Notizen: Particle orbits for a linear magnetic cusp configuration, characteristic for magnetic reconnection, are analyzed within the guiding center approximation. A class of particle orbits encircling the magnetic X-line is identified and the orbit phase space partition is obtained and characterized as a function of dimensionless parameters controlling the orbit topology. The large majority of particles are found to be trapped in the direction of the X-line implying large neoclassical corrections to the plasma resistivity. This may be the key in explaining the high rates of collisionless magnetic reconnection observed in nature. © 2001 American Institute of Physics.

Notizen: Fast collisionless magnetic reconnection is driven and observed in a toroidal magnetic cusp. For low values of the toroidal (guide) magnetic field, reconnection occurs without the formation of a macroscopic current channel. In the absence of a current channel, the measured plasma potential and poloidal flows are consistent with predictions based upon single particle theory. Only for large values of the toroidal magnetic field compared to cusp poloidal field is a current channel present. Also in this case single particle orbit theory provides a good description of the anomalous resistivity observed experimentally. © 2001 American Institute of Physics.

Notizen: The onset of chaotic ion dynamics in electrostatic waves is investigated in a linear magnetized plasma. The existence of a threshold for heating in agreement with the predictions of single particle Hamiltonian theories and the fast time scale for velocity space diffusion are observed in the experiment. Measurements of test-particle dynamics indicate an exponential separation of initially close ion trajectories for amplitudes above the heating threshold. Ion orbits in the different wave–particle interaction regimes are inferred using an optical tagging diagnostic method, which provides the two point correlation function in phase space.

Notizen: Experiments designed for generating internal transport barriers in the plasmas of the Joint European Torus [JET, P. H. Rebut et al., Proceedings of the 10th International Conference, Plasma Physics and Controlled Nuclear Fusion, London (International Atomic Energy Agency, Vienna, 1985), Vol. I, p. 11] reveal cascades of Alfvén perturbations with predominantly upward frequency sweeping. These experiments are characterized by a hollow plasma current profile, created by lower hybrid heating and current drive before the main heating power phase. The cascades are driven by ions accelerated with ion cyclotron resonance heating (ICRH). Each cascade consists of many modes with different toroidal mode numbers and different frequencies. The toroidal mode numbers vary from n=1 to n=6. The frequency starts from 20 to 90 kHz and increases up to the frequency range of toroidal Alfvén eigenmodes. In the framework of ideal magnetohydrodynamics (MHD) model, a close correlation is found between the time evolution of the Alfvén cascades and the evolution of the Alfvén continuum frequency at the point of zero magnetic shear. This correlation facilitates the study of the time evolution of both the Alfvén continuum and the safety factor, q(r), at the point of zero magnetic shear and makes it possible to use Alfvén spectroscopy for studying q(r). Modeling shows that the Alfvén cascade occurs when the Alfvén continuum frequency has a maximum at the zero shear point. Interpretation of the Alfvén cascades is given in terms of a novel-type of energetic particle mode localized at the point where q(r) has a minimum. This interpretation explains the key experimental observations: simultaneous generation of many modes, preferred direction of frequency sweeping, and the absence of strong continuum damping. © 2002 American Institute of Physics.

Notizen: Wave-particle interaction phenomena in the Alfvén Eigenmode (AE) frequency range are investigated at the Joint European Torus [P. H. Rebut and B. E. Keen, Fusion Technol. 11, 13 (1987)] using active and passive diagnostic methods. Fast particles are generated by neutral beam injection, ion cyclotron resonance heating, and fusion reactions. External antennas are used to excite stable AEs and measure fast particle drive and damping separately. Comparisons with numerical calculations lead to an identification of the different damping mechanisms. The use of the active AE diagnostic system to generate control signals based on the proximity to marginal stability limits for AE and low-frequency magnetohydrodynamic (MHD) modes is explored. Signatures of the different nonlinear regimes of fast particle driven AE instabilities predicted by theory are found in the measured spectra. The diagnostic use of AE measurements to get information both on the plasma bulk and the fast particle distribution is assessed. © 2000 American Institute of Physics.

Notizen: The first measurements of plasma parameters in a discharge created by electron cyclotron resonance heating in a toroidal cusp configuration are discussed along with the predictions of particle orbits and confinement from a guiding center model. The configuration appears to be suitable for basic investigations of the physics of plasma flows and instabilities around a magnetic null, hence of magnetic reconnection. © 2000 American Institute of Physics.

Notizen: The design and operation of a new vaporizing assembly used for Q-plasma sources are described in this article. The vaporizing system, consisting of two ovens and an effuser, is used to vaporize and direct atoms onto a hot ionizer plate. The hot plate, which may be of tantalum, tungsten, or rhenium, singly ionizes the atoms on contact. The main advantages of this new assembly, compared to previous designs, are the production of higher plasma densities and the control of the radial plasma profile. The heaters of the two atomic beam ovens are independently controlled and monitored so that the gradients of the radial plasma profile can be modified. Plasma production with two ion species can also be performed.

Notizen: A modulated high frequency wave is used to remotely excite low frequency oscillations in a linear, strongly magnetized plasma column. An electromagnetic wave is launched as an extraordinary mode across the plasma by an external waveguide in the upper-hybrid frequency regime f≈fUH≈fce≈8 GHz, with P≤2 W. By frequency modulating (at fFM≈1–60 kHz, with fci(approximately-equal-to)30 kHz) the pump wave, the resonant layer is swept radially across the profile and perpendicularly to the field lines at f=fFM. The resulting radial oscillation of the electron linear and nonlinear pressure can be considered to act as a source term for the ion wave. A localized virtual antenna is thereby created inside the plasma. Measurements of the ion dielectric response (interferograms and perturbed distribution functions) via laser-induced fluorescence identify the two branches (forward, or ion-acoustic-like, and backward, or Bernstein, modes) of the electrostatic dispersion relation in the ion cyclotron frequency range. By changing the modulation bandwidth, and thus the spatial excursion of the oscillating resonant layer, a control on the perpendicular wavelength of the excited mode can be exerted. In particular, the possibility of selective excitation of the ion Bernstein wave is demonstrated experimentally.

Notizen: There are few data on the use of the 13C-aminopyrine breath test to evaluate the severity of disease in patients with hepatitis C virus-related chronic liver disease, although these patients represent one of the most important problems in clinical hepatology.〈section xml:id="abs1-2"〉〈title type="main"〉Aims:To compare 13C-aminopyrine breath test results of patients with hepatitis C virus-related chronic hepatitis and Child–Pugh class A cirrhosis with those of normal subjects, and to evaluate different methods of expressing 13C-aminopyrine breath test results.〈section xml:id="abs1-3"〉〈title type="main"〉Methods:Twenty-four patients with hepatitis C virus-related chronic hepatitis and 17 patients with Child–Pugh class A cirrhosis underwent 13C-aminopyrine breath test. Breath samples were collected every 30 min up to 2 h after 13C-aminopyrine administration. 13C-Aminopyrine breath test results were expressed as a percentage of the administered dose of 13C recovered per hour (% dose/h) and the cumulative percentage of administered dose of 13C recovered over time (% dose cum). Nineteen healthy subjects served as controls. Patients with hepatitis C virus-related chronic hepatitis were divided into subgroups on the basis of histological staging and grading.〈section xml:id="abs1-4"〉〈title type="main"〉Results:The 13C-aminopyrine breath test result (% dose/h) at 30 min was significantly different among the three subgroups of subjects (normal subjects, 11.5 ± 3.5; chronic hepatitis patients, 8.1 ± 4.1; cirrhosis patients, 5.0 ± 3.1; P 〈 0.0005). Moreover, the differences between chronic hepatitis and cirrhosis patients were statistically significant (P 〈 0.03). The fibrosis score showed a significant inverse correlation with the 13C-aminopyrine breath test result (% dose/h) at 30 min (rs=− 0.409, P=0.05). The 13C-aminopyrine breath test result (% dose/h) at 30 min also allowed normal subjects and chronic hepatitis patients with low (≤ 2) or high (〉 2) fibrosis scores to be distinguished. The 13C-aminopyrine breath test results (% dose cum) at 30, 60 and 90 min allowed discrimination between normal subjects and chronic hepatitis and cirrhosis patients. The 13C-aminopyrine breath test result (% dose cum) was also able to distinguish between normal subjects and chronic hepatitis patients with high but not low fibrosis scores. Both 13C-aminopyrine breath test results (% dose/h and % dose cum) at 120 min allowed the differentiation between normal subjects and chronic hepatitis patients with high (≥ 6) necro-inflammatory activity.〈section xml:id="abs1-5"〉〈title type="main"〉Conclusions:In patients with hepatitis C virus-related chronic liver disease, the 13C-aminopyrine breath test proved to be safe and easy to perform, and was able to evaluate different degrees of liver function impairment which were partly correlated to clinical and histological evaluation. In future studies, 13C-aminopyrine breath test results should be expressed in a standardized fashion to permit comparison.

Notizen: Helicobacter pylori gastric infection has been associated with various digestive and extra-digestive diseases. The systemic influence of gastric H. pylori infection seems to be mediated by the release of various cytokines. In liver disease, bacterial infections have been associated with the impairment of liver metabolic function.〈section xml:id="abs1-2"〉〈title type="main"〉Aims:To evaluate the influence of H. pylori infection on liver function as assessed by means of the monoethylglycinexylidide test, which depends upon liver blood flow and cytochrome P-450 activity, and the 13C-galactose breath test, which depends on cytosolic enzymatic activity and is correlated with hepatic functional mass. Moreover, to evaluate whether H. pylori-associated modifications of liver function may be related to tumour necrosis factor-α serum levels.〈section xml:id="abs1-3"〉〈title type="main"〉Patients and methods:Thirty-five patients with liver cirrhosis of various aetiologies, who underwent monoethylglycinexylidide and 13C-galactose breath tests, were retrospectively evaluated for H. pylori infection by means of anti-H. pylori immunoglobulin G. The main clinical, biochemical and functional characteristics of the patients as well as their tumour necrosis factor-α serum levels were then analysed on the basis of the presence of H. pylori infection.〈section xml:id="abs1-4"〉〈title type="main"〉Results:Twenty-one patients tested positive for H. pylori infection (60%), and 11 tested negative (31.4%). No clinical or biochemical differences were observed between H. pylori-infected and non-infected patients. H. pylori infection showed no difference in distribution according to Child–Pugh classes (A, 55%; B and C, 67%). The monoethylglycinexylidide test results were significantly lower at each sampling time in H. pylori-positive patients compared to H. pylori-negative patients (MEGX15, P=0.027; MEGX30, P=0.014; MEGX60, P=0.028), while 13C-galactose breath test showed no significant differences considering both cumulative percentage dose and percentage dose/h. The median tumour necrosis factor-α serum levels were no different between H. pylori-positive (16.1 pg/mL, 95% confidence interval, 8.7–28.7) and H. pylori-negative (12.3 pg/mL, 95% confidence interval, 8.7–23.4) patients.〈section xml:id="abs1-5"〉〈title type="main"〉Conclusions:In cirrhotic patients, H. pylori infection seems to selectively affect cytochrome P-450 liver activity, while hepatic functional mass does not seem to be impaired. Tumour necrosis factor-α does not seem to be the mediator of this impairment. Further studies are needed to evaluate the impact of H. pylori eradication on parameters of liver function.