Heat- and Particle-Deposition Distribution on Helical Divertor Plates in LHD During Real-Time Magnetic-Axis Swing Operations

Investigations of heat- and particle-deposition distributions on helical divertor plates were performed both experimentally and numerically with the Large Helical Device (LHD). The distributions were measured by thermocouples and Langmuir probe arrays embedded in the divertor plates. They are similar to the distribution of field lines with long connection lengths, which are estimated numerically by field-line tracing calculations. Localized heat- and particle-deposition distributions were observed, and were found to be determined primarily by the magnetic-field line structure in the divertor region. They vary depending on the configuration − the intensively loaded areas move with a change of the magnetic configuration. Using this property, a swing of the magnetic axis successfully dispersed the heat and particle loads on the divertor plate during long-pulse discharges. The magnetic-axis swing around a certain magnetic-axis position is found to be very effective in changing the field-line distribution pattern drastically, and thus dispersing the heat load.