Measurement of tokamak error fields using plasma response and its applicability to ITER

The nonlinear response of a low-beta tokamak plasma to non-axisymmetric fields offers an alternative to direct measurement of the non-axisymmetric part of the vacuum magnetic fields, often termed ‘error fields’. Possible approaches are discussed for determination of error fields and the required current in non-axisymmetric correction coils, with an emphasis on two relatively new methods: measurement of the torque balance on a saturated magnetic island, and measurement of the braking of plasma rotation in the absence of an island. The former is well suited to ohmically heated discharges, while the latter is more appropriate for discharges with a modest amount of neutral beam heating to drive rotation. Both can potentially provide continuous measurements during a discharge, subject to the limitation of a minimum averaging time. The applicability of these methods to ITER is discussed, and an estimate is made of their uncertainties in light of the specifications of ITER’s diagnostic systems. The use of plasma response-based techniques in normal ITER operational scenarios may allow identification of the error field contributions by individual central solenoid coils, but identification of the individual contributions by the outer poloidal field coils or other sources is less likely to be feasible

Randomised double blind placebo controlled trial of prednisolone in children admitted to hospital with respiratory syncytial virus bronchiolitis

BACKGROUND: Experimental and clinical evidence suggests that respiratory syncytial virus (RSV) bronchiolitis is an immune mediated disease. Corticosteroids might therefore be effective in the treatment of RSV bronchiolitis. METHODS: A randomised double blind trial was conducted in children up to two years of age admitted to hospital with RSV bronchiolitis to compare prednisolone (1 mg/ kg/day orally for seven days) with placebo. Variables used for the efficacy analysis were a daily symptom score and the length of time in hospital in the non- ventilated patients, and the duration of mechanical ventilation and the length of time in hospital in the ventilated patients. RESULTS: Fifty four patients were included in the trial, 40 of whom were non- ventilated (20 in each group) and 14 were ventilated (seven in each group). During the first three days of treatment the symptom score decreased significantly faster in the prednisolone group than in the placebo group (mean (SE) decrease -1.2 (0.2) points/day versus -0.6 (0.2) points/day; mean (95% confidence interval (CI)) for difference = - 0.6 (-0.1 to -1.2); p = 0.02). The mean duration of hospital stay of all 40 non-ventilated patients was not significantly different between the two groups. In the ventilated patients the duration of mechanical ventilation was not significantly different, but the length of time in hospital was six days shorter in the prednisolone group than in the placebo group (mean (SE) 11.0 (0.7) versus 17.0 (2.0) days; mean (95% CI) difference = 7.0 (1.8 to 10.2) days; p < 0.01). CONCLUSIONS: These results suggest that prednisolone may be effective in accelerating the clinical recovery of children admitted to hospital with RSV bronchiolitis.