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Register a new userA note on the experiment parameters for the non-resonant streaming instability: competition between left and right circularly polarized modes
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A non-resonant streaming instability driven by cosmic-ray currents, also called Bells instability, is proposed as a candidate for providing the required magnetic turbulence of efficient diffusive shock accelerations. To demonstrate the saturation level and mechanism of the non-resonant streaming instability in a laboratory environment, we attempt to develop an experiment at the Photo Injector Test Facility at DESY, Zeuthen site (PITZ). As an electron beam is used to replace the proton beam to carry the cosmic-ray current in our experiment, the polarization of the non-resonant streaming instability will be modified from the left-handed (LH) mode to the right-handed (RH) mode. The theoretical instability analysis shows that the growth rate of this RH non-resonant mode may be smaller than it of the LH resonant mode. However the LH resonant mode can be ignored in our experiment while the expected wavelength is longer than the used plasma cell. The results of PIC simulations will also support this contention and the occurrence of non-resonant streaming instability in our experiment.
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The gas breakdown produced by high-power pulsed linearly and circularly polarized microwave fields which are much weaker than the atomic fields is investigated in the non-relativistic limit. Obtained the electron distribution function produced by the interaction with intense linearly and circularly polarized microwave fields, it is shown that it is non-equilibrium and anisotropic. Finding the general dispersion relation and analyzing it, we firstly obtain the low frequency oscillations and secondly we show that an instability may develop in the aforementioned system. It will be shown that for linearly polarized microwave fields this instability may always develop but for the circular polarization fields it grows only when ion density is higher than a critical density.
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In plasmas where the thermal energy density exceeds the magnetic energy density ($beta_parallel > 1$), the aperiodic ordinary mode (O-mode) instability is driven by an excess of parallel temperature $A = T_perp /T_parallel < 1$ (where $parallel$ and $perp$ denote directions relative to the uniform magnetic field). When stimulated by parallel plasma streams the instability conditions extend to low beta states, i.e., $beta_parallel <1$, and recent studies have proven the existence of a new regime, where the anisotropy threshold decreases steeply with lowering $beta_parallel to 0$ if the streaming velocity is sufficiently high. However, the occurrence of this instability is questionable especially in the low-beta plasmas, where the electrostatic two-stream instabilities are expected to develop much faster in the process of relaxation of the counterstreams. It is therefore proposed here to identify the instability conditions for the O-mode below those required for the onset of the electrostatic instability. An hierarchy of these two instabilities is established for both the low $beta_parallel <1$ and large $beta_parallel > 1$ plasmas. The conditions where the O-mode instability can operate efficiently are markedly constrained by the electrostatic instabilities especially in the low-beta plasmas.
We give a simple argument for the exclusive existence of mirror and electromaghetic ion cyclotron modes in anisotropic high-$beta$ plasmas. It is shown that, in addition to a large domain of coexistence of both modes, two domains exist in parameter space $(A,beta_perp)$ where solely either mirror modes or electromagnetic ion cyclotron modes can be excited. In the overlap region the modes with the larger growth rate should win. However nonlinear effects may modify such a conclusion.
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