Development of a fourfold dielectric-filled reentrant cavity as a beam position monitor (BPM) in a proton therapy facility

At the Paul Scherrer Institute (PSI), the superconducting cyclotron “COMET” delivers a 250 MeV proton beam for radiation therapy in pulses of 1ns at the cyclotron-RF frequency of 72.85 MHz. Accurate measurement of the beam position at proton beam currents of 0.1-10 nA in the beam transport line downstream of the degrader is of crucial importance for the treatment safety and quality, beam alignment and feedback systems. This is essential for efficient operation and beam delivery. These measurements are usually performed with intercepting monitors such as ionization chambers (ICs). In this paper, we present a novel non-intercepting position sensitive cavity resonator. The resonant monitor, tuned to the second harmonic of the cyclotron's RF, is based on the detection of the transverse magnetic dipole mode of the EM field generated by the beam. This mode is only excited for off-center beam positions and is measured with the help of four floating cavities within a common grounded cylinder. This paper discusses the BPM fundamental characteristics, design optimization and the underlying parametric investigations involving the contribution of the different modes and crosstalk. We estimate the expected signals from the prototype BPM for position offsets from simulations and compare them with test-bench measurements and beam measurements with the prototype and the improvised BPM design. We conclude by summarizing the achieved position sensitivity, precision, and measurement bandwidth

Pedestrian Road Traffic Injuries in Urban Peruvian Children and Adolescents: Case Control Analyses of Personal and Environmental Risk Factors

BACKGROUND: Child pedestrian road traffic injuries (RTIs) are an important cause of death and disability in poorer nations, however RTI prevention strategies in those countries largely draw upon studies conducted in wealthier countries. This research investigated personal and environmental risk factors for child pedestrian RTIs relevant to an urban, developing world setting. METHODS: This is a case control study of personal and environmental risk factors for child pedestrian RTIs in San Juan de Miraflores, Lima, Perú. The analysis of personal risk factors included 100 cases of serious pedestrian RTIs and 200 age and gender matched controls. Demographic, socioeconomic, and injury data were collected. The environmental risk factor study evaluated vehicle and pedestrian movement and infrastructure at the sites in which 40 of the above case RTIs occurred and 80 control sites. FINDINGS: After adjustment, factors associated with increased risk of child pedestrian RTIs included high vehicle volume (OR 7.88, 95%CI 1.97-31.52), absent lane demarcations (OR 6.59, 95% CI 1.65-26.26), high vehicle speed (OR 5.35, 95%CI 1.55-18.54), high street vendor density (OR 1.25, 95%CI 1.01-1.55), and more children living in the home (OR 1.25, 95%CI 1.00-1.56). Protective factors included more hours/day spent in school (OR 0.52, 95%CI 0.33-0.82) and years of family residence in the same home (OR 0.97, 95%CI 0.95-0.99). CONCLUSION: Reducing traffic volumes and speeds, limiting the number of street vendors on a given stretch of road, and improving lane demarcation should be evaluated as components of child pedestrian RTI interventions in poorer countries

Protecting Vulnerable Road Users from Injury

Aymery Constant and Emmanuel Lagarde discuss policies to protect pedestrians, and pedal and motor cyclists, from injury

Global Sawtooth Instability Measured by Magnetic Coils in the Jet Tokamak

The paper describes measurements of the sawtooth instability in JET, in which the instability wave function is shown to extend to the edge where it is measured using magnetic coils. The numerous magnetic probes in JET allow the time evolution of the (n = 0, 1, 2, 3) toroidal Fourier components to be analysed. The n = 1 magnetic component is similar to the m = 1 soft X-ray centroid motion. This fact indicates the potential of edge signals in retrieving the poloidal mode spectrum of the q = m/n = 1 surface. The spectrum evolution of the instability is compared for normal sawteeth (NST) and quasi-stabilized 'monster' sawteeth (MST). The spectrum is slowly decreasing with n for NST and all the components belong to one ballooning-like deformation, whereas MST show a large n = 1 kink-like motion with small and independent accompanying higher n modes. Important equilibrium changes occur already during the growth of the instability and the growth rate is much faster than exponential. Both these facts imply a non-linear nature of the instability growth. Parametric dependences of growth rates, amplitudes, toroidal spectrum shape, etc., are studied to characterize the NST and MST instabilities