic source. It showed that the SQUID sensor has some advantages over the conventional inductive sensor, and also revealed some problems. Theoretical studies have been carried out to investigate the prospects and limitations of the SQUID sensor.

INSTRUMENT DESCRIPTION AND PERFORMANCE EVALUATION OF A HIGH-ORDER ADAPTIVE OPTICS SYSTEM FOR THE 1 m NEW VACUUM SOLAR TELESCOPE AT FUXIAN SOLAR OBSERVATORY

A high-order solar adaptive optics (AO) system including a fine tracking loop and a high-order wavefront correction loop has been installed at the 1 m New Vacuum Solar Telescope of the Fuxian Solar Observatory, in routine operation since 2016. The high-order wavefront correction loop consists of a deformable mirror with 151 actuators, a correlating Shack-Hartmann wavefront sensor with 102 subapertures of which the Absolute Difference Square Algorithm is used to extract the gradients, and a custom-built real-time controller based on a Field-Programmable Gate Array (FPGA) and multi-core Digital Signal Processor (DSP). The frame rate of the wavefront sensor is up to 3500 Hz and this is, to our knowledge, the fastest solar AO system. This AO system can work with a Fried parameter r(0), at the 500 nm wavelength, of larger than 3 cm. The first 65 modes of the Zernike aberrations can be efficiently corrected and the Strehl ratio of the corrected TiO image for the solar pore is superior to 0.75 with the Fried parameter r(0) larger than 10 cm. In this paper, the design of the system is described, and high-resolution solar observational images are presented. Furthermore, the performances of the AO system are evaluated according to the data recorded by the real-time controller.

Real-Time Controller Based on FPGA and DSP for Solar Ground Layer Adaptive Optics Prototype System at 1-m NVST

Solar ground layer adaptive optics (GLAO), containing a large field of view (FOV) wavefront sensor (WFS) and one deformable mirror (DM), can be used to reduce and stabilize the seeing effectively over a wide FOV. As the brain of the GLAO system, the real-time controller (RTC) computes the commands to drive the DM according to the average wavefront errors measured by the multi-direction correlating Shack–Hartmann WFS, which is a time-consuming process. A customized RTC based on a high-speed field programming gate array and a multi-core digital signal processor was developed for the solar GLAO prototype system at the 1-m New Vacuum Solar Telescope. Several parallel acceleration techniques are used to reduce the computation time of the RTC. Compared with the previous RTCs, our RTC architecture has nearly no timing jitter. In this paper, the design of the RTC for our solar GLAO prototype will be introduced. The test results of the RTC are also presented. Moreover, the on-sky Sun observational results of the solar GLAO prototype are shown.

An updated 37-element low-order solar adaptive optics system for 1-m new vacuum solar telescope at Full-Shine Lake Solar Observatory

A low-order solar adaptive optics (AO) system, which consists of a fine tracking loop with a tip/tilt mirror and a correlation tracker, and a high-order correction loop with a 37-element deformable mirror, a correlating Shack-Hartmann wavefront sensor and a high-order wavefront correction controller, had been successfully developed and installed at 1-m New Vacuum Solar Telescope of Full-shine Lake (also called Fuxian Lake) Solar Observatory. This system is an update of the 37-element solar AO system designed for the 26-cm Solar Fine Structure Telescope at Yunnan Astronomical Observatory in 2009. The arrangement of subapertures of the Shack-Hartmann wavefront sensor was changed from square to hexagon to achieve better compensation performance. Moreover, the imaging channel of the updated system was designed to observe the Sun at 710nm and 1555nm simultaneously. The AO system was integrated into the solar telescope in 2011, and AO-corrected high resolution sunspots and granulation images were obtained. The observational results show that the contrast and resolution of the solar images are improved evidently after the correction by the AO system.

Progress on the 1.8m solar telescope: the CLST

In order to study some special solar activities, such as the emergence, evolution and disappearance progress of the sunspot and magnetic flux, and the key role of magnetic field, a new 1.8-meter size high-resolution solar telescope —the CLST will be built in the Institute of Optics and Electronics(IOE), Chinese Academy of Science(CAS), which locates in Chengdu, China. The CLST has a classic Gregorian configuration, alt-azimuth mount, retractable dome. Besides that, a large mechanical de-rotator will be used to cancel the image rotation, and finally it will cooperate with another kind of mechanical de-rotator to cancel both of the pupil rotation and image rotation. Φ3 arc-minute field of view will help the CLST to observe the whole solar activity region, and if necessary the FOV can be enlarged to Φ 6 arc-minute. A 1.8m primary mirror with honeycomb sandwiches structure made by using ULE material will reduce about 70% of weight. Thermal controlling system will also be equipped for the CLST, which including Heat-Stop, primary mirror, tube truss, mount and the other optics elements. An experimental system for validating thermal controlling of primary mirror and Heat-Stop has been built, and the temperature tracking results will be illustrated in this paper. Currently, we have finished the detailed design of the CLST, and some important components also have been manufactured and finished. In this paper, we describe some important progresses and the latest status of the CLST project during these two years.

Solar adaptive optics for 1m new vacuum solar telescope

Adaptive Optics (AO) has become the requisite equipment of the ground-based large solar telescope to correct the wavefront aberration induced by the atmospheric turbulence. Two generation solar AO systems, one is the 37-element loworder AO system with 2100Hz frame rate and the other is 151-element high-order AO system with 3500Hz frame rate, were successfully developed in 2013 and 2015 respectively. In this presentation, the development of the two AO systems for 1-m New Vacuum Solar Telescope (NVST) at Fuxian Solar Observatory (FSO) will be introduced and the solar high resolution observational results are presented.

1.8-m solar telescope in China: Chinese Large Solar Telescope

Abstract. For better understanding and forecasting of solar activity, high resolution observations for the Sun are needed. Therefore, the Chinese Large Solar Telescope (CLST) with a 1.8-m aperture is being built. The CLST is a classic Gregorian configuration telescope with an open structure, alt-azimuth mount, retractable dome, and a large mechanical de-rotator. The optical system with an all reflective design has a field of view of larger than 3 arc-min. The 1.8-m primary mirror is a honeycomb sandwich fused silica lightweight mirror with an ultra lower expansion material and active cooling. The adaptive optics system will be developed to provide the capability for diffraction-limited observations at visible wavelengths. The CLST design and development phase began in 2011 and 2012, respectively. We plan for the CLST’s start of commission to be in 2017. A multiwavelength tomographic imaging system, ranging from visible to near-infrared, is considered as the first light scientific instrument. The main system configuration and the corresponding postfocal instruments are described. Furthermore, the latest progress and current status of the CLST are also reported.

Real time controller for 37-element low-order solar adaptive optics system at 1m new vacuum solar telescope

A low-order solar adaptive optics (AO) system had been successfully built and installed at 1m New Vacuum Solar Telescope (NVST) of Full-shine Lake Solar Observatory. The real time controller (RTC) of the AO system, which consists of a correlation tracker and a high-order wavefront correction controller, was developed. In this system, the absolute difference algorithm is used to detect wavefront gradients. A new architecture with field-programmable gate array (FPGA) and digital signal processor (DSP) for the real-time controller based on systolic array and pipeline was designed. The controller was integrated into the AO system and saw the first light on February 24th, 2011, using solar granulation as the beacon. Later, the AO-corrected high resolution sunspots images were obtained using sunspots as the beacon. The observational results show that the contrast and resolution of the solar images are improved evidently after the correction by the AO system. The design of the RTC and the observational results will be presented.