Measurement of coherent drift-wave ion-fluid velocity field when ion dynamics are stochastic
In order to test the validity of the fluid drift approximation when ion dynamics are stochastic, the time-dependent ion-fluid velocity field in a coherent, drift-Alfvén wave has been measured in Caltech's Encore tokamak using plasma planar laser induced fluorescence. Many measured parameters of the wave are well described by the drift approximation above a threshold for stochastic ion dynamics, including the flow pattern in the single measured component of the ion-fluid velocity field. Surprisingly, the theory fails at a fundamental level by predicting flow speeds 10 times larger than those measured (‖umax‖≊10^5 cm/s).
© 1993 The American Physical Society. Received 4 February 1993. We wish to thank Frank Cosso for assistance with electronics. This work was supported bu NSF Grant No. PHY-9114146.
Published - BAIprl93.pdf