A new method of gas fuelling has been introduced in the HL-1M tokamak. The method consists of a pulsed high speed molecular beam formed by a Laval type nozzle. The velocity of the well collimated hydrogen beam is about 500 m/s. About 6 × 10 19 molecules pass through the nozzle and into the vacuum chamber in each pulse. A series of helium pulses was injected into the HL-1M low density (ne = 4 × 10 18 m −3 ) hydrogen plasma. With penetration depth up to 12 cm, the ramp-up rate of the electron density, dne/dt, was as high as 3.1 × 10 20 m −3 • s −1 at steady state, and the resulting plasma density reached ne = 5.6 × 10 19 m −3 . The profile peaking factor of the electron density, Qn = ne(0)/ ne of about 100 ms after helium molecular beam injection (MBI) reached a maximum value of more than 1.51. The energy confinement time τE measured by diamagnetism is 26 ms, which is over 30% longer than that of the gas puffing (GP) results under the same operational conditions. The improvement of τE and increase of Qn for MBI were comparable to those of small pellet injection (PI) in HL-1M, as well as those of slow PI in ASDEX (Kaufmann, M., et al., Nucl. Fusion 28 (1988) 827). It is argued that the peaked density profile induced by the deepened particle injection is a factor essential for the confinement improvement apart from the isotope effect of helium particles, because the density peaking factor Qn is normally less than 1.4 for GP plasma in HL-1M. The particle confinement time with MBI increased sixfold in comparison with that before injection.

In plasma physics experiments of HL-1M tokamak, three refuelling methods (gas puffing, pellet and supersonic molecular beam (SMB) injection) were used. The penetration characteristics and the average speed of the pellet and molecular beam were analysed and estimated by means of contour plots of H α emissivity distribution. On HL-1M tokamak, the penetration depth of the pellet was up to 0.26 m, and the average speed of the pellet inside the plasma was less than that outside the plasma. The SMB was injected into the plasma from the low-field side and its average speed was more than 1 km s −1 .

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The plasma rotation velocity were measured in HL-1M with Doppler shifts of C III, C II , 0 I1 and H, line by a SKD high resolution spectrometer. The effects of density , hydrogen pellet injection and carbon impurities injected by laser-blow-off on toroidal(V,,) and poloidal (&)rotation velocity have been observed. The & measured from H, line is only half of that from C II impurity line.