This paper summarizes the status of the COMPASS tokamak, its comprehensive diagnostic equipment and plasma scenarios as a baseline for the future studies. The former COMPASS-D tokamak was in ...operation at UKAEA Culham, UK in 1992-2002. Later, the device was transferred to the Institute of Plasma Physics of the Academy of Sciences of the Czech Republic (IPP AS CR), where it was installed during 2006-2011. Since 2012 the device has been in a full operation with Type-I and Type-III ELMy H-modes as a base scenario. This enables together with the ITER-like plasma shape and flexible NBI heating system (two injectors enabling co- or balanced injection) to perform ITER relevant studies in different parameter range to the other tokamaks (ASDEX-Upgrade, DIII-D, JET) and to contribute to the ITER scallings. In addition to the description of the device, current status and the main diagnostic equipment, the paper focuses on the characterization of the Ohmic as well as NBI-assisted H-modes. Moreover, Edge Localized Modes (ELMs) are categorized based on their frequency dependence on power density flowing across separatrix. The filamentary structure of ELMs is studied and the parallel heat flux in individual filaments is measured by probes on the outer mid-plane and in the divertor. The measurements are supported by observation of ELM and inter-ELM filaments by an ultra-fast camera.
Abstract Radial transport of runaway electrons (REs) in tokamaks is affected by the presence of magnetic perturbations, either caused by internal magnetohydrodynamic instabilities or induced by ...external coils. The magnetic field configuration inside the plasma volume consists in general of intact magnetic surfaces alternated with magnetic islands and stochastic layers, which make the usual diffusive approach, based on the Rechester–Rosenbluth formula, inadequate to the study of transport. Here the fractional diffusion approach is employed to model RE transport in presence of intrinsic magnetic perturbations (magnetic islands) in the flat-top phase of RE-dedicated discharges on COMPASS tokamak. The character of RE transport is found to be subdiffusive. The degree of subdiffusion is evaluated by running simulations with the ORBIT code and a time-fractional diffusion equation is applied to calculate the time evolution of RE particle number. The results are compared with the observed RE losses, estimated from the time integrated neutron signal.
The poloidal distribution of electromagnetic loads during fast transients in the vacuum vessel of COMPASS-U tokamak is calculated analytically. The estimates are then compared with CarMa0NL numerical ...simulations. The results show that the poloidal eddy currents in the vacuum vessel must be taken into account for the proper evaluation of disruption forces in the COMPASS-U tokamak.
•The fine structure of ELM and inter-ELM filaments was detected in the SOL region of the COMPASS tokamak.•ELM events are constituted by multiple fragmented filamentary electromagnetic (EM) ...filaments.•The U-probe concept insertable probe allowed the direct evaluation of ELM and inter-ELM EM properties.•A direct measure of the B parallel current density inside ELM and inter-ELM filament is provided.
In fusion devices strong interest is deserved to the edge filament transport both related to turbulent and ELMy structures, because they are believed to provide important interaction with the plasma facing components and divertor plates. Among their features also the electromagnetic (EM) properties are expected to play an important role and in particular for the high beta regimes expected in future devices. The presence of ELM and inter-ELM electromagnetic filaments were detected during H-mode discharges in COMPASS device Scrape-Off Layer, where a new probe head was recently developed and commissioned. The diagnostic allows the simultaneous measurements of electrostatic and magnetic fluctuations with high time resolution, suitable for the identification of EM features of filaments. The method allows in particular the direct measurement of the current density associated to filaments. Detailed electrostatic and electromagnetic features analysis revealed a complex and fragmented structure within a single ELM and strong peaks in parallel current density Jtor are observed to characterize the ELM bunch. Analogous EM structures are observed also in inter-ELM phase, but with more than one order of magnitude lower intensity and time scale.
For ITER-relevant runaway electron studies, such as suppression, mitigation, termination and/or control of a runaway beam, it is important to obtain the runaway electrons after the disruption. In ...this paper we report on the first discharges achieved with a post-disruptive runaway electron beam, termed a ‘runaway plateau’, in the COMPASS tokamak. The runaway plateau is produced by a massive gas injection of argon. Almost all of the disruptions with runaway electron plateaus occurred during the plasma current ramp-up phase. The Ar injection discharges with and without a runaway plateau were compared for various parameters. Parametrisation of the discharges shows that the COMPASS disruptions fulfil the range of parameters important for runaway plateau occurrence. These parameters include electron density, electric field, disruption speed, effective safety factor, and the maximum current quench electric field. In addition to these typical parameters, the plasma current value just before the massive gas injection proved to be surprisingly important.
This paper presents the results from swept probe measurements in the divertor region of the COMPASS tokamak in D-shaped, L-mode discharges, with toroidal magnetic field BT = 1.15 T, plasma current Ip ...= 180 kA and line-average electron densities varying from 2 to 8×1019 m−3. Using neutral beam injection heating, the electron energy distribution function is studied before and during the application of the beam. The current-voltage characteristics data are processed using the first-derivative probe technique. This technique allows one to evaluate the plasma potential and the real electron energy distribution function (respectively, the electron temperatures and densities). At the low average electron density of 2×1019 m−3, the electron energy distribution function is bi-Maxwellian with a low-energy electron population with temperatures 4-6 eV and a high-energy electron group 12-25 eV. As the line-average electron density is increased, the electron temperatures decrease. At line-average electron densities above 7×1019 m−3, the electron energy distribution function is found to be Maxwellian with a temperature of 6-8.5 eV. The effect of the neutral beam injection heating power in the divertor region is also studied.
To examine the effect of a comprehensive transitional care model on the use of skilled nursing facility (SNF) and inpatient rehabilitation facility (IRF) care in the 12 months after acute care ...discharge home following stroke; and to identify predictors of experiencing a SNF or IRF admission following discharge home after stroke.
Cluster randomized pragmatic trial SETTING: Forty-one acute care hospitals in North Carolina.
2262 Medicare fee-for-service beneficiaries with transient ischemic attack or stroke discharged home. The sample was 80.3% White and 52.1% female, with a mean (SD) age of 74.9 (10.2) years and a mean ± SD National Institutes of Health stroke scale score of 2.3 (3.7).
Comprehensive transitional care model (COMPASS-TC), which consisted of a 2-day follow-up phone call from the postacute care coordinator and 14-day in-person visit with the postacute care coordinator and advanced practice provider.
Time to first SNF or IRF and SNF or IRF admission (yes/no) in the 12 months following discharge home. All analyses utilized multivariable mixed models including a hospital-specific random effect to account for the non-independence of measures within hospital. Intent to treat analyses using Cox proportional hazards regression assessed the effect of COMPASS-TC on time to SNF/IRF admission. Logistic regression was used to identify clinical and non-clinical predictors of SNF/IRF admission.
Only 34% of patients in the intervention arm received COMPASS-TC per protocol. COMPASS-TC was not associated with a reduced hazard of a SNF/ IRF admission in the 12 months post-discharge (hazard ratio, 1.20, with a range of 0.95-1.52) compared to usual care. This estimate was robust to additional covariate adjustment (hazard ratio, 1.23) (0.93-1.64). Both clinical and non-clinical factors (ie, insurance, geography) were predictors of SNF/IRF use.
COMPASS-TC was not consistently incorporated into real-world clinical practice. The use of a comprehensive transitional care model for patients discharged home after stroke was not associated with SNF or IRF admissions in a 12-month follow-up period. Non-clinical factors predictive of SNF/IRF use suggest potential issues with access to this type of care.
Abstract To achieve their goals, future thermonuclear reactors such as ITER and DEMO are expected to operate plasmas with a high magnetic field, triangularity and confinement. To address the ...corresponding challenges, the concept of the high-field ( B T ⩽ 5 T), high-current ( I P ⩽ 2 MA) COMPASS Upgrade tokamak was established, and the device is currently being constructed in Prague, Czech Republic. This contribution provides an overview of the priority physics topics for the future physics programme of COMPASS Upgrade, namely: (i) characterisation of alternative confinement modes, (ii) a power exhaust including liquid metals, (iii) operation with a hot first wall and (iv) the influence of plasma shape on pedestal stability and confinement. The main scenarios are presented, as predicted by METIS and FIESTA codes. Pedestal pressure and density are estimated using EPED, multi-machine semi-empirical scaling and a neutral penetration model. Access to detachment is estimated using a detachment qualifier.
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