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Pulsed plasma thrusters (PPT) have demonstrated enormous potential since the 1960s. One major shortcoming is their low thrust efficiency, typically

The inductively-heated plasma generator IPG6-B at Baylor University has been established and characterized in previous years for use as a flexible experimental research facility across multiple applications. The system uses a similar plasma generator design to its twin-facilities at the University of Stuttgart (IPG6-S) and the University of Kentucky (IPG6-UKY). The similarity between these three devices offers the advantage to reproduce results and provides comparability to achieve cross-referencing and verification. Sub- and supersonic flow conditions for Mach numbers between M a = 0 . 3 − 1 . 4 have been characterized for air, argon, helium and nitrogen using a pitot probe. Overall power coupling efficiency as well as specific bulk enthalpy of the flow have been determined by calorimeter measurements to be between η = 0 . 05 − 0 . 45 and h s = 5 − 35 MJ kg−1 respectively depending on gas type and pressure. Electron temperatures of T e = 1 − 2 eV and densities n e = 1 0 1 8 − 1 0 2 0 m−3 have been measured using an electrostatic probe system. At Baylor University, laboratory experiments in the areas of astrophysics, geophysics as well as fundamental research on complex (dusty) plasmas are planned. The study of fundamental processes in low-temperature plasmas connects directly to electric propulsion systems. Most recent experiments include the study of dusty plasmas and astrophysical phenomena and the interaction of charged dust with electric and magnetic fields. In this case, dust can be used as a diagnostic for such fields and can reveal essential information of the magneto-hydrodynamics in low-temperature plasmas. Although some of these goals require further advancement of the facility, it is proposed that several phenomena relevant to electric propulsion as well as to other fields of plasma physics can be studied using the existing facility.

This study focused on the development of a vacuum cathode arc thruster (VAT), particularly on its design, manufacturing process, and demonstration. Characteristically, the proposed thruster does not require any additional propellant feeding system as the cathode electrode is simultaneously used as a propellant. In the ignition system, tiny spots are coated on the cathode surface to induce plasma flow. Such a setup has the advantages of simplicity, low price, small size, and low weight and is suitable for microsatellites. Moreover, a “trigger-less” method with an inductor storage power system was used for generating the pulsed plasma. This discharge method can significantly reduce input power. Thrust is mainly caused by high exhaust velocities of metal ions in the plasma flow, making ion density, ion velocity, and ion charge influential parameters. A battery was used instead of a power supply system to reduce the energy consumption of the entire VAT processing unit. The energy required for a single pulse was estimated to be 0.266 J, by measuring the change between the discharge current and the voltage. The ion current was measured using an ion detector and was 3.55 A, and the ion velocity was 23150 m/s. In the theoretical analysis, the VAT prototype proposed in this study achieved a single impulse of 4.31 μNs, a specific impulse of 1571 s, and a thrust efficiency of approximately 12.5%.

The present study focuses on the influence of applied magnetic fields on argon plasma flows to assess the magnetohydrodynamics (MHD) effects on a pico-sized reentry capsule and their potential as a...

Characterization of IEC tight jet mode is achieved through Faraday probe measurements. Preliminary results indicate that the tight jet is a highly energetic electron beam with scattering of secondary ions and electrons, which result from electron beam impact ionization. A novel analytical model is proposed to evaluate this non-Maxwellian plasma beam, including a compensation of the secondary electron emission effect on the probe's surface. The results show prominent features on the extracted jet's kinetic energy and the respective (electron) current of IEC. In addition, they demonstrate a practical method to characterise non-Maxwellian plasma jets through Faraday probes.

The objective of this work is to study the behavior of surface layers of high-temperature metals in their interaction with a powerful pulsed plasma flow produced by a high-power ablative pulsed plasma thruster. This plasma generator produces plasma flows with a directed velocity of (7–9) × 106 cm/s, an initial diameter of 1.5–2 cm, and a maximum number density of about 1018 cm–3, as well as a maximum power of 5 GW. The main measured values are the residual temperature of the tungsten specimens and the evaporated mass. Also, metallographic analysis of the specimens was performed. The basis of the research method is to analyze the experimental data with the help of a numerical model describing the heating and evaporation of the material upon absorption of pulsed energy fluxes taking into account the evaporation kinetics based on the Hertz–Knudsen expression. Based on the developed numerical model and the obtained experimental data, the kinetics of evaporation of tungsten at high power fluxes to the surface (up to 1 GW/cm2) is investigated.

Challenging space mission scenarios include those in low altitude orbits, where the atmosphere creates significant drag to the S/C and forces their orbit to an early decay. For drag compensation, propulsion systems are needed, requiring propellant to be carried on-board. An atmosphere-breathing electric propulsion system (ABEP) ingests the residual atmosphere particles through an intake and uses them as propellant for an electric thruster. Theoretically applicable to any planet with atmosphere, the system might allow to orbit for unlimited time without carrying propellant. A new range of altitudes for continuous operation would become accessible, enabling new scientific missions while reducing costs. Preliminary studies have shown that the collectible propellant flow for an ion thruster (in LEO) might not be enough, and that electrode erosion due to aggressive gases, such as atomic oxygen, will limit the thruster lifetime. In this paper an inductive plasma thruster (IPT) is considered for the ABEP system. The starting point is a small scale inductively heated plasma generator IPG6-S. These devices are electrodeless and have already shown high electric-to-thermal coupling efficiencies using O 2 and CO 2 . The system analysis is integrated with IPG6-S tests to assess mean mass-specific energies of the plasma plume and estimate exhaust velocities.

An experimental methodology to quantify atomic recombination on high-temperature materials exposed to homonuclear diatomic gases is proposed. Candidate materials are tested in a plasma wind tunnel ...

Electric propulsion offers the advantage of a high specific impulse through a large exhaust velocity and has seen significant progress in space flight applications. Recently, we observed a transient plasma shockwave during pulsed plasma thruster operation when the plasma beam impacted a probe surface. However, details regarding the plasma shockwave formation are still unknown. This work is an experimental investigation of the compression-induced plasma shockwave in the presence of a planar obstruction. To study the complete shockwave buildup and dissipation process, an ultra-high-speed imaging system was set up to visualize the time-resolved shockwave morphology at a sub-microsecond level. In addition, the local magnetic field and plasma density were measured using 2D magnetic coils and a triple Langmuir probe, respectively. The successive images of the shockwave give us a comprehensive understanding of the shockwave buildup process. During the 12 μs operational period of the thruster, two shockwaves were formed during the first cycle of the discharge. It is also interesting to note that there is a 1 μs dissipation period between the two shockwaves with the same cloud of plasma compressing against the probe surface. A shockwave model is also developed to predict the appearance of the two shockwaves. The implication is that the local magnetic field strength can be a key indicator for the plasma shockwave buildup and dissipation process.

The inertial electrostatic confinement (IEC) has been commonly researched in the scope of application for space propulsion and fusions reactors since many years. The utilization as thruster is possible due to a free emitting stream in a so-called jet mode of the IEC source. Depending on the setup, this jet can be operated as high energetic electron beam (tight jet) with electron energies of several keV or as low energetic plasma jet close to quasineutrality (spray jet). These modes are of high interest for thin film applications and plasma treatment. However, the IEC source is still not used in this field of application. Relevant application scopes can be electron substrate heating, surface plasma pretreatment, ionized physical vapor deposition and plasma enhanced chemical vapor deposition. In this paper, a cylindrical IEC source is presented that emits the plasma in both known jet modes, spray jet and tight jet. The jet emission occurs in radial outlet direction along the entire source height (“curtain-like” emission). Furthermore, an ignition test and operational behavior test is introduced. A stable spray jet operation region was examined and dependencies on pressure and voltage are investigated.

The Inertial Electrostatic Confinement (IEC) method is a plasma confinement principle with different operation modes. The work presented investigates the jet mode, which occurs with a jet extraction relevant for space propulsion applications. Two different jet modes were observed, the tight jet mode and the spray jet mode. Depending on propellant, discharge pressure and power these modes occur at different operation conditions and characteristics. Emission spectroscopic investigations show a different plasma species composition of confinement and extraction plasma and the transition between those modes has been examined with a high-speed camera. Finally, the applicability of IEC plasma sources for space propulsion systems is discussed with respect to the experimental results.

In this paper, results of the simulation tools URANUS and PICLas are compared to Plasma wind tunnel experiments. This is done for validation purposes of catalytic modelling within these tools. Therefore, the used experimental setup, from which the discussed simulation case is derived, and challenges in the flow characterization are shown. The main focus is on the validation of the newly developed surface Monte Carlo reconstruction method implemented in PICLas. For this method a brief description is given. It shows good agreements to experiments without a priori fitting of simulation parameters to experiments. However, further validation for evaluation of this method is needed.

To investigate the dissociation and recombination processes in a plasma jet, the characterization of its composition is important. For this purpose, an automated fitting algorithm for emission spectroscopic measurements, based on the radiation simulation tool PARADE, is developed. The algorithm is demonstrated by qualitatively analyzing single carbon dioxide spectra of the inductive plasma generator IPG4, operated at 125 kW anode power with a CO2 mass flow rate of 2.2 g/s. The species O, C, CO, CO+, CN and C2 are fitted with regards to number density, as well as vibrational and rotational temperature. A radial analysis of species composition is performed at two axial positions in the plasma jet. The results show different regions inside the plasma, suggesting increasing CO dissociation towards the centerline, as well as recombination of atomic carbon with molecular nitrogen. Moreover, the species composition distribution is found to be an indicator for the flow conditions in underexpanded free turbulent plasma jets.

The further development of inductive plasma generators (IPGs) for space propulsion applications has driven the need for the development of non-intrusive experimental techniques that can resolve transient discharge cycle behaviour and accommodate a variety of propellant gases and gas-mixtures. In this work, a new approach is presented that simultaneously measures the antenna current, radially-resolved axial magnetic field strength and the radially-resolved emission in the visible range, at a sampling frequency sufficient to capture the driving and discharge cycle frequencies. Experiments were conducted using IPG7: a helical antenna IPG, driven nominally at 586 kHz, with 300 Hz discharge cycles. Nitrogen, argon-nitrogen, and argon-oxygen propellants were tested at capacitive and inductive conditions with input powers ranging from 4 kW to 36 kW. The propellants could be sourced from the space environment under in-situ resource utilisation. Analysis of the mean discharge cycle has made it possible to identify different coupling modes occurring within the cycle. These findings underscore the need to model such plasmas at the timescale of individual discharge cycles and demonstrate the value of the measured data for developing such models.

At the Institute of Space Systems (IRS), experiments have been performed using the high enthalpy, inductively heated plasma generator (IPG) in plasma wind tunnel 3 (PWK3), in order to assess the catalytic behaviour of different materials. Utilising the Upwind Relaxation Algorithm for Non-equilibrium Flows of the University of Stuttgart (URANUS), a methodology for determining catalytic efficiencies by obtaining atomic recombination probabilities γ for high temperature materials, has been developed. This method eliminates the inherent uncertainties produced when using catalytic properties of previously tested materials to infer those of new materials. In this work, eight different candidates for the Thermal Protection System (TPS) of an entry vehicle have been studied, of which six are ceramic materials and the other two are metallic alloys. Thermochemical properties of these specimens are given for surface temperatures between 1000 and 2000 K in pure oxygen and pure nitrogen plasmas. The high enthalpies and relatively low pressure conditions in which these material samples have been tested in PWK3 are relevant for entry applications from Low Earth Orbit (LEO).

In pulsed plasma thrusters (PPTs), a highly ionized plasma is created and accelerated by means of a pulsed triggered vacuum gap discharge with concurrently occurring ablation, ionization, and Lorentz-force-based acceleration of propellant. The plasma flow behavior during the PPT discharge is, therefore, highly dependent on time, space, and operation parameters. Experimental work is seen as the necessary key to further understand the processes involved and to determine future research needs. The application of mechanical probes to measure the Mach number of the plasma flow optically is discussed in this paper. Values of 1.6–3.2 were determined for a variation in time, space, and discharge voltage. An inclination of the PPT plasma flow toward the cathode was observed, which concurs with the previous research results.

Research of magnetoplasmadynamic Pulsed Plasma Thrusters (PPTs), or iMPDs, at the Stuttgart Institute of Space Systems (IRS), led to the thruster design ADD SIMP-LEX. For optimization of the thruster's discharge behavior and of the plasma acceleration, the magnetic self-field is measured. Inductive miniaturized probes are introduced and used to acquire data at points of the volume inside of the thruster's discharge channel. The results are used for analysis to identify the extend of the discharge zone along the discharge channel of the PPT. Measured magnetic field signals along the centerline of the discharge channel are presented. The underlying distribution of the dynamic discharge current is deduced from Amperes circuital law and interpreted in a two-dimensional plot against camera images for the current-plasma-interaction, current motion and validity of today's discharge models. The evaluation of the calculated integral discharge current in a plane of the discharge channel against the recorded thruster discharge current is presented and discussed.

In a pulsed plasma thruster discharge, the propellant utilization efficiency is commonly seen as the weak point for its thrust performance, and for its low thrust efficiency respectively. However, the value depends strongly on operational settings and the design of the pulsed plasma thruster itself. To access this efficiency to understand further the influence of parameters, a method combining experimental and modeling efforts is proposed within this paper. By using various optical methods, including high-speed camera imaging, emission spectroscopy, and Mach–Zehnder interferometry, the plasma bulk velocity for different energy configurations of the SPPT-68 ADD SIMP-LEX is derived. Together with the total ablated mass and an improved slug model, the ratio of mass accelerated in the discharge process is computed and, thus, the propellant utilization efficiency is derived. Velocities in the range of 25 to 55 km/s were measured, leading to propellant utilization efficiencies of about 40 to 60% depending on t...

Several advanced plasma propulsion designs have been developed and characterized at IRS in the past years. Among them are the hybrid thruster TIHTUS, the steady state applied-field thrusters AF-MPD ZT1 and ZT2 and advanced iMPD designs. These concepts show promising potential for future missions. The paper will discuss the designs and their operational features. In addition, more advanced systems are under investigation, among others fusion systems and magnetic sail systems. These systems are not likely to see in-flight testing within the next years, but they offer opportunities for investigation potentially applicable to terrestrial designs.

In this paper a method is described that allows mapping of the forces acting on dust particles in a GEC reference cell. Monodisperse particles are dropped into the plasma environment and their trajectories are tracked using a high-speed camera system to determine local accelerations and respective forces. Collecting data from a large number of particle drops allows the identification of three-dimensional vector fields for the acting forces. The procedure is described and multiple examples in which the method has been applied are given. These examples include a simple plasma sheath, plasmas perturbed by a horizontal and vertical dipole magnet, an array of multiple magnets mimicking the fields found at a lunar swirl, and the fields inside a glass box used for particle confinement. Further applicability in other plasma environments will be discussed shortly.

Design, operation and application of pulsed magnetoplasmadynamic self-field accelerators are described and the facility IMAX (Institut fur Raumfahrtsysteme der Universitat Stuttgart (IRS), Magnetoplasmadynamic Accelerator-Experiment), is considered in further detail on the basis of an experimental reference condition at a capacitor bank load voltage of 12 kV and an ambient air pressure of 10 −3 Pa. This high power coaxial accelerator has been investigated for space propulsion and for terrestrial plasma processes in particular for metal treatment. Lessons learnt from the operation of the facility and its potentially dangerous functional behavior are discussed. Its operational sensitivities are depicted by numerical analysis using an advanced snowplow model. The analysis shows consistency with previously reported experimental results.

The performances of a simple circuit for fast sweep measurements using collecting and emissive Langmuir probes are evaluated. The probes are biased by means of a time dependent ramp voltage signal with a variable pulse frequency and the current voltage curves are measured along the increasing flange of this sawtooth voltage. The response of this fast probe polarization circuit was verified under actual experimental conditions by measuring the properties of a stationary Maxwellian plasma produced by means of a glow discharge. The results are independent of the experimental conditions and essentially rely on the discharge properties for polarization pulse repetition rates below a threshold. This upper bound lies below the ion plasma frequency and is related with the faster time scale involved in the sawtooth signal probe bias voltage. The motion of ions would not follow the rapid change of the electric field around the probe associated to the short decreasing edge of the sawtooth polarization voltage and, therefore, the probe perturbs the local electric field. We conclude that these time scales should be considered for the interpretation of these measurements in addition to the electron and ion plasma frequencies in fast sweep Langmuir probe techniques. We conclude that these time scales should be considered for the interpretation of these measurements in addition to the electron and ion plasma frequencies in fast Langmuir probe techniques. c

The newly qualified IRS facility for the determination of total and spectral emissivities and its recent numerical optimization is described. Values of measured total emissivities of the ceramics HfO2, Al2O3, Yt2O3 and the metals/alloys tungsten, TZM and PM1000 in the temperature regime of 750–1800 K are given. The drastic influence of the oxidation state of PM1000 on the emissivity is discussed. Additionally, results of an investigation of the influence of surface roughness and surface topology on emissivity are presented. Therefore, three SSiC samples with surface roughness from R q = 0.05 to 0.66 have been prepared using common finishing operations. The tests showed that the emissivity increased about 10% with an increase of the surface roughness even in the regime where R q values are in the same magnitude or much smaller than the maximum emitting wavelength. Recombination coefficients for the abovementioned materials have been determined in pure oxygen plasma. The methodology for the determination of recombination coefficients of ceramic and metallic thermal protection system (TPS) materials in single species gases used at IRS and its latest improvements is presented. Test results for the recombination coefficients in oxygen plasma are shown between 1469 and 2072 K.

Set-up, function and application potential of pulsed magnetoplasmadynamic self-field accelerators are described. The focus is on the facility MAX (Magnetoplasmadynamic Accelerator-eXperiment). Here, a high power coaxial accelerator is investigated regarding space propulsion and processes aiming for metal treatment as potential applications. A certain amount of gas is accelerated via magnetic fields while the overall kinetic energy of the plasma has to be maximized. During plasma generation numerous parasitic effects are associated with the discharge of the device. Hence, the characterization of the facility in terms of power balance, functional behaviour and kinetic energy of the plasma is mandatory. The kinetic energy is of importance for both space propulsion and the mentioned plasma material treatment processes. Electrodynamic properties enabling the simulation with a snowplow model have been determined experimentally. The model provides a relation between the plasma movement and the electrodynamic properties. Results of the model are current and voltage histories but also statements on the kinetic energy of the plasma. Based on this calorimeters were designed, manufactured and integrated using adequate measurement technology, e.g. fast thermocouples and an infrared camera allowing for the determination of the temporal and spatial temperature histories on the calorimeters. A thermal analysis model was developed and applied to the calorimeter and compared with the measurements. Hence, the thermal energy could be determined which consequently led to an efficiency of 12% for a load voltage of 12 kV and an ambient pressure of 10 −5 mbar.

The development of the inductively driven plasma wind tunnel PWK3, which enables the electrodeless generation of high-enthalpy plasmas for the development of heat shield materials required for space vehicles performing entry manoeuvres in the atmospheres of Venus, Earth and Mars, is described. The facility with its modular inductive plasma generators allows operation with gases such as carbon dioxide, air, oxygen and nitrogen and was qualified for thermal plasma powers up to 60 kW. Previously developed models for determining plasma properties and plasma source related characteristics enable a maximum plasma power in combination with long operational periods using different operational gases and gas mixtures. This is achieved by an optimization using the optimum operational frequency, a minimization of field losses using very thin plasma tube wall thicknesses and the successful application of MHD effects. Based on the solved cylinder problem for ICPs, a one-dimensional model for radial Lorentz forces and magnetic pressure has been developed. Here, a synthesis of previously published data and works is made where the new algebraic model for the calculation of Lorentz forces and magnetic pressures in an ICP was used and applied to experimental data. In addition, results from the model using the experimental data are shown to be consistent and, in addition, a comparison with a simpler model based on the well-known exponential approach for ICPs showed that the simpler model is covered without fail by the new model. The new model also states that there is a maximum of the Lorentz forces over the damping parameter d/δ (plasma diameter divided by skin depth) which almost corresponds with the position of the maximum plasma power of the cylindric model for ICPs. For the magnetic pressure the position of the maximum pressure is identical to the value for d/δ for the maximum plasma power.

The interaction between a magnetic field and plasma close to a nonconductive surface is of interest for both science and technology. In space, crustal magnetic fields on celestial bodies without atmosphere can interact with the solar wind. In advanced technologies such as those used in fusion or spaceflight, magnetic fields can be used to either control a plasma or protect surfaces exposed to the high heat loads produced by plasma. In this paper, a method will be discussed for investigating magnetic field plasma interactions close to a nonconductive surface inside a Gaseous Electronics Conference reference cell employing dust particles as probes. To accomplish this, a magnet covered by a glass plate was exposed to a low power argon plasma. The magnetic field was strong enough to magnetize the electrons, while not directly impacting the dynamics of the ions or the dust particles used for diagnostics. In order to investigate the interaction of the plasma with the magnetic field and the nonconductive surface, micron-sized dust particles were introduced into the plasma and their trajectories were recorded with a high-speed camera. Based on the resulting particle trajectories, the accelerations of the dust particles were determined and acceleration maps over the field of view were generated which are representative of the forces acting on the particles. The results show that the magnetic field is responsible for the development of strong electric fields in the plasma, in both horizontal and vertical directions, leading to complex motion of the dust particles.

MHD effects arising in plasma sources, such as short-pulsed magnetoplasmadynamic generators and inductively heated plasma generators, are analyzed with both algebraic models and measured data. Functional principles of the sources based on their MHD behavior are explained. Moreover, Stewart numbers in the order of magnitude of at least 10 −1 are calculated for the systems and qualified as an identifier for the magnetic influence on plasmas. Here, the considered plasma systems that are a priori known as MHD systems were used to determine typical values of the Stewart number. Based on this experience the concept of a plasma probe to magnetically influence or control weakly ionized free stream plasma flows is presented.

The method for determining the recombination coefficients for ceramic materials in air plasma and pure oxygen plasma is described. Additionally, a new method lor the in situ determination of the spectral emissivity of high-temperature ceramic materials is presented. Values of the recombination coefficients for considered materials, resulting from the described methodology, are given at temperatures between 1483 and 1851 K and pressures between 356 and 950 Pa and compared with literature. Values of the spectral emissivities of the investigated materials are presented in a temperature range from about 1200 to 1820 K and compared with values obtained by other authors. Obtained results will be used for the development of catalytic sensors in the frame of the European reentry program EXPERT.

At the Institute of Space Systems of the Universitat Stuttgart different plasma sources have been developed for a variety of technical applications. Short-pulsed magnetoplasmadynamic generators, thermal arc devices, inductively heated sources and hybrid generators are in operation. In this paper an overview on the sources and their field of application is given.

Thedesignoftheplasmawindtunnel (PWK3),itsinductivelyheatedplasmagenerator (IPG3),andexperimental results using O 2 and CO2 as operational gases are described. Various operational conditions (mass e ow rate, frequency) were applied. The thermal plasma powers measured with a calorimeter in the chamber of PWK3 are presented, leading to thepossibility to determineefe ciencies. When thepowerwas varied, two discrete operational transitions were observed. The simultaneous differences in the discharge behavior of IPG3 are represented by sudden changes of parameters such as calorimetric powers and local heat e uxes measured with a stationary heat e ux probeinthechamberofthefacility. Additionally,thecoolingpoweroftheIPG3plasmatubeispresented.Here, a plasma stabilization effect appearing with the second operational transition was observed when the tube cooling power decreased suddenly despite the simultaneous increase of the plasma power in the chamber. An imaging spectrometer measuring the radial intensity of the plasma through an axial optical window of IPG3 was used. Both the operational behavior, in particular the stabilization effect, and the heat e ux measurements show that PWK3 enables high-enthalpy tests for both basic thermal protection material tests and atmospheric entry simulation of spacecrafts.

An assessment of a decentralized inductively heated plasma waste treatment system for energy recovery has been done. The modular miniaturized high enthalpy plasma source IPG6 is a reference for the system and has been qualified for inert but also chemically aggressive gas compositions. An identification and review of applications were undertaken. Niches of high environmental and societal importance are considered: hospital waste (threshold countries), shipboard waste and marine litter. The wastes are reviewed deriving relevant parameter for a system analysis aiming for the derivation of energy production and efficiencies. The system analysis shows advantageous constellation due to the wastes’ energy leading to self-feeding systems.

Apart from magnetoplasmadynamic plasma generators (MPG) and thermal arcjet devices (TPG) for re-entry simulation, inductively heated plasma generators (IPG ) have been developed for basic TPS material tests at the IRS. These inductively heated plasma generators consist mainly of a water-cooled coil surrounding a tube in which the plasma is located Due to this setup no electrode erosion appears; impurities in the plasma are minimized. Hence, both the behaviour of the gas components can be examined singularly and basic material tests such as the determination of the catalytic behaviour can be performed. With IPG3 an rf-source is provided where the coil is closer to the plasma than it was with previous designs. Therefore, the electromagnetic field loss is reduced. The water cooling system surrounds both the induction coil and the plasma container. IPG3 was qualified up to an anode power of 180 kW (argon), which is an essential improvement regarding the intended re-entry simulations in combination with the IRS MPG-simulations in the plasma wind tunnels 1 and 2 (PWK). The structure of the rf-plasma source IPG3 and the facility PWK3 are presented in this paper. This paper describes the design of IPG3 and the first experimental results for the plasma source. Power characteristics of IPG3, which were measured under variation of gas, are shown. Within this variation of gas frequency measurements were made, which will be a help for later numerical simulations of IPG3. A CID camera was used to measure the radial intensity of the plasma through an axial optical window of IPG3. The results led to a rough determination of the skin depth for the operation with air.

For atmospheric reentries at high enthalpies ablative heat shield materials are used, such as those for probes entering the atmosphere of Saturn’s moon Titan, such as Cassini-Huygens in December, 2004. The characterization of such materials in a nitrogen/methane atmosphere is of interest. A European ablative material, AQ60, has been investigated in plasma wind tunnel tests at the IRS plasma wind tunnel PWK1 using the magnetoplasma dynamic generator RD5 as plasma source in a nitrogen/methane atmosphere. The dimensions of the samples are 45 mm in length with a diameter of 39 mm. The actual ablator has a thickness of 40 mm. The ablator is mounted on an aluminium substructure. The experiments were conducted at two different heat flux regimes, 1.4 MW/m2 and 0.3 MW/m2. In this paper, results of emission spectroscopy at these plasma conditions in terms of plasma species’ temperatures will be presented, including the investigation of the free-stream species, N2 and N2+, and the major erosion product C2, at a wavelength range around 500 nm–600 nm.

In order to develop inductive electric propulsion as a flexible, throttleable technology for future space operations, a greater understanding of discharge transitions within the inductive plasma generator discharge chamber is required. This paper presents a non-intrusive method to determine the conditions under which transitions between the capacitive, low inductive, and high inductive regimes occur with greater accuracy, as well as determining the proportion of a single discharge cycle the plasma spends in either capacitive or inductive regime. Such a method allows a more robust method of classification of inductive discharges than previously available and can be applied to numerous gases. This approach presents an advantage over previous methods which relied on strongly radiating or thermally reactive gases to exhibit certain behaviour (due to the restriction of classical diagnostics on such high power sources) before a transition could be confirmed. This paper presents results from the proposed method applied to a pure oxygen plasma as well as two combinations of argon and oxygen (at 1:1 and 3:2 Ar:O2 volumetric ratios) in order to assess the tunability of electromagnetic regime transitions through modifications of gas composition rather than mechanical alterations. Transitions to the higher inductive mode were observed for much lower input powers for the argon–oxygen blends, as was expected, allowing final discharge conditions to occupy the inductive regime for 94% and 85% of a single discharge cycle for the 3:2 and 1:1 Ar:O2 mixtures, respectively. Pure oxygen achieved a maximum inductive proportion of 71% by comparison.

the ablative iMPD ADD SIMP-LEX of the Institute of Space Systems in Stuttgart, represents a promising and cheap solution to todays propulsion challenges in space. The work presented in this paper covers new information on the electromagnetic conditions during thrust generation by revealing the temporal and spatial distribution of the vectorial current density between the thruster electrodes. At IRS this is achieved by utilizing self-made and calibrated miniaturized induction probes. The local magnetic eld components of all three spatial directions are combined to derive the current density vector. Quantitative determination of the temporal behavior of vectors at 27 points evenly distributed in three planes delivers for the rst time a comprehensive picture of the position and development of the current sheet in a PPT. Maximum current densities of 80 kA=m 2 and magnetic ux densities of up to 0:82 T have been observed close to the surface of the solid Teon T M -propellant. It should be noted, that in contrast to the slug model by Jahn no distinct movement of the current sheet was observed. The current density data is discussed and compared to high-speed camera pictures taken at IRS.

The emissive Langmuir probes are made up of thin metallic wires exposed to the plasma and heated up to the electron thermoionic emission by a DC current 1,2,3. They are essentially used to determine the local plasma potential V sp 1,2,3 and the electron temperature T e 4. The weak and strong electron operation emission regimes of the probe are determined by means of the probe temperature T w . For probe bias voltages V p < V sp the experimental evidence points out that a fraction of the emitted electron population returns to the probe after colliding. The probe temperature dependent voltage current curves were found in agreement with a simple model, which accounts for this returned electron current. Therefore for low positive probe polarization voltages V p ⌷V sp two electron populations also coexist close to the probe; the electrons from the plasma and also the local emitted electrons of temperature TW that slightly alter the local potential around the probe. Thus, the electron saturation current results from the sum of two drained electron currents, and one of them relies on the wire temperature. The determination of the plasma potential and the electron temperature for polarization potentials V p < V sp by using the floating potential of the probe is also investigated. The plasma potential was obtained from the measurements of the floating potential as a function of the probe temperature. A sharp transition between two different regimes is observed at the temperature where floating potential equals the plasma potential. However, while on theoretical grounds the determination of the electron temperature T e is also possible 4, the results obtained when using emissive and collecting probes differ. The different electron populations close to the probe when V p < V sp would be responsible of this disparity between the experimental results found with both probes.

The examination of a permeable flow element for PPT propellant feeding is presented. The intention is to identify the control parameters for a self-controlled propellant flow through the element. As the element, a permeable \(\hbox{WHIPOX}^{\circledR}\)-fibre ceramic is used, feeding water propellant. It is found that the propellant transport is both driven by pressure gradients within the structure and evaporation into the discharge region. For functional testing, a mass flow rate of 340 μg/s is chosen, the PPT being operated against 5 Pa ambient pressure and showing reproducible ignition behaviour. Finally, the system is compared to a PTFE propellant system by spectrometric and photographic analysis of the plasma and by comparison of the electrodes indicating less erosion for water operation.

Plasma wind tunnel tests using the European ablative materials AQ61 and MONA were conducted in a nitrogen/ oxygen atmosphere at three relevant heat fluxes. Results of the emission spectroscopic investigation of the plasma radiation are presented, for both the freestream (without probe body) and the boundary layer 5 mm in front of the test samples. Emission spectroscopy was conducted at several wavelength ranges (320 nm < λ < 580 nm) and spectral resolutions. Results are compared with respect to the temperatures of the most common plasma species. Here, comparisons are drawn between the plasma emission at the different heat flux regimes and the test specimen material.

Electric space propulsion delivers high exhaust velocities usually in combination with relatively low thrust levels. Raising the thrust level at a constant high exhaust velocity, fuel consumption for a specific mission is reduced and payload mass is increased. Also, an increase in mission flexibility and a reduction of duration can be achieved. Promising thrusters are hybrid concepts like TIHTUS. This thruster combines an arcjet and an ICP in series. The proof of concept already shows promising results. After a description of the thruster system actual experimental and theoretical optimizations of the standalone ICP are summarized. For a decrease of wall thickness from 2.3 mm to 1.25 mm the thermal plasma power is increased by 40 % and the thinner quartz tube can resist higher heat loads, too. These results show the potential for large improvements of the overall thruster parameters and motivate a research program for further optimization of the already promising TIHTUS engine. In this program, theoretical and experimental investigation will be accompanied by numerical simulations for a detailed understanding of the relevant processes and the identification of the prospects of success for further optimization. The current status of development of the numerical tool is also described.

The pulsed plasma thruster Add Simp-lex, developed at the IRS, was investigated at the University of Tokyo to further characterize the thruster’s performance and discharge behavior. This was done by experimental investigation of configurations with a different amount of capacitors and discrete applied voltages. To do so, a measurement system for the discharge current and the optical properties was built up and successfully applied. Further, the numerical model for the prediction of the current-normalized magnetic flux density was improved and the convergence properties of the integration towards the change in inductance studied. From the discharge current waveforms and the pictures taken from the propagating plasma, information about the amount of plasma creations, their propagation velocity and the oscillation behavior was deducted. For further characterization, the energy transfer efficiency and the electrical efficiency was derived from these data, leading to a tool to compare different configurations. It was found, that a middle voltage yields higher electrical efficiencies of about 40% whereas the energy transfer efficiency is higher the lower the applied voltage.

Within this work we investigate the radiative properties of molecular nitrogen with respect to the highly excited electronic states giving rise to radiative transitions occuring in the spectral range of Vacuum–Ultraviolet (VUV) radiation. This is done in order to shed light on the role of VUV radiation of molecular nitrogen on the radiative heat load encountered by a vessel during highspeed atmospheric reentry. The considered transitions are the Lyman-Birge-Hopfield (aΠg − XΣg ), Birge-Hopfield I (bΠu − XΣg ), Birge-Hopfield II (bΣu −XΣg ), Caroll-Yoshino (c4Σu −XΣg ), Worley-Jenkins (c3Πu −XΣg ), Worley (o3 Πu−XΣg ), and eΣu −XΣg bands. The approach to retrieve the relevant parameters for the line by line radiation simulation follows common methods of calculation, which are the reconstruction of the potential energy function via the Rydberg-Klein-Rees (RKR) method and subsequently solving the corresponding radial Schrodinger equation. Absorption and emission spectra are calculated for a known equilibrium test condition of air plasma to illustrate the contribution of the VUV transitions to the radiation. The influence of the VUV radiation on the heat load experienced by a reentry vehicle is illustrated with a CFD calculation.

The Direct Simulation Monte Carlo module of a fully kinetic 3D plasma particle code is currently under development at the Institute of Space Systems (IRS). As the complete discharge simulation of a non-stationary magnetoplasmadynamic thruster is intended, improved models for the DSMC (direct simulation monte carlo) based interaction evaluation in a highly rarefied and strongly disturbed plasma need to be used. For that purpose it is essential to avoid macroscopic quantities (like temperature) in the model approach. Therefore, a collision and reaction evaluation approach was developed and implemented which is based on energy dependent cross section data only. As the thruster propellant is Polytetrafluorethylen (PTFE) a large cross section data base was built, implemented, and verified based on the assumption of an initially fully dissociated and partially ionized plasma. The electron - heavy particle interactions of interest are elastic scattering (including polarization), collisional excitation, de-excitation, and recombination. In this work we present the model approach, details on the implemented Carbon related cross sections as well as the verification procedure which is based on the reproduction of rate coefficients in the range of 20.000 - 200.000 K. © 2010 by the authors.

An experimental investigation was carried out in order to evaluate the possible use of a newly adapted calorimetric heat flux probe in combination with a set of 8 strong permanent ring magnets to influence a high enthalpy argon plasma flow. The plasma wind tunnel facility 1 (PWK1) of Institut fur Raumfahrtsysteme (IRS) was used together with the high enthalpy magneto-plasmadynamic plasma source RD5. The probe was first qualified at well known plasma conditions. Thereafter, it was equipped with permanent magnets and tested at a newly defined argon plasma condition in order to evaluate a possible influence of the magnetic field on the stagnation point heat flux. For each case, with and without magnet, two radial profiles have been recorded as well as several measurements at the center position inside the plasma flow. A definite influence on the stagnation point heat flux has been found, though the results show an increase of 17.78 % at the center position (18.15 % mean value) instead of a decrease. A possible explanation for this result is, that it might originate from the magnetic field configuration of the permanent magnets.

The paper reports the layout and verification of the measurement chain as developed for the EXPERT mission on basis of simulated spectrometer responses. To generate the spectrometer signals, flow field simulations of the EXPERT capsule for several trajectory points are conducted. The results, i.e. excitation temperatures and mole fractions of the plasma species, are presented in the paper. From the data, emission and absorption coefficients along the lines of sight of the RESPECT sensor heads are calculated. Furthermore, the calibration of the sensor system is described. In order to demonstrate the successful measurement chain design of the payload, expected spectrometer signals are presented. Nomenclature