Measurements of neutral beam stopping for hydrogen and helium in the JT-60 plasma

Shine-through for hydrogen and helium beams in a plasma was measured. Shine-through for an atomic hydrogen beam with f₁:f ₂:f₃=7%:32%:61% (where f₁, f₂ and f₃ represent fractions of the full, half and third energy, respectively) and a full energy of 140 keV, was smaller than the value predicted by usual cross-sections without inclusion of excitation processes at an electron density (n_e) above 3*10¹³ cm^-3. A fractional beam stopping increment ( delta ), which was defined by delta =( sigma _s- sigma _s⁽⁰⁾) sigma _s ⁽⁰⁾ (here sigma _s was an experimental stopping cross-section and sigma _s⁽⁰⁾ was the cross-section without including multistep processes via excited states), was about 0.2 at n _e=(3.1-5.0)*10¹³ cm^-3 and Z _eff=1.6-2.5. The value of delta was consistent with the calculation by Janev et al. (1989, Nucl. Fusion 29, 2125). For a 160-190 keV helium beam, the enhancement of the stopping cross-section was not observed, as expected.