Upgrades to the in-vessel calibration light source on JET

Since 2010, an in-vessel calibration light source (ICLS) has been used periodically on JET to calibrate a range of diagnostics at UV, visible, and IR wavelengths. During shutdowns, the ICLS (which is essentially an integrating sphere) is positioned within the vacuum vessel by the remote handling (RH) system. Following the 2013 calibration runs, several changes were made to improve the efficiency and quality of the calibrations. Among these was the replacement of a 20 m "umbilical" cable which carried power and other electrical signals through a vessel port to/from a control cubicle. A lightweight 2 m cable now plugs directly into a single connector on the RH manipulator system, greatly reducing the time required for deployment and improving operational flexibility; e.g., the vessel access "floor" no longer needs to be installed. This change also means the system would be compatible with calibrations after a high neutron-fluence period of operation. An on-board micro-spectrometer now allows for real-time verification of the emitted spectrum. Finally, new "baffles" were designed and installed within the integrating sphere itself, greatly improving the spectral radiance uniformity at non-normal viewing angles (necessary due to orientation uncertainties with the RH system).

Recent developments of in-vessel calibration of mid-IR cameras at JET

Recent improvements in software tools and methodology have allowed us to perform a more comprehensive in-vessel calibration for all mid-infrared camera systems at JET. A comparison of experimental methods to calculate the non-uniformity correction is described as well as the linearity for the different camera systems. Measurements of the temperature are assessed for the different diagnostics.

In-vessel calibration of the imaging diagnostics for the real-time protection of the JET ITER-like wall

The in situ absolute calibration of the JET real-time protection imaging system has been performed for the first time by means of radiometric light source placed inside the JET vessel and operated by remote handling. High accuracy of the calibration is confirmed by cross-validation of the near infrared (NIR) cameras against each other, with thermal IR cameras, and with the beryllium evaporator, which lead to successful protection of the JET first wall during the last campaign. The operation temperature ranges of NIR protection cameras for the materials used on JET are Be 650-1600 °C, W coating 600-1320 °C, and W 650-1500 °C.

X-ray crystal spectrometer upgrade for ITER-like wall experiments at JET

The high resolution X-Ray crystal spectrometer at the JET tokamak has been upgraded with the main goal of measuring the tungsten impurity concentration. This is important for understanding impurity accumulation in the plasma after installation of the JET ITER-like wall (main chamber: Be, divertor: W). This contribution provides details of the upgraded spectrometer with a focus on the aspects important for spectral analysis and plasma parameter calculation. In particular, we describe the determination of the spectrometer sensitivity: important for impurity concentration determination.

Enhanced visible and near-infrared capabilities of the JET mirror-linked divertor spectroscopy system

The mirror-linked divertor spectroscopy diagnostic on JET has been upgraded with a new visible and near-infrared grating and filtered spectroscopy system. New capabilities include extended near-infrared coverage up to 1875 nm, capturing the hydrogen Paschen series, as well as a 2 kHz frame rate filtered imaging camera system for fast measurements of impurity (Be II) and deuterium Dα, Dβ, Dγ line emission in the outer divertor. The expanded system provides unique capabilities for studying spatially resolved divertor plasma dynamics at near-ELM resolved timescales as well as a test bed for feasibility assessment of near-infrared spectroscopy.

A protection system for the JET ITER-like wall based on imaging diagnostics

The new JET ITER-like wall (made of beryllium and tungsten) is more fragile than the former carbon fiber composite wall and requires active protection to prevent excessive heat loads on the plasma facing components (PFC). Analog CCD cameras operating in the near infrared wavelength are used to measure surface temperature of the PFCs. Region of interest (ROI) analysis is performed in real time and the maximum temperature measured in each ROI is sent to the vessel thermal map. The protection of the ITER-like wall system started in October 2011 and has already successfully led to a safe landing of the plasma when hot spots were observed on the Be main chamber PFCs. Divertor protection is more of a challenge due to dust deposits that often generate false hot spots. In this contribution we describe the camera, data capture and real time processing systems. We discuss the calibration strategy for the temperature measurements with cross validation with thermal IR cameras and bi-color pyrometers. Most importantly, we demonstrate that a protection system based on CCD cameras can work and show examples of hot spot detections that stop the plasma pulse. The limits of such a design and the associated constraints on the operations are also presented.

Implementation of an in-vessel calibration light source for JET

An in-vessel calibration light source (ICLS) has been implemented for remote use during extended shutdown periods of the Joint European Torus (JET). The ICLS facilitated the in situ calibration of optical diagnostics, which previously were performed when the diagnostics were removed from JET. Since the ICLS is used to calibrate diagnostics over the entire, exact optical path as used when plasma discharge data are measured, the ICLS calibration implicitly accounts for any vignetting losses in the JET vessel viewports in addition to the vacuum window transmission. At least ten diagnostic systems have benefited from the ICLS during the extended ITER-like wall shutdown of 2009-2011. Examples of the use of the ICLS in JET are given.

Recent improvements of the JET lithium beam diagnostic

A 60 kV neutral lithium diagnostic beam probes the edge plasma of JET for the measurement of electron density profiles. This paper describes recent enhancements of the diagnostic setup, new procedures for calibration and protection measures for the lithium ion gun during massive gas puffs for disruption mitigation. New light splitting optics allow in parallel beam emission measurements with a new double entrance slit CCD spectrometer (spectrally resolved) and a new interference filter avalanche photodiode camera (fast density and fluctuation studies).

A new visible spectroscopy diagnostic for the JET ITER-like wall main chamber

In preparation for ITER, JET has been upgraded with a new ITER-like wall (ILW), whereby the main plasma facing components, previously of carbon, have been replaced by mainly Be in the main chamber and W in the divertor. As part of the many diagnostic enhancements, a new, survey, visible spectroscopy diagnostic has been installed for the characterization of the ILW. An array of eight lines-of-sight (LOS) view radially one of the two JET neutral beam shine through areas (W coated carbon fibre composite tiles) at the inner wall. In addition, one vertical LOS views the solid W tile at the outer divertor. The light emitted from the plasma is coupled to a series of compact overview spectrometers, with overall wavelength range of 380-960 nm and to one high resolution Echelle overview spectrometer covering the wavelength range 365-720 nm. The new survey diagnostic has been absolutely calibrated in situ by means of a radiometric light source placed inside the JET vessel in front of the whole optical path and operated by remote handling. The diagnostic is operated in every JET discharge, routinely monitoring photon fluxes from intrinsic and extrinsic impurities (e.g., Be, C, W, N, and Ne), molecules (e.g., BeD, D(2), ND) and main chamber and divertor recycling (typically Dα, Dβ, and Dγ). The paper presents a technical description of the diagnostic and first measurements during JET discharges.

Development of a mirror-based endoscope for divertor spectroscopy on JET with the new ITER-like wall (invited)

A new endoscope with optimised divertor view has been developed in order to survey and monitor the emission of specific impurities such as tungsten and the remaining carbon as well as beryllium in the tungsten divertor of JET after the implementation of the ITER-like wall in 2011. The endoscope is a prototype for testing an ITER relevant design concept based on reflective optics only. It may be subject to high neutron fluxes as expected in ITER. The operating wavelength range, from 390 nm to 2500 nm, allows the measurements of the emission of all expected impurities (W I, Be II, C I, C II, C III) with high optical transmittance (≥ 30% in the designed wavelength range) as well as high spatial resolution that is ≤ 2 mm at the object plane and ≤ 3 mm for the full depth of field (± 0.7 m). The new optical design includes options for in situ calibration of the endoscope transmittance during the experimental campaign, which allows the continuous tracing of possible transmittance degradation with time due to impurity deposition and erosion by fast neutral particles. In parallel to the new optical design, a new type of possibly ITER relevant shutter system based on pneumatic techniques has been developed and integrated into the endoscope head. The endoscope is equipped with four digital CCD cameras, each combined with two filter wheels for narrow band interference and neutral density filters. Additionally, two protection cameras in the λ > 0.95 μm range have been integrated in the optical design for the real time wall protection during the plasma operation of JET.

Enhancements to the JET poloidally scanning vacuum ultraviolet∕visible spectrometers

Enhancements to the JET poloidally scanning spectrometers are presented, which will aid the exploitation of the recently installed ITER-like wall in JET. They include the installation of visible filter∕photomultiplier tube assemblies and spectrometers and the replacement of large rotating mirrors in the JET vacuum with small oscillating mirrors outside. The upgrade has resulted in a more robust and reliable diagnostic than before, which is described. Drifts in the mirror angle reconstructed from quadrature encoder signals are found, a reference signal being required. The use of the small scanning mirrors necessitated the inclusion of focusing mirrors to maintain throughput into the vacuum ultraviolet spectrometers. The mirror design has taken account of the extreme sensitivity of the focusing to the grazing angle of incidence, an aspect of importance in the design of grazing incidence focusing components on future machines, such as ITER. The visible system has been absolutely calibrated using an in-vessel light source.

Scaling of spontaneous rotation with temperature and plasma current in tokamaks

Using theoretical arguments, a simple scaling law for the size of the intrinsic rotation observed in tokamaks in the absence of a momentum injection is found: The velocity generated in the core of a tokamak must be proportional to the ion temperature difference in the core divided by the plasma current, independent of the size of the device. The constant of proportionality is of the order of 10 km·s(-1)·MA·keV(-1). When the intrinsic rotation profile is hollow, i.e., it is countercurrent in the core of the tokamak and cocurrent in the edge, the scaling law presented in this Letter fits the data remarkably well for several tokamaks of vastly different size and heated by different mechanisms.

ITER-relevant calibration technique for soft x-ray spectrometer

The ITER-oriented JET research program brings new requirements for the low-Z impurity monitoring, in particular for the Be—the future main wall component of JET and ITER. Monitoring based on Bragg spectroscopy requires an absolute sensitivity calibration, which is challenging for large tokamaks. This paper describes both “component-by-component” and “continua” calibration methods used for the Be IV channel (75.9 Å) of the Bragg rotor spectrometer deployed on JET. The calibration techniques presented here rely on multiorder reflectivity calculations and measurements of continuum radiation emitted from helium plasmas. These offer excellent conditions for the absolute photon flux calibration due to their low level of impurities. It was found that the component-by-component method gives results that are four times higher than those obtained by means of the continua method. A better understanding of this discrepancy requires further investigations.

Experimental study of the ion critical-gradient length and stiffness level and the impact of rotation in the JET tokamak

Experiments were carried out in the JET tokamak to determine the critical ion temperature inverse gradient length (R/LTi=R|nablaTi|/Ti) for the onset of ion temperature gradient modes and the stiffness of Ti profiles with respect to deviations from the critical value. Threshold and stiffness have been compared with linear and nonlinear predictions of the gyrokinetic code GS2. Plasmas with higher values of toroidal rotation show a significant increase in R/LTi, which is found to be mainly due to a decrease of the stiffness level. This finding has implications on the extrapolation to future machines of present day results on the role of rotation on confinement.

Evidence of inward toroidal momentum convection in the JET tokamak

Experiments have been carried out on the Joint European Torus tokamak to determine the diffusive and convective momentum transport. Torque, injected by neutral beams, was modulated to create a periodic perturbation in the toroidal rotation velocity. Novel transport analysis shows the magnitude and profile shape of the momentum diffusivity are similar to those of the ion heat diffusivity. A significant inward momentum pinch, up to 20 m/s, has been found. Both results are consistent with gyrokinetic simulations. This evidence is complemented in plasmas with internal transport barriers.

Impact of calibration technique on measurement accuracy for the JET core charge-exchange system

The core charge-exchange diagnostic at the Joint European Torus (JET) provides measurements of the impurity ion temperature T(i), toroidal velocity V(phi), and impurity ion densities n(imp), across the whole minor radius. A contribution to the uncertainty of the measured quantities is the error resulting from the multi-Gaussian fit and photon statistics, usually quoted for each measured data. Absolute intensity calibration and especially alignment of the viewing directions can introduce an important systematic error. The technique adopted at JET to reduce this systematic contribution to the error is presented in this paper. The error in T(i), V(phi), and n(imp) is then discussed depending on their use.

A proposed in-vessel calibration light source for the Joint European Torus

An in-vessel calibration light source (ICLS) is proposed for use during extended shutdown periods of the Joint European Torus (JET). The ICLS is primarily a 12 in. integrating sphere (4 in. opening) with four lamps (of known radiance), which can be positioned inside the JET vacuum vessel via the remote handling arm during interventions in the JET operating schedule. This will facilitate the in situ calibration of optical diagnostics, which rely on absolute light intensity measurements currently made when the diagnostics are removed from JET. The ICLS could ultimately reduce/remove the mechanical stresses associated with the repositioning of diagnostics for calibration purposes. At least 10 diagnostic systems (approximately 20 diagnostic subsystems) could benefit from the ICLS; in some instances the ICLS provides the only viable absolute-calibration strategy. Moreover, the ICLS will be a broad-spectrum white light source, enabling intensity calibrations at all visible wavelengths. A secondary benefit of the ICLS is in its use as an illumination source for making measurements of the reflectance (over a broad spectral range and at multiple angles) from the tiles lining the JET vacuum vessel. During the ITER-like wall intervention new Be, C, and W tiles will be installed in JET and their reflectance measured. Measurements made in subsequent JET interventions will provide data on the effect of high-temperature plasma operation on the reflectance of these tiles.

Modeling the effect of reflection from metallic walls on spectroscopic measurements

A modification of JET is presently being prepared to bring operational experience with ITER-like first wall (Be) and divertor (W) materials, geometry and plasma parameters. Reflectivity measurements of JET sample tiles have been performed and the data are used within a simplified model of the JET and ITER vessels to predict additional contributions to quantitative spectroscopic measurements. The most general method to characterize reflectivity is the bidirectional reflection distribution function (BRDF). For extended sources however, such as bremsstrahlung and edge emission of fuel and intrinsic impurities, the results obtained in the modeling are almost as accurate if the total reflectivity with ideal Lambertian angular dependence is used. This is in contrast to the experience in other communities, such as optical design, lighting design, or rendering who deal mostly with pointlike light sources. This result is so far based on a very limited set of measurements and will be reassessed when more detailed BRDF measurements of JET tiles have been made. If it is true it offers the possibility of in situ monitoring of the reflectivity of selected parts of the wall during exposure to plasma operation, while remeasurement of the BRDF is performed during interventions. For a closed vessel structure such as ITER, it is important to consider multiple reflections. This makes it more important to represent the whole of the vessel reasonably accurately in the model, which on the other hand is easier to achieve than for the more complex internal structure of JET. In both cases the dominant contribution is from the first reflection, and a detailed model of the areas intersected by lines of sight of diagnostic interest is required.

Probing internal transport barriers with heat pulses in JET

The first electron temperature modulation experiments in plasmas characterized by strong and long-lasting electron and ion internal transport barriers (ITB) have been performed in JET using ion cyclotron resonance heating in mode conversion scheme. The ITB is shown to be a well localized narrow layer with low heat diffusivity, characterized by subcritical transport and loss of stiffness. In addition, results from cold pulse propagation experiments suggest a second order transition process for ITB formation.

Poloidal rotation dynamics, radial electric field, and neoclassical theory in the jet internal-transport-barrier region

Results from the first measurements of a core plasma poloidal rotation velocity (upsilontheta) across internal transport barriers (ITB) on JET are presented. The spatial and temporal evolution of the ITB can be followed along with the upsilontheta radial profiles, providing a very clear link between the location of the steepest region of the ion temperature gradient and localized spin-up of upsilontheta. The upsilontheta measurements are an order of magnitude higher than the neoclassical predictions for thermal particles in the ITB region, contrary to the close agreement found between the determined and predicted particle and heat transport coefficients [K.-D. Zastrow, Plasma Phys. Controlled Fusion 46, B255 (2004)]. These results have significant implications for the understanding of transport barrier dynamics due to their large impact on the measured radial electric field profile.

Plasma rotation induced by directed waves in the ion-cyclotron range of frequencies

Changes of the toroidal plasma rotation induced by directed waves in the ion-cyclotron range of frequencies (ICRF) have been identified experimentally for the first time on the JET tokamak. The momentum carried by the waves is initially absorbed by fast resonating ions, which subsequently transfer it to the bulk plasma. Thus, the results provide evidence for the influence of ICRF heated fast ions on plasma rotation.

JET quasistationary internal-transport-barrier operation with active control of the pressure profile

Quasistationary operation has been achieved on the Joint European Torus tokamak in internal-transport-barrier (ITB) scenarios, with the discharge time limited only by plant constraints. Full current drive was obtained over all the high performance phase by using lower hybrid current drive. For the first time feedback control on the total pressure and on the electron temperature profile was implemented by using, respectively, the neutral beams and the ion-cyclotron waves. Although impurity accumulation could be a problem in steady state ITBs, these experiments bring some elements to answer to it.

Observation of zero current density in the core of jet discharges with lower hybrid heating and current drive

Simultaneous current ramping and application of lower hybrid heating and current drive (LHCD) have produced a region with zero current density within measurement errors in the core ( r/a< or =0.2) of JET tokamak optimized shear discharges. The reduction of core current density is consistent with a simple physical explanation and numerical simulations of radial current diffusion including the effects of LHCD. However, the core current density is clamped at zero, indicating the existence of a physical mechanism which prevents it from becoming negative.

Suppression of plasma turbulence during optimized shear configurations in JET

Correlation of density turbulence suppression and reduced plasma transport is observed in the internal transport barrier (ITB) region of JET tokamak discharges with optimized magnetic shear. The suppression occurs in two stages. First, low frequency turbulence and ion transport are reduced across the plasma core by a toroidal velocity shear generated by intense auxiliary heating. Then with the ITB formation, high frequency turbulence and electron transport are reduced locally within the steep pressure gradient region of the ITB.

[Vaccinations for travelers in Germany--1971-1990 adverse vaccine effects caused by travel vaccinations]

Adequate prophylaxis should always be the order of the day if anyone plans to visit a foreign country where he may be at risk of being exposed to infectious diseases. Numerous protective vaccinations are available for this purpose in Germany. Basing on the incidence of recorded damage caused by such vaccinations 1971-1990 we must conclude that the risk of damage to health as a result of such vaccinations is very remote. Hence, the protective vaccinations carried out in Germany are of vital importance in respect of keeping down the number of infections.

[Nosocomial infection as the cause of death]

Hospital-acquired infections are a worldwide problem especially in hospitals for the treatment of acute cases. These infections are among the leading causes of death. Certificates of death of 4656 patients who died in hospitals were analysed. Of these, 564 deaths were caused by nosocomial infections (12.1%). It was estimated that annually around 40,000 deaths in the Federal Republic of Germany are attributable to infections acquired in the hospital.

[Malaria importation into Germany in 1989/90]

Malaria was in 1989/90 the most important imported disease in Germany. Most of all cases were imported by German tourists (about 75%). Africa was the most prominently represented geographic region (about 75%). Kenia and Ghana represented there the biggest share. About 33% of all patients had not done a sufficient prophylaxis against malaria. An adequate prophylaxis against malaria taking into consideration the recommendations for medicaments for different geographical areas is imperative before the number of importations of malaria into Germany can be reduced.

[Importation of leprosy into Germany 1981-1992]

73 cases of leprosy were imported into the Federal Republic of Germany between 1981 and 1992. A large number of imported cases came from Asian countries (32 cases). 61 patients were male, 12 female. 30 patients had the tuberculoid type of leprosy, 29 the lepromatous. From the total of 73 leprosy patients 7 were German nationals. Early diagnosis and efficient treatment play an important role in ensuring a good prognosis.

[Data on the status of the organizational structures of hospital hygiene in Germany. II--Rehabilitation clinics, psychiatric hospitals]

The results of an inquiry about the personnel and organisation of the hospital hygiene in 657 German rehabilitation centres and psychiatric hospitals demonstrate that 24% of these hospitals have a hospital epidemiologist, 44% have infection control nurses and 74% infection control physicians. Infection control committees are present in 64% of these hospitals. 78% of the hospitals use the guideline of the Federal Public Health Office "On the Identification, Prevention and Control of Hospital Infections" as a basis for all decisions on hospital hygiene.

[Outbreaks of food-borne infections and microbe-induced poisonings in West Germany 1991]

Analysis of the outbreaks of food-borne infections and intoxications with a total of 2,610 patients in 1991 demonstrates that these cases were caused in 67.4% by Salmonella species. Eggs were mainly responsible for the outbreaks, whereas poor kitchen hygiene played also a main part in promoting disease.

[Infusion technique as a significant aspect of public health monitoring of hospitals--a case report]

An outbreak of septicaemia caused by Acinetobacter involved eight patients of an ICU within a period of 6 days. All patients were treated with heparin infusions. We isolated Acinetobacter from the blood of all these patients and from a mixture of heparin and isotonic saline solution. As underlying causal event a combination of risk factors and mistakes is suggested. These may include the multiple reuse of infusion bottles by different users, the reuse of perfusor injectors, and underscores the necessity of strict hygienic precautions. This event points to a disseminated risk factor that should be considered within the frame of control systems for hospitals.

[Malaria travel disease--importation to Germany 1988]

Malaria continues to be an important travellers' disease in Germany. In 1988 885 cases of malaria were imported into the Federal Republic of Germany. German tourists to far-away countries represented the biggest share (about 80%). Africa was the most prominently represented continent with 76%. Differentiation according to species of pathogens showed that 68% of the diseases were caused by Plasmodium falciparum. 11 patients died of malaria in 1988, in all cases due to P. falciparum infection. The mortality of the patients increases with age. Only in 5 of 11 persons who died there had been a sufficient prophylaxis against malaria, at least as far as the anamnesis revealed. Careful planning of sufficient prophylaxis taking into consideration the partly very marked resistance to a multitude of drugs, as well as competent medical advice to would-be travellers, are imperative before the number of malaria imports into Germany can be reduced.

[Results on the status of the organizational structures in hospital hygiene in Germany--I. Overall evaluation with special reference to acute hospitals]

The results of an inquiry about the hospital hygiene in 2034 German hospitals demonstrate, that 35% of all hospitals have a hospital epidemiologist, 66% have infection control nurses and 86% infection control physicians. Infection control committees are present in 81% of German hospitals. 88% of all hospitals use the guideline of the Federal Public Health Office "On the Identification, Prevention and Control of Hospital Infections" as a basis for all decisions on hospital hygiene.

[Status of the guideline for hospital hygiene and prevention of infection of the Federal Public Health Office]

1976 the Federal health Office published the guideline "Erkennung, Verhütung und Bekämpfung von Krankenhausinfektionen". The guideline defines the levels of hospital hygiene and gives important directions to physicians and nursing staff. The guideline has been increasingly incorporated in regulations.