Abstract
Dipole and stellarator geometries are capable of confining plasmas of arbitrary neutrality, ranging from pure electron plasmas through to quasineutral. The diocotron mode is known to be important in non-neutral plasmas and has been widely studied. However, drift mode dynamics, dominating quasineutral plasmas, has received very little by way of attention in the non-neutral context. Here, we show that non-neutral plasmas can be unstable respect to both density-gradient- and temperature-gradient-driven instabilities. A local shearless slab limit is considered for simplicity. A key feature of non-neutral plasmas is the development of strong electric fields, in this local limit of straight field line geometry, the effect of the corresponding $\boldsymbol{E}\times \boldsymbol{B}$ drift is limited to the Doppler shift of the complex frequency $\unicode[STIX]{x1D714}\rightarrow \unicode[STIX]{x1D714}-\unicode[STIX]{x1D714}_{E}$ . However, the breaking of the quasineutrality condition still leads to interesting dynamics in non-neutral plasmas. In this paper we address the behaviour of a number of gyrokinetic modes in electron–ion and electron–positron plasmas with arbitrary degree of neutrality.
Highlights
Plasmas of arbitrary neutrality, ranging from pure electron plasmas through to standard quasineutral ion–electron plasmas, can be confined in both stellarator (CNT) (Pedersen et al 2004) and levitated dipole (RT-1, APEX) geometries (Pedersen et al 2003; Yoshida et al 2006)
We have studied the gyrokinetic stability of non-neutral electron– positron–ion plasmas by solving, both analytically and numerically, the dispersion relation (2.17) in a slab geometry and relaxing the quasineutrality condition
We found that in most cases the physics of these instabilities was different in non-neutral plasmas
Summary
Plasmas of arbitrary neutrality, ranging from pure electron plasmas through to standard quasineutral ion–electron plasmas, can be confined in both stellarator (CNT) (Pedersen et al 2004) and levitated dipole (RT-1, APEX) geometries (Pedersen et al 2003; Yoshida et al 2006) Despite their laboratory and astrophysical relevance, relatively little has been done in terms of investigating the myriad of instabilities which can exist in such plasmas. Of particular relevance to this work, such oscillations have been observed for quasineutral plasmas in CNT In their weakly non-neutral plasmas, multiple modes are excited and it becomes impossible to identify clear drift-wave signals (Sarasola & Pedersen 2012). We use gyrokinetic theory to examine the stability of drift waves in plasmas of arbitrary neutrality in a shearless slab
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