Electric probe methods for diagnostics of plasmas are reviewed with emphasis on the link between the appropriate probe theories and the instrumental design. The starting point is an elementary discussion of the working principles and a discussion of the physical quantities that can be measured by the probe method. This is followed by a systematic classification of the various regimes of probe operation and a summary of theories and methods for measurements of charged particle distributions. Application of a single probe and probe clusters for measurements of fluid observables is discussed. Probe clusters permit both instantaneous and time-averaged measurements without sweeping the probe voltage. Two classes of applications are presented as illustrations of the methods reviewed. These are measurements of cross sections and collision frequencies (plasma electron spectroscopy), and measurements of fluctuations and anomalous transport in magnetized plasma.

An electric-probe method for the diagnostics of electron-distribution functions (EDFs) in plasmas is reviewed with emphasis on receiving reliable results while taking into account appropriate probe construction, various measurement errors and the limitations of theories. The starting point is a discussion of the Druyvesteyn method for measurements in weakly ionized, low-pressure and isotropic plasma. This section includes a description of correct probe design, the influence of circuit resistance, ion current and plasma oscillations and probe-surface effects on measurements. At present, the Druyvesteyn method is the most developed, consistent and routine way to measure the EDF. The following section of the review describes an extension of the classical EDF measurements into higher pressures, magnetic fields and anisotropic plasmas. To date, these methods have been used by a very limited number of researchers. Therefore, their verification has not yet been fully completed, and their reliable implementation still requires additional research. Nevertheless, the described methods are complemented by appropriate examples of measurements demonstrating their potential value.

No abstract

Temporal measurement of electron density, metastable-atom density, and reduced electric field are used to infer the dynamic behavior of the excitation rates describing electron-atom collision-induced excitation in the positive column of a 1 Torr argon plasma by invoking plausible assumptions regarding the shape of the electron energy distribution function performed in Adams et al (2012 Phys. Plasmas 19 023510). These inferred rates are used to predict the 420.1 nm to 419.8 nm argon emission ratio, which agree with experimental results when the assumptions are applicable. Thus the observed emission ratio is demonstrated to be dependent on the metastable-atom density, electron density, and reduced electric field. The established confidence in the validity of this emission-line-ratio model allows us to predict metastable argon-atom density during the post-transient phase of the pulse as suggested by De Joseph et al (2005 Phys. Rev. E 72 036410). Similar inferences of electron density and reduced electric field based on readily available diagnostic signatures may also be afforded by this model. Keywords: optical emission spectroscopy (OES), 420.1-419.8 nm emission-line ratio, 1s 5 metastable argon atom, reduced electric field (E/N), electron energy distribution, time-resolved, extended corona model

On page 4 in equations (4) and (5) as well as in the first line in the right column, 'f 0' should be replaced by 'f'. On page 4, equation (9) should be replaced by On page 5, equation (11) should be replaced by

It is demonstrated for the first time that the presence of a small number of fast, nonlocal electrons can dramatically change the thickness of and electric field in the near-wall sheath. Even if the density of the nonlocal fast group, , is much less than the density of the bulk electrons, n(b) (n(f) approximately 10(-5) n(b)), the near-wall potential can increase dramatically resulting in a comparable increase in the sheath thickness. Because of this low fractional density, the average energy (electron temperature ) of all electrons is little changed from that of the bulk, yet the near-wall potential drop can increase to tens of T(e)/e. More importantly, due to the nonlocal nature of this group of electrons, the near-wall sheath potential is found to be independent of and is determined only by the energy of the fast group.

A system of two cylindrical probes aligned along the magnetic field, and equipped with insulating end plugs, is proposed for measurement of low-frequency fluctuations of the electrostatic field in a magnetized plasma. It is demonstrated by modeling and experiments that the plug probe floats close to the plasma potential. The electric field component in a given direction is obtained by subtracting the plasma potentials obtained on two spatially separated plug probes. The probe system is applied to low-frequency electrostatic fluctuations in a simple magnetized torus, and reveals the presence of global oscillations, large scale propagating structures (mϭ1 modes͒, and developed turbulence with power-law spectra. Two different mode branches for the fluctuations are identified by comparing results from plug probes with results from conventional probes. Sources of errors arising from applying floating potential of conventional probes for electric field measurements are pointed out and discussed.

Temporal measurements of the emission intensities of the Ar 419.8 and 420.1 nm spectral lines combined with Ar plasma modeling were used to examine the metastable atom and electron density behavior in the initial stage of a pulsed dc discharge. The emission intensity measurements of these spectral lines near the start of a pulsed dc discharge in Ar demonstrated a sharp growth of metastable atom and electron densities which was dependent on the applied reduced electric fields. For lower electric fields, the sharp growth of metastable atom density started earlier than the sharp electron density growth. The reverse situation was observed for larger electric fields. This presents the possibility for controlling plasma properties which may be useful for technological applications. Similar measurements with spectral lines of corresponding transitions in other rare gases are examined.