M. Asif

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.

Measurement of the runaway electrons in the HT-7 tokamak

A thermographic camera and four hard x-ray detectors have been developed to measure the runaway electrons in the HT-7 tokamak. The synchrotron radiation originated from the runaway electrons was measured by an infrared (IR) camera working in the wavelength ranges of 7.5–13μm. With a tangential viewing into the plasma in the direction of the electron approach on the equatorial plane, the synchrotron radiation from the runaway electrons was measured in a full poloidal cross section. Three NaI scintillators are used to monitor the hard x-ray radiation (HXR) in the energy ranges of 0.5–7MeV, and a CdTe detector is used to monitor the low-energy HXR in the energy ranges of 0.3–1.2MeV. The combination of infrared camera and hard x-ray detectors provides a powerful tool to investigate the runaway electron dynamics in HT-7. Runaways in the core and edge regions are monitored simultaneously. The parameters of runaway beam in the core are deduced from the IR pictures. The interaction of runway electrons with toroid...

The Beam Property of DCN Laser

In this paper the lasing modes and the propagation property of a CW DCN laser, which cavity is a 50 mm inner diameter with length of 3.4 m, were studied. The modes of 195 and 190 μm lines are well identified by the micrometer mount of the movable mirror in one end of the cavity. The beam profile is found to be qualitatively Gaussian in the far-field (Z > 4 m).

Study of Density Behavior During LHCD and IBW Heating in the HT-7 Superconducting Tokamak

A new method using special shape parameters has been introduced to study density behavior with synergy of lower hybrid current drive (LHCD) and ion Bernstein wave (IBW) heating in the HT-7 superconducting tokamak. During the synergy of the LHCD and IBW heating an improved confinement plasma was achieved, and the electron density was increased and peaked.

Experimental Study with LaB6 Cathode on DCN Laser

A new LaB6 cathode has been developed on DCN laser in this experiment. The LaB6 cathode is expected with long-life time at high current discharge. Optimization of various parameters for maximum output power with the LaB6 cathode at the DCN laser were performed and reported in this paper.