Wave and Joule heating in a rotating plasma

Abstract. We have recently performed a detailed characterization of ion Joule heating perpendicular to an axial magnetic field in the laboratory in a simulated ionospheric plasma environment which contains localized electric field structuring. Since Joule heating is often regarded as an important mechanism contributing to energization of outflowing heavy ions observed by higher-altitude auroral satellites, this work has particular relevance to space physics issues, and, to our knowledge, has not been investigated systematically in a controlled environment. Since transverse (to B) ionospheric electric fields are often spatially and temporally structured, with scale lengths often as small as an ion gyroradius, the ability to systematically vary the spatial extent and magnitude of an electric field region and to observe the effect on ion energy is important. The experiment makes use of a concentric set of separately biasable ring anodes which generate a radial electric field with controllable scale length perpendicular to an ambient axial magnetic field. Joule heating results from ion-neutral collisions occurring within this transverse, dc electric field. Until there is sufficient neutral pressure to raise the ion-neutral collision frequency (vin) to an observable Joule heating threshold, ion cyclotron wave heating, which is induced by shear in E x B rotation, can be the primary channel for ion energization. We have discussed in earlier papers the conditions under which this occurs, and we have treated the transition between the two forms of ion heating. We concentrate primarily in this work on constructing the fields themselves and on the relationship between the subsequent collisional heating and the Pedersen conductivity as an initial indication of the validity of the measurement results. We are able to demonstrate that measurable heating is produced by even relatively small scale structures of the order of the ion gyroradius. In addition, we show that measured heating is consistent with predictions of Joule heating as a function of ion-neutral collisions. Finally, this work can have major implications for ionospheric studies where large-scale electric fields are often assumed in the calculation of Joule heating. IntroductionJoule heating in the ionosphere can be induced by transverse electric fields in a collisional plasma. Collisions between ions and neutrals are integral to the Joule heating process since they lead to a cross-magnetic field (Pedersen) current density (Jp) and therefore a Jp ß E dissipation of electric field energy. The mechanism by which ion heating occurs (i.e., wave and/or Joule heating) has important geophysical consequences since heavy ion (oxygen) distribution functions measured at higher altitudes often display heating which is argued to have 1807

Section: Structured Electric Fields Broadband Waves and Transverse Ionmentioning

confidence: 99%

Section: Equilibrium Properties Of the Plasmamentioning

confidence: 99%

Characterization of Joule heating in structured electric field environments

Walker¹,

Amatucci²,

Ganguli³

2001

“…In Figure 4 temperature drops off sharply in both directions beyond the region where ν in /Ω i = 1, and it also reaches a maximum very near this point. As neutral pressure becomes low (λ in ≫ L E ) we expect there to be essentially no contribution to ion heating from collisions [ Amatucci et al , 1999].…”

Section: Summary Plot Of Ion Temperature Versus Pressurementioning

confidence: 99%

“…In this regard, for example, combined incoherent scatter radar in addition to satellite in situ measurements have unequivocally established that irregular field structures encountered in regions of small convective velocity are associated with ion heating. Earlier laboratory investigations [ Amatucci et al , 1999; Walker et al , 2001] have shown that there are two dominant processes responsible for ion temperature enhancement in the presence of transverse electric fields: (1) Joule, or collisional, heating in regions of high convective velocity and sufficient neutral density and, (2) wave heating via plasma instabilities in the presence of velocity shear. These works demonstrate conclusively the transition between these two forms of heating as a function of plasma neutral density.…”

Section: Introductionmentioning

confidence: 99%

Ion Joule heating as a function of electric field scale size

Walker¹,

Amatucci²,

Ganguli³

et al. 2002

[1] In an earlier work we described a laboratory-based experimental series that demonstrated the transition from velocity-shear-driven ion cyclotron wave heating to ion Joule heating as a function of ion-neutral collision frequency. As part of this effort, we demonstrated the ability to control the magnitude and direction of the electric field (or the sign of potential change) in space in a simulated ionospheric environment. In the results presented here we have calculated the electric field by differentiation of a fit to the potential profile and have used the full width at half maximum of this field as a marker for the size of the region. In the case of the ion temperature measurements, which are derived from energy analyzer data by conventional techniques, we demonstrate increased ion temperature consistent with increasing electric field region length. We also have been able to demonstrate a peak in the ion temperature as a function of collision frequency and the Joule heating rate. The data suggest that for approximately constant pressure and electric field strength, the normalized ion temperature increase will be limited for a given scale size. Finally, we argue that these observations are consistent with the notion of a limit to ion heating based on a comparison of the scale length of the region to the mean free path for ion-neutral collisions.

“…A variety of experiments simulating space plasma phenomena has been performed in the chamber [Walker et al, , 1997Amatucci et al, 1996Amatucci et al, , 1998Amatucci et al, , 1999. Table 1 outlines the basic plasma parameters for a 50 cm diameter argon plasma column as representative of various experimental environments in the SPSC.…”

Section: Chamber Environmentmentioning

confidence: 99%

Discharging spacecraft through neutral gas release: Experiment and theory

Walker¹,

Amatucci²,

Bowles³

et al. 1999

Self Cite

Abstract. We describe experimental and theoretical research related to the mitigation of spacecraft charging by the release of neutral gas through specially designed nozzles. The experiments were conducted in the large Space Physics Simulation Chamber (SPSC) at the Naval Research Laboratory. A realistic near-Earth space environment can be simulated in this device for which minimum scaling needs to be performed to relate the data to space plasma regimes. The environment of the SPSC is similar to that encountered by spacecraft in low Earth orbit. The experimental arrangement consists of an aluminum cylinder which can be biased to high voltage (0.4 < V < 10 kV). The cylinder incorporates a neutral gas release valve designed for millisecond release times, a pressure-regulated neutral gas reservoir, and variable Mach number nozzles. After the cylinder is charged to high voltage the neutral gas is released, inducing a breakdown of the gas in the strong electric field about the cylinder. Collection of ions from the newly created dense plasma, along with secondary electron emission from the cylinder surface, provides the return current necessary for grounding the body. We treat the breakdown theoretically as a Townsend discharge and use the fundamental assumption of exponential electron growth as one proceeds from the cathode toward the anode during neutral gas breakdown. In addition, the nozzle release of neutral gas is modeled, and a simple linear spatial dependence of the applied potential is assumed. This basic model produces quite good results when compared to the experiment.