A new absolute extreme ultraviolet image system designed for studying the radiated power of the Joint Texas Experimental Tokamak discharges

Abstract

A bolometer imaging system mounted on different toroidal and poloidal locations used for radiation observation has been developed in the Joint Texas Experimental Tokamak (J-TEXT tokamak). Three miniature pinhole AXUV16ELG (16 elements absolute extreme ultraviolet silicon photodiodes) array cameras, which are settled down in the same toroidal position but in three different poloidal places, can provide a broad viewing angle that covers the whole plasma cross-section, and hence can measure the total radiated power and provide the radiated emissive profile, while nine AXUV10EL (10 elements absolute extreme ultraviolet silicon photodiodes) array cameras are divided into three groups and will be mounted on different toroidal locations to observe the toroidal radiated power distribution. Among these detectors, one element of the AXUV16ELG array is absolutely calibrated by the synchrotron radiation source to verify the system reliability. Although there are some discrepancies between the typical responsivity given by IRD Co. and the calibrated results, it is confirmed that the discrepancies have no major effect on the final result after the simulation. The details of the system as well as observations are presented in the paper.

Dissipation of runaway current by massive gas injection on J-TEXT

“…Here gives the estimated impurity assimilation rate η=38% in red dashed line based on the pressure balance η=N imp /N inj = V plasma T inj /V vaccum T imp when using the assumption T imp = T inj , where N inj , T imp , T inj , and V vaccum are the total injected impurity quantity, the temperature of the ionized impurity in the RE plasma, the temperature of the neutral impurity, and the volume of the vacuum vessel respectively. It can be found that the maximum assimilation rate η of the krypton impurity can fit the estimated impurity assimilation rate 38% when the total injected impurity quantity is lower than 2×10 21 . Then the assimilation rate η decreases when the injected impurity quantity is larger than 2×10 21 .…”

“…The total radiated power is calculated by using the A and D arrays of the No.1 AXUV imaging subsystem at port 3. The calculation method is shown in the [21]. The polarizing interferometer (named as POLARIS on J-TEXT) with 17 vertical chords is used to measure the electron density profile [22].…”

“…So we use the differential of plasma current - Actually, the number of injected impurity in these shots are much lower than that in the shots with similar runaway currents. From figure 9(b), it can be found that the runaway current dissipation rate increases with the injected impurity quantity and saturates when the impurity quantity reaches to about 2×10 21 . The max runaway current dissipation rate can be about 28 MA s −1 on J-TEXT.…”

“…Note that this assumed kinetic energy may be larger than the actual one. The total self-inductance L of the RE plasma can be assumed as , it can be found that the radiated energy increases with the increase of the injected impurity quantity, but it saturates when the impurity quantity reaches to 2×10 21 . The saturations of the radiation energy and the runaway current dissipation rate mean that the dissipation efficiency of the runaway current cannot be increased by increasing the injected impurity quantity when the quantity exceeds a certain value on J-TEXT.…”

The reconstruction and research progress of the TEXT-U tokamak in China

“…Another nine AXUV10EL (ten elements) array cameras are divided into three groups and mounted at different toroidal locations to observe the toroidal radiated power distribution. The AXUV array has a sensitivity from 0.20 to 0.27 A W −1 for photon energies of 25 eV-6 keV and has a temporal resolution of 20 µs [13]. (6) A spectrometer with 2400 lines mm −1 grating is used to record the emission spectrum from 200 to 1100 nm along a vertical centre chord through the plasma.…”