Maximum Beta Research Articles

Improved confinement in TEXTOR

A new regime of enhanced confinement (I-mode) is found in plasmas with circular cross-sections in the pump limiter tokamak TEXTOR with boronized walls. This regime is obtained with three types of auxiliary heating, namely NBI co-injection, NBI counter-injection+ICRH and NBI co-injection+NBI counter-injection, and has many similarities with the H-mode regime obtained in divertor tokamaks. The energy confinement times obtained in these discharges scale as favourably as those in stationary H-mode discharges with edge localized modes. A detailed analysis of the scaling of the confinement time with plasma current, heating power and plasma density is presented. Characteristic electron density and temperature profiles are observed, with large central values and well developed edge pedestals. They are compared with those found in H-mode discharges and supershots. A poloidal beta limit of 1.6 is found in the I-mode discharges of TEXTOR. The maximum toroidal beta values obtained reach nearly 1%, i.e. 0.7 times the Troyon limit in TEXTOR. I-mode confinement is always linked with low recycling and absence of MHD activity. If these conditions are not met. L-mode scaling is retrieved. MHD activity, which is more likely to occur at low plasma densities and currents, can cause a sudden drop to L-mode scaling. So far, no transition from the L-mode scaling to the I-mode scaling has been observed

Circulating interleukin-1 beta and tumor necrosis factor-alpha concentrations after burn injury in humans.

To measure plasma interleukin-1 beta (IL-1 beta) and tumor necrosis factor-alpha (TNF alpha) concentrations after burn injury and to determine if these concentrations relate to clinical status. Prospective assessment. Hospital burn unit. Thirty-one patients with second- or third-degree burns, covering 10% to 95% of body surface area. Initial concentrations of IL-1 beta were increased (mean 188 +/- 31 pg/mL), and the concentrations for each patient correlated with body temperature at the time of the blood sample (rho = 0.51, p < .015) (rho is a nonparametric statistical measure; a nonparametric analysis is mandatory for data that is categorical [Acute Physiology and Chronic Health Evaluation, APACHE, scores] and data that are not normally distributed [IL-1 beta and tumor necrosis factor, TNF, data]). Mean TNF alpha concentrations were initially 264 +/- 132 pg/mL, and these concentrations were positively related to body temperature (rho = 0.41, p < .05) and inversely related to the total WBC count (rho = -0.45, p < .025). Through the course of hospitalization, plasma cytokine levels fluctuated, but transient increases (sometimes into the nanogram/mL range) did not consistently correspond to changes in clinical signs or severity of illness, as determined by APACHE II scores. The maximum plasma cytokine levels in any patient were not related to age, but maximum IL-1 beta concentrations were inversely related to burn size (rho = -0.46, p < .015). The final IL-1 beta concentrations measured in the patients who died (n = 7) were significantly less than measurements in surviving patients matched for burn size and age taken at approximately the same time after admission. These results indicate that early after burn injury there is a correspondence of IL-1 beta and TNF alpha with certain host responses, but these correlations disappear with the progression of illness. In general, IL-1 beta and TNF alpha appear to be poor indicators of prognosis during burn injury; however, the association of mortality with low circulating IL-1 beta values supports the concept of IL-1 beta as being an essential mediator of host defenses.

Ideal MHD stability of internal kinks in circular and shaped tokamaks

Stability limits for the internal kink mode are calculated for tokamaks with different current profiles and plasma cross-sections using ideal magnetohydrodynamics (MHD). The maximum stable poloidal beta at the q=1 surface (βp) is sensitive to the current profile, but for circular cross-sections it is typically between 0.1 and 0.2. Large aspect ratio theory gives similar predictions when the appropriate boundary conditions are applied at the plasma-vacuum surface. It is found that the internal kink is significantly destabilized by ellipticity. For JET geometry, the ideal MHD limit in βp is typically between 0.03 and 0.1, and arbitrarily low limits can result if the shear is reduced at the q=1 surface. A large aspect ratio expansion of the Mercier criterion retaining the effects of ellipticity and triangularity is used to illustrate the destabilizing influence of ellipticity

Regional differences of ?1- and ?2-adrenoceptor-mediated functions in feline heart

The effects of (-)-adrenaline and (-)-noradrenaline were studied on isolated preparations of kitten heart. To define the contribution of beta 1-adrenoceptors (beta 1AR) and beta 2-adrenoceptors (beta 2AR) we used as tools the highly beta 1AR-selective antagonist CGP 20,712 A and non-linear analysis of antagonism. The beta 2AR-mediated responses to the catecholamines, disclosed by CGP 20,712 A, were verified by blockade with the beta 2AR-selective ICI 118,551. The relative density and contribution of beta 1AR and beta 2AR to (-)-adrenaline- and (-)-noradrenaline-induced adenylyl cyclase stimulation was also estimated in right ventricular membranes. 1. In the sinoatrial pacemaker (-)-adrenaline caused positive chronotropic effects through both beta 1AR and beta 2AR while (-)-noradrenaline does so predominantly through beta 1AR. During beta 1AR blockade (-)-adrenaline did cause the same maximum effects through beta 2AR as (-)-noradrenaline did through beta 1AR. 2. In left atria (-)-adrenaline caused positive inotropic effects predominantly through beta 1AR. CGP 20,712 A also uncovered a beta 2AR component at high (-)-adrenaline concentrations comprising one third of the maximum beta 1AR-mediated response. 3. Receptor binding assays revealed that 80% of right ventricular beta AR were beta 1AR and 20% beta 2AR. Consistent with this finding, around 80% of the adenylyl cyclase stimulation by both (-)-noradrenaline and (-)-adrenaline was mediated through beta 1AR, around 20% through beta 2AR. The positive inotropic effects of (-)-noradrenaline appeared to be nearly exclusively mediated through beta 1AR in right ventricular papillary muscles. 4. The positive inotropic effects of (-)-adrenaline were quite variable with regard to beta 1AR and beta 2AR in right ventricular papillary muscles. Although beta 1AR-mediated effects are predominant in many muscles with only a small contribution of beta 2AR, in some muscles beta 2AR mediated around 50% of the maximum effect elicited through beta 1AR. In 3 out of 17 muscles beta 2AR mediated the same maximum effect of (-)-adrenaline as beta 1AR. 5. On occasion, we found marked beta AR heterogeneity amongst two muscles from the same right ventricle. One muscle only exhibited beta 1AR-mediated effects of (-)-adrenaline whereas in the other muscle maximal effects could be elicited through beta 2AR.(ABSTRACT TRUNCATED AT 400 WORDS)

Application of laser-produced plasmas to a heliotron/torsatron device, SHATLET-M.

An l=2, m=12 modular-coil heliotron/torsatron device, SHATLET-M, has been filled with plasmas produced by the irradiation of an intense pulsed CO2 laser beam on a tiny freefalling deutrium pellet. Plasma parameters, namely, line-integrated density, spatially averaged beta value, their decay constants, and plasma currents are measured. The size of the deutrium pellets is in typical cases 0.2mm in diameter and 1mm in length. The pellets are irradiated by a CO2 laser pulse with a total energy of about 300J and a pulse width of 1μs. Within 10 μs, a toroidal plasma is rapidly formed that has a small ititial toroidal plasma current with a peak value of less than 150A. This initial toroidal current is rapidly damped in about 20μs leaving a net-currentfree toroidal plasma for another 200-400 μs. The diamagnetic loop measurement shows that the initial peak value of spatially averaged beta which may contain non-thermal components ranges from 3 to 6%, where the average densety is about 1×1013cm-3. The density increases in proportion to B1.8±0.2 (B is the magnetic field strength.), and the maximum averaged beta increases about in proportion to B. The decay time constants of the averaged beta values are less than about 100μs and no disruptive instability has been observed within these periods.

Pharmacokinetic and Pharmacodynamic Comparison of Metoprolol CR/ZOK Once Daily with Conventional Tablets Once Daily and in Divided Doses

Four studies of identical design, each on 18 young healthy subjects, were undertaken to study the pharmacokinetics and beta 1-receptor blockade at steady state after a once daily dose (od) of 100, 200, 300 and 400 mg of metoprolol CR/ZOK (a new controlled release preparation) in comparison with 100 mg dosages (od, bid, tid and qid, respectively) of conventional metoprolol tablets (CT). All studies were of randomized three-way crossover design with 7-day double-blind treatment periods separated by 7-day single-blind washout periods. A number of predose plasma concentrations and assessments of beta 1-blockade were made during the study and a full pharmacokinetic and pharmacodynamic study was performed on day 7. The maximal plasma concentration, Cmax, was significantly lower after metoprolol CR/ZOK compared to CT after all doses--the most pronounced difference being observed after the 100 mg dose when both preparations were given once daily (145 nmol/L vs 606 nmol/L) and the least difference after the 400 mg dose when metoprolol CT was given every 6 hours (837 nmol/L vs 1111 nmol/L). The maximal plasma concentration occurred later after metoprolol CR/ZOK than CT in all studies (median 2.5-4.1 hours vs 1.0-1.2 hours). The trough plasma concentration, Cmin, was significantly higher after 100 mg metoprolol CR/ZOK compared to CT dosed once daily; CminS were comparable between the two preparations in the 200 mg and 300 mg studies and lower after metoprolol CR/ZOK in the 400 mg study (278 nmol/L vs 469 nmol/L). In all four studies the AUCs were significantly lower after metoprolol CR/ZOK compared to CT with the mean relative bioavailability being approximately similar (73-84%). All metoprolol treatments produced a statistically significant beta 1-blockade (measured as percent reduction of exercise induced tachycardia) throughout the whole day compared to placebo except in the 100 mg study where the effect of once daily CT did not differ from placebo during the last 6 hours. Consequently, a significantly higher beta 1-blockade was observed after metoprolol CR/ZOK compared to CT in this latter period. The maximum beta 1-blockade (Emax) after CR/ZOK 100 mg was significantly lower than after CT 100 mg once daily (12.6% vs 23.3%) but when CT was given in divided doses from 200 to 400 mg daily, Emax did not differ between the two formulations. Once daily administration of 100 mg of both products resulted in a significantly higher beta 1-blockade 24 hours after dosing with CR/ZOK compared to CT, but when CT was taken in divided doses this difference between the treatments was less pronounced.(ABSTRACT TRUNCATED AT 400 WORDS)

Achievement of high gain in a planar heterojunction bipolar transistor with lateral current flow

The authors have demonstrated transistor action in an L-HBT (lateral heterojunction bipolar transistor) device with multiple, quantum sized base channels. The small size of the individual channels has made it possible to increase the steepness of the alloy composition grading at the emitter-base junction of the transistor when the emitter is formed by Si diffusion disordering. It is well known that this interfacial grading must be optimized in order to achieve the maximum transistor device performance. As a result of these and other design modifications, transistor action with a maximum gain beta well in excess of 200 was achieved. These gain values demonstrate the practicality of transistor devices of the L-HBT design.

Linear resistive magnetohydrodynamic stability analysis of reversed field pinch configurations at finite beta

A linear resistive magnetohydrodynamic (MHD) stability analysis of a finite beta, cylindrical reversed field pinch (RFP) plasma is presented. The equilibrium distributions are specified by a model describing both the parallel and the perpendicular current density components. The average beta (⟨β⟩) of the configurations is varied by using the parameter χ (0 ≤ χ ≤ 1) which ensures that Suydam's necessary condition for stability is satisfied. It is found that there are configurations which are stable with respect to ideal pressure driven modes at rather high ⟨β⟩ values (up to 30%), although small changes in the equilibrium can produce a drastic reduction in the maximum achievable beta value. In this model, in which viscosity and Hall term effects are not taken into account, resistive g-modes are in general found to be always unstable, independent of the beta value. However, by considering only modes with ‘sufficiently’ high growth rates, it is possible to deduce some stability boundaries and ‘beta limits’ for relatively low values of the magnetic Reynolds number.

Maximum beta for a small-aspect-ratio tokamak

Ideal linear magnetohydrodynamic (MHD) stability calculations demonstrate reasonable adherence at low aspect ratio (AR&amp;lt;2) to the Troyon scaling relationship for maximum beta, resulting in a broad regime of stable high-beta equilibria. For a specific low-aspect-ratio case (AR=5/3), a wide range of stable equilibria having volume-averaged beta, 〈β〉, in excess of 20% is found. A systematic approach for estimating the maximum beta is used. First, the aspect ratio is reduced, for fixed shape and profiles, starting from the Troyon optimized case at AR=2.5; the plasma cross-section shape is then varied for fixed profiles at fixed AR=5/3; and finally, pressure and safety factor profiles are varied for fixed shape and aspect ratio. The calculations are carried out for low n (n=1–3), usually with a conducting wall at a radius of 1.5 times the plasma minor radius, for n=∞ ballooning modes, and for Mercier stability. Several additional ‘‘spot checks’’ on the effects of moving the conducting wall to infinity and of the stability of n=0 and n=4 and 5 modes indicate good stability properties for these, also. The calculations presented here demonstrate a straightforward extrapolation of the Troyon scaling formula to low aspect ratio, in spite of qualitative differences previously noted in low-aspect-ratio equilibria.

Beta limit of crescent and bean shaped tokamaks

The maximum attainable beta values which can be expected in tokamaks with crescent (BEAN 1) and rounded (BEAN 2) bean shaped cross-sections are obtained numerically by using the linear ideal MHD stability analysis code ERATO. The current profiles are optimized with a fixed pressure profile for high values of beta, keeping Mercier, high-n ballooning and n = 1 kink modes stable. The poloidal plasma cross-sections are inscribed in a rectangle with an aspect ratio of three and an ellipticity of two. A confocal wall, the distance of which from the plasma surface is equal to the horizontal minor plasma radius, is present to stabilize against the kink mode. Depending on the shape and triangularity (indentation), a beta value of 10 to 17% is obtained. It is also shown that the coefficient of the Troyon-type beta scaling increases for an indented plasma. In the case of small indentation, the BEAN 1 type tokamaks show higher beta values than the BEAN 2 type. For strong indentation, the BEAN 2 type gives the highest beta value.

Two-fluid MHD model of migma: Equilibrium and stability

MHD equations describing the stable stationary equilibrium of migma plasma are shown to result from the natural evolution of a magnetofluid in which magnetic helicity, cross helicity, and modified kinetic helicity are conserved. These equations are solved in two dimensions to yield distributions of azimuthal velocity, mass density, magnetic field, and current density. The radial expansion of migma as a function of plasma beta (diamagnetism) and the maximum obtainable beta as a function of the uniformity of the vacuum magnetic field are also found. If one assumes that the kinetic pressure is entirely due to Maxwellian electrons, then self-consistent expressions for the electron temperature and radial electric field can be found. The radial ion motions make a non-negligible contribution to the total internal energy, however. Modification to the basic equations arising from finite ion pressure is derived, and some preliminary conclusions are drawn.

Current and beta limitations for the TCV tokamak

Initial ideal MHD stability results for the Tokamak Configuration Variable (TCV) tokamak with variable elongation are presented. Two configurations have been studied: a racetrack shape and a D-shape at a fixed elongation of 2.5. Low beta studies indicate the existence of stable racetrack equilibria at currents up to an edge safety factor value of qs = 2, but the window of operation is limited in qo to narrow bands above each integer value. For the D-shape, qs = 3 gives the current limit at low beta, but the operating range in q0 is much wider than that for the racetrack. Beta optimization studies show that the maximum beta set by the n= 1 freeboundary stability limit decreases as the current increases, except for the lowest currents in the range studied. Although further optimization cannot be ruled out, considerable enhancement of the beta over that for an equivalent circular cross-section of the same major radius and aspect ratio can be obtained by elongation of the plasma cross-section.

Plasma Transport in a Compact Ignition Tokamak

Nominal predicted plasma conditions in a Compact Ignition Tokamak (CIT) are illustrated by transport simulations using experimentally calibrated plasma transport models. The range of uncertainty in these predictions is explored by using various models that have given almost equally good fits to experimental data. Using a transport model that best fits the data, thermonuclear ignition occurs in a CIT design with a major radius of 1.32 m, plasma half-width of 0.43 mn, elongation of 2.0, and toroidal field and plasma current ramped in 6 s from 1.7 to 10.4 T and 0.7 to 10 MA, respectively. Ignition is facilitated by 20 MW of heating deposited off the magnetic axis near the /sup 3/He minority cyclotron resonance layer. Under these conditions, sawtooth oscillations are small and have little impact on ignition. Tritium inventory is minimized by preconditioning most discharges with deuterium. Tritium is injected, in large frozen pellets, only after minority resonance preheating. Variations of the transport model, impurity influx, heating profile, and pellet ablation rates have a large effect on ignition and on the maximum beta that can be achieved.

Resistive ballooning stability of ASDEX equilibria

Experiments on the maximum attainable beta values of ASDEX discharges show that the limits for this parameter lie in the range of theoretical predictions. In a previous publication a theoretical identification of the corresponding instabilities has been attempted. No significant correlation with global plasma instabilities could be found, but the two-dimensional MHD equilibria calculated on the basis of ASDEX experimental parameters turned out to be close to the marginal ideal ballooning limit. In the work presented here, the previous investigation on resistive ballooning modes is extended. Separatrix bounded as well as limiter controlled plasma equilibria are considered. Because of the small aspect ratio of ASDEX (A ≅ 4) all equilibrium as well as stability calculations are performed in full toroidal geometry. After the formulation of a system of four equations describing the resistive evolution of velocity and magnetic fields in the high-m stability limit in co-ordinate invariant form and its Fourier approximation in the neighbourhood of a localization field line, the resulting quasimode equations are solved, applying methods of finite-element discretization. Complex growth rates γ are found, with a positive real part for values of the toroidal mode number n below 100. Calculated values of Re {γ} ≤ 10−3/τA S−1 (with τA being the Alfvén time) are small and therefore in agreement with the experimentally observed non-disruptive behaviour at the βp limit. Thus we believe that the characteristic signatures which govern ASDEX high βp discharges can be explained by resistive ballooning modes.

Density fluctuations in a reversed-field pinch

Density fluctuations have been studied using the multichord interferometer over a wide range of plasma parameters in the ZT-40M reversed-field pinch experiment [Nucl. Fusion 20, 1255 (1980)]. The total fluctuation power does not strongly depend upon the plasma current, and therefore, the relative fluctuation level decreases with increasing the current. Antisymmetric oscillations in the frequency region from 100–200 kHz are strongly excited in the outer region of the plasma column with increasing current. The maximum beta value attained seems to be inversely proportional to the magnitude of the fluctuations in this frequency region.

Treatment of hepatocellular carcinoma (HCC) with radiolabeled Lipiodol: a preliminary report.

Fatty acid esters such as Lipiodol or Ethiodol (Savage Laboratories, Melville, New York) are known to selectively localize in vascular hepatocellular carcinomas (HCC), following intra-arterial hepatic administration. Lipiodol was labeled with radioactive 131I and administered in 47 patients with HCC for both imaging and therapy. The short term preliminary results suggest radiolabeled Lipiodol is effective in eliminating ascites, shrinking the tumor by a high internal radiation dose, and in improving symptomatology of these tumors. In the future, 90Y, which is a stronger pure beta-emitter (maximum beta energy of 2.27 MeV, a half life of 64 h, and a maximum penetration or beta range of 11mm), than 131I will be used for more effective treatment of HCC.

Responses of Thermoluminescent Materials to Beta Radiation and Low Energy Photons

The responses in terms of the individual dose equivalent, superficial, Hs(d), of a number of commercially available thermoluminescent materials to beta radiation were investigated and compared with the responses of the same materials to low energy photons. The maximum beta energies used ranged from 0.067 to 2.27 MeV and the photon energies ranged from 0.033 to 0.662 MeV. All irradiations were carried out on appropriate tissue-equivalent phantoms. The results of these studies serve to identify materials and configurations suitable for personal dosimetry in mixed beta-photon fields.

Responses of Thermoluminescent Materials to Beta Radiation and Low Energy Photons

Abstract The responses in terms of the individual dose equivalent, superficial, Hs(d), of a number of commercially available thermoluminescent materials to beta radiation were investigated and compared with the responses of the same materials to low energy photons. The maximum beta energies used ranged from 0.067 to 2.27 MeV and the photon energies ranged from 0.033 to 0.662 MeV. All irradiations were carried out on appropriate tissue-equivalent phantoms. The results of these studies serve to identify materials and configurations suitable for personal dosimetry in mixed beta-photon fields.

Stability calculations for the m = 1/n = 1 mode in heliotron configurations using the three-dimensional MHD equilibrium and stability (BETA) code

Stability against the m = 1/n =1 internal mode is investigated in a Heliotron E model configuration for both currentless and flux conserving torus (FCT) equilibria. The beta limit in the first stability region is β̄ ≤ 2%, where β̄ denotes the average beta. This is consistent with the maximum beta value obtained in Heliotron E. For β̄ ⩾ 5%, a second stability region appears. It is found that the stability is sensitive to additional vertical magnetic fields. When the magnetic axis is shifted inward, the stability degrades, whereas, when it is shifted outward, the instability disappears for the above-given range of beta values. – The stability is also examined in another heliotron configuration which has a rotational transform larger than unity for all flux surfaces. Its first stability beta limit is larger than that for Heliotron E. For this configuration, an unstable free boundary mode with m = 1/n = 1 is found. A comparison of these results with analyses based on the stellarator expansion method is given.

Inductive inhibition of cold-plasma stabilization of curvature-driven modes in finite-length plasmas

A modified quasistatic theory that incorporates inductive effects in earlier electrostatic models connects the conventional electrostatic and magnetohydrodynamic (MHD) pictures of line tying by cold plasma. The modified theory predicts that curvature-driven flute modes in mirror-confined plasmas can be stabilized by moderate concentrations of cold plasma if the beta of the hot, mirror-confined plasma is less than a critical value. The maximum stable beta for an idealized stratified model of a hot-ion plasma, separated from conducting end walls by cold plasma, is given approximately by βcrit≂(4RpRc/LhLc) ×[ω2pe(cold)/ (k2⊥c2+ω2pe(cold))]. For ω2pe(cold) ≪k2⊥ c2, this result is identical with the predictions of electrostatic models. In the opposite limit, the result resembles the predictions of ideal MHD models, namely, that unstable curvature-driven modes can occur even in the presence of dense cold plasmas if the hot-plasma beta exceeds a limiting value estimated to be π2RpRc/L2.