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 Delta n = 0 transitions of neutral helium. Results for the dipole-allowed transitions 3(3)S-3 P-3, 3 P-3- 3 D-3, 3 S-1-3 P-1, 3 D-1-3 P-1, 4 S-1-4 P-1 and 4 D-1-4 P-1 are given for an electron temperature range of 3-7 eV. For the transitions 3 S-3-3 P-3 and 3 P-3-3 D-3 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.