@techreport{oai:nifs-repository.repo.nii.ac.jp:00010469,
 author = {"Yokoyama,  M. and Nakajima,  N. and Okamoto,  M. and Nakamura,  Y. and Wakatani,  M."},
 month = {Feb},
 note = {"Roles of bumpy field on collisionless particle confinement in helica1-axis heliotrons are investigated with the model magnetic field and particle orbit calculations in the Boozer coordinates. The mod-B_min contours can be shifted in the major radius direction with the control of the bumpy field, where B_min is the minimum value of |B| in the toroidal direction within one field period. The area of closed mod-B_min contours is a useful measure to evaluate global collisionless particle confinement as long as the mod-B_min contours connect toroidally. Negative value of ratio between the bumpy and the helicity components contributes to obtain the largest area of closed mod-B_min contours for finite ratio between the toroidicity and the helicity components. The radial variation of the bumpy field attributes to realize a toroidally localized mod-B_min Structure, which is significantly effective to improve collisionless particle confinement."},
 title = {Roles of Bumpy Field on Collisionless Particle Confinement in Helical-Axis Heliotrons},
 year = {1999}
}