Magnetic Field Dependence of Plasma Properties Observed with Tomography in PANTA (original) (raw)
Related papers
Keywords Langmuirprobe, electron temperature, density,longitudinal magnetic field. PACS 52.25.Xz, 52.80.Hc, 52.70.Ds Thev ariations of plasma parameters of ad cd ischarge in an on-uniform magnetized plasma were measured usingf ast floatingd oubleL angmuirp robes. As olenoidi su sed to produce au niform magnetic field parallel to thed ischarge axis. Thea xial changes of thep lasma parameters are presented in ther ange of longitudinal magnetic fields 200 to 600 Gauss at thepressure range 0 . 3 to 2 . 1 Torr and discharge currents 5 and 15 mA in argon gas. Theexperimental results indicatethat,asaconsequence of theaxial magnetic field and thevariations in thedischarge tube radii, theplasma parameters at smallradius exhibitobvious changes in theirdistributions along theaxiscompared to thesituationofunmagnetized plasma.
Experimental Study of Low Magnetic Field Density Peaking in Helicon Plasma
Single density peak has been commonly observed in low magnetic field (<100 G) helicon discharges. In this paper, we report the observations of multiple density peaks in low magnetic field (<100 G) helicon discharges produced in the linear helicon plasma device [Barada et al., Rev. Sci. Instrum. 83, 063501 (2012)]. Experiments are carried out using argon gas with m ¼ þ1 right helical antenna operating at 13.56 MHz by varying the magnetic field from 0 G to 100 G. The plasma density varies with varying the magnetic field at constant input power and gas pressure and reaches to its peak value at a magnetic field value of $25 G. Another peak of smaller magnitude in density has been observed near 50 G. Measurement of amplitude and phase of the axial component of the wave using magnetic probes for two magnetic field values corresponding to the observed density peaks indicated the existence of radial modes. Measured parallel wave number together with the estimated perpendicular wave number suggests oblique mode propagation of helicon waves along the resonance cone boundary for these magnetic field values. Further, the observations of larger floating potential fluctuations measured with Langmuir probes at those magnetic field values indicate that near resonance cone boundary; these electrostatic fluctuations take energy from helicon wave and dump power to the plasma causing density peaks. V C 2013 AIP Publishing LLC [http://dx.
Experimental Study of Double Layer in Helicon Plasma with Diverging Magnetic Field
Density peaking phenomena have been studied in different magnetic field configurations in a low field (< 100 Gauss) helicon discharge. The study has been carried out in the linear helicon plasma device (Barada et. al., Rev. Sci. Instrum. 83, 063501, 2012) using argon gas with m = +1 right helical antenna operating at 13.56 MHz by varying the magnetic field from 0 Gauss to 100 Gauss (G) with two different magnetic field geometry. The plasma density varies with varying the magnetic field at constant input power and gas pressure and reaches to its peak value at a critical magnetic field value (s). For a magnetic field of 88 G near the antenna the density rises at an axial location away from the antenna in the diffusion chamber having a diverging magnetic field. On the m=-1 propagation side of the antenna, the density peak vanishes around 30 G which is well evident on the m=+1 propagation side. The results are explained on the basis of resonance cone propagation of right circularly polarized helicon waves and the vanishing of density peak at 30 G along with observation of density peak at 5 G and 12 G at z=-18 cm (m=-1) propagation side are explained with polarization reversal mechanism of electromagnetic waves.
Plasma Emission Processes in a Magnetoactive Plasma
Australian Journal of Physics, 1972
Plasma emission (i.e. emission at about the plasma frequency and twice this frequency) is treated taking into account the effects of the magnetic field on the electron plasma waves, on the conversion processes, and on the escaping radiation. The expected degrees of polarization of the fundamental and second harmonic are calculated in the weak field limit. The results are used to estimate the magnetic field strength B at the 80 MHz level from the observed polarization of type III bursts; the result B < 0�04 G is smaller than previous estimates. The possible importance of electron-cyclotron waves in an application to type I bursts is noted.
Tomography of a simply magnetized toroidal plasma
Plasma Science and Technology
Optical emission spectroscopy is a passive diagnostic technique, which does not perturb the plasma state. In particular, in a hydrogen plasma, Balmer-alpha (H α) emission can be easily measured in the visible range along a line of sight from outside the plasma vessel. Other emission lines in the visible spectral range from hydrogen atoms and molecules can be exploited too, in order to gather complementary pieces of information on the plasma state. Tomography allows us to capture bi-dimensional structures. We propose to adopt an emission spectroscopy tomography for studying the transverse profiles of magnetized plasmas when Abel inversion is not exploitable. An experimental campaign was carried out at the Thorello device, a simple magnetized torus. The characteristics of the profile extraction method, which we implemented for this purpose are discussed, together with a few results concerning the plasma profiles in a simply magnetized torus configuration.
Tomographic Measurements of Temperature Fields in Non-Stationary Arc Plasma
Contributions To Plasma Physics, 1984
The paper presents results of the use of computational tomography techniques for the processing of experimental data obtained with the help of a plasma tomograph. On the basis of the data acquired, physical processes have been determined taking place in plasma, and the behaviour of some integral characteristics of an electric are discharge in a longitudinal magnetic field has been explained. A possibility to determine optically a certain effective electric field strength of an unsteady state plasma has also been demonstrated.
Initial characterization of Argon plasmas in the "MAGnetized Plasma Interaction Experiment" (MAGPIE)
RF magnetic fluctuation probes and symmetric double Langmuir probes have been utilized to characterize Argon helicon plasma in a converging magnetic field. We observe that when enough RF power is supplied an Ar II blue core mode is formed suggestive of the presence of fast electrons (~30 eV) ([1], [2]). Results indicate a linear increase in the plasma density in the direction of increasing magnetic field. During high power operation (2.1 kW) the plasma density reaches a peak near the maximum gradient of the converging magnetic field, the helicon's phase velocity matches the electron thermal velocity and its wavelength becomes half the antenna size. Radial wavefield measurements during the blue core suggest the presence of an m = +1 second radial mode.
Field-aligned beams of accelerated ions and plasma structures of various durations with quasi-isotropic velocity distribution functions are often observed in the interface region between the magnetotail lobe and the plasma sheet. We present and discuss one case of multipoint Cluster observations which demon-strates that during a long interval of northward IMF and low geomagnetic ac-tivity this interface region represents a mixture of discrete magnetic tubes filled with plasma with different characteristics. The magnetic tubes connected with the current sheet (CS) localized acceleration sources are filled with ions with field-aligned velocity distribution function streaming earthward with velocity ∼ 700 km/s. Magnetic tubes which are not connected with the acceleration sources are filled with "old" already isotropic plasma. Multipoint observations revealed that both types of structures have spatial origin and co-exist. These findings conform to previous studies demonstratin...
Spectroscopic determination of the magnetic-field distribution in an imploding plasma
Physics of Plasmas, 1998
The time-dependent radial distribution of the magnetic field in a high density z-pinch plasma has been determined by observation of the contribution of the Zeeman effect to the spectral profiles of ionic emission lines. The dominance of the line profiles by the Stark broadening required high-accuracy profile measurements and the use of polarization spectroscopy. The plasma implodes in Ӎ600 ns, and the field distribution was measured up to 90 ns before stagnation on axis. During the implosion the plasma was found to conduct the entire circuit current. By comparing the data to the solution of the magnetic diffusion equation the electrical conductivity of the plasma was determined, found to be in agreement with the Spitzer value. These measurements, together with our previously measured ion velocity distributions, allowed for the determination of the time-dependent relative contributions of the magnetic and thermal pressure to the ion radial acceleration across the plasma shell.