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| 2. |
- Pirozhkov, A. S., et al.
(författare)
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Diagnostic of laser contrast using target reflectivity
- 2009
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 94:24
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Tidskriftsartikel (refereegranskat)abstract
- Using three different laser systems, we demonstrate a convenient and simple plasma based diagnostic of the contrast of high-power short-pulse lasers. The technique is based on measuring the specular reflectivity from a solid target. The reflectivity remains high even at relativistic intensities above 10(19) W/cm(2) in the case of a high-contrast prepulse-free laser. On the contrary, the specular reflectivity drops with increasing intensities in the case of systems with insufficient contrast due to beam breakup and increased absorption caused by preplasma.
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| 3. |
- Blackburn, Tom, 1989, et al.
(författare)
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Benchmarking semiclassical approaches to strong-field QED: Nonlinear Compton scattering in intense laser pulses
- 2018
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Ingår i: Physics of Plasmas. - : AIP Publishing. - 1089-7674 .- 1070-664X. ; 25:8
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Tidskriftsartikel (refereegranskat)abstract
- The recoil associated with photon emission is key to the dynamics of ultrarelativistic electrons in strong electromagnetic fields, as found in high-intensity laser-matter interactions and astrophysical environments such as neutron star magnetospheres. When the energy of the photon becomes comparable to that of the electron, it is necessary to use quantum electrodynamics (QED) to describe the dynamics accurately. However, computing the appropriate scattering matrix element from strong-field QED is not generally possible due to multiparticle effects and the complex structure of the electromagnetic fields. Therefore, these interactions are treated semiclassically, coupling probabilistic emission events to classical electrodynamics using rates calculated in the locally constant field approximation. Here, we provide comprehensive benchmarking of this approach against the exact QED calculation for nonlinear Compton scattering of electrons in an intense laser pulse. We find agreement at the percentage level between the photon spectra, as well as between the models' predictions of absorption from the background field, for normalized amplitudes a0> 5. We discuss possible routes towards improved numerical methods and the implications of our results for the study of QED cascades.
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| 4. |
- Blackburn, Thomas, 1989, et al.
(författare)
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Radiation beaming in the quantum regime
- 2020
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Ingår i: Physical Review A. - 2469-9926. ; 101:1
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Tidskriftsartikel (refereegranskat)abstract
- Classical theories of radiation reaction predict that the electron motion is confined to the plane defined by the electron's instantaneous momentum and the force exerted by the external electromagnetic field. However, in the quantum radiation reaction regime, where the recoil exerted by individual quanta becomes significant, the electron can scatter "out of plane," as the photon is emitted into a cone with finite opening angle. We show that Monte Carlo implementation of an angularly resolved emission rate leads to substantially improved agreement with exact QED calculations of nonlinear Compton scattering. Furthermore, we show that the transverse recoil caused by this finite beaming, while negligible in many high-intensity scenarios, can be identified in the increase in divergence, in the plane perpendicular to the laser polarization and wave vector, of a high-energy electron beam that interacts with a linearly polarized, ultraintense laser.
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| 5. |
- Bulanov, S. S., et al.
(författare)
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Depletion of intense fields
- 2017
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Ingår i: AIP Conference Proceedings. - : Author(s). - 1551-7616 .- 0094-243X. - 9780735414808 ; 1812:1, s. Article no. UNSP 100006 -
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Konferensbidrag (refereegranskat)abstract
- The problem of backreaction of quantum processes on the properties of the background field still remains on the list of outstanding questions of high intensity particle physics. Usually, photon emission by an electron or positron, photon decay into electron-positron pairs in strong electromagnetic fields, or electron-positron pair production by such fields are described in the framework of the external field approximation. It is assumed that the external field has infinite energy and is not affected by these processes. However, the above-mentioned processes have a multi-photon nature, i.e., they occur with the absorption of a significant number of field photons. As a result, the interaction of an intense electromagnetic field with either a highly charged electron bunch or a fast growing population of electrons, positrons, and gamma photons (as in the case of an electromagnetic cascade) may lead to a depletion of the field energy, thus making the external field approximation invalid. Taking the multi-photon Compton process as an example, we estimate the threshold of depletion and find it to become significant at field strengths (a0∼103) and electron bunch charge of about tens of nC. © 2017 Author(s).
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| 6. |
- Moiseev, Sergey, et al.
(författare)
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Association of venous thromboembolic events with skin, pulmonary and kidney involvement in ANCA-associated vasculitis : A multinational study
- 2021
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Ingår i: Rheumatology. - : Oxford University Press (OUP). - 1462-0332 .- 1462-0324. ; 60:10, s. 4654-4661
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Tidskriftsartikel (refereegranskat)abstract
- Objective: To investigate the occurrence of venous thromboembolic events (VTE) in a large cohort of patients with antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV) across the European Union, Turkey, Russia, UK and North America. Methods: Patients with a definite diagnosis of AAV who were followed for at least 3 months and had sufficient documentation were included. Data on VTE, including either deep vein thrombosis or pulmonary embolism, were collected retrospectively from tertiary vasculitis centres. Univariate and multivariate regression models were used to estimate odds ratios (ORs) and 95% CIs. Results: Over a median follow-up of 63 (interquartile range: 29, 101) months, VTE occurred in 278 (9.7%) of 2869 AAV patients with a similar frequency across different countries (from 6.3% to 13.7%), and AAV subtype [granulomatosis with polyangiitis: 9.8% (95% CI: 8.3, 11.6%); microscopic polyangiitis: 9.6% (95% CI: 7.9, 11.4%); and eosinophilic granulomatosis with polyangiitis: 9.8% (95% CI: 7.0, 13.3%)]. Most VTE (65.6%) were reported in the first-year post-diagnosis. Multiple factor logistic regression analysis adjusted for sex and age showed that skin (OR 1.71, 95% CI: 1.01, 2.92), pulmonary (OR 1.78, 95% CI: 1.04, 3.14) and kidney [eGFR 15-60 ml/min/1.73 m2, OR 2.86 (95% CI: 1.27, 6.47); eGFR <15 ml/min/1.73 m2, OR 6.71 (95% CI: 2.94, 15.33)] involvement were independent variables associated with a higher occurrence of VTE. Conclusion: Two-thirds of VTE occurred during the initial phase of active disease. We confirmed previous findings from smaller studies that a decrease in kidney function, skin involvement and pulmonary disease are independently associated with VTE.
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| 7. |
- Moiseev, Sergey, et al.
(författare)
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Traditional and Disease-Specific Risk Factors for Cardiovascular Events in Antineutrophil Cytoplasmic Antibody-Associated Vasculitis : A Multinational Retrospective Study
- 2023
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Ingår i: Journal of Rheumatology. - : The Journal of Rheumatology. - 0315-162X .- 1499-2752. ; 50:9, s. 1145-1151
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Tidskriftsartikel (refereegranskat)abstract
- Objective. To investigate the occurrence of cardiovascular events (CVEs) in a large cohort of patients with antineutrophil cytoplasmic antibody (ANCA)-Associated vasculitis (AAV) across the European Union, China, Turkey, Russia, the United Kingdom, and the USA. Methods. Patients with a definite diagnosis of AAV who were followed for ? 3 months and had sufficient documentation were included. Data on myocardial infarction (MI) and stroke were collected retrospectively from tertiary vasculitis centers. Univariate and multivariate Cox regression models were used to estimate hazard ratios (HRs) and 95% CIs. Results. Over a median follow-up of 62.0 months (IQR 22.6-100.0), CVEs (mostly MIs) occurred in 245 (10.7%) of 2286 patients with AAV, with a higher frequency in China and the UK. On multivariate regression analysis, older age (55-64.9 yrs, HR 2.93, 95% CI 1.99-4.31), smoking (HR 1.98, 95% CI 1.48-2.64), Chinese origin (HR 4.24, 95% CI 3.07-5.85), and pulmonary (HR 1.50, 95% CI 1.09-2.06) and kidney (HR 3.02, 95% CI 2.08-4.37) involvement were independent variables associated with a higher occurrence of CVEs. Conclusion. We showed that geographic region and both traditional and disease-specific (kidney involvement in particular) factors were independently associated with CVEs. Proper assessment and management of modifiable cardiovascular (CV) risk factors are essential for prevention of CV morbidity in patients with AAV.
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| 8. |
- Sarri, G, et al.
(författare)
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The application of laser-driven proton beams to the radiography of intense laser–hohlraum interactions
- 2010
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Ingår i: New Journal of Physics. - : IOP Publishing Ltd. - 1367-2630. ; 12:4, s. 045006-
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Tidskriftsartikel (refereegranskat)abstract
- Plasma expansion following the interaction of an intense laser beam with the inner surface of gold hohlraums, emulating conditions relevant to indirect drive inertial confinement fusion (ICF), has been investigated by a radiographic technique which employs a beam of laser-accelerated protons. This probing technique has made it possible to measure the electric field distribution associated with the plasma front and its propagation throughout the interior of the hohlraum with a temporal and spatial resolution of the order of a few ps and μm, respectively. The data indicate that the expanding plasma slows down approaching the opposite walls, possibly due to the interaction with x-ray heated plasma from the non-irradiated walls. The electric field at the plasma front shows a bipolar structure, suggesting the presence of ion-acoustic soliton-like structures cotraveling with the front. Data obtained using enclosed hohlraums suggest the feasibility of this type of diagnosis in gas-filled hohlraums, as currently employed in ICF experiments.
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| 9. |
- Seipt, D., et al.
(författare)
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Depletion of Intense Fields
- 2017
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Ingår i: Physical Review Letters. - 1079-7114 .- 0031-9007. ; 118:15, s. 154803-
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Tidskriftsartikel (refereegranskat)abstract
- The interaction of charged particles and photons with intense electromagnetic fields gives rise to multiphoton Compton and Breit-Wheeler processes. These are usually described in the framework of the external field approximation, where the electromagnetic field is assumed to have infinite energy. However, the multiphoton nature of these processes implies the absorption of a significant number of photons, which scales as the external field amplitude cubed. As a result, the interaction of a highly charged electron bunch with an intense laser pulse can lead to significant depletion of the laser pulse energy, thus rendering the external field approximation invalid. We provide relevant estimates for this depletion and find it to become important in the interaction between fields of amplitude a0?103 and electron bunches with charges of the order of 10 nC.
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