Langmuir probe diagnostic studies of pulsed hydrogen plasmas in planar microwave reactors
A. Rousseau, E. Teboul, N. Lang, M. Hannemann, J. Röpcke
备注：
16 pages including 18 figures. The following article has been accepted by J. Appl. Phys. After it is published, it will be found at http://link.aip.org
朗缪尔探针技术已被用来研究时间和空间分辨的电子密度和电子温度的脉冲调制氢放电在两个不同的平面微波反应器（fmicrowave= 2.45 GHz，tpulse= 1 ms）。反应器是（i）驻波辐射开槽波导反应器和（ii）改进的行波辐射开槽波导反应器，它们在约350 cm ^2至500 cm ^2的面积上产生相对较大的等离子体。这些反应器类型的等离子体特性特别令人感兴趣，因为它们已用于基础研究和等离子体处理，例如用于表面处理和层沉积。在本研究中，反应器中的压力和微波功率分别在33和55 Pa和600和3600 W之间变化。在具有高电磁场的区域中，使用屏蔽的朗缪尔探针以避免探针特性的干扰。靠近反应器的微波窗口，电子密度和电子温度都表现出强烈的不均匀性。在驻波反应器的不均匀性被发现是空间调制的位置的槽。电子温度的最大值约为10 eV，电子密度在0.2 ~ 14*10^11 cm^-3之间变化。放电脉冲中的稳态电子温度在几十微秒内达到，而电子密度需要几百微秒才能达到稳态。取决于反应器，电子密度在脉冲开始后的80至200微秒之间达到最大值。
英文摘要：
Langmuir probe techniques have been used to study time and spatially resolved electron densities and electron temperatures in pulse-modulated hydrogen discharges in two different planar microwave reactors (fmicrowave= 2.45 GHz, tpulse= 1 ms). The reactors are (i) a standing-wave radiative slotted waveguide reactor and (ii) a modified travelling-wave radiative slotted waveguide reactor, which generate relatively large plasmas over areas from about 350 cm^2 to 500 cm^2. The plasma properties of these reactor types are of particular interest as they have been used for basic research and for plasma processing, e.g. for surface treatment and layer deposition. In the present study the pressures and microwave powers in the reactors were varied between 33 and 55 Pa and 600 and 3600 W, respectively. In regions with high electromagnetic fields shielded Langmuir probes were used to avoid disturbances of the probe characteristic. Close to the microwave windows of the reactors both the electron density and the electron temperature showed strong inhomogeneities. In the standing-wave reactor the inhomogeneity was found to be spatially modulated by the position of the slots. The maximum value of the electron temperature was about 10 eV and the electron density varied between 0.2 and 14*10^11 cm^-3. The steady state electron temperature in a discharge pulse was reached within a few tens of microseconds whereas the electron density needed some hundreds of microseconds to reach a steady state. Depending on the reactor the electron density reached a maximum between 80 and 200 microseconds after the beginning of the pulse.
This paper reports on experimental measurements of the gas temperature in a dielectric barrier discharge reactor powered by a high voltage pulsed signal. It is shown that the thermal behavior of the reactor follows a first order model. However, an unexpected runaway phenomenon was observed at a frequency of 300Hz. A sudden increase in the power source and consequently in reactor temperature which reaches 170°C is observed. This behavior is discussed in terms of input power variation with temperature, possibly due to a resonance phenomenon.
We have carried out a detailed analysis that compares steady state versus pulsed tokamak reactors. The motivations are as follows. Steady state current drive has turned out to be more difficult than expected - it takes too many watts to drive an Ampere, which has a negative effect on power balance and economics. This is partially compensated by the recent development of high temperature REBCO superconductors, which offers the promise of more compact, lower cost tokamak reactors, both steady state and pulsed. Of renewed interest is the reduction in size of pulsed reactors because of the possibi…
A system of automated computerized Langmuir probe measurements is used in order to determine the plasma parameters in a plasma reactor constructed for cleaning of metallic artifacts by RF discharge. A compensated probe insures the suppression of the RF interference. The probe data are collected using a commercial data acquisition unit connected to a portable computer. The raw data are processed using wavelet transforms techniques which assures the de-noising of the probe signal without distortion of the probe I-V characteristic. The first and second derivatives of the I-V characteristic are de…
Initial evaluation of miniature ultra-high-field commercial stellarator reactors with breeding external to resistive coils
Laboratorio Nacional de Fusión, CIEMAT（国家聚变实验室，CIEMAT）；Departamento de Física, Universidad Carlos III de Madrid（马德里卡洛斯三世大学物理系）；Oak Ridge National Laboratory (ORNL)（橡树岭国家实验室）；University of Texas, Austin（德克萨斯大学奥斯汀分校）
This paper presents a novel micropropulsion system for nanosatellite applications - a liquid fed pulsed-plasma thruster (LF-PPT) comprised of a Lorentz-force pulsed plasma accelerator (PPA) and a low-energy surface flashover (LESF) igniter. A 3 μF / 2 kV capacitor bank, offering shot energies of < 6 J, supported PPA current pulsed durations of ~ 16 μs with observed peaks of 7.42 kA. Plasma jet exhaust velocity was measured at ~ 32 km/s using a time-of-flight technique via a set of double probes located along the jet's path. Intensified charge coupled device (ICCD) photography was concurrently …
Time resolved electron density measurements in pulsed RF discharges are shown using a hairpin resonance probe using low cost electronics, on par with normal Langmuir probe boxcar mode operation. Time resolution of less than one microsecond has been demonstrated. A signal generator produces the applied microwave frequency; the reflected waveform is passed through a directional coupler and filtered to remove the RF component. The signal is heterodyned with a frequency mixer and read by an oscilloscope. At certain points during the pulse, the plasma density is such that the applied frequency is t…
A 13.56 MHz RF discharge in hydrogen was studied within the pressure range of 1-17 10 Pa, and at power range of 400-1000 W. The electron energy distribution function and 18 electron density were measured by a Langmuir probe. The gas temperature was determined by 19 the Fulcher-$α$ system in pure H2, and by the second positive system of nitrogen using N2 as the 20 probing gas. The gas temperature was constant and equal to 450 $\pm$ 50 K in the Capacitively 21 Coupled Plasma mode (CCP), and it was increasing with pressure and power in the Inductively 22 Coupled Plasma mode (ICP). Also the vibrat…
The use of dielectric barrier discharge (DBD) plasmas has become a practical way to carry out surface treatment and one seeks to do it in a more efficient way, which requires to have control of the plasma parameters like rotational and vibrational temperatures (T_rot and T_vib). Since the T_vib of an atmospheric pressure plasma jet is an important parameter related to improvement of surface treatments, in this work it was analyzed two methods to increase the values of T_vib in the DBD plasma. One of the methods is to reduce the exit size of the DBD reactor, and the other is to change the gas f…
Negative atomic hydrogen ion (H$^{-}$) densities were measured in a pulsed low-pressure E-mode inductively-coupled radio-frequency (rf) driven plasma in hydrogen by means of laser photodetachment and a Langmuir probe. This investigation focuses on the influence of different metallic surface materials on the volume production of H$^{-}$ ions. The H$^{-}$ density was measured above a thin disc of either tungsten, stainless steel, copper, aluminium, or molybdenum placed onto the lower grounded electrode of the plasma device as a function of gas pressure and applied rf power. For copper, aluminium…
A new breakthrough in jet propulsion technology since the invention of the jet engine is achieved. The first critical tests for future air-breathing magneto-plasma propulsion systems have been successfully completed. In this regard, it is also the first time that a pinching dense plasma focus discharge could be ignited at one atmosphere and driven in pulse mode using very fast, nanosecond electrostatic excitations to induce self-organized plasma channels for ignition of the propulsive main discharge. Depending on the capacitor voltage (200-600 V) the energy input at one atmosphere varies from …
