The heating neutral beam injectors (HNBs) of ITER are designed to deliver 16.7 MW of 1 MeV D 0 or 0.87 MeV H 0 to the ITER plasma for up to 3600 s. They will be the most powerful neutral beam(NB) injectors ever, delivering higher energy NBs to the plasma in a tokamak for longer than any previous systems have done. The design of the HNBs is based on the acceleration and neutralisation of negative ions as the efficiency of conversion of accelerated positive ions is so low at the required energy that a realistic design is not possible, whereas the neutralisation of H − and D − remains acceptable (≈56%).The design of a long pulse negative ion based injector is inherently more complicated than that of short pulse positive ion based injectors because:• negative ions are harder to create so that they can be extracted and accelerated from the ion source;• electrons can be co-extracted from the ion source along with the negative ions, and their acceleration must be minimised to maintain an acceptable overall accelerator efficiency;• negative ions are easily lost by collisions with the background gas in the accelerator;• electrons created in the extractor and accelerator can impinge on the extraction and acceleration grids, leading to high power loads on the grids;• positive ions are created in the accelerator by ionisation of the background gas by the accelerated negative ions and the positive ions are back-accelerated into the ion source creating a massive power load to the ion source;• electrons that are co-accelerated with the negative ions can exit the accelerator and deposit power on various downstream beamline components.The design of the ITER HNBs is further complicated because ITER is a nuclear installation which will generate very large fluxes of neutrons and gamma rays. Consequently all the injector components have to survive in that harsh environment. Additionally the beamline components and the NB cell, where the beams are housed, will be activated and all maintenance will have to be performed remotely.This paper describes the design of the HNB injectors, but not the associated power supplies, cooling system, cryogenic system etc, or the high voltage bushing which separates the vacuum of the beamline from the high pressure SF 6 of the high voltage (1 MV) transmission line, through which the power, gas and cooling water are supplied to the beam source. Also the magnetic field reduction system is not described.

This short-term longitudinal study examined activities at recess and peer relations. We were interested in changes over the school year, and the sex and ethnic mix of groups. Data came from systematic observations of 129 pupils (61 boys and 68 girls) aged 7-8 years. Results showed that peer interaction dominated recess. Ball games increased over the year, and chasing games decreased. Aggression was most common during vigorous play and conversation, but not ball games. Cleavage in boys' and girls' play and activity was common but not inevitable. Mixed-sex play was not supported by particular game types. Boys' game networks were larger than those of girls but there were no sex differences in active networks. There was little ethnic group segregation on playgrounds, and games became more integrated with time. The results indicate that playground activities can have a positive role in social relations between different ethnic groups.

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Teaching assistants (TAs) are part of a growing international trend toward paraprofessionals working in public services. There has been controversy over TAs' deployment and appropriate role when supporting the learning of pupils with special educational needs (SEN) in mainstream schools. Such debates have been transformed by findings from a large study of school support staff in the UK (the DISS project). The findings from this study show that TA support has a negative impact on pupils' academic progress, especially pupils with SEN. The findings render the current system of support for SEN highly questionable: TAs have inadvertently become the primary educators of pupils with SEN. This paper sets out the likely explanations for the negative effects in terms of three 'frames' -deployment, practice and preparedness -and then uses these frames to identify specific implications for pupils with SEN. We offer suggestions on how to make the most productive use of TA support. IntroductionTeaching assistants 1 (TAs) are part of a growing international trend toward paraprofessionals working in different professional areas, often in public services (e.g., health and social care). There has been controversy over TAs' deployment and their appropriate role in supporting learning. But recent findings from the largest ever study of TAs (the Deployment and Impact of Support Staff (DISS) project), presented in this paper, have called into question current ways in which TAs are deployed. Other findings from the DISS project presented in this paper show that the implications of TA support are greatest for pupils with special educational needs (SEN) included in mainstream schools.In this paper, we will use three 'frames' -deployment, practice and preparedness -to organise the presentation of findings from the DISS project and to explore the implications they have on the use of TAs to support pupils with SEN. We will see how the current system of support for pupils with SEN (in the UK at least) is highly questionable. We argue that the effects of this system, in terms of the impact on pupil outcomes, is best understood in the context of wider, interlinking factors, concerning the decisions made about, rather than by, TAs. *Corresponding author. Email: r.webster@ioe.ac.uk. 320 R. Webster et al.We first summarise the context in which the DISS project was carried out, and then describe the distinctive research design. We provide the impetus for the main body of the paper by presenting key findings on the impact of TA support on pupils' learning. We then move on to the findings on TA deployment, practice and preparedness, which help to explain the impact results and expose the current system of support for pupils with SEN as inappropriate. We will consider the implications for pupils with SEN and how we might reconceptualise the work of TAs in relation to the support they provide for these pupils. Background to the DISS projectThe rise in support staff In 2009, more than half of the school workforce in England and Wales were paraprofessio...