Ion collection from a plasma by a pinhole

Ion focusing by a biased pinhole is studied numerically. Laplace's equation is solved in 3-D for cylindrical symmetry on a constant grid to determine the potential field produced by a biased pinhole in a dielectric material. Focusing factors are studied for ions of uniform incident velocity with a 3-D Maxwellian distribution superimposed. Ion currents to the pinhole are found by particle tracking. The focusing factor of positive ions as a function of initial velocity, temperature, injection radius, and hole size is reported. For a typical Space Station Freedom environment (oxygen ions having a 4.5 eV ram energy, 0.1 eV temperature, and a -140 V biased pinhole), a focusing factor of 13.35 is found for a 1.5 mm radius pinhole

Plasma sheath effects on ion collection by a pinhole

This work presents tables to assist in the evaluation of pinhole collection effects on spacecraft. These tables summarize results of a computer model which tracks particle trajectories through a simplified electric field in the plasma sheath. A technique is proposed to account for plasma sheath effects in the application of these results and scaling rules are proposed to apply the calculations to specific situations. This model is compared to ion current measurements obtained by another worker, and the agreement is very good

Towards a new theory of practice for community health psychology

The article sets out the value of theorizing collective action from a social science perspective that engages with the messy actuality of practice. It argues that community health psychology relies on an abstract version of Paulo Freire’s earlier writing, the Pedagogy of the Oppressed, which provides scholar-activists with a ‘map’ approach to collective action. The article revisits Freire’s later work, the Pedagogy of Hope, and argues for the importance of developing a ‘journey’ approach to collective action. Theories of practice are discussed for their value in theorizing such journeys, and in bringing maps (intentions) and journeys (actuality) closer together

Vertical beam size, non-closure and LEP performance

The luminosity in LEP is critically dependent on the vertical beam size and thus on the effective control of contributing factors. Electrostatic separation bumps are used in LEP to avoid parasitic beam encounters and to allow the possibility of running with bunch trains. These vertical bumps are not closed at highest energies. The non-closure leads to different orbits for electrons and positrons and prevents effective minimisation of the residual vertical dispersion for both beams simultaneously. The various sources of the non-closure and a correction scheme which globally minimises the effects of this non-closure using only a few degrees of freedom are presented. The contributions to the vertical beam size from dispersion, coupling, beam-beam and other effects are quantified and the means used to control them are discussed

Physics Opportunities with the FCC-hh Injectors

In this chapter we explore a few examples of physics opportunities using the existing chain of accelerators at CERN, including potential upgrades. In this context the LHC ring is also considered as a part of the injector system. The objective is to find examples that constitute sensitive probes of New Physics that ideally cannot be done elsewhere or can be done significantly better at theCERN accelerator complex. Some of these physics opportunities may require a more flexible injector complex with additional functionality than that just needed to inject protons into the FCC-hh at the right energy, intensity and bunch structure. Therefore it is timely to discuss these options concurrently with the conceptual design of the FCC-hh injector system.Comment: 13 pages, chapter 5 in Physics at the FCC-hh, a 100 TeV pp collide

Experience with Bunch Train in LEP

Since 1995 LEP is operated with the new bunch train scheme. This scheme allows head-on collisions of four trains of up to four bunches within a train. The first experience with this new scheme and the problems encountered during the commissioning and the operation are reviewed and discussed. The performance of LEP and the results from dedicated experiments are shown and compared with expectations. The modifications and improvements to allow a successful operation at LEP2 energies are discussed and the performance at energies above 80 GeV is presented

Bunch Trains for LEP

Since 1995 LEP has been operated with a bunch train scheme which allows head-on collisions of four trains of up to four bunches within a train. The proposal and its implementation are presented, and the consequences for the beam dynamics are discussed in detail. In particular the side effects due to the separation scheme itself and the parasitic beam-beam encounters are computed. The necessity of a self consistent treatment is shown and emphasis is placed on a comparison between the expectations and the observations

Action research in physical education: focusing beyond myself through cooperative learning

This paper reports on the pedagogical changes that I experienced as a teacher engaged in an action research project in which I designed and implemented an indirect, developmentally appropriate and child‐centred approach to my teaching. There have been repeated calls to expunge – or at least rationalise – the use of traditional, teacher‐led practice in physical education. Yet despite the advocacy of many leading academics there is little evidence that such a change of approach is occurring. In my role as teacher‐as‐researcher I sought to implement a new pedagogical approach, in the form of cooperative learning, and bring about a positive change in the form of enhanced pupil learning. Data collection included a reflective journal, post‐teaching reflective analysis, pupil questionnaires, student interviews, document analysis, and non‐participant observations. The research team analysed the data using inductive analysis and constant comparison. Six themes emerged from the data: teaching and learning, reflections on cooperation, performance, time, teacher change, and social interaction. The paper argues that cooperative learning allowed me to place social and academic learning goals on an even footing, which in turn placed a focus on pupils’ understanding and improvement of skills in athletics alongside their interpersonal development