| 1. |
- Batistoni, Paola, et al.
(författare)
-
Calibration of neutron detectors on the Joint European Torus
- 2017
-
Ingår i: Review of Scientific Instruments. - : AMER INST PHYSICS. - 0034-6748 .- 1089-7623. ; 88:10
-
Tidskriftsartikel (refereegranskat)abstract
- The present paper describes the findings of the calibration of the neutron yield monitors on the Joint European Torus (JET) performed in 2013 using a Cf-252 source deployed inside the torus by the remote handling system, with particular regard to the calibration of fission chambers which provide the time resolved neutron yield from JET plasmas. The experimental data obtained in toroidal, radial, and vertical scans are presented. These data are first analysed following an analytical approach adopted in the previous neutron calibrations at JET. In this way, a calibration function for the volumetric plasma source is derived which allows us to understand the importance of the different plasma regions and of different spatial profiles of neutron emissivity on fission chamber response. Neutronics analyses have also been performed to calculate the correction factors needed to derive the plasma calibration factors taking into account the different energy spectrum and angular emission distribution of the calibrating (point) Cf-252 source, the discrete positions compared to the plasma volumetric source, and the calibration circumstances. All correction factors are presented and discussed. We discuss also the lessons learnt which are the basis for the on-going 14 MeV neutron calibration at JET and for ITER.
|
|
| 2. |
- Craciunescu, Teddy, et al.
(författare)
-
Maximum likelihood bolometric tomography for the determination of the uncertainties in the radiation emission on JET TOKAMAK
- 2018
-
Ingår i: Review of Scientific Instruments. - : AMER INST PHYSICS. - 0034-6748 .- 1089-7623. ; 89:5
-
Tidskriftsartikel (refereegranskat)abstract
- The total emission of radiation is a crucial quantity to calculate the power balances and to understand the physics of any Tokamak. Bolometric systems are the main tool to measure this important physical quantity through quite sophisticated tomographic inversion methods. On the Joint European Torus, the coverage of the bolometric diagnostic, due to the availability of basically only two projection angles, is quite limited, rendering the inversion a very ill-posed mathematical problem. A new approach, based on the maximum likelihood, has therefore been developed and implemented to alleviate one of the major weaknesses of traditional tomographic techniques: the difficulty to determine routinely the confidence intervals in the results. The method has been validated by numerical simulations with phantoms to assess the quality of the results and to optimise the configuration of the parameters for the main types of emissivity encountered experimentally. The typical levels of statistical errors, which may significantly influence the quality of the reconstructions, have been identified. The systematic tests with phantoms indicate that the errors in the reconstructions are quite limited and their effect on the total radiated power remains well below 10%. A comparison with other approaches to the inversion and to the regularization has also been performed.
|
|
| 3. |
- Dal Molin, A., et al.
(författare)
-
Development of a new compact gamma-ray spectrometer optimised for runaway electron measurements
- 2018
-
Ingår i: Review of Scientific Instruments. - : AMER INST PHYSICS. - 0034-6748 .- 1089-7623. ; 89:10
-
Tidskriftsartikel (refereegranskat)abstract
- A new compact gamma-ray spectrometer was developed in order to optimise the measurement of bremsstrahlung radiation emitted from runaway electrons in the MeV range. The detector is based on a cerium doped lutetium-yttrium oxyorthosilicate (LYSO:Ce) scintillator coupled to a silicon photomultiplier and is insensitive to magnetic fields. Adedicated electronic board was developed to optimise the signal readout as well as for online control of the device. The detector combines a dynamic range up to 10 MeV with moderate energy non-linearity, counting rate capabilities in excess of 1 MHz, and an energy resolution that extrapolates to a few % in the MeV range, thus meeting the requirements for its application to runaway electron studies by bremsstrahlung measurements in the gamma-ray energy range.
|
|
| 4. |
- Figueiredo, J., et al.
(författare)
-
JET diagnostic enhancements testing and commissioning in preparation for DT scientific campaigns
- 2018
-
Ingår i: Review of Scientific Instruments. - : AMER INST PHYSICS. - 0034-6748 .- 1089-7623. ; 89:10
-
Tidskriftsartikel (refereegranskat)abstract
- In order to optimize the scientific exploitation of JET (Joint European Torus) during the upcoming deuterium-tritium experiments, a set of diagnostic systems is being enhanced. These upgrades focus mainly on the experimental and operational conditions expected during tritium campaigns. It should be stressed that measurements relevant for burning plasmas are specifically targeted. Previously non-available capabilities, such as a current measurement system fully covering all poloidal field circuits, are described in detail. Instrument descriptions, performance prediction, testing, and initial commissioning results of these systems are presented.
|
|
| 5. |
- Giacomelli, L., et al.
(författare)
-
Neutron emission spectroscopy of D plasmas at JET with a compact liquid scintillating neutron spectrometer
- 2018
-
Ingår i: Review of Scientific Instruments. - : AMER INST PHYSICS. - 0034-6748 .- 1089-7623. ; 89:10
-
Tidskriftsartikel (refereegranskat)abstract
- Neutron emission spectroscopy is a diagnostic technique that allows for energy measurements of neutrons born in nuclear reactions. The JET tokamak fusion experiment (Culham, UK) has a special role in this respect as advanced spectrometers for 2.5 MeV and 14 MeV neutrons have been developed here for the first time for measurements of the neutron emission spectrum from D and DT plasmas with unprecedented accuracy. Twin liquid scintillating neutron spectrometers were built and calibrated at the Physikalisch-Technische Bundesanstalt (PTB) (Braunschweig, Germany) and installed on JET in the recent years with tangential-equatorial (KM12) and vertical-radial (KM13) view lines, with the latter only recently operational. This article reports on the performance of KM12 and on the development of the data analysis methods in order to extract physics information upon D ions kinematics in JET auxiliary-heated D plasmas from 2.5 MeV neutron measurements. The comparison of these results with the correspondents from other JET neutron spectrometers is also presented: their agreement allows for JET unique capability of multi-lines of sight neutron spectroscopy and for benchmarking other 14 MeV neutron spectrometers installed on the same lines of sight in preparation for the DT experimental campaign at JET.
|
|
| 6. |
- Grenfell, G., et al.
(författare)
-
High-heat flux ball-pen probe head in ASDEX-Upgrade
- 2022
-
Ingår i: Review of Scientific Instruments. - : AIP Publishing. - 0034-6748 .- 1089-7623. ; 93:2
-
Tidskriftsartikel (refereegranskat)abstract
- A new high heat flux ball-pen probe head installed on the midplane manipulator is currently being used in ASDEX-Upgrade (AUG). The probe was designed to withstand high heat fluxes making possible the investigation of the plasma edge under harsh conditions, such as low power H-mode. Composed of seven pins (four Langmuir probes, mounted in two Mach probe pairs, and three ball-pen probes), the new probe head allows us to measure several plasma parameters simultaneously and with high temporal resolution. A novel method to correct the sheath potential dynamically accounting for the total secondary electron emission is introduced together with applications to obtain the electron temperature and plasma potential profiles. The total secondary electron emission yield is obtained from particle in cell simulations in AUG condition and probe realistic impact angle with respect to the magnetic field. Finally, the probe capability to investigate turbulence around the separatrix of AUG is discussed.& nbsp;
|
|
| 7. |
- Hawkes, N. C., et al.
(författare)
-
Instrumentation for the upgrade to the JET core charge-exchange spectrometers
- 2018
-
Ingår i: Review of Scientific Instruments. - : AMER INST PHYSICS. - 0034-6748 .- 1089-7623. ; 89:10
-
Tidskriftsartikel (refereegranskat)abstract
- Charge-exchange spectroscopy on JET has become particularly challenging with the introduction of the ITER-like wall. The line intensities are weaker and contaminated by many nuisance lines. We have therefore upgraded the instrumentation to improve throughput and allow the simultaneous measurement of impurity and fuel-ion charge exchange by splitting the light between two pairs of imaging spectrometers using dichroic beam splitters. Imaging instruments allow us to stack 11 x 1 mm diameter fibres on the entrance slits without cross talk. CCD cameras were chosen to have 512 x 512 pixels to allow frame transfer times <0.2 ms which with minimum exposure times of 5 ms give tolerable smearing even without a chopper. The image plane is optically demagnified 2:1 to match the sensor size of these cameras. Because the image plane of the spectrometer is tilted, the CCD must also be tilted to maintain focus over the spectrum (Scheimpflug condition). To avoid transverse keystoning (causing the vertical height of the spectra to change across the sensor), the configuration is furthermore designed to be telecentric by a suitable choice of the lens separation. The lens configuration is built almost entirely from commercial off-the-shelf components, which allowed it to be assembled and aligned relatively rapidly to meet the deadline for in-vessel calibration in the JET shutdown.
|
|
| 8. |
- Jacobsen, A. S., et al.
(författare)
-
Velocity-space sensitivities of neutron emission spectrometers at the tokamaks JET and ASDEX Upgrade in deuterium plasmas
- 2017
-
Ingår i: Review of Scientific Instruments. - : AMER INST PHYSICS. - 0034-6748 .- 1089-7623. ; 88:7
-
Tidskriftsartikel (refereegranskat)abstract
- Future fusion reactors are foreseen to be heated by the energetic alpha particles produced in fusion reactions. For this to happen, it is important that the energetic ions are sufficiently confined. In present day fusion experiments, energetic ions are primarily produced using external heating systems such as neutral beam injection and ion cyclotron resonance heating. In order to diagnose these fast ions, several different fast-ion diagnostics have been developed and implemented in the various experiments around the world. The velocity-space sensitivities of fast-ion diagnostics are given by so-called weight functions. Here instrument-specific weight functions are derived for neutron emission spectrometry detectors at the tokamaks JET and ASDEX Upgrade for the 2.45 MeV neutrons produced in deuterium-deuterium reactions in deuterium plasmas. Using these, it is possible to directly determine which part of velocity space each detector observes.
|
|
| 9. |
- Krawczyk, N., et al.
(författare)
-
Application of the VUV and the soft x-ray systems on JET for the study of intrinsic impurity behavior in neon seeded hybrid discharges
- 2018
-
Ingår i: Review of Scientific Instruments. - : AMER INST PHYSICS. - 0034-6748 .- 1089-7623. ; 89:10
-
Tidskriftsartikel (refereegranskat)abstract
- This paper reports on impurity behavior in a set of hybrid discharges with Ne seeding-one of the techniques considered to reduce the power load on reactor walls. A series of experiments carried out with light gas injection on JET with the ITER-Like-Wall (ILW) suggests increased tungsten release and impurity accumulation [C. Challis et al., Europhysics Conference Abstracts 41F, 2.153 (2017)]. The presented method relies mainly on the measurements collected by vacuum-ultra-violet and soft X-ray (SXR) diagnostics including the "SOXMOS" spectrometer and the SXR camera system. Both diagnostics have some limitations. Consequently, only a combination of measurements from these systems is able to provide comprehensive information about high-Z [e.g., tungsten (W)] and mid-Z [nickel (Ni), iron (Fe), copper (Cu), and molybdenum (Mo)] impurities for their further quantitative diagnosis. Moreover, thanks to the large number of the SXR lines of sight, determination of a 2D radiation profile was also possible. Additionally, the experimental results were compared with numerical modeling based on integrated simulations with COREDIV. Detailed analysis confirmed that during seeding experiments, higher tungsten release is observed, which was also found in the past. Additionally, it was noticed that besides W, the contribution of molybdenum to SXR radiation was greater, which can be explained by the place of its origin.
|
|
| 10. |
- Refy, D. I., et al.
(författare)
-
Sub-millisecond electron density profile measurement at the JET tokamak with the fast lithium beam emission spectroscopy system
- 2018
-
Ingår i: Review of Scientific Instruments. - : AMER INST PHYSICS. - 0034-6748 .- 1089-7623. ; 89:4
-
Tidskriftsartikel (refereegranskat)abstract
- Diagnostic alkali atom (e.g., lithium) beams are routinely used to diagnose magnetically confined plasmas, namely, to measure the plasma electron density profile in the edge and the scrape off layer region. A light splitting optics system was installed into the observation system of the lithium beam emission spectroscopy diagnostic at the Joint European Torus (JET) tokamak, which allows simultaneous measurement of the beam light emission with a spectrometer and a fast avalanche photodiode (APD) camera. The spectrometer measurement allows density profile reconstruction with similar to 10 ms time resolution, absolute position calculation from the Doppler shift, spectral background subtraction as well as relative intensity calibration of the channels for each discharge. The APD system is capable of measuring light intensities on the microsecond time scale. However similar to 100 mu s integration is needed to have an acceptable signal to noise ratio due to moderate light levels. Fast modulation of the beam up to 30 kHz is implemented which allows background subtraction on the 100 mu s time scale. The measurement covers the 0.9 < rho(pol) < 1.1 range with 6-10 mm optical resolution at the measurement location which translates to 3-5 mm radial resolution at the midplane due to flux expansion. An automated routine has been developed which performs the background subtraction, the relative calibration, and the comprehensive error calculation, runs a Bayesian density reconstruction code, and loads results to the JET database. The paper demonstrates the capability of the APD system by analyzing fast phenomena like pellet injection and edge localized modes.
|
|
