Influence of finite ion temperature on plasma blob dymanics

P. Manz1,2, G. Birkenmeier2, D. Carralero2, G. Fuchert3, H.W. Mller2, S.H. Mller4,

B.D. Scott2, U. Stroth2,1, E. Wolfrum 2 and the ASDEX Upgrade Team1 Physik-Department E28, Technische Universitt Mnchen, Garching, Germany

2 Max-Planck-Institut fr Plasmaphysik, Garching, Germany3 IJL, Universite de Lorraine, CNRS (UMR 7198), BP 40239, Vandoeuvre-le`s-Nancy, France

4 CMTFO, University of California at San Diego, USA

One of the critical issues of magnetically confined fusion devices is the exhaust of particlesand heat without seriously damaging the vessel walls of the device. The transport in the regionof open field lines beyond the confined region, called scape-off layer (SOL), is dominated byfilamentary structures also called plasma blobs. Blob motion has been extensively studied infusion devices and basic low-temperature experiments, where especially the latter show verysatisfying results compared with the present theory implying a robust theoretical descriptionof the plasma blob dynamics. On the other hand the experimental results in high-temperaturefusion experiments are less satisfactory. The reason for this discrepancy might be related to thefact that most of the blob theories and simulations invoke cold ion models. While Ti Te isrealistic for most basic plasma physics experiments, it is not realistic for the tokamak scrape-offlayer (SOL), where Ti > Te is typical.

An analytic model for blob propagation has been derived for finite ion temperatures basedon a full drift-interchange-Alfvn fluid model. The general expression derived reduces to thestandard blob model in the cold ion case. It will be shown how the ion temperature affectsthe dynamics of the blob and modifies the scaling laws for blob velocity in dependence ofblob size. For instance, the ion temperature enhances the interchange drive, which is responsi-ble for charge separation, propagation and therefore for the transport capabilities of the blobs.Furthermore, it leads to polarisation currents and thus alters the vorticity. Simplifications for ex-perimentally relevant sheath dissipation, collisional and electromagnetic regimes are discussed.A detailed comparison of the analytic results with experimental data from ASDEX Upgradeis used to demonstrate the effect of the ion temperature on blob propagation. In addition theanalytic model is compared with data from gyrofluid simulations on open field lines done withthe GEMR code.

41st EPS Conference on Plasma Physics I4.112