Electron and Ion Heating Characteristics during Magnetic Reconnection in the MAST Spherical Tokamak.

Electron and ion heating characteristics during merging reconnection start-up on the MAST spherical tokamak have been revealed in detail using a 130 channel yttrium aluminum garnet (YAG) and a 300 channel Ruby-Thomson scattering system and a new 32 chord ion Doppler tomography diagnostic. Detailed 2D profile measurements of electron and ion temperature together with electron density have been achieved for the first time and it is found that electron temperature forms a highly localized hot spot at the X point and ion temperature globally increases downstream. For the push merging experiment when the guide field is more than 3 times the reconnecting field, a thick layer of a closed flux surface form by the reconnected field sustains the temperature profile for longer than the electron and ion energy relaxation time ~4-10 ms, both characteristic profiles finally forming a triple peak structure at the X point and downstream. An increase in the toroidal guide field results in a more peaked electron temperature profile at the X point, and also produces higher ion temperatures at this point, but the ion temperature profile in the downstream region is unaffected.

Polarimetric Thomson scattering measurements in Joint European Torus high temperature plasmas.

Thomson scattered light is polarized in the same orientation as the incident laser beam at low electron temperatures (Te). At high Te, part of the spectrum begins to become randomly polarized due to relativistic reasons. First measurements of the depolarized Thomson scattering spectrum were obtained from Joint European Torus (JET) pulses in 2016. This paper builds upon these initial measurements with the data obtained during 2021. These new measurements improve upon first results, in particular, by obtaining spectral measurements of the depolarized spectrum. The recent JET campaign was well suited to these measurements with long and hot plasmas. The resulting data are averaged over many plasmas and laser pulses to obtain a measurement of the amount of "p" and "s" scattered light as a function of Te. This experimentally obtained d(p/s)/dTe is then fitted and found to show reasonable agreement with the theoretically predicted depolarized fraction. Error estimates on the measured "p/s" have been obtained and show that the measurements are meaningful. This is good news for ITER for which the intention is to use this measurement as a check on Te determined by the core plasma Thomson scattering diagnostic by using conventional spectral measurement techniques.

Kinetic instabilities that limit ß in the edge of a tokamak plasma: a picture of an H-mode pedestal.

Plasma equilibria reconstructed from the Mega-Amp Spherical Tokamak have sufficient resolution to capture plasma evolution during the short period between edge-localized modes (ELMs). Immediately after the ELM, steep gradients in pressure, P, and density, n(e), form pedestals close to the separatrix, and they then expand into the core. Local gyrokinetic analysis over the ELM cycle reveals the dominant microinstabilities at perpendicular wavelengths of the order of the ion Larmor radius. These are kinetic ballooning modes in the pedestal and microtearing modes in the core close to the pedestal top. The evolving growth rate spectra, supported by gyrokinetic analysis using artificial local equilibrium scans, suggest a new physical picture for the formation and arrest of this pedestal.

First divertor Thomson scattering measurements on MAST-U.

MAST-U is equipped with a Super-X divertor, which aims to reduce heat flux to the target and promote detachment. Measurements of plasma electron density and temperature in the Super-X chamber offer insight into the processes at work in this type of divertor. First data have been obtained from the MAST-U divertor Thomson scattering diagnostic designed to measure these quantities. Following a Raman scattering calibration in nitrogen, the diagnostic operated over a number of plasma pulses in the first physics campaign. Electron density and temperature measurements have been taken in attached and detached conditions as the strike leg moved through the field of view of the diagnostic. The system operated with a dedicated 30 Hz laser with timing synchronized to seven similar lasers installed in the core Thomson system. Electron densities in the range of 1 × 1018-5 × 1019 m-3 have been measured by the system throughout these regimes. Although the system was specified to measure from 1 to 40 eV, electron temperatures in the Super-X divertor in the first campaign were low, and measurement down to 0.5 eV has been critical, particularly close to the detachment front. This generation of polychromator has been designed with increased stray light rejection compared to those used in the core system. This has proved successful with very low levels of stray light observed.

Design elements and first data from a new Doppler backscattering system on the MAST-U spherical tokamak.

A new Doppler backscattering (DBS) system has been installed and tested on the MAST-U spherical tokamak. It utilizes eight simultaneous fixed frequency probe beams (32.5, 35, 37.5, 40, 42.5, 45, 47.5, and 50 GHz). These frequencies provide a range of radial positions from the edge plasma to the core depending on plasma conditions. The system utilizes a combination of novel features to provide remote control of the probed density wavenumber, the launched polarization (X vs O-mode), and the angle of the launched DBS to match the magnetic field pitch angle. The range of accessible density turbulence wavenumbers (kθ) is reasonably large with normalized wavenumbers kθρs ranging from ≤0.5 to 9 (ion sound gyroradius ρs = 1 cm). This wavenumber range is relevant to a variety of instabilities believed to be important in establishing plasma transport (e.g., ion temperature gradient, trapped electron, electron temperature gradient, micro-tearing, kinetic ballooning modes). The system is specifically designed to address the requirement of density fluctuation wavevector alignment which can significantly reduce the SNR if not accounted for.

Low temperature Thomson scattering on MAST-U.

A new divertor Thomson scattering system has been developed for the MAST-U tokamak. The diagnostic will produce electron density and temperature profiles along the Super-X strike leg. The existing polychromator design has been adapted for low temperature measurements. A new 1061 nm channel with 2 nm bandwidth has been added to enable measurements down below the previous ∼5 eV limit on the core system. The optical filters used in the system have OD6 light rejection alongside a 1064.1 nm laser line filter to reduce stray light in the digitized channels. A new averaging technique has been applied to the scattered signal traces to improve the core Thomson data in the scrape-off layer. The technique reduces the systematic noise level in this region. This leads to a reduction in the error values for electron density and temperature measurements and, in particular, the digitizer noise. The technique has been applied to produce a radial profile for a number of L-mode MAST discharges down to very low densities of ∼1 × 1018 m-3.

Magnetic reconnection triggering magnetohydrodynamic instabilities during a sawtooth crash in a Tokamak plasma.

Thomson scattering measurements with subcentimeter spatial resolution have been made during a sawtooth crash in a Mega Ampere Spherical Tokamak fusion plasma. The unparalleled resolution of the temperature profile has shed new light on the mechanisms that underlie the sawtooth. As magnetic reconnection occurs, the temperature gradient at the island boundary increases. The increased local temperature gradient is sufficient to make the helical core unstable to ideal magnetohydrodynamic instabilities, thought to be responsible for the rapidity of the collapse.

Design of the collection optics for the Core Plasma Thomson Scattering (CPTS) in ITER.

In the ITER Core Plasma Thomson Scattering, the scattered light collection optics system is installed both inside and outside the diagnostic port under vacuum. The length of the optical path (∼6 m) and the need to shield the neutron and γ radiation increased the complexity of the system with the inclusion of multiple dog-legs, forcing the use of many elements with optical power. Multiple rounds of design have been required in order to satisfy iteratively the system requirements in terms of resolution, aberration, and shielding. The adoption of quasi-free-form reflective surfaces for several mirrors eventually allowed the correct compromise between all conflicting requirements.

Edge profile analysis of Joint European Torus (JET) Thomson scattering data: Quantifying the systematic error due to edge localised mode synchronisation.

The Joint European Torus (JET) high resolution Thomson scattering (HRTS) system measures radial electron temperature and density profiles. One of the key capabilities of this diagnostic is measuring the steep pressure gradient, termed the pedestal, at the edge of JET plasmas. The pedestal is susceptible to limiting instabilities, such as Edge Localised Modes (ELMs), characterised by a periodic collapse of the steep gradient region. A common method to extract the pedestal width, gradient, and height, used on numerous machines, is by performing a modified hyperbolic tangent (mtanh) fit to overlaid profiles selected from the same region of the ELM cycle. This process of overlaying profiles, termed ELM synchronisation, maximises the number of data points defining the pedestal region for a given phase of the ELM cycle. When fitting to HRTS profiles, it is necessary to incorporate the diagnostic radial instrument function, particularly important when considering the pedestal width. A deconvolved fit is determined by a forward convolution method requiring knowledge of only the instrument function and profiles. The systematic error due to the deconvolution technique incorporated into the JET pedestal fitting tool has been documented by Frassinetti et al. [Rev. Sci. Instrum. 83, 013506 (2012)]. This paper seeks to understand and quantify the systematic error introduced to the pedestal width due to ELM synchronisation. Synthetic profiles, generated with error bars and point-to-point variation characteristic of real HRTS profiles, are used to evaluate the deviation from the underlying pedestal width. We find on JET that the ELM synchronisation systematic error is negligible in comparison to the statistical error when assuming ten overlaid profiles (typical for a pre-ELM fit to HRTS profiles). This confirms that fitting a mtanh to ELM synchronised profiles is a robust and practical technique for extracting the pedestal structure.

Peripherally inserted central catheters in an acute-care hospital.

BACKGROUND: Peripherally inserted central catheterization is a relatively new approach for intravenous therapy in acute-care hospitals. Few studies are available on peripherally inserted central catheters (PICCs) used in adult patients in an acute-care setting. We examine the natural history and outcome of PICC use in our hospital. METHODS: A retrospective review was undertaken of all hospitalized patients who had PICCs inserted in an acute-care, metropolitan teaching hospital for any reason from July 1991 through July 1992. Patients who had PICCs inserted, used, and then removed in the same hospitalization were evaluated. RESULTS: A total of 135 PICCs were inserted in 114 patients. Six PICCs (4.4%) were inserted in intensive care unit settings and 129 (95.6%) in general medical or surgical service. The mean duration catheters were in place before removal was 14.1 days. Sixty-three catheters (46.7%) were removed following completion of therapy. The rate of PICC-related infection was 2.2% (three catheters). The occlusion rate was higher for 20-gauge catheters (18.4%) than for 18-gauge catheters (8.2%) (P = .08). When the rate of complications was compared as a function of catheter use (total parenteral nutrition vs any other use), there was no statistically significant difference (P = .12). Overall complications related to catheter insertion and removal were uncommon. CONCLUSIONS: Based on our study, we conclude that the PICC provides a reasonable and safe alternative to other centrally placed venous devices. In addition, the convenience of maintaining a PICC compared with peripheral intravenous access makes this an attractive method for in-hospital use.

(+/-)-trans-2-[3-methoxy-4-(4-chlorophenylthioethoxy)-5-(N-methyl-N- hydroxyureidyl)methylphenyl]-5-(3,4, 5-trimethoxyphenyl)tetrahydrofuran (CMI-392), a potent dual 5-lipoxygenase inhibitor and platelet-activating factor receptor antagonist.

By incorporating an N-hydroxyurea functionality onto diaryltetrahydrofurans, a novel series of compounds was investigated as dual 5-lipoxygenese (5-LO) inhibitor and platelet-activating factor (PAF) receptor antagonist. These dual functional compounds were evaluated in vitro for 5-LO inhibition in RBL cell extracts and human whole blood, and PAF receptor antagonism in a receptor binding assay. PAF-induced hemoconcentration and arachidonic acid- and TPA-induced ear edema in mice were used to determine in vivo activities. The structure-activity relationship analysis to define a preclinical lead is presented. (+/-)-trans-2-[3-methoxy-4-(4-chlorophenylthioethoxy)-5-(N-methyl- N-h ydroxyureidyl)methylphenyl]-5-(3,4, 5-trimethoxyphenyl)tetrahydrofuran (40, CMI-392) was selected for further study. In the arachidonic acid-induced mouse ear edema model, 40 was more potent than either zileuton (a 5-LO inhibitor) or BN 50739 (a PAF receptor antagonist), and it demonstrated the same inhibitory effect as a physical combination of the latter two agents. These results suggest that a single compound which both inhibits leukotriene synthesis and blocks PAF receptor binding may provide therapeutic advantages over single-acting agents. The clinical development of compound 40 is in progress.

Dual acting antihistaminergic agents.

Histamine is a primary mediator in allergic response and acts in concert with other agents to impact disease progression. Respiratory disorders such as asthma, rhinitis and dermatological conditions such as urticaria involve histamine along with other mediators. An antihistamine that possesses an additional property of counteracting the effects mediated by these other mediators should offer some therapeutic benefit over a selective antihistaminergic agent.

Design of a real-time two-color interferometer for MAST Upgrade.

A single chord two-color CO2/HeNe (10.6/0.633 µm) heterodyne laser interferometer has been designed to measure the line integral electron density along the mid-plane of the MAST Upgrade tokamak, with a typical error of 1 × 10(18) m(-3) (∼2° phase error) at 4 MHz temporal resolution. To ensure this diagnostic system can be restored from any failures without stopping MAST Upgrade operations, it has been located outside of the machine area. The final design and initial testing of this system, including details of the optics, vibration isolation, and a novel phase detection scheme are discussed in this paper.

Edge Thomson scattering diagnostic on COMPASS tokamak: installation, calibration, operation, improvements.

The core Thomson scattering diagnostic (TS) on the COMPASS tokamak was put in operation and reported earlier. Implementation of edge TS, with spatial resolution along the laser beam up to ∼1/100 of the tokamak minor radius, is presented now. The procedure for spatial calibration and alignment of both core and edge systems is described. Several further upgrades of the TS system, like a triggering unit and piezo motor driven vacuum window shutter, are introduced as well. The edge TS system, together with the core TS, is now in routine operation and provides electron temperature and density profiles.

Investigating fusion plasma instabilities in the Mega Amp Spherical Tokamak using mega electron volt proton emissions (invited).

The proton detector (PD) measures 3 MeV proton yield distributions from deuterium-deuterium fusion reactions within the Mega Amp Spherical Tokamak (MAST). The PD's compact four-channel system of collimated and individually oriented silicon detectors probes different regions of the plasma, detecting protons (with gyro radii large enough to be unconfined) leaving the plasma on curved trajectories during neutral beam injection. From first PD data obtained during plasma operation in 2013, proton production rates (up to several hundred kHz and 1 ms time resolution) during sawtooth events were compared to the corresponding MAST neutron camera data. Fitted proton emission profiles in the poloidal plane demonstrate the capabilities of this new system.

Correction of the spectral calibration of the Joint European Torus core light detecting and ranging Thomson scattering diagnostic using ray tracing.

This work isolated the cause of the observed discrepancy between the electron temperature (T(e)) measurements before and after the JET Core LIDAR Thomson Scattering (TS) diagnostic was upgraded. In the upgrade process, stray light filters positioned just before the detectors were removed from the system. Modelling showed that the shift imposed on the stray light filters transmission functions due to the variations in the incidence angles of the collected photons impacted plasma measurements. To correct for this identified source of error, correction factors were developed using ray tracing models for the calibration and operational states of the diagnostic. The application of these correction factors resulted in an increase in the observed T(e), resulting in the partial if not complete removal of the observed discrepancy in the measured T(e) between the JET core LIDAR TS diagnostic, High Resolution Thomson Scattering, and the Electron Cyclotron Emission diagnostics.

Spatial resolution of the JET Thomson scattering system.

The instrument function of the high resolution Thomson scattering (HRTS) diagnostic in the Joint European Torus (JET) has been calculated for use in improved pedestal profile analysis. The full width at half maximum (FWHM) of the spatial instrument response is (22 ± 1) mm for the original HRTS system configuration and depends on the particular magnetic topology of the JET plasmas. An improvement to the optical design of the laser input system is presented. The spatial smearing across magnetic flux surfaces is reduced in this design. The new input system has been implemented (from JPN 78742, July 2009) and the HRTS instrument function corresponding to the new configuration has been improved to approximately FWHM = (9.8 ± 0.8) mm. The reconstructed instrument kernels are used in combination with an ad hoc forward deconvolution procedure for pedestal analysis. This procedure produces good results for both the old and new setups, but the reliability of the deconvolved profiles is greatly reduced when the pedestal width is of the same order as, or less than the FWHM of the instrument kernel.

A field programmable gate array unit for the diagnosis and control of neoclassical tearing modes on MAST.

A real-time system has been developed to trigger both the MAST Thomson scattering (TS) system and the plasma control system on the phase and amplitude of neoclassical tearing modes (NTMs), extending the capabilities of the original system. This triggering system determines the phase and amplitude of a given NTM using magnetic coils at different toroidal locations. Real-time processing of the raw magnetic data occurs on a low cost field programmable gate array (FPGA) based unit which permits triggering of the TS lasers on specific amplitudes and phases of NTM evolution. The MAST plasma control system can receive a separate trigger from the FPGA unit that initiates a vertical shift of the MAST magnetic axis. Such shifts have fully removed m∕n = 2∕1 NTMs instabilities on a number of MAST discharges.

High-resolution Thomson scattering system on the COMPASS tokamak: evaluation of plasma parameters and error analysis.

The electron density and temperature profiles measured by the Thomson scattering diagnostic on the COMPASS tokamak are used for estimation of electron kinetic energy, energy confinement time, and effective charge number Z(eff). Data are compared with the line-integrated electron density measured by a microwave interferometer in an ohmically heated plasma with a circular cross section. An error analysis of both electron temperature and density are performed by two methods-a constant chi-square boundaries method and a Monte Carlo simulation, determining asymmetrical error bars for the electron temperature.

Deconvolution of Thomson scattering temperature profiles.

Deconvolution of Thomson scattering (TS) profiles is required when the gradient length of the electron temperature (T(e)) or density (n(e)) are comparable to the instrument function length (Δ(R)). The most correct method for deconvolution to obtain underlying T(e) and n(e) profiles is by consideration of scattered signals. However, deconvolution at the scattered signal level is complex since it requires knowledge of all spectral and absolute calibration data. In this paper a simple technique is presented where only knowledge of the instrument function I(r) and the measured profiles, T(e, observed)(r) and n(e, observed)(r), are required to obtain underlying T(e)(r) and n(e)(r). This method is appropriate for most TS systems and is particularly important where high spatial sampling is obtained relative to Δ(R).