Ephrem D. Mezonlin

Neutral particle analyzer measurements on the SSPX spheromak

A neutral particle analyzer is used to measure the time-resolved energy spectrum of neutral hydrogen leaving a spheromak plasma. A gas cell filled with 10-50 mTorr of helium is used to strip electrons from incoming neutral hydrogen, lowering the minimum detectable energy well below that obtained with thin foils. Effective neutral particle temperature is calculated by fitting a Maxwellian energy distribution to the measured energy spectrum above and below approximately 300 eV. A computational model with approximated profiles of plasma density and neutral density is used with the measured neutral hydrogen flux to estimate the ion temperature. Measurement of the power flux due to neutral hydrogen emitted at the measurement location is extended to the whole plasma surface to estimate the total charge exchange power loss from the plasma. The initial results indicate that the charge exchange power loss represents only 2% of the total input gun power during the sustainment phase of the discharge.

Turbulent microwave plasma thermodynamics for fundamental fluctuation modes

Microwave plasmas are generated in helium, neon, argon, krypton, and xenon at a range of microwave powers from 300 to 1800 W. A floating Langmuir double probe is employed to determine plasma electron density and temperature for all five species. The standard turbulence analysis is carried out by using time resolved neutral line emission data form these gases at a sampling rate of 100 MHz. From the Fourier power spectrum of the data, the strongest fluctuation frequency is found to be consistently the fundamental or a second harmonic of a turbulence characteristic frequency in the spectra. In all five species the strongest frequency is not influenced by increased microwave power even though other thermodynamic parameters are changed. The low chaotic dimension for all species seems independent of microwave power and of turbulent fluctuation energy. The phase space trajectories show simplicity and periodicities are consistent with the low chaotic dimension and with the peak frequencies obtained from the fluct...

Critical turbulent energy reductions in plasmas using weak magnetic fields

With an arc-driven shock tube, laser induced fluorescence, and a multipoint density diagnostic technique, we study the turbulence behind an ionizing shock wave in the presence of a magnetic field. The magnetic field is directed either parallel to or antiparallel to the direction of the shock wave’s propagation, and is configured in such a way as to couple with turbulent velocity fluctuations in the plane perpendicular to the direction of flow. We find that the magnetic field can be used to reduce the turbulent energy in a plasma system. Further, when the evolution to turbulence is treated as a second-order phase transformation, the critical turbulent energy decreases with increasing magnetic field.

Evidence of turbulence in laser-induced plasmas

By focusing a pulsed single mode Nd:YAG laser, we created low temperature plasmas at various pressures with various target gases and collected spectral light emissions to investigate the possibility of turbulent behavior in these types of plasmas. Characteristic fluctuation frequencies, chaotic dimensions, spectral indices, and turbulent fluctuation energies are determined from fluctuations in these spectral light emissions. Values calculated for the spectral index and the chaotic index for each plasma event are found to be within the known values for other turbulent plasma systems. Thus, turbulent fluctuations on a nanosecond time scale are confirmed in the time evolutions of various singly ionized and neutral spectral lines of various gases.

Low energy ion distribution measurements in Madison Symmetric Torus plasmas

Charge-exchange neutrals contain information about the contents of a plasma and can be detected as they escape confinement. The Florida A&M University compact neutral particle analyzer (CNPA), used to measure the contents of neutral particle flux, has been reconfigured, calibrated, and installed on the Madison Symmetric Torus (MST) for high temperature deuterium plasmas. The energy range of the CNPA has been extended to cover 0.34–5.2 keV through an upgrade of the 25 detection channels. The CNPA has been used on all types of MST plasmas at a rate of 20 kHz throughout the entire discharge (∼70 ms). Plasma parameter scans show that the ion distribution is most dependent on the plasma current. Magnetic reconnection events throughout these scans produce stronger poloidal electric fields, stronger global magnetic modes, and larger changes in magnetic energy all of which heavily influence the non-Maxwellian part of the ion distribution (the fast ion tail).

Design of a retarding potential grid system for a neutral particle analyzer

The ion energy distribution in a magnetically confined plasma can be inferred from charge exchange neutral particles. On the Madison Symmetric Torus (MST), deuterium neutrals are measured by the Florida A&M University compact neutral particle analyzer (CNPA) and the advanced neutral particle analyzer (ANPA). The CNPA energy range covers the bulk deuterium ions to the beginning of the fast ion tail (0.34-5.2 keV) with high-energy resolution (25 channels) while the ANPA covers the vast majority of the fast ion tail distribution (∼10-45 keV) with low energy resolution (10 channels). Though the ANPA has provided insight into fast ion energization in MST plasma, more can be gained by increasing the energy resolution in that energy range. To utilize the energy resolution of the CNPA, fast ions can be retarded by an electric potential well, enabling their detection by the diagnostic. The ion energy distribution can be measured with arbitrary resolution by combining data from many similar MST discharges with different energy ranges on the CNPA, providing further insight into ion energization and fast ion dynamics on MST.

Turbulent transport manipulation in the internal combustion engine as a second order phase transformation

Using hot-wire anemometry in a motored engine, new turbulence physics is observed in the evolution and sensitivity of characterizing parameters to changing molecular weights. Turbulent manipulation of mixing is afforded along with a role for nonequilibrium statistical mechanics in turbulence phenomenology.

Atomic effects in the turbulent properties of microwave generated plasmas

Summary form only given, as follows. Microwave plasmas are generated in helium, neon, argon, krypton, and xenon at various microwave powers and neutral gas pressures. A floating Langmuir double probe is employed to diagnose plasma electron density and temperature. Bias voltage and current characteristic curves are analyzed for the determination of electron temperature and density for all five gases. Turbulence analysis is carried out by using time resolved neutral line emission data from these gases at a sampling rate of 100 MHz. Fourier spectra of emission fluctuations allow determinations of the total turbulent energy and the characteristic turbulent fluctuation frequency, which is also evidenced by the periodic motion in the phase space trajectory. The computations for chaotic dimension are also carried out for all five species. Systematic trends in the turbulent parameters show a dependence on atomic weight. These trends are consistent with observations of molecular influence on turbulent transport found in other plasmas and neutral gases and with current theoretical models.