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| 2. |
- Graves, J. P., et al.
(författare)
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RECENT ADVANCES IN SAWTOOTH CONTROL
- 2011
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Ingår i: Fusion science and technology. - 1536-1055 .- 1943-7641. ; 59:3, s. 539-548
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Tidskriftsartikel (refereegranskat)abstract
- Important advances have been made recently in the invention and application of experimental methods to control the sawtooth instability in tokamak plasmas. The primary means of control involves the application of either ion cyclotron resonance heating (ICRH), or electron cyclotron heating, with resonance very close to the q = 1 radius in the plasma core. Reported here are experiments that have successfully applied these methods to either shorten or lengthen the sawteeth deliberately, in a variety of plasma conditions, in three tokamaks: Joint European Torus (JET), TCV, and Tore Supra. It is shown that despite the sensitivity of the sawtooth period to the resonance position, sawteeth can be controlled using either real-time control of the electron cyclotron deposition, or in the case of ion cyclotron heating, very careful adjustment of the magnetic field strength and minority ion concentration. The latter technique has been guided by theoretical advances that have enabled the control of sawteeth in JET with ITER-relevant ICRH scenarios.
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| 3. |
- Andrew, P, et al.
(författare)
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Outer divertor target deposited layers during reversed magnetic field operation in JET
- 2005
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Ingår i: Journal of Nuclear Materials. - : Elsevier BV. - 0022-3115 .- 1873-4820. ; 337:1-3, s. 99-103
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Tidskriftsartikel (refereegranskat)abstract
- Divertor surface temperatures are significantly affected by the presence of deposited surface layers. This phenomenon can be used to monitor deposited layer evolution on a shot-by-shot basis. It was found that during an experimental campaign where the B x del B direction was reversed that the outer target, normally an erosion zone, became a deposition zone.
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| 4. |
- Bhowmick, Asmit, et al.
(författare)
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Structural evidence for intermediates during O2 formation in photosystem II
- 2023
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Ingår i: Nature. - : Springer Nature. - 0028-0836 .- 1476-4687. ; 617:7961, s. 629-636
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Tidskriftsartikel (refereegranskat)abstract
- In natural photosynthesis, the light-driven splitting of water into electrons, protons and molecular oxygen forms the first step of the solar-to-chemical energy conversion process. The reaction takes place in photosystem II, where the Mn4CaO5 cluster first stores four oxidizing equivalents, the S0 to S4 intermediate states in the Kok cycle, sequentially generated by photochemical charge separations in the reaction center and then catalyzes the O–O bond formation chemistry. Here, we report room temperature snapshots by serial femtosecond X-ray crystallography to provide structural insights into the final reaction step of Kok’s photosynthetic water oxidation cycle, the S3→[S4]→S0 transition where O2 is formed and Kok’s water oxidation clock is reset. Our data reveal a complex sequence of events, which occur over micro- to milliseconds, comprising changes at the Mn4CaO5 cluster, its ligands and water pathways as well as controlled proton release through the hydrogen-bonding network of the Cl1 channel. Importantly, the extra O atom Ox, which was introduced as a bridging ligand between Ca and Mn1 during the S2→S3 transition, disappears or relocates in parallel with Yz reduction starting at approximately 700 μs after the third flash. The onset of O2 evolution, as indicated by the shortening of the Mn1–Mn4 distance, occurs at around 1,200 μs, signifying the presence of a reduced intermediate, possibly a bound peroxide.
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