@techreport{oai:nifs-repository.repo.nii.ac.jp:00009528,
 author = {Burhenn,  R. and Feng,  Y. and Ida,  K. and Kalinina,  D. and Maassberg,  H. and McCarthy,  K.J. and Morita,  S. and Nakamura,  Y. and Nozato,  H. and Okamura,  S. and Sudo,  S. and Suzuki,  C. and Tamura,  N. and Weller,  A. and Yoshinuma,  M. and Zurro,  B.},
 month = {Oct},
 note = {The Large Helical Device (LHD) and Wendelstein 7-X (W7-X, under construction) are experiments specially designed to demonstrate long pulse (quasi steady-state) operation, which is an intrinsic property of Stellarators and Heliotrons. Significant progress was made in establishment of high performance plasmas. A crucial point is the increasing impurity confinement towards high density as observed at several machines (TJ-II, W7-AS, LHD) which can lead to impurity accumulation and early pulse termination by radiation collapse at high density. In addition, theoretical predictions for non-axisymmetric configurations prognosticate the absence of impurity screening by ion temperature gradients in standard ion root plasmas. Nevertheless, scenarios were found where impurity accumulation was successfully avoided in LHD and/or W7-AS by the onset of drag forces in the high density and low temperature scrape-off-layer, the generation of magnetic islands at the plasma boundary and to a certain degree also by ELMs, flushing out impurities and reducing the net-impurity influx into the core. Additionally, a reduction of impurity core confinement was observed in the W7-AS High Density Hmode (HDH) regime and by application of sufficient ECRH heating power. The exploration of such purification mechanisms is a demanding task for successful steady-state operation. The impurity transport at the plasma edge/SOL was identified to play a major role for the global impurity behaviour in addition to the core confinement.},
 title = {On Impurity Handling in High Performance Stellarator/Heliotron Plasmas},
 year = {2008}
}