| 1. |
- Bernardo, J., et al.
(författare)
-
Ion temperature and toroidal rotation in JET's low torque plasmas
- 2016
-
Ingår i: Review of Scientific Instruments. - : AIP Publishing. - 0034-6748 .- 1089-7623. ; 87:11
-
Tidskriftsartikel (refereegranskat)abstract
- This paper reports on the procedure developed as the best method to provide an accurate and reliable estimation of the ion temperature T-i and the toroidal velocity v(phi) from Charge-eXchange Recombination Spectroscopy (CXRS) data from intrinsic rotation experiments at the Joint European Torus with the carbon wall. The low impurity content observed in such plasmas, resulting in low active CXRS signal, alongside low Doppler shifts makes the determination of Ti and v(phi) particularly difficult. The beam modulation method will be discussed along with the measures taken to increase photon statistics and minimise errors from the absolute calibration and magneto-hydro-dynamics effects that may impact the CXRS passive emission.
|
|
| 2. |
- Craciunescu, Teddy, et al.
(författare)
-
Evaluation of reconstruction errors and identification of artefacts for JET gamma and neutron tomography
- 2016
-
Ingår i: Review of Scientific Instruments. - : American Institute of Physics (AIP). - 0034-6748 .- 1089-7623. ; 87:1
-
Tidskriftsartikel (refereegranskat)abstract
- The Joint European Torus (JET) neutron profile monitor ensures 2D coverage of the gamma and neutron emissive region that enables tomographic reconstruction. Due to the availability of only two projection angles and to the coarse sampling, tomographic inversion is a limited data set problem. Several techniques have been developed for tomographic reconstruction of the 2-D gamma and neutron emissivity on JET, but the problem of evaluating the errors associated with the reconstructed emissivity profile is still open. The reconstruction technique based on the maximum likelihood principle, that proved already to be a powerful tool for JET tomography, has been used to develop a method for the numerical evaluation of the statistical properties of the uncertainties in gamma and neutron emissivity reconstructions. The image covariance calculation takes into account the additional techniques introduced in the reconstruction process for tackling with the limited data set (projection resampling, smoothness regularization depending on magnetic field). The method has been validated by numerically simulations and applied to JET data. Different sources of artefacts that may significantly influence the quality of reconstructions and the accuracy of variance calculation have been identified.
|
|
| 3. |
- 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.
|
|
| 4. |
- 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.
|
|
| 5. |
- Delabie, E., et al.
(författare)
-
In situ wavelength calibration of the edge CXS spectrometers on JET
- 2016
-
Ingår i: Review of Scientific Instruments. - : AMER INST PHYSICS. - 0034-6748 .- 1089-7623. ; 87:11
-
Tidskriftsartikel (refereegranskat)abstract
- A method for obtaining an accurate wavelength calibration over the entire focal plane of the JET edge CXS spectrometers is presented that uses a combination of the fringe pattern created with a Fabry-Perot etalon and a neon lamp for cross calibration. The accuracy achieved is 0.03 angstrom, which is the same range of uncertainty as when neglecting population effects on the rest wavelength of the CX line. For the edge CXS diagnostic, this corresponds to a flow velocity of 4.5 km/s in the toroidal direction or 1.9 km/s in the poloidal direction.
|
|
| 6. |
- Eriksson, Benjamin, et al.
(författare)
-
New method for time alignment and time calibration of the TOFOR time-of-flight neutron spectrometer at JET
- 2021
-
Ingår i: Review of Scientific Instruments. - : American Institute of Physics (AIP). - 0034-6748 .- 1089-7623. ; 92:3
-
Tidskriftsartikel (refereegranskat)abstract
- The TOFOR time-of-flight (TOF) neutron spectrometer at the Joint European Torus (JET) is composed of 5 start (S1) and 32 stop (S2) scintillation detectors. Recently, the data acquisition system (DAQ) of TOFOR was upgraded to equip each of the 37 detectors with its own waveform digitizer to allow for correlated time and pulse height analysis of the acquired data. Due to varying cable lengths and different pulse processing pathways in the new DAQ system, the 160 (5.32) different TOF pairs of start-stop detectors must be time-aligned to enable the proper construction of a summed TOF spectrum. Given the time (energy) resolution required by the entire spectrometer system to measure different plasma neutron emission components, it is of importance to align the detector pairs to each other with sub-nanosecond precision. Previously, the alignment partially depended on using fusion neutron data from Ohmic heating phases of JET experimental pulses. The dependence on fusion neutron data in the time alignment process is, however, unsatisfactory as it involves data one would wish to include in an independent analysis for physics results. In this work, we describe a method of time-aligning the detector pairs by using gamma rays. Given the known geometry and response of TOFOR to gamma rays, the time alignment of the detector pairs is found by examining gamma events interacting in coincidence in both S1-S1 and S1-S2 detector combinations. Furthermore, a technique for separating neutron and gamma events in the different detector sets is presented. Finally, the time-aligned system is used to analyze neutron data from Ohmic phases for different plasma conditions and to estimate the Ohmic fuel ion temperature.
|
|
| 7. |
- Ferreira, Diogo R., et al.
(författare)
-
Robust regression with CUDA and its application to plasma reflectometry
- 2015
-
Ingår i: Review of Scientific Instruments. - : AIP Publishing. - 0034-6748 .- 1089-7623. ; 86:11
-
Tidskriftsartikel (refereegranskat)abstract
- In many applications, especially those involving scientific instrumentation data with a large experimental error, it is often necessary to carry out linear regression in the presence of severe outliers which may adversely affect the results. Robust regression methods do exist, but they are much more computationally intensive, making it difficult to apply them in real-time scenarios. In this work, we resort to graphics processing unit (GPU)-based computing to carry out robust regression in a time-sensitive application. We illustrate the results and the performance gains obtained by parallelizing one of the most common robust regression methods, namely, least median of squares. Although the method has a complexity of O(n(3) log n), with GPU computing, it is possible to accelerate it to the point that it becomes usable within the required time frame. In our experiments, the input data come from a plasma diagnostic system installed at Joint European Torus, the largest fusion experiment in Europe, but the approach can be easily transferred to other applications.
|
|
| 8. |
- Figueiredo, J., et al.
(författare)
-
JET diagnostic enhancements in preparation for DT operations
- 2016
-
Ingår i: Review of Scientific Instruments. - : AMER INST PHYSICS. - 0034-6748 .- 1089-7623. ; 87:11
-
Tidskriftsartikel (refereegranskat)abstract
- In order to complete the exploitation of the JET ITER-like Wall and to take full benefit from deuterium-tritium experiments on JET, a set of diagnostic system refurbishments or upgrades is in progress. These diagnostic enhancements focus mainly on neutron, gamma, fast ions, instabilities, and operations support. These efforts intend to provide better spatial, temporal, and energy resolution while increasing measurement coverage. Also previously non-existing capabilities, such as Doppler reflectometry is now available for scientific exploitation. Guaranteeing diagnostic reliability and consistency during the expected DT conditions is also a critical objective of the work and systems being implemented. An overview of status and scope of the ongoing projects is presented.
|
|
| 9. |
- 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.
|
|
| 10. |
- Gatu Johnson, Maria, 1978-, et al.
(författare)
-
The TOFOR neutron spectrometer and its first use at JET
- 2006
-
Ingår i: Review of Scientific Instruments. - American Institute of Physics : AIP Publishing. - 0034-6748 .- 1089-7623. ; 77:10E702, s. 1-3
-
Tidskriftsartikel (refereegranskat)abstract
- A time-of-flight neutron spectrometer (TOFOR) has been developed to measure the 2.45 MeV d+d3He+n neutron emission from D plasmas. The TOFOR design features the capability to operate at high rates in the 100 kHz 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.
|
|
