Field reversed configuration confinement enhancement through edge biasing and neutral beam injection.

Field reversed configurations (FRCs) with high confinement are obtained in the C-2 device by combining plasma gun edge biasing and neutral beam injection. The plasma gun creates an inward radial electric field that counters the usual FRC spin-up. The n = 2 rotational instability is stabilized without applying quadrupole magnetic fields. The FRCs are nearly axisymmetric, which enables fast ion confinement. The plasma gun also produces E × B shear in the FRC edge layer, which may explain the observed improved particle transport. The FRC confinement times are improved by factors 2 to 4, and the plasma lifetimes are extended from 1 to up to 4 ms.

Spectroscopic measurement of ion temperature and ion velocity distributions in the flux-coil generated FRC.

One aim of the flux-coil generated field reversed configuration at Tri Alpha Energy (TAE) is to establish the plasma where the ion rotational energy is greater than the ion thermal energy. To verify this, an optical diagnostic was developed to simultaneously measure the Doppler velocity-shift and line-broadening using a 0.75 m, 1800 groves/mm, spectrometer. The output spectrum is magnified and imaged onto a 16-channel photomultiplier tube (PMT) array. The individual PMT outputs are coupled to high-gain, high-frequency, transimpedance amplifiers, providing fast-time response. The Doppler spectroscopy measurements, along with a survey spectrometer and photodiode-light detector, form a suite of diagnostics that provide insights into the time evolution of the plasma-ion distribution and current when accelerated by an azimuthal-electric field.

Doppler spectroscopy and D-alpha emission diagnostics for the C-2 FRC plasma.

Two Doppler spectroscopy diagnostics with complementary capabilities are developed to measure the ion temperatures and velocities of FRC plasmas in the C-2 device. First, the multichord ion doppler diagnostic can simultaneously measure 15 chords of the plasma using an image intensified camera. Second, a single-chord fast-response ion Doppler diagnostic provides much higher faster time response by using a 16-channel photo-multiplier tube array. To study the neutral density of deuterium under different wall and plasma conditions, a highly sensitive eight-channel D-alpha diagnostic has been developed and calibrated for absolute radiance measurements. These spectroscopic diagnostics capabilities, combined with other plasma diagnostics, are helping to understand and improve the field reversed configuration plasmas in the C-2 device.

Dynamic formation of a hot field reversed configuration with improved confinement by supersonic merging of two colliding high-ß compact toroids.

A hot stable field-reversed configuration (FRC) has been produced in the C-2 experiment by colliding and merging two high-ß plasmoids preformed by the dynamic version of field-reversed θ-pinch technology. The merging process exhibits the highest poloidal flux amplification obtained in a magnetic confinement system (over tenfold increase). Most of the kinetic energy is converted into thermal energy with total temperature (T{i}+T{e}) exceeding 0.5 keV. The final FRC state exhibits a record FRC lifetime with flux confinement approaching classical values. These findings should have significant implications for fusion research and the physics of magnetic reconnection.

Impact of positive end-expiratory pressure on chest wall and lung pressure-volume curve in acute respiratory failure.

To investigate whether chest-wall mechanics could affect the total respiratory system pressure-volume (P-V) curve in patients with acute respiratory failure (ARF), and particularly the lower inflection point (LIP) of the curve, we drew the total respiratory system, lung, and chest-wall P-V curves (P-Vrs, P-VL, and P-VW, respectively) for 13 patients with ARF, using the supersyringe method together with the esophageal balloon technique. Measurements were randomly repeated at four different levels of positive end-expiratory pressure (PEEP) (0, 5, 10, 15 cm H2O) and from each P-V curve we derived starting compliance (Cstart), inflation compliance (Cinf), and end compliance (Cend). With PEEP of 0 cm H2O (ZEEP), an LIP on the P-Vrs curve was observed in all patients (7.5 +/- 3.9 cm H2O); in two patients an LIP was detected only on the P-VL curve (8.6 and 8.7 cm H2O, respectively); whereas in seven patients an LIP was observed only on the P-VW curve (3.4 +/- 1.1 cm H2O). In four patients, an LIP was detected on both the P-VL and P-VW curves (8.5 +/- 3.4 and 2.2 +/- 1.0 cm H2O, respectively). The LIP was abolished by PEEP, suggesting that a volume-related mechanism was responsible for the observed LIP on both the P-VL and P-VW curves. At high levels of PEEP, an upper inflection point (UIP) appeared on the P-Vrs and P-VL curves (11.7 +/- 4.9 cm H2O and 8.9 +/- 4.2 cm H2O above PEEP, respectively) suggesting alveolar overdistension. In general, PaO2 increased with PEEP (from 81.7 +/- 35.5 mm Hg on ZEEP to 120 +/- 43.8 mm Hg on PEEP 15 cm H2O, p < 0.002); however, the increase in PaO2 with PEEP was significant only in patients with an LIP on the P-VL curve (from 70.5 +/- 16.2 mm Hg to 117.5 +/- 50.7 mm Hg, p < 0.002), the changes in PaO2 in patients without an LIP on the P-VL curve not being significant (from 91.3 +/- 45.4 mm Hg to 122.2 +/- 41.1 mm Hg). We conclude that in ventilator-dependent patients with ARF: (1) the chest-wall mechanics can contribute to the LIP observed on the P-Vrs curve; (2) the improvement in PaO2 with PEEP is significant only in patients in whom LIP is on the lung P-V curve and not on the chest wall curve; (3) high levels of PEEP may overdistend the lung, as reflected by the appearance of a UIP; (4) measurement of P-Vrs alone may be misleading as a guide for setting the level of PEEP in some mechanically ventilated patients, at least in the supine position, although it helps to prevent excessive alveolar overdistension by indicating the inflection volume above which UIP may appear.

[Assessment of various new predictive parameters of the outcome of mechanical ventilation weaning]. / Valutazione di alcuni nuovi parametri predittivi dell'esito dello svezzamento dalla ventilazione meccanica.

OBJECTIVE: To evaluate new indexes predicting weaning outcome from mechanical ventilation. EXPERIMENTAL DESIGN: Prospective study with two main end-points: a comparison of weaning indexes between successful and unsuccessful groups and an evaluation of their predicting value. ENVIRONMENT: Surgical-Medical Intensive Care Unit. PATIENTS: Patients ventilated for more than 72 hours and subjected to a weaning trial until spontaneous ventilation. MEASUREMENTS: Traditional weaning parameters [respiratory rate (fsb), expiratory minute volume (Vesb), Maximal Inspiratory Pressure (MIP)] along with the new indexes [fsb/Vtsb) (rate to tidal volume ratio), CROP index (Compliance Rate Oxygenation Pressure), P0.1/MIP, IEQ (Inspiratory Effort Quotient), WI (Weaning Index)] were measured before discontinuation of ventilation support. RESULTS: A statistically significant difference was observed between successful and unsuccessful groups for the following parameters: fsb, MIP, fsb/.Vtsb, CROP, Po.1/MIP and WI while no differences were observed for Vesb and IEQ. The sensitivity and specificity for the new indexes were respectively: fsb/Vtsb: 0.65 and 0.58; CROP: 0.70 and 0.63; P0.1/MIP: 0.85 and 0.36; WI: 0.69 and 0.47. CONCLUSION: A statistically significant difference between successful and unsuccessful groups was observed for some but not all new indexes; the diagnostic accuracy of the new indexes were no better than additional parameters.