Cryogenic pellet launcher adapted for controlling of tokamak plasma edge instabilities.

One of the main challenges posed recently on pellet launcher systems in fusion-oriented plasma physics is the control of the plasma edge region. Strong energy bursts ejected from the plasma due to edge localized modes (ELMs) can form a severe threat for in-vessel components but can be mitigated by sufficiently frequent triggering of the underlying instabilities using hydrogen isotope pellet injection. However, pellet injection systems developed mainly for the task of ELM control, keeping the unwanted pellet fueling minimized, are still missing. Here, we report on a novel system developed under the premise of its suitability for control and mitigation of plasma edge instabilities. The system is based on the blower gun principle and is capable of combining high repetition rates up to 143 Hz with low pellet velocities. Thus, the flexibility of the accessible injection geometry can be maximized and the pellet size kept low. As a result the new system allows for an enhancement in the tokamak operation as well as for more sophisticated experiments investigating the underlying physics of the plasma edge instabilities. This article reports on the design of the new system, its main operational characteristics as determined in extensive test bed runs, and also its first test at the tokamak experiment ASDEX Upgrade.

Significance of anticentromere antibody in idiopathic Raynaud's syndrome.

Fifty-eight patients with Raynaud's syndrome who had no evidence of definite underlying connective tissue disease had serum analyzed for the presence of anticentromere antibody using indirect immunofluorescence techniques on HEp-2 cell lines. Eighteen patients (31 percent) were anticentromere antibody-positive. The anticentromere antibody-positive group demonstrated significantly more frequent digital telangiectases, digital edema, elevated levels of immunoglobulins, and low C4 values. Photoplethysmography revealed significantly diminished blood flow in the anticentromere antibody-positive group. Capillary microscopy revealed significantly increased avascularity and number of dilated loops in the anticentromere antibody-positive group. Giant loops were seen exclusively in the anticentromere antibody-positive group. The clinical findings in the anticentromere antibody-positive group are suggestive of a transition to a connective tissue disease with features of the CREST syndrome.

Avalanche photodiode based detector for beam emission spectroscopy.

An avalanche photodiode based (APD) detector for the visible wavelength range was developed for low light level, high frequency beam emission spectroscopy (BES) experiments in fusion plasmas. This solid state detector has higher quantum efficiency than photomultiplier tubes, and unlike normal photodiodes, it has internal gain. This paper describes the developed detector as well as the noise model of the electronic circuit. By understanding the noise sources and the amplification process, the optimal amplifier and APD reverse voltage setting can be determined, where the signal-to-noise ratio is the highest for a given photon flux. The calculations are compared to the absolute calibration results of the implemented circuit. It was found that for a certain photon flux range, relevant for BES measurements (≈10(8)-10(10) photons/s), the new detector is superior to both photomultipliers and photodiodes, although it does not require cryogenic cooling of any component. The position of this photon flux window sensitively depends on the parameters of the actual experimental implementation (desired bandwidth, detector size, etc.) Several detector units based on these developments have been built and installed in various tokamaks. Some illustrative results are presented from the 8-channel trial BES system installed at Mega-Ampere Spherical Tokamak (MAST) and the 16-channel BES system installed at the Torus Experiment for Technology Oriented Research (TEXTOR).

Beam emission spectroscopy for density turbulence measurements on the MAST spherical tokamak.

Beam emission spectroscopy (BES) of the energetic deuterium (D(0)) heating beams can provide a means of characterizing the density turbulence in tokamak plasmas. First such measurements have been performed on the MAST spherical tokamak using a trial BES system, which shares the collection optics of the charge-exchange recombination spectroscopy system. This system, with eight spatial channels covering the outer part of the plasma cross section, uses avalanche photodiode detectors with custom preamplifiers to provide measurements at 1 MHz bandwidth with a spatial resolution of 4 cm. Simulations of the measurement, including the beam absorption and excitation, line-of-sight integration of the emission spectrum, and the characteristics of the detection system have been benchmarked against the measured absolute intensity of the Doppler shifted Dalpha fluorescence from the 50 keV beam. This gives confidence in predictions of the performance of a two-dimensional imaging BES system planned for MAST. Correlation techniques have also provided information on the characteristics of the density turbulence at the periphery of L-mode plasmas as well as density perturbations due to coherent magnetohydrodynamic activity at the edge of H-mode plasmas. Precursor oscillations of the density in the pedestal region to edge-localized modes occurring during H-mode plasmas with a single-null diverted magnetic configuration are also observable in the raw signals from the trial BES system.

Digital blood flow and nailfold capillary microscopy in Raynaud's phenomenon.

Digital blood flow was assessed by photoplethysmography, ultrasonic arterial flow tracing and measurement of systolic blood pressure, and compared to nailfold capillary microscopy in 20 normal controls, 16 patients with primary Raynaud's phenomenon, 40 with undifferentiated connective tissue disease and 30 with systemic sclerosis. All 4 measurements showed significant differences between controls, Raynaud's phenomenon and systemic sclerosis but only capillaroscopy (mean number of enlarged capillary loops and avascular score) was able to differentiate between primary Raynauds and undifferentiated connective tissue disease. Capillaroscopy (mean numbers of enlarged capillary loops) was the most sensitive (100%) and specific (81%) test with a positive predictive value of 90% for systemic sclerosis.

Nifedipine in the treatment of idiopathic Raynaud's syndrome.

Thirty-nine patients with idiopathic Raynaud's syndrome were randomized into a double-blind controlled trial comparing nifedipine 10 mg TID to placebo during the winter months between November, 1981 and March, 1983. The pills were doubled at 5 weeks in the absence of subjective improvement. Frequency and severity of vasospastic attacks were recorded in a diary. Over the 10-week treatment period, there was a 48.2% reduction in frequency of attacks in the nifedipine group compared to a 24.6% reduction in the placebo group (p less than 0.05). Treatment reduced the frequency of attacks by at least 30% in 10 of 15 patients. The severity of attacks was also significantly improved. Further, analysis suggests a trend towards diminished effectiveness over time. Side effects occurred in all patients taking nifedipine but were usually mild and well tolerated. Nifedipine is effective in reducing the frequency and severity of vasospastic attacks in idiopathic Raynaud's syndrome over a 10-week period.

Neurologic complications associated with gold therapy for rheumatoid arthritis.

Neurologic complications of gold are rare and include peripheral neuropathy, a Guillain-Barré-type syndrome, cranial nerve palsies and encephalopathy. Three cases of cranial neuropathy complicating chrysotherapy for rheumatoid arthritis are described. One also had a sensorimotor neuropathy associated with segmental demyelination and axonal degeneration, and another developed an encephalopathy which, on contrast enhanced computed tomographic scanning, showed reversible cerebral and cerebellar white matter lesions. Early recognition and prompt withdrawal of chrysotherapy are the mainstay of management of this lesser known complication.