Cascades of Parametric Instabilities in the Tokamak Plasma Edge during Electron Cyclotron Resonance Heating

We report observations of nonlinear two-plasmon decay instabilities (TPDIs) of a high-power microwave beam, a process similar to half-harmonic generation in optics, during electron cyclotron resonance heating in a tokamak. TPDIs are found to occur regularly in the plasma edge due to wave trapping in density fluctuations for various confinement modes, and the frequencies of both observed daughter waves agree with modeling. Emissions from a cascade of subsequent decays, which indicate a generation of ion Bernstein waves, are correlated with fast-ion generation. This emphasizes the limitations of standard linear microwave propagation models and possibly paves the way for novel microwave applications in plasmas.

Vertical electron cyclotron emission diagnostic on the tokamak à configuration variable

In this paper, a diagnostic for the measurement of the electron cyclotron emission (ECE) from non-thermal electrons in magnetically confined fusion plasmas is presented. The diagnostic employs a vertical viewing line of sight that allows us to directly infer the energy of the emitting electrons. Previous incarnations of this diagnostic on other machines have been limited by refraction, which can cause stray radiation to enter the line of sight, polluting the signal. By tuning the toroidal magnetic field on the Tokamak à Configuration Variable, TCV, and by carefully selecting the range of frequencies that are used to measure the ECE spectrum, refraction can be mitigated and background radiation power reduced to below the noise power of the instrumentation. A novel technique for calibrating the diagnostic based on plasma measurements and modeling has been developed. The paper will describe the Vertical ECE (V-ECE) diagnostic on TCV, the calibration method, and the first results from the measurements.

[Anterior shoulder instability with Hill-Sachs on-track. Bankart or Bankart-remplissage?]

INTRODUCTION

in patients with anterior glenohumeral (GH) instability together with an off-track or engaging Hill-Sachs (HS) defect, Bankart-remplissage (B-R) surgery reduces the recurrence rate when compared to Bankart (B) surgery alone. There is controversy regarding whether the recurrence rate also decreases in patients with on-track or non-engaging Hill-Sachs defects.

OBJECTIVE

to compare the recurrence rate and clinical evolution of patients with anterior glenohumeral instability with 'on-track' Hill-Sachs defect treated with either B or B-R surgery.

MATERIAL AND METHODS

non-randomized, retrospective, single-center cohort study of patients with anterior glenohumeral instability and on-track Hill-Sachs defect, operated between January 2010 and December 2018. Patients operated with B versus B-R were compared. Recurrence, complications and re-operation were recorded. In addition, VAS, SSV, WOSI and qDASH scores were obtained and compared in both groups.

RESULTS

of the 105 patients who met the inclusion criteria, 78 (74.3%) patients had a complete follow-up (52 B and 26 B-R, 4.3 years median follow-up). There was a higher recurrence rate in group B compared to B-R, with this difference not reaching statistical significance (17.3% vs 7.7%, p = 0.21). There were no significant differences in residual pain, feeling of instability, complications or VAS, qDASH, SSV or WOSI scores between both groups. In the subgroup analysis, patients who practiced contact sports and were operated with B showed higher recurrence rates (24.1% vs 0%, p = 0.08) and complications (41.4% vs 18.2%, p = 0.16) when compared to B + R, although these differences were not significant.

CONCLUSION

there were no significant differences in recurrence rates and functional evolution between patients with anterior glenohumeral instability operated with B or B-R surgery. Comparative, prospective studies should be performed to establish definitive recommendations.

V-band nanosecond-scale pulse reflectometer diagnostic in the TCV tokamak

This article describes the realization of a novel approach to short pulse (∼1 ns) reflectometry (SPR) recently implemented in the tokamak configuration variable tokamak. Taking advantage of a fast arbitrary waveform generator and vector-network-analyzer extension modules, the design offers flexibility regarding pulse output frequency, duration, and repetition rate. Such flexibility allows the instrument to overcome traditional SPR spatial sampling limitations while reducing hardware complexity. In order to measure the group-delay of nanosecond-scale pulses, both traditional analog and novel digital sampling techniques have been explored. A group-delay range resolution of 17 ps (2.6 mm) in average over the V-band has been achieved with both timing techniques against a waveguide mirror featuring 10 dB power fluctuations. Direct pulse sampling during L-mode plasmas shows that reflected pulse widths increase only by 4% in average. However, pulse width dispersion does occur in L-mode plasmas and leads to an increase in the group-delay uncertainty up to 40 ps (6 mm). Raw histograms of group-delay data show interesting qualitative changes from the L mode to the H-mode. Frequency spectra of group-delay data allow the identification of macroscopic density fluctuations as well as edge quasicoherent modes during edge-localized mode-free H-modes. Finally, fast changes to the density profile have been measured with microsecond time resolution and subcentimeter spatial resolution in both O and X-mode polarizations.

V-band Doppler backscattering diagnostic in the TCV tokamak

A variable configuration V-band heterodyne Doppler back-scattering diagnostic has been recently made operational in the tokamak à configuration variable. This article describes the hardware setup options, flexible quasi-optical launcher antenna, data-analysis techniques, and first data. The diagnostic uses a fast arbitrary waveform generator as the main oscillator and commercial vector network analyzer extension modules as the main mm-wave hardware. It allows sweepable single or multi-frequency operation. A flexible quasi-optical launcher antenna allows 3D poloidal (10°-58°) and toroidal (-180° to 180°) steering of the beam with 0.2° accuracy. A pair of fast HE₁₁ miter-bend polarizers allow flexible coupling to either O or X mode and programmable polarization changes during the shot. These have been used to measure the magnetic-field pitch angle in the edge of the plasma by monitoring the backscattered signal power. Ray-tracing simulations reveal an available k_⊥ range between 3 and 16 cm^-1 with a resolution of 2-4 cm^-1. Perpendicular rotation velocity estimates compare well against ExB plasma poloidal rotation estimates from charge exchange recombination spectroscopy.

Design of tangential viewing phase contrast imaging for turbulence measurements in JT-60SA

A tangential viewing phase contrast imaging system is being designed for the JT-60SA tokamak to investigate microturbulence. In order to obtain localized information on the turbulence, a spatial-filtering technique is applied, based on magnetic shearing. The tangential viewing geometry enhances the radial localization. The probing laser beam is injected tangentially and traverses the entire plasma region including both low and high field sides. The spatial resolution for an Internal Transport Barrier discharge is estimated at 30%-70% of the minor radius at k = 5 cm^-1, which is the typical expected wave number of ion scale turbulence such as ion temperature gradient/trapped electron mode.

"Snowflake" H mode in a tokamak plasma

An edge-localized mode (ELM) H-mode regime, supported by electron cyclotron heating, has been successfully established in a "snowflake" (second-order null) divertor configuration for the first time in the TCV tokamak. This regime exhibits 2 to 3 times lower ELM frequency and 20%-30% increased normalized ELM energy (ΔWELM/Wp) compared to an identically shaped, conventional single-null diverted H mode. Enhanced stability of mid- to high-toroidal-mode-number ideal modes is consistent with the different snowflake ELM phenomenology. The capability of the snowflake to redistribute the edge power on the additional strike points has been confirmed experimentally.

Endoscopic sphincterotomy of the major duodenal papilla in acute relapsing pancreatitis associated with pancreas divisum: a case report

We report a case of acute relapsing pancreatitis associated with pancreas divisum, who underwent major papilla sphincterotomy after failed minor papilla cannulation. Long-term results were satisfactory. The possible explanations of the efficacy of major papilla endoscopic resection in this particular case are discussed.

Risk factors for cardiac and pyloric stenosis after endoscopic submucosal dissection, and efficacy of endoscopic balloon dilation treatment

BACKGROUND AND STUDY AIMS

Bleeding and perforation are major complications of endoscopic submucosal dissection (ESD) for early gastric cancer (EGC), but post-ESD stenosis represents a severe delayed complication that can result in clinical symptoms such as dysphagia and nausea. The aims of this study were to determine the risk factors and evaluate the clinical treatment for post-ESD stenosis.

METHODS

A total of 2011 EGCs resected by ESD at our institution between 2000 and 2005 were reviewed retrospectively. Resection was defined as cardiac when any mucosal defect was located in the squamocolumnar junction, and as pyloric when any mucosal defect was located < 1 cm from the pylorus ring. Post-ESD stenosis was defined when a standard endoscope could not be passed through the stenosis. We examined the incidence of post-ESD stenosis, its relationship with relevant factors, and the clinical course of post-ESD stenosis patients.

RESULTS

Post-ESD stenosis occurred with seven of 41 cardiac resections (17 %) and eight of 115 pyloric resections (7 %). Circumferential extent of the mucosal defect of > 3/4 and longitudinal extent > 5 cm were each significantly related to occurrence of post-ESD stenosis with both cardiac and pyloric resections. All 15 affected patients were successfully treated by endoscopic balloon dilation.

CONCLUSIONS

A circumferential extent of the mucosal defect of > 3/4 or longitudinal extent of > 5 cm in length were both demonstrated to be risk factors for post-ESD stenosis, in both cardiac and pyloric resections, and endoscopic balloon dilation was shown to be effective in treating post-ESD stenosis.

Sawtooth-control mechanism using toroidally propagating ion-cyclotron-resonance waves in tokamaks

The sawtooth control mechanism in plasmas employing off-axis toroidally propagating ion cyclotron resonance waves in tokamaks is reinvestigated. The radial drift excursion of energetic passing ions distributed asymmetrically in the velocity parallel to the magnetic field determines stability when the rational q=1 surface resides within a narrow region centered about the shifted fundamental cyclotron resonance.

Suprathermal electron studies in the TCV tokamak: design of a tomographic hard-x-ray spectrometer

Electron cyclotron resonance heating and electron cyclotron current drive, disruptive events, and sawtooth activity are all known to produce suprathermal electrons in fusion devices, motivating increasingly detailed studies of the generation and dynamics of this suprathermal population. Measurements have been performed in the past years in the tokamak a configuration variable (TCV) tokamak using a single pinhole hard-x-ray (HXR) camera and electron-cyclotron-emission radiometers, leading, in particular, to the identification of the crucial role of spatial transport in the physics of ECCD. The observation of a poloidal asymmetry in the emitted suprathermal bremsstrahlung radiation motivates the design of a proposed new tomographic HXR spectrometer reported in this paper. The design, which is based on a compact modified Soller collimator concept, is being aided by simulations of tomographic reconstruction. Quantitative criteria have been developed to optimize the design for the greatly variable shapes and positions of TCV plasmas.

Diagnostic techniques for measuring suprathermal electron dynamics in plasmas (invited)

Plasmas, both in the laboratory and in space, are often not in thermodynamic equilibrium, and the plasma electron distribution function is accordingly non-Maxwellian. Suprathermal electron tails can be generated by external drives, such as rf waves and electric fields, or internal ones, such as instabilities and magnetic reconnection. The variety and importance of the phenomena in which suprathermal electrons play a significant role explains an enduring interest in diagnostic techniques to investigate their properties and dynamics. X-ray bremsstrahlung emission has been studied in hot magnetized plasmas for well over two decades, flanked progressively by electron-cyclotron emission in geometries favoring the high-energy end of the distribution function (high-field-side, vertical, oblique emission), by electron-cyclotron absorption, by spectroscopic techniques, and at lower temperatures, by Langmuir probes and electrostatic analyzers. Continuous progress in detector technology and in measurement and analysis techniques, increasingly sophisticated layouts (multichannel and tomographic systems, imaging geometries), and highly controlled suprathermal generation methods (e.g., perturbative rf modulation) have all been brought to bear in recent years on an increasingly detailed, although far from complete, understanding of suprathermal electron dynamics.

Inductive current density perturbations to probe electron internal transport barriers in tokamaks

Improved electron energy confinement in tokamak plasmas, related to internal transport barriers, has been linked to nonmonotonic current density profiles. This is difficult to prove experimentally since usually the current profiles evolve continuously and current injection generally requires significant input power. New experiments are presented, in which the inductive current is used to generate positive and negative current density perturbations in the plasma center, with negligible input power. These results demonstrate unambiguously for the first time that the electron confinement can be modified significantly solely by perturbing the current density profile.

Rapid and localized electron internal-transport-barrier formation during shear inversion in fully noninductive TCV discharges

Clear evidence is reported for the first time of a rapid localized reduction of core electron energy diffusivity during the formation of an electron internal-transport barrier. The transition occurs rapidly (approximately = 3 ms), during a slow (approximately = 200 ms) self-inductive evolution of the magnetic shear. This crucial observation, and the correlation of the transition with the time and location of the magnetic shear reversal, lend support to models attributing the reduced transport to the local properties of a zero-shear region, in contrast to models predicting a gradual reduction due to a weak or negative shear.

Destabilization of fast-ion-induced long sawteeth by localized current drive in the JET tokamak

In a tokamak fusion reactor the energetic alpha particles will transiently stabilize the magnetohydrodynamic activity causing sawtooth oscillations. The crash events terminating long sawtooth free periods can provide seed islands for neoclassical tearing modes [Phys. Rev. Lett. 88, 105001 (2002)]]. To shorten the sawtooth periods localized current drive near the q=1 surface is a possibility. This Letter provides the first experimental evidence for the effectiveness of this method in the different physics regime associated with fast-ion-induced long sawteeth on the JET tokamak.

Circadian rhythm of hunger sensation in patients affected by dysthymic disorder

PURPOSE

The present study investigates the daily pattern of hunger sensation (HS), namely orexia, in patients affected by "Dysthymic Disorder" (DD). The aim is to detect whether there are changes in the circadian rhythm (CR) of HS, herein investigated as a "marker rhythm", that can reveal a dysfunction of the "circadian biological clock" (CBC). In such a circumstance, one could be authorised to suggest a resynchronizing therapy, via antidepressant chronizing drugs and/or morning exposure to bright light, as it is currently done in other types of human depression, having a documented dysfunction of the CBC.

MATERIALS AND METHODS

Volunteered with informed consent for the study 6 women (age = 34-56 years; mean BMI = 22.7 +/- 4.8 kg/m2) affected by DD. 10 clinically healthy women (CHW, age = 21-52 years; mean BMI = 24.0 +/- 0.5 kg/m2) were recruited as the controls. Both of the dysthymic patients (DP) and CHW were asked to compile the "orexigram", which was chronobiometrically analyzed by means of the 1. conventional statistical methods; 2. rhythmometric analysis for the CR; 3. spectral analysis for the harmonic components of the orexigram.

RESULTS

The DP were found to be characterized by a normal daily level of HS, with 1. the CR of the orectic stimulus to be preserved and well located in its acrophase, and 2. the spectrogram of the orexigram to be substantially well configured.

CONCLUSIONS

The above-cited results suggest that the DP show no alterations in the HS marker rhythm that can be taken as an evidence for declaring that the DD is not characterized by a relevant dysfunction of the CBC. Lacking in particular a phase-shift in HS marker rhythm, it can be argued that the DD is an affective disorder for which a resynchronizing therapy (exposure to bright light or pharmacological chronizers) seems to be "a priori" not indicated.

Circadian rhythm of hunger sensation in obese patients: effects of a short-term, moderately hypocaloric diet with a substitutive meal

This investigation deals with the circadian rhythm (CR) of hunger sensation (HS) in obese patients before and after a four-week, moderately hypocaloric diet with a substitutive meal. The study was performed on 25 non-diabetic obese patients (5 males and 20 females, mean age: 39.7 +/- 7, mean BMI: 27.9 1.4 Kg/m2), whose obesity was not associated with impaired glucose tolerance (IGT), binge eating, nor endocrine diseases. Their daily HS profile (orexigram) was analysed chronobiometrically. The moderately hypocaloric diet with a substitutive meal reduced the daily HS by about 10% by the fourth week. This reduction was apparently due to a tonic and amplitude modulation of the HS CR and was not accompanied by its disruption. No conclusions, however, could be drawn with regard to its orectic and clinical effects beyond four weeks.

[Daily sensation of hunger, before and after phototherapy, in subjects with depression-type seasonal affective disorder]

OBJECTIVE

The present study investigates the daily pattern of hunger sensation (HS) in women affected by "seasonal affective disorder--depression type" (SAD-DT), before and after therapeutic exposure to bright light (phototherapy). The aim is to detect whether there are disorders in daily HS during the active phase of the disease which can be normalized by an effective treatment of the depressive status, via phototherapy.

MATERIALS AND METHODS

Volunteered for the study 4 women affected by SAD-DT, 32-58 years old (BMI: 17.8-29.6 Kg/m2); 10 clinically healthy women (CHW), 21-52 years old (BMI: 23 e 25 Kg/m2) were recruited as controls. Both of the SAD-DT patients and CHW were asked to compile the "orexigram", which was chronobiometrically analyzed by means of the 1. conventional statistical methods; 2. rhythmometric analysis; 3. spectral analysis.

RESULTS

Before phototherapy, the SAD-DT patients were found to be characterized by an increased HS (hyperorexia), with the circadian rhythm of the orectic stimulus (OS) which is shifted in its acrophase, being prone to become "free running". After phototherapy, the SAD-DT patients were found to show a little insignificant decrease in their OS, which still maintains a delayed phase in its circadian rhythm as well as the tendency to be "free running".

CONCLUSIONS

The pre-treatment findings suggest that the SAD-DT patients are affected by hyperorexia associated with a "phase-shift" for the circadian periodicity of their HS, which is prone to the desynchronization. Such a dyschronism reinforces the hypothesis that the SAD-DT may be pathogenetically sustained by a mechanism of "phase-shift". The post-treatment findings suggest that both the hyperorexia and dyschronism of the orectic circadian rhythm are uncorrected by the phototherapy, even though the SAD-DT patients seem to have had beneficial antidepressive effects from the therapeutic intervention. The persisting dyschronism indicates that the photic stimulus is not able to completely reset the biological clock of the suprachiasmatic nuclei, at least for the phasic modulation of the HS circadian rhythm. The orexigram, thus, could be enclosed among the clinical tools in order to assess the complete efficacy of the phototherapy in SAD-DP patients.

[Identification of "presumptive risk" of hypertension crises with fractal interpolation of the 24-hour arterial pressure. III: study of normotensive subjects]

PURPOSE

The present study is devoted to identify the normotensive subjects who are at a "presumptive risk" (PR) for hypertensive crisis, by applying the "fractal interpolation" (FI) to blood pressure 24-h pattern.

MATERIALS AND METHODS

The investigation was performed on 109 ascertained cases of normotension, who underwent a non-invasive ambulatory monitoring of their 24-h blood pressure, by applying the FI to their daily mean arterial pressure.

RESULTS

The study showed that the PR for hypertensive crisis can be found in 12% out of the investigated normotensives. The proportion of such a risk is not significantly higher in non-dippers as compared to dippers. Vice versa, the prevalence of cases with a PR for hypertensive crisis was found to be significantly increased in normotensives who were deprived by a significant blood pressure circadian rhythm as compared to those who showed the blood pressure circadian rhythm to be preserved. Furthermore, the cases "at risk" were found to show a different spectrum for the harmonic formants which compose the complex harmonic structure of the blood pressure 24-h variability.

CONCLUSIONS

The PR for hypertensive crisis in normotensives seems to be increased by the loss of the blood pressure circadian rhythm, due to a change in the harmonic structure which confers the 24-h periodicity to the hemodynamic variable. This means that the abrogation of the blood pressure circadian rhythm in conditions of normotension promotes an adjunctive disorder for which the PR for hypertensive crisis is augmented.

Signature of turbulent zonal flows observed in the DIII-D tokamak

The spectrum of turbulent density fluctuations at long poloidal wavelengths in the edge plasma of the DIII-D tokamak peaks at nonzero radial wave number. The associated electric-potential fluctuations cause sheared E x B flows primarily in the poloidal direction. These zonal flows have been predicted by theory and are believed to regulate the overall level of turbulence and anomalous transport. This study provides the first indirect experimental identification of zonal flows.