Improved accuracy and robustness of electron density profiles from JET's X-mode frequency-modulated continuous-wave reflectometers.

JET's frequency-modulated continuous wave (FMCW) reflectometers have been operating well with the current design since 2005, and density profiles have been automatically calculated intershot since then. However, the calculated profiles had long suffered from several shortcomings: poor agreement with other diagnostics, sometimes inappropriately moving radially by several centimeters, elevated levels of radial jitter, and persistent wriggles (strong unphysical oscillations). In this research, several techniques are applied to the reflectometry data analysis, and the shortcomings are significantly improved. Starting with improving the equilibrium reconstruction that estimates the background magnetic field, adding a ripple correction in the reconstructed magnetic field profile, and adding new inner-wall reflection positions estimated through ray-tracing, these changes not only improve the agreement of reconstructed profiles to other diagnostics but also solve density profile wriggles that were present during band transitions. Other smaller but also persistent wriggles were also suppressed by applying a localized correction to the measured beat frequency where persistent oscillations are present. Finally, the burst analysis method, as introduced by Varela et al. [Nucl. Fusion 46 S693 (2006)], has been implemented to extract the beat frequency from stacked spectrograms. Due to the strong suppression of spurious reflections, the radial jitter that sometimes would span several centimeters has been strongly reduced. The stacking of spectrograms has also been shown to be very useful for stacking recurring events, like small gas puff modulations, and extracting transport coefficients that would otherwise be below the noise level.

Conceptual study of energy resolved x-ray measurement and electron temperature reconstruction on ITER with low voltage ionization chambers.

In tokamaks with tungsten-based plasma facing components, such as ITER, pollution of the plasma by heavy impurities is a major concern as it can lead to radiative breakdown. The radiation emitted by such impurities is mainly composed of x-rays in the [0.1; 100] keV range. A diagnostic allowing for the reconstruction of the impurity distribution is of high interest. The ITER requirements for the x-ray measurement system make it mandatory for the detector to provide spectral information. Due to the radiation environment during the ITER nuclear phase, advanced detectors exhibiting high resilience to neutrons and gamma rays, such as gas-filled detectors, are required. The use of Low Voltage Ionization Chambers (LVICs) for this purpose is investigated in this paper. Several anodes have been added to the detector in order to allow for spectral deconvolution. This article presents a conceptual study of the use of a multi-anode LVIC for energy resolved x-ray measurement on ITER. It covers the design of the multi-anode LVIC and its modeling, the method for spectral deconvolution, and its application to energy resolved x-ray tomography, as well as the computation of the electron temperature from the reconstructed local x-ray emissivity.

Modeling a low voltage ionization chamber based tomography system on ITER.

Soft x-ray (SXR) tomography is a key diagnostic method for impurity transport study in tokamaks since it allows for local impurity density reconstruction. The International Thermonuclear Experimental Reactor (ITER) radiative environment in deuterium-deuterium and deuterium-tritium phases will limit the choices of SXR detector technologies, and gas detectors are one of the most promising solutions. In this paper, we, thus, investigate the SXR tomography possibilities on ITER using Low Voltage Ionization Chambers (LVICs). The study contains the development of a LVIC synthetic diagnostic and its application to estimate the LVIC tomographic capabilities in an ITER D-T scenario, including the influence of LVIC parameters and noise in the measurements.

Polycapillary lenses for soft x-ray transmission in ITER: Model, comparison with experiments, and potential application.

Measuring Soft X-Ray (SXR) radiation [0.1 keV; 15 keV] in tokamaks is a standard way of extracting valuable information on the particle transport and magnetohydrodynamic activity. Generally, the analysis is performed with detectors positioned close to the plasma for a direct line of sight. A burning plasma, like the ITER deuterium-tritium phase, is too harsh an environment to permit the use of such detectors in close vicinity of the machine. We have thus investigated in this article the possibility of using polycapillary lenses in ITER to transport the SXR information several meters away from the plasma in the complex port-plug geometry.

Design of a dispersion interferometer combined with a polarimeter to increase the electron density measurement reliability on ITER.

A dispersion interferometer is a reliable density measurement system and is being designed as a complementary density diagnostic on ITER. The dispersion interferometer is inherently insensitive to mechanical vibrations, and a combined polarimeter with the same line of sight can correct fringe jump errors. A proof of the principle of the CO2 laser dispersion interferometer combined with the PEM polarimeter was recently conducted, where the phase shift and the polarization angle were successfully measured simultaneously. Standard deviations of the line-average density and the polarization angle measurements over 1 s are 9 × 1016 m-2 and 0.19°, respectively, with a time constant of 100 µs. Drifts of the zero point, which determine the resolution in steady-state operation, correspond to 0.25% and 1% of the phase shift and the Faraday rotation angle expected on ITER.

Electron cyclotron emission measurements on JET: Michelson interferometer, new absolute calibration, and determination of electron temperature.

At the fusion experiment JET, a Michelson interferometer is used to measure the spectrum of the electron cyclotron emission in the spectral range 70-500 GHz. The interferometer is absolutely calibrated using the hot/cold technique and, in consequence, the spatial profile of the plasma electron temperature is determined from the measurements. The current state of the interferometer hardware, the calibration setup, and the analysis technique for calibration and plasma operation are described. A new, full-system, absolute calibration employing continuous data acquisition has been performed recently and the calibration method and results are presented. The noise level in the measurement is very low and as a result the electron cyclotron emission spectrum and thus the spatial profile of the electron temperature are determined to within ±5% and in the most relevant region to within ±2%. The new calibration shows that the absolute response of the system has decreased by about 15% compared to that measured previously and possible reasons for this change are presented. Temperature profiles measured with the Michelson interferometer are compared with profiles measured independently using Thomson scattering diagnostics, which have also been recently refurbished and recalibrated, and agreement within experimental uncertainties is obtained.

Laser beam combiner for Thomson scattering core LIDAR.

The light detection and ranging Thomson scattering (TS) diagnostic is advantageous since it only requires a single view port into the tokamak. This technique requires a short pulse laser at high energy, usually showing a limited repetition rate. Having multiple lasers will increase the repetition rate. This paper presents a scanning mirror as a laser beam combiner. Measurements of the position accuracy and jitter show that the pointing stability of the laser beam is within ±25 µrad for over tens of seconds. A control feedback loop is implemented to demonstrate the long term stability. Such a system could be applied for ITER and JET.

Multiband reflectometry system for density profile measurement with high temporal resolution on JET tokamak.

A new system has been installed on the JET tokamak consisting of six independent fast-sweeping reflectometers covering four bands between 44 and 150 GHz and using orthogonal polarizations. It has been designed to measure density profiles from the plasma edge to the center, launching microwaves through 40 m of oversized corrugated waveguides. It has routinely produced density profiles with a maximum repetition rate of one profile every 15 µs and up to 100,000 profiles per pulse.

Observation of confined current ribbon in JET plasmas.

We report the identification of a localized current structure inside the JET plasma. It is a field-aligned closed helical ribbon, carrying current in the same direction as the background current profile (cocurrent), rotating toroidally with the ion velocity (corotating). It appears to be located at a flat spot in the plasma pressure profile, at the top of the pedestal. The structure appears spontaneously in low density, high rotation plasmas, and can last up to 1.4 s, a time comparable to a local resistive time. It considerably delays the appearance of the first edge localized mode.

First density profile measurements using frequency modulation of the continuous wave reflectometry on JET.

We present the main design options and implementation of an X-mode reflectometer developed and successfully installed at JET using an innovative approach. It aims to prove the viability of measuring density profiles with high spatial and temporal resolution using broadband reflectometry operating in long and complex transmission lines. It probes the plasma with magnetic fields between 2.4 and 3.0 T using the V band [approximately (0-1.4)x10(19) m(-3)]. The first experimental results show the high sensitivity of the diagnostic when measuring changes in the plasma density profile occurring ITER relevant regimes, such as ELMy H-modes. The successful demonstration of this concept motivated the upgrade of the JET frequency modulation of the continuous wave (FMCW) reflectometry diagnostic, to probe both the edge and core. This new system is essential to prove the viability of using the FMCW reflectometry technique to probe the plasma in next step devices, such as ITER, since they share the same waveguide complexity.

Giant oscillations of electron temperature during steady-state operation on Tore Supra.

During fully noninductively driven discharges in the Tore Supra tokamak, large spontaneous oscillations of the core electron temperature (DeltaTe/Te>50%) have been observed for the first time. They occurred during the standard O regime, which is itself characterized by periodic oscillations of much smaller amplitude. The "giant" oscillations appear to involve distinct mechanisms with respect to the O regime and provide a spectacular example of the complex nonlinear interactions between energy confinement, noninductive current sources, and MHD that may occur in a tokamak plasma during steady-state operation.

[Twelve years' experience with Carbomedics bileaflet valves]. / Douze ans d'expérience avec la prothèse valvulaire a ailettes Carbomedics. Influence de l'age des patients.

The authors report long-term results of a cohort of patients who underwent valve replacement with a Carbomedics bileaflet mechanical prosthesis. The influence of patient age on the results was examined. Three hundred and ninety patients were operated between 1988 and 2000. Complete follow-up was available in 98.5% of cases. For aortic valve replacement, the total experience was 1,061 person-years. The hospital mortality was 2.3%. Global actuarial 12 year survival was 74 +/- 7%. The actuarial probability of absence of thrombo-embolic complications at 12 years was 95 +/- 3%, and of absence of haemorrhagic complications 89 +/- 4%. For mitral valve replacement, the total experience was 610 person-years. The hospital mortality was 3.4%. The global actuarial 12 year survival was 78 +/- 5%. The actuarial probability of absence of thrombo-embolic complications at 12 years was 79 +/- 9% and of absence of haemorrhagic complications 82 +/- 5%. The results of survival and prosthesis-related complications were comparable to those reported in the literature with second generation mechanical prostheses, with the exception of thromboses of the mitral valve for which a higher linear rate was observed. Multivariate analysis showed an increased (x 2.3) risk of haemorrhage after 60 years of age irrespective of the site of implantation of the prosthesis. In patients over 60 years of age, the risks of long-term anticoagulant therapy should raise questions concerning the modality of follow-up and the indications. The use of biological prostheses is a possible alternative.

[Epstein-Barr virus-associated cutaneous plasmacytoma post-solid organ transplantation]. / Plasmocytomes cutanés associés au virus Epstein-Barr chez les transplantés d'organes.

BACKGROUND: Post-transplantation lymphoproliferative disorders develop in 1 to 10p. 100 of organ transplant recipients and are frequently associated with Epstein-Barr virus (EBV). Among post-transplantation lymphoproliferative disorders, plasmacytoma with cutaneous involvement is exceptional. Association with EBV has been rarely reported in post-transplantation plasmacytomas and the latency type of EBV has never been characterized. We report 2 new cases of cutaneous monotype EBV-related plasmacytomas. CASE-REPORTS: Clinical presentation was a sub-cutaneous tumor on the thigh in the first case and an ulcerated nodule of the leg in the second case, occurring respectively 7 and 8 years after organ transplantation (liver transplantation and heart transplantation). In both lesions, tumor cells exhibited lambda light chain restriction and the association with EBV was confirmed using immunohistochemistry and in situ hybridization. The expression of EBV genes in tumor cells demonstrated type III latency. DISCUSSION: The classification of post-transplantation lymphoproliferative disorders is not well defined and some authors retain 3 categories. Among the latter, plasmacytomas have been rarely described. Cutaneous involvement is reported in 4 cases and an association with EBV in only 2 cases without description of viral latency. Clinical and histological features of post-transplantation plasmacytomas appear polymorphic. We report EBV-association in both cases, with a type III latency clearly demonstrated in one case, as has been reported in other lymphoproliferative diseases in patients with congenital or acquired immunodeficiency. We also discuss various possible therapeutic strategies for post-transplantation lymphoproliferative disorders.

[Secondary displacement of an Amplatz occluder for atrial septal defect. 2 case reports]. / Déplacement secondaire d'une prothèse d'Amplatz de communication interauriculaire. A propos de 2 cas.

The authors report two cases of secondary displacement of an Amplatz occluder of isolated ostium secundum atrial septal defects. The displacement was observed at 1 month and the prosthesis removed at 3 months. To the best of the authors' knowledge, these are the first two reported cases of secondary displacement of this type of device. The main risk factor in the two cases was the absence of a subaortic septal remnant observed at surgical removal. This anatomical characteristic can be identified by transoesophageal echocardiography, but was poorly assessed by transthoracic echocardiography. Three-dimensional transoesophageal echocardiography should improve selection of atrial septal defects suitable for percutaneous treatment by better identification of their form and anatomical characteristics.

Localization of the ventricular preexcitation site in Wolff-Parkinson-White syndrome with Doppler tissue imaging.

PURPOSE: The objective of this study was to evaluate the ability of Doppler tissue imaging (DTI) to localize the ventricular emergence site of accessory atrioventricular pathways (Wolff-Parkinson-White syndrome). METHODS: Thirty-three patients were studied prospectively by Doppler tissue imaging (128XP and Sequoia 256 echocardiographic systems; Acuson, Mountain View, Calif) before investigation of Wolff-Parkinson-White syndrome and after radiofrequency ablation of the accessory pathways. The normal appearance of the ventricular contractions was defined in a group of 10 control subjects. The preexcitation zone was determined as a zone of maximum acceleration in "DTI acceleration mode" or as a coded contraction zone in "DTI velocity mode," at the time of the delta wave or before the onset of the QRS complex. RESULTS: The earliest ventricular activation site was correctly localized for 12 of the 15 left-sided pathways (8 anterior or anterolateral, 2 lateral or posterolateral, 2 inferior). When wall motion abnormalities were detected in the left ventricle by DTI, the left-sided localization was confirmed by electrophysiologic exploration. For the right-sided pathways, the localization was correct in only 4 of 11 cases (3 posteroseptal and 1 anterolateral). After effective ablation in all patients, the abnormalities corresponding to the electrophysiologic data disappeared totally in only 11 of 16 patients. CONCLUSION: In the presence of Wolff-Parkinson-White syndrome, DTI localizes contraction abnormalities associated with early activation of a part of the ventricle. However, the interpretation of the images remains difficult because the normal coding of the contraction of the ventricular walls depends on the incidence for which they are investigated. This noninvasive examination seems to be an effective tool for localizing the left-sided accessory pathways of the left ventricle, in particular in the anterior, anterolateral, or inferior walls.

[Diagnostic value of stress echocardiography under dobutamine and myocardial scintigraphy for restenosis at 6 months after angioplasty of the left anterior descending artery]. / Valeur diagnostique de l'échocardiographie de stress sous dobutamine et de la scintigraphie myocardique d'effort dans le dépistage de la resténose à 6 mois d'une angioplastie de l'interventriculaire antérieure.

This study compared prospectively the diagnostic value of dobutamine echocardiography and exercise myocardial scintigraphy for restenosis at 6 months after angioplasty of the left anterior descending artery. Forty-one patients aged 58 +/- 10 years, admitted to hospital for myocardium infarction (N = 22) or unstable angina (N = 19), with single vessel disease, were treated by angioplasty of one lesion of the left anterior descending artery after initial evaluation of the left ventricular ejection fraction by echocardiography. At 6 months, left ventricular function was reassessed by echocardiography, dobutamine echocardiography and exercise myocardial scintigraphy (Thallium 201) performed without treatment. Coronary angiography was performed at the same time and showed 8 restenosis (19.5%). Overall, in this series, dobutamine echo and scintigraphy had respectively a sensitivity of 37.5% and 75%, and a specificity of 97% and 70% (p < 0.02). Nine patients had left ventricular dysfunction unchanged compared with the initial measurement without viability in the territory of the left anterior descending artery with low dose dobutamine (group 1); thirty-two patients had improved or normal left ventricular ejection fraction with myocardial viability (group 2). In group 1, no cases of restenosis were detected by dobutamine echocardiography but_of them had myocardial scintigraphic evidence of ischaemia. In group 2, the sensitivity of the two techniques was comparable but dobutamine echo was more specific than scintigraphy (96 versus 75%, p = 0.03). In conclusion, dobutamine echocardiography may be indicated in the diagnosis of restenosis of the left anterior descending artery and in cases of viability in its territory. In its absence, myocardial scintigraphy seems to be preferable.

[Comparative study of post-infarction myocardial viability after fibrinolysis by stress tomoscintigraphy and echography: can viability be detected without ischemia?]. / Etude comparée de la viabilité du myocarde en post-infarctus après fibrinolyse par tomoscintigraphie et échographie de stress: peut-on détecter la viabilité sans l'ischémie?

The objectives of this prospective study was to define the comparative ability of stress myocardial scintigraphy and dobutamine stress echocardiography to demonstrate post-MI myocardial viability, assessed on the functional recovery in terms of improvement of global and segmental kinetics by cardiac gamma-angiography after revascularization. 18 patients (11 anterior MI, 7 lateral or inferior MI) and 162 segments were analysed semiquantitatively. All patients with persistent significant stenosis underwent secondary revascularization of the artery responsible for myocardial infarction. The prevalence of viability was high, as only 34% of segments initially presented a segmental kinetic abnormality and contraction was improved at 6 months in 54% of cases. Stress scintigraphy and dobutamine echocardiography detected viability with a sensitivity of 96% and 70%, a specificity of 88% and 82%, a positive predictive value of 89% and 77% and a negative predictive value of 95% and 76%, respectively. Only the wall score index with low-dose dobutamine was correlated with the ejection fraction at 6 months. Stress echocardiography is a more reliable predictor of the degree of functional recovery after revascularization. Scintigraphy visualizes much more extensive abnormalities than echocardiography. This often corresponds to ischaemic territories with normal contraction under baseline conditions and low doses of dobutamine. It therefore seems preferable both examinations for optimal assessment of thrombolized patients following myocardial infarction.

Twelve-year experience with the 19 mm Carpentier-Edwards pericardial aortic valve.

BACKGROUND AND AIMS OF THE STUDY: In patients with small aortic annuli, the choice of prosthesis should be based on hemodynamics and valve durability. The Carpentier-Edwards pericardial valve offers good hemodynamic performance and long-term valve durability. We reviewed our 12-year experience with 121 patients who received a 19 mm prosthesis. METHODS: A total of 121 patients (97 females, 24 males; mean age 73.2 +/- 9.4 years) underwent isolated aortic valve replacement with a 19 mm Carpentier-Edwards pericardial bioprosthesis in our institution between July 1984 and December 1995. Patients were followed up for an average of 4.84 years after surgery; total follow up was 581 patient-years (pt-yr). RESULTS: The operative mortality rate was 3.3% (4/121). At the present time, 77 patients (86%) are in NYHA class I or II with a mean gradient of 18.0 +/- 6.9 mmHg and mean effective orifice area 1.1 +/- 0.23 cm2. There were 25 late deaths. After 12 years the actuarial survival rate was 42 +/- 26%. Eight patients died of valve-related cause (one endocarditis, one structural failure, two thromboembolisms, one anticoagulant-related hemorrhage, three sudden deaths). At 12 years, the actuarial rate of freedom from valve-related death was 61 +/- 37% and from non-sudden valve-related death 88 +/- 11%. Valve-related complications included six thromboembolic episodes (1.0%/pt-yr), one endocarditis (0.17%/pt-yr), two reoperations (0.34%/pt-yr) and two structural valve failures (0.34%/pt-yr). After 12 years, freedom from reoperation was 89 +/- 11%, from valve failure 92 +/- 8%, from thromboembolic episodes 82 +/- 16% and from endocarditis 99 +/- 1%. CONCLUSION: With a low rate of structural valve failure at 12 years and a good clinical performance, the Carpentier-Edwards prosthesis is a reliable alternative for small aortic annuli.

Carpentier-Edwards pericardial bioprosthesis in aortic or mitral position: a 12-year experience.

BACKGROUND: The first generation of pericardial valves was withdrawn from the market for a high rate of premature failure. With an original design, Carpentier-Edwards pericardial valves promised improved results. METHODS: Seven hundred eighty-seven patients who underwent isolated aortic valve replacement and 182 patients who underwent isolated mitral valve replacement between July 1984 and December 1995 with Carpentier-Edwards pericardial bioprostheses in our institution were followed up. The patients' mean age was 68.3 (aortic valve replacement, AVR) and 63.9 (mitral valve replacement, MVR) years. All but five AVR patients were followed up for an average of 4.7 years after operation, with a total follow-up of 3,624 patient-years. All patients with MVR were followed up for an average of 5.3 years after operation, with a total follow-up of 969 patient-years. RESULTS: After 12 years, actuarial survival rate is 53% for AVR and 54% for MVR. Freedom from valve-related complications for aortic versus mitral valve replacement is, respectively, 68% and 55%, freedom from valve-related death is 84% and 85%, freedom from thromboembolism 87% and 94%, and freedom from endocarditis 97% and 94%. The behavior of the aortic valve is better than that of the mitral valve: freedom from reoperation is 92% and 76%, respectively; freedom from valve failure is 94% and 78%. Age is an important factor, especially in the mitral position: freedom from valve failure is 52% in patients younger than 60 years and 100% in patients older than 60 years. CONCLUSIONS: With a low rate of valve-related events at 12 years and a low rate of structural deterioration, this prosthesis is a reliable choice for AVR and in patients over 60 years for MVR. A more durable mitral bioprosthesis is needed for patients younger than 60 years.