Xiaokang Zhang

Plasma density behavior with new graphite limiters in the Hefei Tokamak-7

A new set of actively cooled toroidal double-ring graphite limiters has been developed in the Hefei Tokamak-7 (HT-7) [X. Gao et al., Phys. Plasmas 7, 2933 (2000)] for long pulse operation. The extension of operational region and density behavior with graphite (C) limiters have been studied in this paper. Extended high-density region at the high plasma current low-qa was obtained. The density profile with the C limiter was studied to compare with the previous molybdenum (Mo) limiter. The critical density of multifaceted asymmetric radiation from the edge (MARFE) onset is observed in the region of Zeff1∕2fGW=0.9∼1.2, where fGW=n¯e∕nGW. (Here n¯e is the maximum line average electron density and nGW is the Greenwald density.) Under the same injected power, the critical density of MARFE onset with the new C limiter is much higher than the previous Mo limiter.

Operational region and sawteeth oscillation in the EAST tokamak

The first plasma discharges were successfully achieved on the experimental advanced superconducting tokamak (EAST) in 2006. The sawteeth behaviours were observed by means of soft x-ray diagnostics and ECE signals in the EAST. The displacement and radius of the q = 1 surface was studied and compared with the result of equilibrium calculation. The density sawtooth oscillation was also observed by the HCN laser interferometer diagnostics. The structure of the EAST operational region was studied in detail. Plasma performance was obviously improved by the boronization and wall conditioning. It was observed that lower qa and a wider stable operating region is extended by the GDC boronization.

Evaluation of ACPs in China Fusion Engineering Test Reactor Using CATE 2.1 Code

Activated corrosion products (ACPs) are the dominant radiation hazard in water-cooled fusion reactor under normal operation conditions and directly determine the occupational radiation exposure during operation and maintenance. Recently, the preliminary design of China Fusion Engineering Test Reactor (CFETR) has been just completed. Evaluation of ACPs is an important work for the safety of CFETR. In this paper, the ACPs analysis code CATE 2.1 was used to simulate the spatial distribution of ACPs along the blanket cooling loop of CFETR, in which the influence of adopting different pulse handling methods was researched. At last, the dose rate caused by ACPs around the blanket cooling loop was calculated using the point kernel code ARShield. The results showed that the dose rate under normal operation for 1.2 years at contact is 1.02u2009mSv/h and at 1u2009m away from pipe is 0.45u2009mSv/h. And after shutting down the reactor, there will be a rapid decrease of dose rate, because of the rapid decay of short-lived ACPs.

Multichannel heterodyne radiometers with fast-scanning backward-wave oscillators for ECE measurement on HT-7 tokamak

Abstract Two sets of fast-scanning heterodyne radiometer receiver systems employing backward-wave oscillators (BWOs) in 78–118 and 118–178 GHz were developed and installed for electron cyclotron emission (ECE) measurements on HT-7 superconducting tokamak. The double sideband (DSB) radiometer in 78–118 GHz measures 16 ECE frequency points with a scanning time period of 0.65 ms. The other radiometer in 118–178 GHz consists of one independent channel of DSB heterodyne receiver with intermediate frequency (IF) of 100–500 MHz and two channels of single sideband (SSB) heterodyne receiver that are sensitive to upper sideband and lower sideband individually; the IF frequency of the SSB channels are 1.5 GHz around the local oscillator frequencies with 1 GHz bandwidth. By employing a novel design, this unique radiometer measures 3 ECE frequency points at each of the 16 local oscillator frequency points in 118–178 GHz, and the full band can be swept in 0.65 ms period, thus the radiometer measures 48 ECE frequency points in 0.65 ms in principle. Each of the local oscillators’ frequency points can be preset by program to meet specific physics interests. Horizontal view of ECE was installed to measure electron temperature profiles; vertically viewing optics along a perpendicular chord was also installed to study nonthermal ECE spectra. Preliminary measurement results were presented during ohmic and pellet injection plasmas.