Suprathermal fuel ions from alpha-particle knock-on collisions in fusion DT plasmas are predicted to cause a weak feature in the neutron spectrum of d+t-->alpha+n. The knock-on feature has been searched for in the neutron emission of high ( >1 MW) fusion-power plasmas produced at JET and was found using a magnetic proton recoil type neutron spectrometer of high performance. Measurement and predictions agree both in absolute amplitude and in plasma-parameter dependence, supporting the interpretation and model. Moreover, the results provide input to projecting alpha-particle diagnostics for future self-heated fusion plasmas.
Measurement and analysis of the energy distribution of the neutron
emission from the nuclear burnup of tritons produced at 1 MeV in d + d → t + p reactions are reported. The results refer to
deuterium plasmas with a strongly pulsed neutron production attained with
neutral beam heating in the JET tokamak representing both quasi-steady and
transient plasma conditions. The measured triton produced neutron spectrum
is described with reference to the triton slowing down behaviour in the plasma
and pertinent parameter dependences as predicted with a time dependent model.
The first study of the triton burnup neutron spectrum
for both transient and quasi-steady-state plasma conditions is presented and
a description based on classical confinement and slowing down of fast tritons
is largely supported.
Dose calculation plays an important role in the accuracy of radiotherapy treatment planning and beam delivery. The Monte Carlo (MC) method is capable of achieving the highest accuracy in radiotherapy dose calculation and has been implemented in many commercial systems for radiotherapy treatment planning. The objective of this task group was to assist clinical physicists with the potentially complex task of acceptance testing and commissioning MC-based treatment planning systems (TPS) for photon and electron beam dose calculations. This report provides an overview on the general approach of clinical implementation and testing of MC-based TPS with a specific focus on models of clinical photon and electron beams. Different types of beam models are described including those that utilize MC simulation of the treatment head and those that rely on analytical methods and measurements. The trade-off between accuracy and efficiency in the various source-modeling approaches is discussed together with guidelines for acceptance testing of MC-based TPS from the clinical standpoint. Specific recommendations are given on methods and practical procedures to commission clinical beam models for MC-based TPS.
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