Effect of squeeze on electrostatic TG wave damping
- Conference date: 27–30 August 2012
- Location: Greifswald, Germany
We present a 1D theory, neglecting radial dependency, for the damping of cylindrically symmetric plasma modes due to a cylindrically symmetric squeeze potential Vsq (z), applied to the axial midpoint of a non-neutral plasma column. Inside the plasma, particles experience a much smaller, Debye shielded squeeze potential φ0(z) of magnitude φ s . The squeeze divides the plasma into passing and trapped particles; the latter cannot pass over the squeeze. Both analytical and computer simulation methods were used to study a 1D squeezed plasma mode. For our analytical study, in the regime where qφ s /T ≪ 1, we assume the trapped particle population to be negligibly small and we treat qφ0(z) as a pertubation in the equilibrium hamiltonian. Our computer simulations consist of solving the 1D Vlasov-Poisson system and obtaining the damping rate for a self-consistent plasma mode. Damping of the mode in collisionless theory is caused by Landau resonances at energies En for which the bounce frequency ω b (En ) and the wave frequency ω satisfy . Particles experience a non-sinusoidal wave potential along their bounce orbits due to the squeeze potential. As a result, the squeeze induces bounce harmonics with n ≫ 1 in the perturbed distribution. The harmonics allow resonances at energies En ≤ T and cause a substantial damping, even at wave phase velocities much larger than the thermal velocity, which is not expected for an unsqueezed plasma. In the regime (k is the wave number) and T ≫ qφ s , the resonance damping rate has a |Vsq |2 dependence. This behavior is consistent with the observed experimental results.
- Plasma waves
- Computer simulation
- Electrostatic waves
- Collision theories
- Nonneutral plasmas
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