Boltzmann expansion in a radiofrequency conical helicon thruster operating in xenon and argon

A low pressure (~ 0.5 mTorr in xenon and ~ 1 mTorr in argon) Boltzmann expansion is experimentally observed on axis within a magnetized (60 to 180 G) radiofrequency (13.56 MHz) conical helicon thruster for input powers up to 900 W using plasma parameters measured with a Langmuir probe. The axial forces, respectively, resulting from the electron and magnetic field pressures are directly measured using a thrust balance for constant maximum plasma pressure and show a higher fuel efficiency for argon compared to xenon

Supporting Special Educational Needs and Disability (SEND) Youth Co-Production: An Exploration of Practitioner Views

The UK Government’s Special Educational Needs and Disability (SEND) Code of Practice: 0 to 25 years (Department for Education & Department of Health, 2015), highlights the need for children and young people (CYP) to participate in decisions that affect their lives. However, concerns have been raised around failures to support those with SEND in participating effectively (United Nations Committee on the Rights of the Child, 2016). In 2017, practitioners in the North West set up an interest group to explore practices around the participation and co-production with CYP with SEND, from which Participation Learning Events were subsequently created. Data from practitioners from two events, using World Café and storyboard methods led to the creation of Principles of Co-Production: Practitioners' Perspectives (see Figure 1) in order to fill the knowledge gap in this area, hoping these principles could be used to support their practice and that of others. The overarching principle includes the development of a co-production culture, which is supported by other principles of: understanding of co-production; developing engagement opportunities; accessibility and representation; evidence-based practice; creating sustainable systems; creating goals and assigning responsibility; reviewing goals and challenging practice; and sharing practice. It is hoped that these principles along with reflective questioning will support thoughtful discussions and, in turn, co-produced practices at individual and strategic levels. Research implications, limitations and areas for further research are considered

Axial force imparted by a conical radiofrequency magneto-plasma thruster

Direct thrust measurements of a low pressure (∼0.133 Pa) conical radiofrequency (rf at 13.56 MHz) argon plasma source show a total axial force of about 5 mN for an effective rf power of 650 W and a maximum magnetic field of 0.018 T, of which a measured value of 2.5 mN is imparted by the magnetic nozzle. A simplified model of thrust including contributions from the electron pressure and from the magnetic fieldpressure is developed. The magnetic nozzle is modelled as a “physical” nozzle of increasing cross-sectional area

A magnetic nozzle calculation of the force on a plasma

The measured axial force imparted from a magnetically expanding current-free plasma has been shown recently [Takahashi, Phys. Rev. Lett. 107, 235001 (2011)] to equal the axial force on that plasma calculated by a two-dimensional fluid model. Here, we calculate the same axial force on the plasma by a quasi one-dimensional model of a magnetic nozzle. The quasi one-dimensional magnetic nozzle model provides us with an estimate of the force on the plasma that is similar to that found by the more accurate two-dimensional model.This research has been partially supported by the Israel Science Foundation (Grants 864/07 and 765/11)

Direct thrust measurements and modelling of a radio-frequency expanding plasma thruster

It is shown analytically that the thrust from a simple plasma thruster (in the absence of a magnetic field) is given by the maximum upstream electron pressure, even if the plasma diverges downstream. Direct thrust measurements of a thruster are then performed using a pendulum thrust balance and a laser displacement sensor. A maximum thrust of about 2 mN is obtained at 700 W for a thruster length of 17.5 cm and a flow rate of 0.9 mg s1, while a larger thrust of 4 mN is obtained at a similar power for a length of 9.5 cm and a flow rate of 1.65 mg s1. The measured thrusts are in good agreement with the maximum upstream electron pressure found from measurements of the plasma parameters and in fair agreement with a simple global approach used to model the thruster.Dr. K. Takahashi would like to thank the Faculty of Engineering at Iwate University (sabbatical year), the TEPCO Research Foundation in Japan, the MEXT in Japan (Grant-in-Aid for Young Scientists A 22684031), and the SP3 laboratory (Australian Research Council Discovery Grant No. DP 1096653) for financial support

Particle-in-cell simulation of an electron shock wave in a rapid rise time plasma immersion ion implantation process

A one-dimensional Monte Carlo collision–particle-in-cell plasma computer code was used to simulate plasma immersion ion implantation by applying a negative voltage pulse to the substrate while the reactor wall is grounded. The results presented here show the effect of short rise time pulses: for rise times shorter than the electron plasma period (typically 5ns∕kV), an electron shock wave is observed where a rapidly expanding sheath heats the electrons up to high energies. Many of these fast electrons are expelled from the plasma leading to a high plasma potential and thus to a high surface electric field on the earthed electrode which could give rise to non-negligible electron field emission

Measurement of the energy distribution of trapped and free electrons in a current-free double layer

In the high potential plasma, upstream of the double layer, the measuredelectron energy distribution function(EEDF) shows a very clear change in slope at energies (εbreak) corresponding to the double layer potential drop. Electrons with lower energy are Maxwellian with a temperature of 8eV, whereas those with higher energy have a temperature of 5eV. The EEDF in the downstream plasma has a temperature of 5eV. Over the range of pressures wherein the double layer and accelerated ion beam are detected by analysis of a retarding field energy analyzer, the strength of the double layer corresponds to the energy where the slope changes in the EEDF(εbreak). We deduce that the downstream electrons come from upstream electrons that have sufficient energy to overcome the potential of the double layer, and that only a single upstream plasma source is required to maintain this phenomenon.This work was supported by Tohoku University 21st COE program, System Construction of GlobalNetwork Oriented Information Electronics, and by the Japan Society for the Promotion of Science for Young Scientists. It was also supported by a Visiting Fellowship of the Research School of Physical Sciences and Engineering

Comorbidity in context: Part 1. Medical considerations around HIV and tuberculosis during the COVID-19 pandemic in South Africa

Infectious diseases pandemics have devastating health, social and economic consequences, especially in developing countries such as South Africa. Scarce medical resources must often be rationed effectively to contain the disease outbreak. In the case of COVID-19, even the best-resourced countries will have inadequate intensive care facilities for the large number of patients needing admission and ventilation. The scarcity of medical resources creates the need for national governments to establish admission criteria that are evidence-based and fair. Questions have been raised whether infection with HIV or tuberculosis (TB) may amplify the risk of adverse COVID-19 outcomes and therefore whether these conditions should be factored in when deciding on the rationing of intensive care facilities. In light of these questions, clinical evidence regarding inclusion of these infections as comorbidities relevant to intensive care unit admission triage criteria is investigated in the first of a two-part series of articles. There is currently no evidence to indicate that HIV or TB infection on their own predispose to an increased risk of infection with SARS-CoV-2 or worse outcomes for COVID-19. It is recommended that, as for other medical conditions, validated scoring systems for poor prognostic factors should be applied. A subsequent article examines the ethicolegal implications of limiting intensive care access of persons living with HIV or TB