Carolyn Jacobs

Measurements of Air Plasma/Ablator Interactions in an Inductively Coupled Plasma Torch

Studies of the ultraviolet and visible emission from an atmospheric pressure air plasma and its interaction with two carbon-based ablative materials were performed in an inductively coupled plasma torch. These experiments were conducted at a plate power of 40 kW, which produced an air plasma in local thermodynamic equilibrium with a maximum temperature of approximately 6200 K, corresponding to a specific enthalpy of 16.4  MJ/kg. Three techniques were developed to measure the ablator surface temperature. Recession rates and product species profiles were measured for two different materials (ASTERM™ and carbon-bonded carbon fiber) at a plasma velocity of approximately 20  m/s. Measured surface temperatures were in the range of 2100 to 2300 K, and corresponding hot-wall heat fluxes were approximately 1.4  MW/m2. Spatially resolved profiles of the main species detected in the boundary layer were recorded, and they showed evidence of strong coupling between the ablated material and the freestream.

Cyclic tetrapeptides via the ring contraction strategy: Chemical techniques useful for their identification

Cyclic tetrapeptides are a class of natural products that have been shown to have broad ranging biological activities and good pharmacokinetic properties. In order to synthesise these highly strained compounds a ring contraction strategy had previously been reported. This strategy was further optimised and a suite of techniques, including the Edman degradation and mass spectrometry/mass spectrometry, were developed to enable characterisation of cyclic tetrapeptide isomers. An NMR solution structure of a cyclic tetrapeptide was also generated. To illustrate the success of this strategy a library of cyclic tetrapeptides was synthesised.

Atmospheric pressure argon surface discharges propagated in long tubes: physical characterization and application to bio-decontamination

Pulsed corona discharges propagated in argon (or in argon with added water vapor) at atmospheric pressure on the interior surface of a 49 cm long quartz tube were investigated for the application of surface bio-decontamination. H2O molecule dissociation in the argon plasma generated reactive species (i.e. OH in ground and excited states) and UV emission, which both directly affected bacterial cells. In order to facilitate the evaluation of the contribution of UV radiation, a DNA damage repair defective bacterial strain, Escherichia coli DH-1, was used. Discharge characteristics, including propagation velocity and plasma temperature, were measured. Up to ~5.5 and ~5 log10 reductions were observed for E. coli DH-1 bacteria (from 106 initial load) exposed 2 cm and 44 cm away from the charged electrode, respectively, for a 20 min plasma treatment. The factors contributing to the observed bactericidal effect include desiccation, reactive oxygen species (OH) plus H2O2 accumulation in the liquid phase, and UV-B (and possibly VUV) emission in dry argon. The steady state temperature measured on the quartz tube wall did not exceeded 29 °C; the contribution of heating, along with that of H2O2 accumulation, was estimated to be low. The effect of UV-B emission alone or in combination with the other stress factors of the plasma process was examined for different operating conditions.

A simulation technique for radiating shock tube flows

We describe a numerical modelling technique used to simulate the gas flow in the complete X2 facility in non-reflected shock tube mode. The technique uses a one-dimensional model to simulate piston dynamics and diaphragm rupture and couples this to an axisymmetric simulation of the shock tube which captures viscous and finite-rate chemistry effects. This technique is used to simulate a nonequilibrium radiation condition relevant to a Titan atmospheric manoeuvre. The condition is a 7,km/s shock propagating into a N2/CH4 mixture at 80,Pa. The results show that the shock remains relatively planar at the exit of the shock tube such that there should be little difficulty for the optics. In terms of modelling, the finite-rate chemistry gas performs better than the equilibrium gas for these flows with regards to flow property estimates.

Radiometric temperature analysis of the Hayabusa spacecraft re-entry

Hayabusa, an unmanned Japanese spacecraft, was launched to study and collect samples from the surface of the asteroid 25143 Itokawa. In June 2010, the Hayabusa spacecraft completed it’s seven year voyage. The spacecraft and the sample return capsule (SRC) re-entered the Earth’s atmosphere over the central Australian desert at speeds on the order of 12 km/s. This provided a rare opportunity to experimentally investigate the radiative heat transfer from the shock-compressed gases in front of the sample return capsule at true-flight conditions. At these conditions, the total heat transfer to the vehicle has a significant radiative component and this can be estimated by studying the radiation emitted from the shock layer and the hot surface. Such measurements can be compared with numerical simulations of the flow and with results from ground-based testing in shock tunnels and expansion tubes. This in turn leads to a better understanding of the complex thermochemistry occurring within the shock layer and aids in the design of more efficient thermal protection systems for future spacecraft.

Radiation measurements in rarefied Titan atmospheres

For reentry operations into atmospheres such as Titan, accurate, reliable radiation data is essential for estimating the total heat transfer experienced by the vehicle. Experiments are being undertaken in the X2 facility at the University of Queensland to measure the radiation produced by superorbital entry in the rarefied section of the trajectory. These experiments use the Nonreflected Shock Tube (NRST) mode of experimentation, which allows full-scale measurement of the radiation in the flow. This paper presents results from the continuing experimental work being conducted in the X2 facility, focussing on freestream pressures between 2 and 13 Pa for a 98% N2, 2% CH4 Titan gas mixture. For radiating flows with Titan gas, the main radiator of interest is CN (cyanogen), formed in high concentrations in the nonequilibrium region behind the shock. The experimental data includes static and pitot pressure measurements of the flows and a spectrometer is used to capture the radiation in the CN violet band. Flow visualisation is also achieved with a high speed camera.

Vacuum ultraviolet radiation studies in a plasma torch facility

For many Earth atmospheric reentry conditions, the vacuum ultraviolet portion of the radiative heating can be significant. As a result, information on this region can be important to the development of thermal protection systems. Few experimental data are available in the this spectral region due to the difficulty of measuring emission in a spectral region where air strongly absorbs the radiation. The 50 kW radio-frequency inductively coupled plasma torch recently installed at the Laboratoire EM2C (Ecole Centrale Paris) has been used to conduct equilibrium emission spectroscopy measurements in the vacuum ultraviolet region for relevant Earth reentry conditions. Absolute intensity emission spectra measured in the range 170 - 200 nm are obtained and compared with the prediction of the line-by-line Specair code.

Super-Orbital Re-entry in Australia: Laboratory Measurement, Simulation and Flight Observation

There are large uncertainties in the aerothermodynamic modelling of super-orbital re-entry which impact the design of spacecraft thermal protection systems (TPS). Aspects of the thermal environment of super-orbital re-entry flows can be simulated in the laboratory using arc- and plasma jet facilities and these devices are regularly used for TPS certification work [5]. Another laboratory device which is capable of simulating certain critical features of both the aero and thermal environment of super-orbital re-entry is the expansion tube, and three such facilities have been operating at the University of Queensland in recent years[10]. Despite some success, wind tunnel tests do not achieve full simulation, however, a virtually complete physical simulation of particular re-entry conditions can be obtained from dedicated flight testing, and the Apollo era FIRE II flight experiment [2] is the premier example which still forms an important benchmark for modern simulations. Dedicated super-orbital flight testing is generally considered too expensive today, and there is a reluctance to incorporate substantial instrumentation for aerothermal diagnostics into existing missions since it may compromise primary mission objectives. An alternative approach to on-board flight measurements, with demonstrated success particularly in the ‘Stardust’ sample return mission, is remote observation of spectral emissions from the capsule and shock layer [8]. JAXA’s ‘Hayabusa’ sample return capsule provides a recent super-orbital reentry example through which we illustrate contributions in three areas: (1) physical simulation of super-orbital re-entry conditions in the laboratory; (2) computational simulation of such flows; and (3) remote acquisition of optical emissions from a super-orbital re entry event

Radiative Heat Transfer Measurements in a Nonreflected Shock Tube at Low Pressures

At high flight speeds, radiation becomes an important component of aerodynamic heat transfer, and its coupling with the flow field can significantly change the macroscopic features of the flow. As radiating flight conditions are typically encountered in re-entry trajectories, the associated flight regimes range from rarefied to continuum, and may have many levels of thermal, chemical and electronic nonequilibrium. Accurate estimates of the nonequilibrium radiation involved in high speed operations such as reentry are essential in order to more efficiently design thermal protection systems.