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 f 1 :f 2 :f 3 =7%:32%:61% (where f 1 , f 2 and f 3 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*10 13 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)*10 13 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.