Helium line ratio imaging in the C-2W divertor

A 2D imaging instrument has been designed and deployed on C-2W ("Norman") [H. Gota et al., Nucl. Fusion 61, 106039 (2021)] to study the plasma in the expander divertor by simultaneously measuring three neutral helium spectral lines. Ratios of these images, in conjunction with a collisional-radiative model, yield 2D maps of electron temperature and density. Almost the entire radial plasma cross-section (∼60 cm) can be mapped with a spatial resolution ≲1 cm. These data can, in principle, be acquired at 3 kHz. The neutral helium target is provided by a custom-built supersonic gas injector located inside the divertor vessel, which injects helium toward the magnetic axis and perpendicular to the camera sight-cone. Images of helium emission and reconstructed electron density and temperature profiles of the plasma produced from an end gun are presented. Voltages applied to concentric annular electrodes located in the divertors are used to stabilize beam-driven field reversed configuration plasmas. Magnetic field expansion is also employed to thermally isolate electrons from the end electrodes. Measurements of electron temperature and density in the divertor are important in order to study the effects of both the electrostatic biasing and the divertor magnetic field on electron confinement, neutral gas transport, and the overall machine performance.

Development of a three-wave far-infrared laser interferometry and polarimetry diagnostic system for the C-2W field-reversed configuration plasmas

Great advancements in modern field-reversed configuration (FRC) experiments motivated the development of a 14-chord three-wave far infrared (FIR) laser interferometry and polarimetry diagnostic system, which can provide simultaneous high temporal resolution measurements of density and Faraday rotation profiles with high accuracy. The unique challenges facing FIR diagnostics in high beta FRC plasmas are the extremely small (<0.5°) Faraday rotation angles, and severe laser beam refraction effects due to high density gradient and choice of long wavelength. The diagnostic system design and development are described with methods to overcome the challenges, and initial experimental data are also presented.

Characterization of compact-toroid injection during formation, translation, and field penetration

We have developed a compact toroid (CT) injector system for particle refueling of the advanced beam-driven C-2U field-reversed configuration (FRC) plasma. The CT injector is a magnetized coaxial plasma gun (MCPG), and the produced CT must cross the perpendicular magnetic field surrounding the FRC for the refueling of C-2U. To simulate this environment, an experimental test stand has been constructed. A transverse magnetic field of ∼1 kG is established, which is comparable to the C-2U axial magnetic field in the confinement section, and CTs are fired across it. On the test stand we have been characterizing and studying CT formation, ejection/translation from the MCPG, and penetration into transverse magnetic fields.

The upgrade of the Thomson scattering system for measurement on the C-2/C-2U devices

The C-2/C-2U Thomson scattering system has been substantially upgraded during the latter phase of C-2/C-2U program. A Rayleigh channel has been added to each of the three polychromators of the C-2/C-2U Thomson scattering system. Onsite spectral calibration has been applied to avoid the issue of different channel responses at different spots on the photomultiplier tube surface. With the added Rayleigh channel, the absolute intensity response of the system is calibrated with Rayleigh scattering in argon gas from 0.1 to 4 Torr, where the Rayleigh scattering signal is comparable to the Thomson scattering signal at electron densities from 1 × 10¹³ to 4 × 10¹⁴ cm^-3. A new signal processing algorithm, using a maximum likelihood method and including detailed analysis of different noise contributions within the system, has been developed to obtain electron temperature and density profiles. The system setup, spectral and intensity calibration procedure and its outcome, data analysis, and the results of electron temperature/density profile measurements will be presented.

Development of a magnetized coaxial plasma gun for compact toroid injection into the C-2 field-reversed configuration device

A compact toroid (CT) injector was developed for the C-2 device, primarily for refueling of field-reversed configurations. The CTs are formed by a magnetized coaxial plasma gun (MCPG), which consists of coaxial cylindrical electrodes and a bias coil for creating a magnetic field. First, a plasma ring is generated by a discharge between the electrodes and is accelerated by Lorenz self-force. Then, the plasma ring is captured by an interlinkage flux (poloidal flux). Finally, the fully formed CT is ejected from the MCPG. The MCPG described herein has two gas injection ports that are arranged tangentially on the outer electrode. A tungsten-coated inner electrode has a head which can be replaced with a longer one to extend the length of the acceleration region for the CT. The developed MCPG has achieved supersonic CT velocities of ∼100 km/s. Plasma parameters for electron density, electron temperature, and the number of particles are ∼5 × 10(21) m(-3), ∼40 eV, and 0.5-1.0 × 10(19), respectively.

Subsyndromal depression in the United States: prevalence, course, and risk for incident psychiatric outcomes

BACKGROUND

Subsyndromal depression (SD) may increase risk for incident major depressive and other disorders, as well as suicidality. However, little is known about the prevalence, course, and correlates of SD in the US general adult population. Method Structured diagnostic interviews were conducted to assess DSM-IV Axis I and II disorders in a nationally representative sample of 34 653 US adults who were interviewed at two time-points 3 years apart.

RESULTS

A total of 11.6% of US adults met study criteria for lifetime SD at Wave 1. The majority (9.3%) had <5 total symptoms required for a diagnosis of major depression; the remainder (2.3%) reported ⩾5 symptoms required for a diagnosis of major depression, but denied clinically significant distress or functional impairment. SD at Wave 1 was associated with increased likelihood of developing incident major depression [odds ratios (ORs) 1.72-2.05], as well as dysthymia, social phobia, and generalized anxiety disorder (GAD) at Wave 2 (ORs 1.41-2.92). Among respondents with SD at Wave 1, Cluster A and B personality disorders, and worse mental health status were associated with increased likelihood of developing incident major depression at Wave 2.

CONCLUSIONS

SD is prevalent in the US population, and associated with elevated rates of Axis I and II psychopathology, increased psychosocial disability, and risk for incident major depression, dysthymia, social phobia, and GAD. These results underscore the importance of a dimensional conceptualization of depressive symptoms, as SD may serve as an early prognostic indicator of incident major depression and related disorders, and could help identify individuals who may benefit from preventive interventions.

Two-color CO2/HeNe laser interferometer for C-2 experiment

A six-channel two-color interferometer has been developed for plasma electron density measurements in the C-2 field reversed configuration experiment. A CO(2) laser is utilized as the main probe beams, while copropagating visible HeNe laser beams are mainly sensitive to vibration. Density measurements in C-2 plasmas have shown that this is a reliable turn-key system. The maximum residual phase noise after vibration compensation is less than ±5°, corresponding to a line integral density of 3×10(18) m(-2). The time resolution for routine operation is 2 μs.

Multiple shift patient classification: is it necessary?

Efficient, cost-effective patient classification systems are an essential component of information needed for staffing projections, budgeting, productivity monitoring, and determining the cost of nursing services. Data collection on every shift is typical of GRASP-based patient classification systems. In this study, comparisons among multiple shift measurements showed that no relevant information was being gained by multiple daily assessments of patient care requirements.