A. Taniike et al., CHARGE FRACTIONS AND ENERGY WIDTH OF HEAVY-ION BEAM PROBE FOR LARGE HELICAL DEVICE, Fusion engineering and design, 34-5, 1997, pp. 675-678
A heavy ion beam probe (HIBP) has been used as a reliable method to me
asure the plasma potential and its fluctuation in a magnetically confi
ned fusion plasma. On the large helical device (LHD) an Au+ beam produ
ced by a 3 MV tandem acceleration system will be used. It is necessary
to optimize the charge fractions and minimize the energy broadening o
f the Au+ beam. Charge fractions can be calculated from electron loss
and electron capture cross-sections. It is predicted that the optimum
gas thickness for Au+ beam production is about 4 x 10(14) cm(-2). The
broadening due to electron stripping is calculated to be several elect
ronvolts and does not depend on the target mass. The energy straggling
due to multiple collisions at the optimum target thickness can be cal
culated theoretically taking the lower limit of the impact parameter i
nto account. Consequently, the total energy width of the Au+ beam prod
uced by a tandem system might be about 100 eV. (C) 1997 Elsevier Scien
ce S.A.