Laboratory results are presented to show the existence of a new type of double layer which has monotonic potential variations but can be triggered with an electron drift velocity less than the electron thermal velocity. These double layers are always found to evolve from virtual-cathode potential wells at the electron injection boundary, independent of the electron drift velocity. However, the amplitudes of these double layers are determined by the initial drift velocity of the injected electrons. Double layers with potential drops less than the ambient electron temperature are found to be unstable to ion-ion streaming instabilities and decay into ion acoustic double layers. PACS numbers: 52.35.Mw, 52.35.Dm
In this paper, we present the results of a study of the preionization effects for the Korean Superconducting Tokamak Advanced Research (KSTAR) tokamak (0 = 1 8 m, = 0 5 m, = 2 = 0 8 = 3 5 T, = 2 MA, pulse = 300 s) that is under construction by the Korea Basic Science Institute (KBSI). The preionization will be given by the Electron Cyclotron Heating (ECH) System with an 84-GHz 500-kW gyrotron tube being made by Communications and Power Industries. The ECH preionization effects are investigated by a 0-dimensional code (TECHP0D 1) that includes the operational scenarios of KSTAR tokamak. The code is now improved and advanced with carbon, oxygen, and iron impurity effects, and with the self and mutual inductances of seven pairs of superconducting poloidal coils for the KSTAR tokamak. Index Terms-Electron cyclotron heating (ECH), gyrotron, Korean superconducting tokamak advanced research (KSTAR), poloidal, preionization.
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