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A broadband fast frequency hopping reflectometer designed for measuring plasma turbulence is in operation at TJ-II. The main feature of the reflectometer is its possibility to be tuned to any selected frequency within a fraction of a millisecond. This property enables us to probe several plasma layers within a short time interval during the discharge, permitting the characterization of the radial distribution of plasma fluctuations. The system uses a standard antennas arrangement designed to probe the plasma perpendicularly. Although the present reflectometer arrangement was not meant to measure the perpendicular rotation velocity, the system allows us to extract important information about the velocity shear layer, namely its spatial localization. Reflectometry measurements showing the so-called phase run-away have permitted the spatial localization of the velocity shear layer that develops spontaneously in TJ-II plasmas at a certain critical density. A comparison with results obtained using Langmuir probes helps in interpretation of the results. Besides, the interpretation of the experimental results has been crosschecked with results obtained using a two-dimensional full-wave code.

Microwave reflectometry is an important diagnostic to characterize the plasma electron density in fusion experiments. The broadband frequency swept microwave reflectometry system of the ASDEX Upgrade tokamak covers the frequency range of 16 to 100 GHz. In order to fully exploit the diagnostic capabilities it is mandatory to upgrade the data acquisition and control system. It should comply with shorter frequency sweep times and improved time resolution as well as accuracy allowing, for example, plasma position and shape measurements for control purposes, as it is foreseen for ITER. A new PCI-based system is under development based on a digitizer card with two channels, 12-bit resolution, and a waveform generator with one channel, 16-bit resolution. Both cards have 512 Mbytes of memory, a digital signal processor (DSP) for advanced processing modes, and a field programmable gate array (FPGA) for real-time algorithms and complex trigger managing modes. The system is able to support multiple cards (digitizers and signal generators) operating synchronously at a maximum rate of 210 MSamples/second.

We discuss a method of the turbulence poloidal spectrum measurements, which utilizes conventional fixed frequency O-mode reflectometry. The method is extended to the case of arbitrary plasma density profiles employing the stratified model of radial density distribution. The technique is applied to estimate the poloidal spectrum, amplitude and rotation velocity of density fluctuations in the edge plasma during a standard H-mode discharge on the ASDEX Upgrade tokamak, making use of the available edge reflectometer channels.

We present a novel numerical signal injection technique allowing unidirectional injection of a wave in a wave-guiding structure, applicable to 2D finite-difference time-domain electromagnetic codes, both Maxwell and wave-equation. It is particularly suited to continuous wave radar-like simulations. The scheme gives an unidirectional injection of a signal while being transparent to waves propagating in the opposite direction (directional coupling). The reflected or backscattered waves (returned) are separated from the probing waves allowing direct access to the information on amplitude and phase of the returned wave. It also facilitates the signal processing used to extract the phase derivative (or group delay) when simulating radar systems. Although general, the technique is particularly suited to swept frequency sources (frequency modulated) in the context of reflectometry, a fusion plasma diagnostic. The UTS applications presented here are restricted to fusion plasma reflectometry simulations for different physical situations. This method can, nevertheless, also be used in other dispersive media such as dielectrics, being useful, for example, in the simulation of plasma filled waveguides or directional couplers.

Microwave reflectometry has been proposed as an alternative/backup approach to the usual magnetic systems in long pulse operation on the International Thermonuclear Experimental Reactor (ITER) for plasma position and shape control. This new application of reflectometry must be fully demonstrated in present machines in view of its importance for ITER. First experiments performed in ASDEX Upgrade with frequency modulated continuous wave with reflectometry diagnostic showed that radial variations of the plasma column occurring during preprogrammed horizontal as well as vertical plasma displacements could be followed with sufficient accuracy (⩽1 cm) in phases with approximately constant density. In this article we determine the plasma edge position simultaneously in the inner and outer midplane, of ohmic L-mode density limit and ELMy H-mode discharges in ASDEX Upgrade, both with significant density variations. It is shown that if normalized density layers are selected, at a certain percentage of the average line density, the results from reflectometry are in good agreement with the corresponding data, separatrix position, derived from the magnetics. Further work aiming at the full demonstration of plasma position and shape measurements from reflectometry is discussed.

Reflectrometry is influenced by plasma perturbations and turbulence, making the understanding of how signals are affected by such phenomena of prime importance. In this work we look at the effect magnetic islands with turbulence have on the amplitude and phase of reflectometry signals. For this purpose we resort to a two-dimensional finite difference time domain code and use a turbulence model based on experimental data. We investigate the possibility of occurrence of destructive interference due to a chain of islands and the role turbulence plays. The simulation of an island with turbulence present at the resonant surface q=2, with dimensions of the same order of magnitude as the phenomena observed on ASDEX Upgrade on Tore Supra, is also done with results which are in agreement with experimental observations.

The discovery of advanced tokamak scenarios opened new possibilities for the realization of more compact machines with long pulse operation. This requires the simultaneous optimization of the plasma shape, and of the pressure, current and electric field profiles. In this complex process the diagnostics are crucial to understand the plasma physics, to validate the theoretical models and to measure parameters for control purposes. Here we present results obtained in ASDEX Upgrade showing the great potential of reflectometry for conventional and advanced tokamak investigation, derived from the diagnostic capability to perform a wide range of measurements with high spatial and temporal resolution, both at the edge and plasma core. The abrupt formation of sharp density gradients at the zones where internal and external transport barriers are formed, as well as the modifications of the turbulence parameters in those narrow plasma regions are shown. Density profile changes associated with fast events like ELMs and the L-H transition are resolved. Enhanced fluctuations that may be important for the transport across the edge barrier are also detected by reflectometry. The measurement of the radial profile of E×B velocity on ASDEX Upgrade is discussed and results are compared with vE×B profiles obtained in W7-AS stellarator. The first experimental demonstration that edge density profiles from reflectometry can provide accurate and reliable measurements of the temporal evolution of the plasma position is presented. This is essential to prove that reflectometry can be used as an alternative approach to supplement the magnetic measurements, for the control of plasma shape and position in long pulse operation, as it is proposed for ITER. Finally new applications of reflectometry under development are discussed.

An amplitude modulation reflectometry system is in operation at the stellarator TJ-II. Recently, the first electron density profiles were obtained, showing good agreement with profiles measured by Thomson scattering and lithium beam diagnostics. In order to measure density profiles from the plasma edge, the extraordinary mode of polarization is used. A hyper-abrupt varactor-tuned oscillator used in combination with active multipliers generate two frequency segments: 25-36 and 36-50 etc GHz sharing a unique common wave-guide system (Ka band). The signal is amplitude modulated at 200 MHz and the phase demodulation is done at lower intermediate frequency. The time evolution of the electron density profile was measured under different experimental conditions. In this paper, we present the temporal evolution of the profiles obtained during a transition to an enhanced confinement mode and during cold pulse propagation experiments. We also report the modification in the shape of the density profile measured during a magnetic configuration scan in which a low-order rational surface is moved from the scrape-off layer into the plasma confinement region.

Broadband reflectometry is used to obtain density profiles in fusion plasmas using waves reflected at different plasma layers. The reflected signal can be severely affected by plasma fluctuations and/or fast density changes. In order to understand the plasma response, a finite difference time domain two-dimensional full wave code was developed. The code was used to study typical situations of fusion plasmas where important profile movements occur: when a rotating magnetic island is present and during an ELM. The numerical results are in good agreement with experimental results obtained in ASDEX and ASDEX Upgrade in the situations above. Our study demonstrates that contributions from the plasma movements are important and should be taken into account to obtain accurate profile measurements.

The broadband reflectometry system on ASDEX Upgrade is now routinely providing electron density profiles with a minimum temporal spacing of 30 μs. The plasma is probed from zero density to ne=6.64×1019 m−3 at the low field side with combined O and X modes, and from ne=0.318×1019 to ne=6.64×1019 m−3 at the high field side using O mode. Here we analyze the performance of the diagnostic for profile measurements taking into account its design options and the experimental results obtained in a wide range of plasma regimes. We address several questions, in particular the measuring range of the antennas and the range of density gradients. It is shown that it is possible to obtain a detailed evolution of the density profile and density gradient even in the presence of turbulence, providing that sufficient data can be extracted from the plasma. The radial movements of the plasma can be measured with great accuracy, which is especially important for the use of reflectometry for plasma position control, as is propos...

Reflectometry is a powerful and complex diagnostic that needs to be efficiently operated in order to take advantage of all the generated data. For this reason the control and data acquisition system of the ASDEX-Upgrade reflectometry diagnostic has been recently improved making the data acquisition more flexible and simplifying the operation procedures. A single daemon-server application runs on a workstation and is responsible for every task required by the operation as well as keeping a log about acquired shots. Multiple users can connect to this server, through internet sockets, using a client application. Although only one of the connected clients is allowed to make changes to the system, other users can monitor the current system status. In the future, data analysis tools will be included in the operating software improving the interaction between the acquired data and the operation.

Herein we propose a data processing method to analyse broadband reflectometry signals based on the Wigner–Ville distribution (WVD). The method offers the advantage of good localization of the reflectometry signal energy in the time-frequency domain. Simulations are presented to test the ability of this technique to follow the average beat frequency that is the relevant quantity to invert the plasma profile. The method is compared with the short-time fourier transform (STFT) analysis both for simulated and for ASDEX Upgrade plasmas. It is shown that the WVD has potential advantages for the routine evaluation of density profiles. The method can also be useful to study fluctuations, namely when abrupt changes of turbulence occur at the L–H transition.

Équipe 107 : Physique des plasmas chauds; International audience; A 2D finite-differences time-domain full-wave code is used to simulate the measurements of plasma filaments with fixed frequency O-mode reflectometry. The plasma is modeled by a linear slab plasma plus a Gaussian perturbation propagating in a direction that can vary from poloidal to radial. The plasma background density gradient is chosen in agreement with the steep edge transport barrier of H-modes in the ASDEX Upgrade (AUG) tokamak. Illustrative results are presented and different types of reflectometry responses are observed depending on filament sizes and propagation directions. The reflectometry signatures obtained here with numerical simulations support previous experimental findings on filament measurements.

The measurement of electron density in the JET pumped divertor by conventional reflectometry techniques is difficult because of poor access to the divertor region,unfavourable plasma geometry and the small plasma size. This paper presents a new reflectometer diagnostic which can operate in the difficult conditions of the pumped divertor. It is a `comb' reflectometer in which a number of microwave signals with different frequencies are launched simultaneously into the plasma, and the peak electron density along the sightline is estimated by determining which signals are transmitted and which are reflected. The design and operating principles of the diagnostic are described, and preliminary results illustrating its performance are presented.

Reflectometry will be used on ITER to measure the density profile in the main plasma and divertor regions, and to measure the plasma position and shape in order to provide a standby reference for the magnetic diagnostics in long pulse discharges. The high temperatures of the ITER core and the resultant significant relativistic downshift of the second-harmonic electron cyclotron absorption imply that both low-field side O-mode and high-field side lower cut-off (X−l mode) systems are required to access the full plasma profile. A low-field side upper cut-off (X−u mode) system will also be required for measurements of the scrape-off layer. For measurements of the plasma position and shape, an O-mode system is optimum due to the large range of magnetic field along the plasma periphery and the wide range of possible plasma configurations achievable on ITER. A robust real-time calibration technique of the whole transmission line is required. It is likely that an accurate estimate of the position of the plasma will require the simultaneous use of signals from the profile reflectometer. For the divertor, profiles with peak densities in the range 1019–1022/m3 are to be measured with a target resolution of 3 mm. The large density range will necessitate the use of more than one system. Installing these reflectometers on ITER incurs additional difficulties such as the routing of the millimetre wave radiation around the complicated first wall and divertor structures and design of antennas able to operate through the first wall and blanket.

The Tore-Supra doppler reflectometer (TSDR) aims at measuring the poloidal wave number spectrum (k spectrum) of the density fluctuations. To evaluate the performance and the sensitivity of the TSDR, simulations were made using a global full-wave code. The TSDR modeling with a finite-difference time-domain scheme and the required constraints of the simulation are presented, namely the account of the real size of the system: Distance horn plasma and plasma size. Particular attention is given to the role of the radiation pattern both on the TSDR spatial resolution and the wave number detection.

The broadband frequency modulation-continuous wave microwave/millimeter wave reflectometer of ASDEX upgrade tokamak (Institut fur Plasma Physik (IPP), Garching, Germany) developed by Centro de Fusao Nuclear (Lisboa, Portugal) with the collaboration of IPP, is a complex system with 13 channels (O and X modes) and two types of operation modes (swept and fixed frequency). The control system that ensures remote operation of the diagnostic incorporates VME and CAMAC bus based acquisition/timing systems. Microprocessor input/output boards are used to control and monitor the microwave circuitry and associated electronic devices. The implementation of the control system is based on an object-oriented client/server model: a centralized server manages the hardware and receives input from remote clients. Communication is handled through transmission control protocol/internet protocol sockets. Here we describe recent upgrades of the control system aiming to: (i) accommodate new channels; (ii) adapt to the heterogeneity of computing platforms and operating systems; and (iii) overcome remote access restrictions. Platform and operating system independence was achieved by redesigning the graphical user interface in JAVA. As secure shell is the standard remote access protocol adopted in major fusion laboratories, secure shell tunneling was implemented to allow remote operation of the diagnostic through the existing firewalls.

The contribution of the initial plasma to density profiles reconstructed from the dφ/df vs f curve obtained with reflectometry is studied. It is shown that the initial phase information determines to a great extent the accuracy of the inverted profiles at the edge. As it is difficult to measure the edge contribution models are required to initialize the profile evaluation. A novel method is presented that uses the phase information from the lowest frequency waves to obtain dφ/df below the first probing frequency F1, by imposing the continuity with the measured dφ/df characteristic and its derivative at F1. An approximate shape of the edge profile is obtained because low‐frequency waves are sensitive to the initial plasma where they propagate without reflection. The accuracy of the inverted profiles is thereby improved, as shown by simulation studies performed for profiles with an exponential‐like decay and with an edge density plateau (typical of H‐mode regimes during ELMs). It is found that the contribut...

A single channel microwave interferometer has been developed for a tokamak with an improved detection that uses an heterodyne configuration and is based on a differential quadrature phase concept. With the new detection very sensitive and accurate direct phase measurements are obtained due to the elimination of the spurious variations of the detected signals resulting from the nonideal behavior of the output mixers. As a result, the line integrated density along the vertical central chord of the vacuum chamber can be determined during the whole plasma discharge. Fast density variations occurring both at the formation phase of the plasma and during sawtooth cycles could also be measured.

Achieving higher levels of plasma performance control in present fusion experiments requires that diagnostics be upgraded to deliver processed physical parameters in real-time (RT). A key element in a diagnostic RT upgrade is the data acquisition system (DAS), that should be capable of delivering the acquired data to the data processing resources with very low latencies and in the shortest possible time. Adequate standard commercial solutions with these characteristics are not easily found in the market, what leads most of the times to the development of complex custom high-performance designs from ground-up. A mixed solution, partially based on commercial off-the-shelf (COTS) components, is under development to upgrade the existing ASDEX Upgrade (AUG) broadband reflectometry diagnostic so that a full demonstration of plasma position control using RT reflectometry density profile measurements can be performed. The 8-channel (12-bit/100 MSPS) DAS being designed features a PCI Express (PCIe) x8 interface to enable direct memory access (DMA) data transfers with throughputs in excess of 1 GB/s. The use of COTS components resulted in a faster hardware design cycle without compromising system performance and flexibility. The architecture of the system and its main design constraints as well as the system integration in the AUG RT diagnostic network are herein discussed. Preliminary benchmark results for data throughput and overall measurement latency are also presented.

An overview of reflectometry measurements of density profiles and density fluctuations in fusion devices, is presented. The results are analysed in the light of the expectations from recent theoretical and numerical studies. The spatial resolution of the diagnostic and the wave number sensitivity are discussed. The diagnostic capabilities are considered in view of its application in next generation devices.

In broadband microwave reflectometry, coherent detection is widely used to obtain the phase information and to improve the systems sensitivity, both in diagnostics measuring the electronic density profile and plasma fluctuations. Coherent detection uses a translated version of the probing signal to guarantee a stable intermediate frequency. Here, a novel technique to generate the frequency translation by double frequency conversion is presented and its advantages over the commonly used single frequency conversion techniques employing image rejection mixers are discussed. The results obtained with the new frequency translator modules developed for the three JET FM-CW reflectometers, operating successfully at JET since mid-2009, are presented.

We present a study performed in ASDEX Upgrade H mode regime based on results from the broadband FM‐CW reflectometry diagnostic, equipped with the unique capability of measuring the plasma density profile both at the low and high field sides of the tokamak. The plasma edge dynamics due to fast events such as the Edge Localized Modes (ELMs) is analyzed displaying important characteristics of the ELMs and showing the high accuracy of the reflectometry diagnostic measurements.

An O-mode correlation reflectometer, broadband tuneable in the frequency range 18–26.5GHz, is being developed to study density fluctuations on the ISTTOK tokamak namely to determine the fluctuations correlation length. In this paper the basic principles of correlation reflectometry measurements are presented and the developed microwave and control systems for the diagnostic are described.

Reflectometry applied to the measurement of density profiles on fusion plasmas has been subject to many recent developments. After a brief reminder of the principles of reflectometry, the theoretical accuracy of reflectometry measurements is discussed. The main difficulties limiting the performance, namely the plasma fluctuations and the quality of the transmission lines, are analysed. The different techniques used for reflectometry are then presented grouped into three different categories, depending on the frequency spectrum of the probing wave: single frequency, few discrete frequencies, or broad spectrum. The present status and achievements of actual implementations of these techniques are demonstrated, with an analysis of their respective limitations and merits, as well as foreseen developments. Finally, a discussion of the various reflectometry techniques is made, in particular their ability to cope with plasma fluctuations and complex transmission lines, in view of the application to next step machines and very severe environments.

Millimeter-wave reflectometers for performing density fluctuations have traditionally used either tunable fixed frequency (heterodyne and homodyne) systems or multichannel fixed frequency arrangements. Only recently novel systems were brought into operation with the ability to hop from one frequency to another over a large bandwidth, during each plasma discharge, while retaining the quality of fixed frequency phase locked sources. The new broadband fast hopping millimeter-wave reflectometer incorporates frequency synthesizers for both plasma signal and local oscillators, and the receivers are heterodyne producing full phase/amplitude outputs. Two identical systems were recently installed in (ASDEX upgrade tokamak - IPP-MPG Germany) covering the Q band (33–50 GHz) and the V band (50–75 GHz). In the present article the system is described and the particular implementation on ASDEX, using monostatic antenna system, is presented showing the possibility of correlation studies in fully optimized antenna scenari...

New transmission lines and antennas recently installed at Join European Torus (JET) under the European Fusion Development Agreement enhancement project millimeter wave access meet the performance requirements of broadband reflectometry for density profile measurements. A fast swept frequency modulation continuous wave [H. Bottollier, Curtet-et al., Rev. Sci. Instrum. 58, 539 (1987); F. Simonet et al., ibid. 56, 664 (1985); A. Silva et al., ibid. 70, 664 (1999); S. Hacquin et al., ibid. 75, 3834 (2004)] using coherent detection of the reflected signal was developed to probe the midplane plasma in the X-mode polarization in the 50–75 GHz frequency range, aiming at measuring the edge density profile in the JET advanced scenarios with an axial magnetic field of 2.4 T. The operating principles of the new system are described and some preliminary results obtained with it are presented. Special attention is given to the capability of operating on bistatic antenna arrangements over long waveguides using a local g...

The broadband FMCW reflectometry system on ASDEX Upgrade has had significant improvements extending its measuring capabilities both on high and low density plasmas: (i) the upgrade of the W band to probe electron densities up to 12.4×1019 m−3 with O mode, (ii) Q and V frequency bands operating in X mode to probe the edge plasma and to provide information for O-mode profile initialization, and (iii) a new dynamic frequency calibration method to take into account all existing delays in the hyperabrupt varactor-tuned oscillator (HTO) tuning port and driver electronics. These improvements are particularly important to measure accurately the edge pedestal region of high density ITER relevant discharges. Density profiles obtained in high density discharges are presented and compared with results from both Li-beam and Thomson scattering diagnostics.

The reflectometry system installed in the tokamak ASDEX Upgrade has 11 channels primarily aimed at profile measurements and two dedicated channels operating at fixed frequency to study density fluctuations. The channels used for profile measurements can also be operated at fixed frequency. In this article we describe the potential of the system to study important characteristics of the plasma turbulence, from combined fixed frequency and profile measurements (to localize the reflecting layers). The numerical tools used to treat fixed frequency data are briefly described. Using a set of similar discharges and the ability of the microwave reflectometry system to probe simultaneously different layers with several channels, we obtain the time evolution of the integrated power spectra of the different signals versus the minor radius of the plasma. In plasma with H-mode edge and internal transport barrier we could identify a zone at the plasma core and another at the edge with reduced fluctuation levels, coinci...

A new data analysis technique has been developed for the evaluation of the density profiles from broadband reflectometry in the presence of plasma turbulence. The method is based on the spectrogram of the reflected signals and uses the complete information of the beat frequency spectrum. The application of the Floyd best path algorithm, that takes into account the history of the beat frequency curve, enables us to extract the slow component due to the plasma profile. The statistics of the group delay data points is also considered to validate (or reject) data with great confidence. The results obtained in a wide range of plasma regimes show that accurate and detailed profiles can be measured automatically. One and two dimensional moving averaging over consecutive sweeps is also available to reduce the variance of the inverted profile while retaining a good temporal resolution.

The broadband microwave reflectometry system on ASDEX Upgrade has been recently upgraded with new channels. It has now 12 channels that probe simultaneously the high and low fields plasma, with ultrafast sweeping (20–100 μs). X mode (33–75 GHz) is used for the scrape off layer, and the O mode (16–110 GHz) is reflected from densities between 0.3×1019 and 1.5×1019 m−3. A fast sweeping heterodyne system was developed for the highest frequency channels (50–110 GHz) to cope with higher losses and lower incident power. Fixed frequency operation is employed for fluctuation measurements. A dedicated channel (33–55 GHz) operating in fixed frequency provides a signal to continuously monitor the level of density fluctuations (e.g., L–H transition), during the whole discharge. The diagnostic is fully operated by remote control. The acquisition system is based on specially developed VME boards with up to 1 Gsamp/s sampling rates. Automatic profile inversion was recently implemented using data validation and rejection ...

Corrugated circular transmission lines are considered as high performance, low loss, broadband lines for reflectometry on ITER. These lines are proposed as a possible solution for the equatorial low-field-side system and as a part (receiver-vacuum vessel) of the transmission lines for the high-field side and the out-of-midplane reflectometer system, because of their restricted access. Theoretical and experimental studies show the good properties of these lines: low losses, a smooth characteristic transmission, and a Very low level of parasitic reflections. Quasioptical systems are also proposed as a solution for the coupling of several microwave emitter receivers, working in a fundamental waveguide, into a single broadband corrugated line. (C) 1997 American Institute of Physics.

Microwave reflectometry is a diagnostic well suited to measure the plasma density profile in large fusion devices. The possibility to make reflectometry measurements with unfavourable propagation of the incident microwaves is especially important in devices where significant modifications of the flux surfaces are expected, as will be the case of ITER. The sensitivity of reflectometry to D-shaped and circular plasma configurations was studied in ASDEX Upgrade. Ray tracing was used to model the experiments and to determine the limits for reflectometry measurements.

A reflectometry system has been developed for ASDEX Upgrade to measure the plasma profile from the scrape‐off layer until the bulk plasma, simultaneously at the high and low field sides. Unique features of the system are the ultrafast broadband frequency modulation of a continuous wave using solid state stable hyper abrupt tuned oscillators (down to 10 μs), high and low field side channels and fully remote control operation, via optical fiber links. Due to the special design of the transmission line, with decoupled in going and out going lines and one‐antenna configuration, the system is optimized for reception and spurious reflections are eliminated. The ultrafast operation guarantees that the effect of plasma turbulence is greatly reduced. Both features determine the high performance of the diagnostic. A dedicated data acquisition system handles the large amounts of data generated by the broadband operation. Recent developments include the operation of new channels and an automatic and accurate frequency calibration circuit. Also, advanced digital signal processing techniques were applied to obtain density profiles with high spatial and temporal (20 μs) resolutions under turbulent plasma regions, e.g., the scrape‐off layer. Experimental results are presented showing the great sensitivity of the diagnostic to plasma radial movements and its tolerance to vertical movements of the plasma. Density profiles measured in ELMy regimes illustrate the capabilities of the diagnostic to detect fast profile changes.

Convolutional neural networks (CNNs) have found applications in many image processing tasks, such as feature extraction, image classification, and object recognition. It has also been shown that the inverse of CNNs, so- called deconvolutional neural networks, can be used for inverse problems such as plasma tomography. In essence, plasma tomography consists in reconstructing the 2D plasma profile on a poloidal cross-section of a fusion device, based on line-integrated measurements from multiple radiation detectors. Since the reconstruction process is computationally intensive, a deconvolutional neural network trained to produce the same results will yield a significant computational speedup, at the expense of a small error which can be assessed using different metrics. In this work, we discuss the design principles behind such networks, including the use of multiple layers, how they can be stacked, and how their dimensions can be tuned according to the number of detectors and the desired tomographic resolution for a given fusion device. We describe the application of such networks at JET and COMPASS, where at JET we use the bolometer system, and at COMPASS we use the soft X-ray diagnostic based on photodiode arrays.