First neutron spectroscopy measurements with a pixelated diamond detector at JET (original) (raw)

Capabilities of a Diamond Detector matrix for neutron spectroscopy measurements at JET

Single-crystal Diamond Detectors (SDDs) feature high radiation hardness, fast response and compact size. This makes SDDs ideal candidates for fast neutron detectors in environment where high neutron flux is an issue such as the next generation burning plasmas experiments. Neutron detection in SDD is based on the collection of electron-hole pairs produced by charged particles generated by neutron interaction with 12C nuclei. For neutron energies above about 7 MeV neutron spectroscopy is possible by measuring the deposited energy into the detector via the reaction 12C(n,α) 9Be. This is indeed the cases of SDD measurements of 14 MeV neutrons of DT plasmas. A single pixel SDD (4.5x4.5x0.5 mm^3) prototype was installed at JET in 2013 and the achieved results allowed to assess also the neutron spectroscopic capability of deuterium plasmas. A 12-pixels SDD matrix has been recently realized and will be installed in 2015 at JET for DT plasmas as part of the Vertical Neutron Spectrometer project. In this paper calibration of the SDD matrix with alpha particles in the laboratory and 14 MeV neutrons performed at the ENEA Frascati Neutron Generator will be presented. These calibrations have been performed with a fast charge preamplifier combined to a fast digital data acquisition, which allows for neutron spectroscopy measurements with simultaneously high energy resolution and high count rate capability. Both requirements are essential for neutron spectroscopy of high power fusion plasmas. The calibrations results achieved extrapolate favourably in view of future neutron spectroscopy measurements at JET using diamond detectors.

Neutron detection at jet using artificial diamond detectors

Fusion Engineering and Design, 2007

Artificial diamond neutron detectors recently proved to be interesting devices to measure the neutron production on large experimental fusion machines. Diamond detectors are very promising detectors to be used in fusion environment due to their radiation hardness, low sensitivity to gamma rays, fast response and high energy resolution. High quality "electronic grade" diamond films are produced through microwave Chemical Vapour Deposition (CVD) technique. Two CVD diamond detectors have been installed and operated at Joint European Torus (JET), Culham Science Centre, UK. One of these detectors was a polycrystalline CVD diamond film, about 12mm 2 area and 30µm thickness while the second was a monocrystalline film of about 5mm 2 area and 20µm thick. Both diamonds were covered with 2µm of Lithium Fluoride (LiF) 95% enriched in 6 Li. The LiF layer works as a neutron-to-charged particle converter so these detectors can measure thermalized neutrons. Their output signals were compared to JET total neutron yield monitors (KN1 diagnostic) realized with a set of Uranium fission chambers. Despite their small active volumes theour diamond detectors were able to measure total neutron yields with good reliability and stability during the recent JET experimental campaign of 2006.

Neutron spectroscopy by means of artificial diamond detectors using a remote read out scheme

Nuclear Science, …, 2010

Artificial crystal diamond neutron detectors are under test at JET tokamak since 2003 and they have demonstrated to be reliable and stable as well as to withstand the harsh working condition available in a large tokamak. Up to now they were used to measure the total and time dependent neutron emission while neutron spectroscopy was never attempted. On the other hand neutron spectrometry con yields important information on the burning plasma and it is requested for future experiments that will use DT plasmas so producing 14 MeV neutrons. Neutron spectrometry can only be attempted by using single crystal diamond (SCD) which, as it has been demonstrated, can show an energy resolution (FWHM) as low as 0.5%.

Single-crystal diamond: a potential gem in neutron instrumentation

Journal of Applied Crystallography, 2009

Calculations have been performed showing that single-crystal diamond has the highest performance of all materials proposed in the past and presently used as neutron monochromators. If large mosaic crystals were available, the presently available flux on most neutron scattering instruments could be increased by factors of between 1.5 and 4. Thanks to recent progress in chemical vapour deposition technology the growth of diamond single-crystal layers with a suitable mosaic spread has become feasible. Provided an adequate research and development effort is made, it is expected that the high potential of this extraordinary material can be exploited in the not too distant future.

Development of single crystal diamond neutron detectors and test at JET tokamak

Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2008

During the 2005-2007 JET experimental campaigns a Single Crystal Diamond detector (SCD) covered with a 2µm thick LiF film 95% enriched in 6 Li, was installed at JET and operated continuously during the whole experimental campaign with the goal to measure both the total and the time dependent neutron emission from plasmas. After reviewing the history of diamond as neutron detector for tokamak application, this paper reports on the experimental measurements performed during that time window. The obtained results are compared with those obtained with detectors routinely working at JET (fission chambers and silicon diodes). In particular it was demonstrated that using a SCD detector covered with a 6 LiF film it has been possible to discriminate between the total and the 14MeV neutrons coming from triton burn-up. This allowed, for the first time using a single detector, the contemporary measurement of the total and 14MeV neutron yields as well as their time dependency with very good reliability and stability.

Single crystal CVD diamonds as neutron detectors at JET

Fusion Engineering and Design, 2009

This paper reports on the three new Single Crystal Diamond (SCD) detectors installed at JET for the 2008 campaigns. The yields of both total and 14-MeV neutrons produced during DD plasma pulses as well as the time dependent neutron emission have been measured. The first detector, installed in the Vertical Port (Oct-1) of JET, is 200µm thick and is embedded in paraffin. It has a detection efficiency of about 2.9*E-05 counts/n * cm 2 for the 14MeV neutrons. The second detector, located in Oct-1 Limb 1 / 2 , is 104µm thick and is covered by a thermally evaporated 3 ºm thick 6 LiF film in order to detect the total and the 14MeV neutrons. In addition, it is surrounded by a 2.5-cm-thick polyethylene shield to enhance its thermal neutron response. The third detector is mounted in the main horizontal port (Oct-6) and it is operated in an innovative way, that is with a single low capacitance super screened cable and the whole electronic chain is outside the JET Torus Hall. Furthermore it uses fast electronics, suitable to the fast diamond response pulse (<1ns). It is 75µm thick, covered by a 3µm thick 6 LiF film and surrounded by a 2.5cm-thick layer of polyethylene. All the detectors have been previously tested and qualified at the ENEA-Frascati Neutron Generator with 2.5MeV and 14.7MeV neutron beams. After the description of their main features, the results of the measurements so far performed are reported showing a very good matching with other standard detectors, such as fission chambers and Si diodes, routinely used at JET.

Single-crystal diamonds for neutrons

The European Physical Journal Plus, 2014

Single crystal Chemical Vapour Deposition (CVD) diamond detectors feature a superb Signal-to-Noise ratio, timing response and good energy resolution. These properties make CVD diamonds interesting for neutron detection. In the present contribution we discuss different measurements of neutron energy with CVD diamonds applied to relatively low and high energy neutrons. For the low energy range a compact neutron Time-of-Flight spectrometer for high flux environments has been developed. Such a detector would allow to measure neutron spectra in the range from 250 keV up to few MeV with 20-40% resolution in the neutron fluxes 10 5 < φn < 10 9 n/cm 2 /s. The first prototype of this spectrometer was tested at ENEA FNG 3 MeV quasi-monochromatic neutron beam and demonstrated feasibility of the concept. However, the test evidenced inadequacy of existing amplifiers providing insufficient timing resolution to extract a sensible neutron spectrum in MeV range. This particular diamond detector application, among with many others, calls for a development of a fast amplifier featuring an order of magnitude higher Signal-to-Noise ratio. On the other hand, to measure the neutron flux in a wide neutron energy range (1-100 MeV) at counting rate ∼2 MHz a single diamond crystal coupled to a fast (tens of ns) shaping preamplifier was used. The test performed at the NT OF neutron beam line at CERN revealed the capability of using such a detector for spectroscopic measurement: the energy resolution achieved is about 4% at the n-α peak at 9.3MeV, i. e. for 15 MeV neutrons. CVD diamond detectors have been proposed, successfully tested and applied as neutron flux monitors in nuclear reactor and around tokamaks. Furthermore, the possibility to extend the application of diamond films to neutron spectroscopy for a wide range of applications can be envisaged and already tested in fusion tokamak and around accelerators.

Diamond detectors for fast neutron measurements at pulsed spallation sources

Journal of Instrumentation, 2012

The performance of a single crystal diamond (4.7x4.7x0.5mm 3 active volume) detector was tested in the ISIS pulsed neutron beam using biparametric (time of flight and pulse height) data acquisition. Three characteristic regions in the biparametric spectra are observed: i) low pulse height events with very short time of flight induced by γ-rays; ii) low pulse height events at longer flight times (i.e. neutron energies E n >3.5-6 MeV), possibly due to neutron elastic scattering off 12 C; iii) events with large pulse height and flight times corresponding to E n >6 MeV mainly due to inelastic reactions such as 12 C(n,α) 9 Be and 12 C(n,n')3α. The potential use of this detector is discussed in relation to the ChipIr neutron beam line for fast neutron irradiation of electronic components at the ISIS spallation source.

Diamond mosaic crystals for neutron instrumentation: First experimental results

Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2011

Diamond single crystals were recently proposed as monochromators of unprecedented performance [1] ). In the present paper we describe how diamond crystals with a suitable mosaic spread can be produced using a specific plasma CVD technique. Up to 2 mm thick samples with an average mosaic spread of 0.21 have been produced. We report on X-and gamma-ray characterisation checking the uniformity of the mosaic structure and present the results of a first study regarding the neutron reflection properties of this outstanding material. These promising results show that the diamond diffraction properties are not too far from the theoretical expectations. For example, 34% peak reflectivity has been obtained for a 1 mm thick crystal at 1Å wavelength.