Jan Källne

The TOFOR neutron spectrometer and its first use at JET

A time-of-flight neutron spectrometer (TOFOR) has been developed to measure the 2.45u2002MeVu2002d+d→3He+n neutron emission from D plasmas. The TOFOR design features the capability to operate at high rates in the 100u2002kHz range, data collection with fast time digitizing and storing, and monitoring of the signals from the scintillation detectors used. This article describes the principles of the instrument and its installation at JET and presents preliminary data to illustrate the TOFOR performance as a neutron emission spectroscopy diagnostic.

Magnetic proton recoil spectrometer for fusion plasma neutrons

Abstract The design of a magnetic proton recoil (MPR) spectrometer for measurement of thermonuclear neutrons is presented. It is shown to have sufficient energy resolution and efficiency for use in the diagnosis of tokamak fusion plasmas. The overall performance is substantially higher than offered by conventional techniques, particularly, with regard to count rate capability, signal selectivity, background discrimination and calibrations. Some of the unique measurement capabilities of the MPR spectrometer for burning plasma studies in deuterium-tritium are illustrated.

Calculated neutron emission spectrum with knock-on effects for RF heated (3He)D plasmas

The neutron emission from (3He)D plasmas with RF heating is calculated using a model that includes supra-thermal (knock-on) components of the deuteron population. The RF generation of fast 3He ions is described and the knock-on components were determined with the help of newly derived 3He + d scattering cross sections. Results are presented on the neutron emission spectrum and its contributions from different deuteron velocity components. It is shown that knock-on leaves an observable feature in the spectrum with a clear dependence on absorbed RF power. The importance of the nuclear interaction in the elastic cross section is demonstrated. The results represent a step forward in the use of neutron emission spectroscopy to diagnose fusion plasmas with minority supra-thermal components in their fuel ion composition.

Cross section of the d + 3He → α + p reaction of relevance for fusion plasma applications

The cross section of the d + 3He → α + p fusion reaction has been determined with regard to its systematic variation with energy (ECM) based on the available experimental data. Information is provided on the angular distribution dσ/dΩ(θp, E) at energies up to ECM = 8.0 MeV and the total cross section σ(ECM) for the range ECM = 3.0–8.0 MeV. The relevance of the presented results for fusion plasmas heated with RF heating of 3He minority in D and DT plasmas is discussed.

Neutron spectroscopy measurements of tritium beam transport at JET

A detailed description of the 14 MeV neutron emission in plasmas heated by neutral beam injection has been carried out by coupling Monte Carlo calculations of the neutron emission spectrum with TRANSP modelling of the beam ion energy distributions. The model is used to study tritium beam injection experiments of the JET trace tritium campaign for internal transport barrier (ITB) and H-mode discharges. For ITB discharges, the measured neutron emission spectrum is well described by modelling using as input the beam ion distribution calculated with TRANSP. For H mode discharges the neutron spectrum can be reproduced only if high energy tritons are lost from the plasma, suggesting the possible role of low frequency tearing modes on the beam ions. The presented results are of relevance for tritium beam transport studies in trace tritium experiments and, more generally, for deuterium and tritium transport studies in high power experiments using neutron emission spectroscopy.

The TOFOR spectrometer for 2.5 MeV neutron measurements at JET

Neutron emission spectroscopy has been demonstrated to be a powerful plasma diagnostic at tokamaks. This was shown with the magnetic proton recoil spectrometer developed for measurement of the 14 MeV neutron emission from deuterium–tritium (DT) plasmas at the Joint European Torus (JET). For diagnosis of D plasmas, a 2.5 MeV spectrometer is needed with a factor of 100 higher efficiency to maintain the count rate because of the lower neutron emission rate. The time-of-flight (TOF) technique has the right attributes for these measurements. However, previous instruments have not achieved the full potential of the technique, especially, with respect to count rate capability. A TOF spectrometer for optimized rate (TOFOR) has been conceptually defined and is now under design and development for construction and use at JET. The TOFOR design goal is a count rate capability of about 300 kHz which should be attainable in high power D discharges at JET. The TOFOR project is now in a research and development stage whe...

Reaction analysis of neutron emission from D and DT plasmas with/without 3 He

The effects of nuclear elastic scattering (knock-on) from energetic light ions on the neutron emission spectrum in fusion plasmas are studied. The knock-on spectral features in D and DT plasmas without and with radio frequency heating on a 3He minority component are determined through Monte Carlo simulations. The neutron production magnitudes are determined relative to those due to fuel ions in the thermal bulk state (down to the level of 10?5), and the interference of higher order terms in the outlying spectral regions where these dominate is evaluated. The study completes the mapping of nuclear reaction and elastic scattering effects on the neutron emission spectrum including first-, second- and third-order processes. Included are the cross-couplings between dd and dt fusion reactions as manifested in the full neutron spectrum (En?=?0?20?MeV) for DT plasmas of varying isotopic composition. This study determines the relationship between components of the neutron emission spectra and those of the underlying ion velocity distributions, which provides a general basis for judging the plasma diagnostic information that can potentially be extracted from measurement and analysis of such neutron data.

Diagnosing NB plasmas on the EAST tokamak with new time-of-flight neutron spectrometer

The new neutron spectrometer time-of-flight enhanced diagnostics (TOFED) for the EAST tokamak is presented and its characteristics are described in terms of simulation results, as well as the interface in the torus hall along with new neutral beam (NB) injectors. The use of TOFED for studies of the slowing down of NB-injected deuterons is illustrated. The implications of measuring the neutron emission on a long pulse machine are discussed together with the experimental challenges and diagnostic possibilities approaching those to be encountered in continuous operation.

Second generation fusion neutron time-of-flight spectrometer at optimized rate for fully digital data acquisition.

The progress on high-rate event recording of data is taken as starting point to revisit the design of fusion neutron spectrometers based on the TOF (time-of-flight) technique. The study performed was aimed at how such instruments for optimized rate (TOFOR) can be further developed to enhance the plasma diagnostic capabilities based on measurement of the 2.5 MeV dd neutron emission from D plasmas, especially the weak spectral components that depend on discrimination of extraneous events. This paper describes a design (TOFOR II) adapted for use with digital wave form recording of all detector pulses providing information on both amplitude (pulse height) and timing. The results of simulations are presented and the performance enhancement is assessed in comparison to the present.

Neutron emission study of DT plasmas heated with tritium neutral beams

The neutron emission energy spectrum from deuterium–tritium fusion reactions has been measured in experiments carried out at the Joint European Torus for plasmas heated with high power neutral beam (NB) injection of tritium beams at Eb≈150u200akeV using a magnetic proton recoil neutron spectrometer. High quality data were obtained in which up to three spectral components due to different ion reactions could be distinguished with the help of dedicated model calculations of the fusion neutron emission based on Monte Carlo simulations. The analysis model involved neutrons from reactions of NB ions on passing and trapped orbits interacting with thermal bulk ions. Moreover, a narrow Gaussian component, due to neutrons from thermal d+t→α+n reactions, could be resolved in some cases. Results are presented and the plasma information obtained is discussed as an illustration of the capabilities of neutron emission spectroscopy diagnostics.