Measurement of rate coefficients for electron-atom collisions in a helium plasma by laser-induced fluorescence

We present experimentally obtained rate coefficients for electron-atom collisions for n = 0 transitions of neutral helium. Results for the dipole-allowed transitions 3 3 S-3 3 P, 3 3 P-3 3 D, 3 1 S-3 1 P, 3 1 D-3 1 P, 4 1 S-4 1 P and 4 1 D-4 1 P are given for an electron temperature range of 3-7 eV. For the transitions 3 3 S-3 3 P and 3 3 P-3 3 D results down to temperatures below 1 eV were obtained. The measurements were performed in a magnetic multipole plasma source by a laser perturbation method. The plasma parameters were measured by employing a Langmuir probe. The electron density was in the range of 10 11 to several 10 12 cm -3 at helium filling pressures of a few Pascal. The results are compared with the theoretical and experimental data available in the literature.