Calibrating the absorption imaging of cold atoms under high magnetic fields

We develop a theoretical model for calibrating the absorption imaging of cold atoms under high magnetic fields. Comparing to zero or low magnetic fields, the efficiency of the absorption imaging becomes lower while it requires an additional correction factor to obtain the absolute atom number under the Beer-Lambert law. Our model is based on the rate equations and can account many experimental imperfections such as Zeeman level crossing, failures of hyperfine structures, off-resonant couplings, and low repumping efficiency, etc. Based on this method, we can precisely calculate the correction factor for atom number measurement without any empirical or fitting parameters. Meanwhile, we use a cold-atom apparatus of rubidium-85 to experimentally verify our model. Besides these, we find our work can also serve as a benchmark to measure the polarization impurity of a circular-polarized laser beam with high sensitivities. We believe this work will bring convenience for most of cold-atom experiments using absorption imaging.Comment: 9 pages, 5 figure

Design of the klystron filament power supply control system for EAST LHCD

A filament is a critical component of the klystron used to heat the cathode. There are totally 44 klystrons in experimental advanced superconducting tokamak (EAST) lower hybrid current drive (LHCD) systems. All klystron filaments are powered by AC power suppliers through isolated transformers. In order to achieve better klystron preheat, a klystron filament power supply control system is designed to obtain the automatic control of all filament power suppliers. Klystron filament current is measured by PLC and the interlock between filament current and klystron high voltage system is also implemented. This design has already been deployed in two LHCD systems and proves feasible completely

Research activities and progress on the long pulse ECRH launcher for EAST

A long pulse Electron Cyclotron Resonance Heating (ECRH) system is developed on EAST tokamak for plasma heating and current profile tailoring. The ECRH system is designed to operate at 140GHz and to inject 4MW CW power. With respect to the physical objectives of the newly built ECRH system, a quasi-optical launcher is designed to inject 4MW continuous wave into plasma through an equatorial port. Gaussian beams delivered from evacuated corrugation waveguides will be focused and reflected by high thermal conductive metal mirrors, and then steered by using push-rod steering mechanism with entire scanning range of ±25° toroidally and over 30° poloidally in plasma cross section. The mirrors are carefully designed with mega watts power handling capability and optimum optical characteristics. The performance of steering mechanism has been tested before installation, an open-loop control system for ECRH launcher has been implemented for required mirror movement and proper polarization between plasma discharges. This paper will present the overall design and progress of the launcher, along with the performance in EAST campaigns. Considerations and possible upgrade of the design features relevant to long pulse operation are discussed

Research activities and progress on the long pulse ECRH launcher for EAST

A long pulse Electron Cyclotron Resonance Heating (ECRH) system is developed on EAST tokamak for plasma heating and current profile tailoring. The ECRH system is designed to operate at 140GHz and to inject 4MW CW power. With respect to the physical objectives of the newly built ECRH system, a quasi-optical launcher is designed to inject 4MW continuous wave into plasma through an equatorial port. Gaussian beams delivered from evacuated corrugation waveguides will be focused and reflected by high thermal conductive metal mirrors, and then steered by using push-rod steering mechanism with entire scanning range of ±25° toroidally and over 30° poloidally in plasma cross section. The mirrors are carefully designed with mega watts power handling capability and optimum optical characteristics. The performance of steering mechanism has been tested before installation, an open-loop control system for ECRH launcher has been implemented for required mirror movement and proper polarization between plasma discharges. This paper will present the overall design and progress of the launcher, along with the performance in EAST campaigns. Considerations and possible upgrade of the design features relevant to long pulse operation are discussed

Recent progress of the development of a long pulse 140GHz ECRH system on EAST

A long pulse ECRH system with a goal of 140GHz 4MW 100~1000s has been developed to meet the requirement of steady-state operation on EAST. Gycom gyrotrons are employed in the No.1 and No.3 systems, CPI gyrotrons are used in the No.2 and No.4 systems. The development of the two Gycom gyrotron systems has been finished. The first short pulse EC wave injection has been demonstrated successfully during the EAST 2015 Spring campaign. In the commissioning and operation towards steady-state operation, 0.4MW 100s has been injected to plasma successfully by using the No.1 system, 4.7keV 102s L-mode and 102s H-mode plasma have been achieved on EAST with the help of ECRH. Recently, a longest pulse of 0.55MW 1000s has been obtained based on calorimetric dummy load measurements on the No.3 gyrotron. The No.2 gyrotron also has been installed and partially tested, 500kW 80s has been demonstrated in the dummy load. The remaining No.4 gyrotron will be ready to test in 2018 or 2019. The whole 4MW system will be completed within two years. The 400s fully non-inductive H-mode operation would be expected in the next four years in the condition of fully tungsten diverter on EAST

Recent progress of the development of a long pulse 140GHz ECRH system on EAST

A long pulse ECRH system with a goal of 140GHz 4MW 100~1000s has been developed to meet the requirement of steady-state operation on EAST. Gycom gyrotrons are employed in the No.1 and No.3 systems, CPI gyrotrons are used in the No.2 and No.4 systems. The development of the two Gycom gyrotron systems has been finished. The first short pulse EC wave injection has been demonstrated successfully during the EAST 2015 Spring campaign. In the commissioning and operation towards steady-state operation, 0.4MW 100s has been injected to plasma successfully by using the No.1 system, 4.7keV 102s L-mode and 102s H-mode plasma have been achieved on EAST with the help of ECRH. Recently, a longest pulse of 0.55MW 1000s has been obtained based on calorimetric dummy load measurements on the No.3 gyrotron. The No.2 gyrotron also has been installed and partially tested, 500kW 80s has been demonstrated in the dummy load. The remaining No.4 gyrotron will be ready to test in 2018 or 2019. The whole 4MW system will be completed within two years. The 400s fully non-inductive H-mode operation would be expected in the next four years in the condition of fully tungsten diverter on EAST