The electron density ne of stationary plasma can be easily obtained on the basis of the resonance frequency f of a curling probe (CP) measured by a network analyzer (NWA). However, in pulsed plasma with discharge period T, the ne and f values periodically change with time. This study extends the conventional CP technique to a time-resolved measurement of the pulse-modulated electron density. The condition necessary for the measurement is revealed to be synchronization of NWA with the pulse modulation, which is expressed as (n − 1)T/TSWP = integer (1, 2, …) for a number n of data point and sweep time TSWP.

No abstract

A new intermetallic compound, MnGa2Sb2, has been synthesized by direct reaction from Mn and GaSb at 6 GPa and 500°C for 30 min using a belt-type high pressure apparatus. The compound crystallizes into an orthorhombic structure with the space group Iba2 (No. 45). The structure was refined by the Rietveld analysis of the powder X-ray diffraction data and the lattice constant was determined to be a = 1.180(7) nm, b = 0.5968(2) nm, c = 0.5858(2) nm. The structure consists of -Mn-MnMn-linear chains parallel to the c-axis. The compound exhibits metallic conductivity and itinerant-electron ferromagnetic behavior with the Curie temperature of 310 K.

A plasma-induced shift in the resonance frequency of a curling probe measured by using a network analyzer (NWA) yields the electron density. This technique was applied here for measuring time-varying electron density in pulsed DC glow discharges. Using the NWA in an on-sweep synchronization mode with the discharge pulse allows measuring at pulse frequencies below 0.5 kHz. For higher pulse frequencies, an on-point mode was introduced which enabled time-resolved measurements of electron density at pulse frequencies reaching 25 kHz, with the minimal time interval of 2 µs, typically for nitrogen discharge at 10 Pa. In the afterglow regime, the decay time constant of electron density was measured for nitrogen and argon discharges at 40 Pa. In the case of argon, the electron density was observed to decrease in three steps. This characteristic behavior was tentatively attributed to a bi-Maxwellian electron energy distribution and Ramsauer effect, supported by Langmuir probe measurements.

A curling probe (CP) based on microwave resonance is applied to the measurement of electron density in a pulsed DC glow discharge under surface magnetic confinement (SMC) provided by a number of permanent magnets on a chamber wall. Owing to the SMC effects, a 1 m scale large-volume plasma is generated by a relatively low voltage (~1 kV) at low pressure (~1 Pa) in various gases (Ar, CH 4 , and C 2 H 2 ). Temporal variation of the electron density is measured for pulse frequency f = 0.5-25 kHz for various discharge-on times (T ON ) with a high resolution time (~0.2 µs), using the on-point mode. In general, the electron density starts to increase at time t = 0 after turn-on of the discharge voltage, reaches peak density at t = T ON , and then decreases after turn-off. The peak electron density is observed to increase with the pulse frequency f for constant T ON owing to the residual plasma. This dependence is successfully formulated using a semi-empirical model. The spatio-temporal evolution of the cathode sheath in the pulsed discharge is revealed by a 1 m long movable CP. The measured thickness of the high-voltage cathode fall in a steady state coincides with the value of the so-called Child-Langmuir sheath.