Parasitic excitation of ion Bernstein waves is observed from a Faraday shielded fast wave loop antenna in the ion cyclotron frequency range. Local analysis of the Vlasov-Maxwell equations demonstrates the role of plasma density gradient in the coupling process. The effects of plasma density and of parallel wave number on the excitation process are investigated. DrSCLAIMERThis report was prepared as an account or work sr.inrorcd by an agency of the United Stales Government. Neither the United Stales Government nor any agency therccr. nor any of their employees, makes any warranty, cypress or implied, or assumes any legal liability or responsi bility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents thai its use would not infringe privately owned rights. Refer ence herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise docs not necessarily constitute or imply its endorsement, recom mendation, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily stale or reflect those of the United States Government or any agency thereof. is important to understand the physics of wave coupling so that appropriate antennas may be designed for these applications.In particular, the role played by the slow wave in fast wave coupling is considered here. Generally, it is assumed that the presence of a Faraday shield will suppress the excitation of slow waves from a fast wave polarized antenna. Tne ionBernstein wave and/or anomalous ion heating is observed, however, in fast wave experiments and it is uncertain whether or not this is due to direct parasitic excitation. 2,3In this paper we report the observation of parasitic ion Bernstein wave •*™t™ * U" -Uy, 1 "+ 15 Two different density profiles were used, corresponding to the two means of producing the electron beam. The lanthanum cathode tends to produce a more square profile (Fig. 5b). The filament produces a more level gradient (
Ion Bernstein wave excitation and propagat on via finite ion-Larmor-radius mode-transformation are invest''gated theore tically and experimentally. It is shown that in the ion cyclo tron range of frequencies m < 4:-
Application of Ion Bernstein Wave Heating (IBWH) into the Princeton Beta Experiment-Modification (PBX-M) [Phys. Fluids B 2, 1271 (1990)] tokamak stabilizes sawtooth oscillations and generates peaked density profiles. A transport barrier, spatially correlated with the IBWH power deposition profile, is observed in the core of IBWH-assisted neutral beam injection (NBI) discharges. A precursor to the fully developed barrier is seen in the soft x-ray data during edge localized mode (ELM) activity. Sustained IBWH operation is conducive to a regime where the barrier supports large ∇ne, ∇Te, ∇νφ, and ∇Ti, delimiting the confinement zone. This regime is reminiscent of the H(high) mode, but with a confinement zone moved inward. The core region has better than H-mode confinement while the peripheral region is L(low)-mode-like. The peaked profile enhances NBI core deposition and increases nuclear reactivity. An increase in central Ti results from χi reduction (compared to the H mode) and better beam penetration. Bootstrap current fractions of up to 0.32–0.35 locally and 0.28 overall were obtained when an additional NBI burst is applied to this plasma.
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