Flow visualization and density measurement of the supersonic molecular beam for fusion plasma fueling.

The supersonic molecular beam injection (SMBI) technique is widely used in magnetic fusion devices for plasma fueling and active control of particles. The beam flow formed by the SMBI system is directly visualized by a newly established schlieren diagnostic system on the SMBI testing platform. This schlieren system could provide a 2D density distribution of the beam with the sub-mm spatial resolution by detecting the change in the refractive index of the medium caused by the SMBI in the low-pressure vacuum chamber.

Influences of fusion neutrons on Compton suppressed γ-spectrum analyses at the HL-2A tokamak.

The newly-built Compton suppression system at the HL-2A tokamak works in a harsh fusion neutron field especially when the second neutral beam injection system is put into application. The present paper performed Geant4 simulations to study the influences of fusion neutrons on Compton suppressed γ-spectrum analyses. The simulation data show that the influence of fusion neutrons on suppressed γ-spectrum shape is limited, while the influence on detection efficiencies is considerable.

Geant4 simulation study on detection efficiencies of the Compton suppression system at the HL-2A tokamak.

A Compton suppression system (CSS), which plays an important role in γ-ray diagnostics, has been developed to acquire the γ-ray emission spectra generated in the HL-2A tokamak plasma. It takes advantages of the anti-coincidence method of two branches of γ-ray signals, one is from a high purity germanium (HPGe) detector, and the other from several bismuth germinate (BGO) detectors, to output the suppressed spectra. In the present paper, a Geant4 simulation, together with its subsequent data processing which took accidental coincidences into account, was performed to study the detection efficiencies of the CSS for γ-rays with energies between 0.