| J-TEXT is a medium-sized, with iron core and conventional magnet tokamak device. It belongs to the key laboratory of fusion and advanced electromagnetic technology, ministry of education. It's the only medium-sized tokamak in the universities of China. The TEXT-U device in Texas of America is the predecessor, which was shipped to Huazhong University of Science and Technology in China in 2002.The designed parameter of the J-TEXT is:plasma major radius 1.05m; minor radius 0.25-0.29m with movable limiter; the maximal plasma current is 350kA; the line-averaged density of ion in the central plasma is 3×1019m-3; and the central ion and electron temperature can reach 1kev; the maximal magnetic field in the central of vessel is 3 Tesla. The device was rebuilt in 2005, and it realized its first plasma 150kA-200ms at the end of 2007.This paper analyses the poloidal field configuration for the plasma breakdown and current set up. Study and test the field-null region for the breakdown especially. In order to guide the test in future, we get corresponding capacitor banks preset values for different plasma current plat-top in experiment. Based on the coupled relation between plasma current and ohmic heating field (OH) coil current, together with the OH circuit equation, we acquire the transfer function of the plasma current feedback control system, take the simulation and set up the plasma current control system. We employ the multi-section control as the feature of the J-TEXT power supply. And design the control strategy of the joint especially. The results show that the reliability and accuracy of the control system meet the experiment's need.In order to provide the measurement signals for the position control system, we acquire the ceramics as the substrate of the printed circuit board (PCB), design two sets of magnetic coils for detecting the horizontal and vertical displacement of J-TEXT device. Each set of coils consists of a variable cross-section Rogowski and a saddle coils. The four coils are mounted in the vacuum vessel and protected by the stainless steel. This makes the coils meet the high vacuum and temperature requirements of J-TEXT discharge. The plasma position measurement results are concordant with the results given by the radiation measurement. This design is the first case of magnetic coils for using PCB and putting in vacuum vessel all over the world. It is of great significance for ITER and commercial reactor to product magnetic measurement coils.We adopt the current filament model and the force balance equations on horizontal and vertical directions, acquire the relationship between the horizontal displacement (or vertical displacement) and the vertical field (or horizontal field). Combine the vertical (or horizontal) coils circuit equation, get the transfer function of horizontal (or vertical) displacement feedback control system, take the simulation and test in experiment. According to the feature of the J-TEXT discharge operation, we also employ the multi-section control and design the control strategy of the joint especially, and analyze the joint between two sections especially. Now, we can control the horizontal displacement from -2 to 4 cm and vertical displacement from -3 to 3 cm as preset in plasma current flat-top, and can control the plasma position sliding in the plasma current flat-top as experimental needs.This paper considers the requirements of J-TEXT device discharge operation, set up the plasma current, horizontal and vertical position feedback control system. Take some theoretical and experimental researches; ensure the device for generating, heating, maintaining and stabilizing the plasma. The plasma breakdown model for J-TEXT tokamak and test in the experiment show the suitable way of breakdown for the J-TEXT. The design and experiment of plasma current feedback control system of J-TEXT, give viable way for the similar system design. The PCB magnetic coils design indicates that this way of magnet design technique can be used in ITER. The way of designing the plasma horizontal and vertical displacement control system and multi-section control strategy, provide the example for the similar system design.
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