| 1. |
- Murari, A., et al.
(författare)
-
A control oriented strategy of disruption prediction to avoid the configuration collapse of tokamak reactors
- 2024
-
Ingår i: Nature Communications. - 2041-1723 .- 2041-1723. ; 15:1
-
Tidskriftsartikel (refereegranskat)abstract
- The objective of thermonuclear fusion consists of producing electricity from the coalescence of light nuclei in high temperature plasmas. The most promising route to fusion envisages the confinement of such plasmas with magnetic fields, whose most studied configuration is the tokamak. Disruptions are catastrophic collapses affecting all tokamak devices and one of the main potential showstoppers on the route to a commercial reactor. In this work we report how, deploying innovative analysis methods on thousands of JET experiments covering the isotopic compositions from hydrogen to full tritium and including the major D-T campaign, the nature of the various forms of collapse is investigated in all phases of the discharges. An original approach to proximity detection has been developed, which allows determining both the probability of and the time interval remaining before an incoming disruption, with adaptive, from scratch, real time compatible techniques. The results indicate that physics based prediction and control tools can be developed, to deploy realistic strategies of disruption avoidance and prevention, meeting the requirements of the next generation of devices.
|
|
| 2. |
- Akiyama, Kazunori, et al.
(författare)
-
The persistent shadow of the supermassive black hole of M 87: I. Observations, calibration, imaging, and analysis*
- 2024
-
Ingår i: Astronomy and Astrophysics. - 0004-6361 .- 1432-0746. ; 681
-
Tidskriftsartikel (refereegranskat)abstract
- In April 2019, the Event Horizon Telescope (EHT) Collaboration reported the first-ever event-horizon-scale images of a black hole, resolving the central compact radio source in the giant elliptical galaxy M 87. These images reveal a ring with a southerly brightness distribution and a diameter of ∼42 μas, consistent with the predicted size and shape of a shadow produced by the gravitationally lensed emission around a supermassive black hole. These results were obtained as part of the April 2017 EHT observation campaign, using a global very long baseline interferometric radio array operating at a wavelength of 1.3 mm. Here, we present results based on the second EHT observing campaign, taking place in April 2018 with an improved array, wider frequency coverage, and increased bandwidth. In particular, the additional baselines provided by the Greenland telescope improved the coverage of the array. Multiyear EHT observations provide independent snapshots of the horizon-scale emission, allowing us to confirm the persistence, size, and shape of the black hole shadow, and constrain the intrinsic structural variability of the accretion flow. We have confirmed the presence of an asymmetric ring structure, brighter in the southwest, with a median diameter of 43.3-3.1+1.5 μas. The diameter of the 2018 ring is remarkably consistent with the diameter obtained from the previous 2017 observations. On the other hand, the position angle of the brightness asymmetry in 2018 is shifted by about 30 relative to 2017. The perennial persistence of the ring and its diameter robustly support the interpretation that the ring is formed by lensed emission surrounding a Kerr black hole with a mass ∼6.5× 109M. The significant change in the ring brightness asymmetry implies a spin axis that is more consistent with the position angle of the large-scale jet.
|
|
| 3. |
- Deane, R. P., et al.
(författare)
-
The VLBA CANDELS GOODS-North Survey -I. survey design, processing, data products, and source counts
- 2024
-
Ingår i: Monthly Notices of the Royal Astronomical Society. - 0035-8711 .- 1365-2966. ; 529:3, s. 2428-2442
-
Tidskriftsartikel (refereegranskat)abstract
- The past decade has seen significant advances in wide-field cm-wave very long baseline interferometry (VLBI), which is timely given the wide-area, synoptic survey-driven strategy of major facilities across the electromagnetic spectrum. While wide-field VLBI poses significant post-processing challenges that can severely curtail its potential scientific yield, man y dev elopments in the km-scale connected-element interferometer sphere are directly applicable to addressing these. Here we present the design, processing, data products, and source counts from a deep (11 μJy beam -1 ), quasi-uniform sensitivity, contiguous wide-field (160 arcmin 2 ) 1.6 GHz VLBI surv e y of the CANDELS GOODS-North field. This is one of the best-studied extragalactic fields at milli-arcsecond resolution and, therefore, is well-suited as a comparative study for our Tera-pixel VLBI image. The derived VLBI source counts show consistency with those measured in the COSMOS field, which broadly traces the AGN population detected in arcsecond-scale radio surv e ys. Ho we ver, there is a distinctive flattening in the S 1.4GHz ∼100-500 μJy flux density range, which suggests a transition in the population of compact faint radio sources, qualitatively consistent with the excess source counts at 15 GHz that is argued to be an unmodelled population of radio cores. This surv e y approach will assist in deriving robust VLBI source counts and broadening the disco v ery space for future wide-field VLBI surv e ys, including VLBI with the Square Kilometre Array, which will include new large field-of-view antennas on the African continent at ≲1000 km baselines. In addition, it may be useful in the design of both monitoring and/or rapidly triggered VLBI transient programmes.
|
|
| 4. |
|
|
