| 1. |
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| 2. |
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| 3. |
- Audet, T. L., et al.
(author)
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Electron injector for compact staged high energy accelerator
- 2016
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In: Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment. - : Elsevier BV. - 0168-9002. ; 829, s. 304-308
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Journal article (peer-reviewed)abstract
- An electron injector for multi-stage laser wakefield experiments is presented. It consists of a variable length gas cell of small longitudinal dimension (⩽10mm). The gas filling process in this cell was characterized both experimentally and with fluid simulation. Electron acceleration experiments were performed at two different laser facilities. Results show low divergence and low pointing fluctuation electron bunches suitable for transport to a second stage, and a peaked energy distribution suitable for injection into the second stage wakefield accelerator.
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| 4. |
- Borges, A. H., et al.
(author)
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Nonnucleoside Reverse-transcriptase Inhibitor- vs Ritonavir-boosted Protease Inhibitor-based Regimens for Initial Treatment of HIV Infection: A Systematic Review and Metaanalysis of Randomized Trials
- 2016
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In: Clinical Infectious Diseases. - : Oxford University Press (OUP). - 1058-4838 .- 1537-6591. ; 63:2, s. 268-280
-
Journal article (peer-reviewed)abstract
- Background. Previous studies suggest that nonnucleoside reverse-transcriptase inhibitors (NNRTIs) cause faster virologic suppression, while ritonavir-boosted protease inhibitors (PI/r) recover more CD4 cells. However, individual trials have not been powered to compare clinical outcomes. Methods. We searched databases to identify randomized trials that compared NNRTI-vs PI/r-based initial therapy. A meta-analysis calculated risk ratios (RRs) or mean differences (MDs), as appropriate. Primary outcome was death or progression to AIDS. Secondary outcomes were death, progression to AIDS, and treatment discontinuation. We calculated RR of virologic suppression and MD for an increase in CD4 cells at week 48. Results. We included 29 trials with 9047 participants. Death or progression to AIDS occurred in 226 participants in the NNRTI arm and in 221 in the PI/r arm (RR, 1.03; 95% confidence interval, .87-1.22; 12 trials; n = 3825), death in 205 participants in the NNRTI arm vs 198 in the PI/r arm (1.04; 0.86-1.25; 22 trials; n = 8311), and progression to AIDS in 140 participants in the NNRTI arm vs 144 in the PI/r arm (1.00; 0.80-1.25; 13 trials; n = 4740). Overall treatment discontinuation (1.12; 0.93-1.35; 24 trials; n = 8249) and from toxicity (1.21; 0.87-1.68; 21 trials; n = 6195) were comparable, but discontinuation due to virologic failure was more common with NNRTI (1.58; 0.91-2.74; 17 trials; n = 5371). At week 48, there was no difference between NNRTI and PI/r in virologic suppression (RR, 1.03; 0.98-1.09) or CD4(+) recovery (MD, -4.7 cells; -14.2 to 4.8). Conclusions. We found no difference in clinical and viro-immunologic outcomes between NNRTI-and PI/r-based therapy.
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| 5. |
- Desforges, F. G., et al.
(author)
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Analysis of Electron Injection in Laser Wakefield Acceleration Using Betatron Emission in Capillary Tubes
- 2015
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In: Laser Acceleration of Electrons, Protons, and Ions III; and Medical Applications of Laser-Generated Beams of Particles III. - : SPIE. - 1996-756X .- 0277-786X. ; 9514, s. 95140-95140
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Conference paper (peer-reviewed)abstract
- The dynamics of ionization-induced electron injection in the high density (similar to 1.2 x 10(19)cm(-3)) regime of Laser Wakefield Acceleration (LWFA) was investigated by analyzing betatron X-ray emission inside dielectric capillary tubes. A comparative study of the electron and betatron X-ray properties was performed for both self-injection and ionization-induced injection. Direct experimental evidence of early onset of ionization-induced injection into the plasma wave was obtained by mapping the X-ray emission zone inside the plasma. Particle-In-Cell (PIC) simulations showed that the early onset of ionization-induced injection, due to its lower trapping threshold, suppresses self-injection of electrons. An increase of X-ray fluence by at least a factor of two was observed in the case of ionization-induced injection due to an increased trapped charge compared to self-injection mechanism.
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| 6. |
- Desforges, F. G., et al.
(author)
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Dynamics of ionization-induced electron injection in the high density regime of laser wakefield acceleration
- 2014
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In: Physics of Plasmas. - : AIP Publishing. - 1070-664X .- 1089-7674. ; 21:12
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Journal article (peer-reviewed)abstract
- The dynamics of ionization-induced electron injection in high density (similar to 1.2 x 10(19) cm(-3)) regime of laser wakefield acceleration is investigated by analyzing the betatron X-ray emission. In such high density operation, the laser normalized vector potential exceeds the injection-thresholds of both ionization-injection and self-injection due to self-focusing. In this regime, direct experimental evidence of early on-set of ionization-induced injection into the plasma wave is given by mapping the X-ray emission zone inside the plasma. Particle-In-Cell simulations show that this early on-set of ionization-induced injection, due to its lower trapping threshold, suppresses the trapping of self-injected electrons. A comparative study of the electron and X-ray properties is performed for both self-injection and ionization-induced injection. An increase of X-ray fluence by at least a factor of two is observed in the case of ionization-induced injection due to increased trapped charge compared to self-injection mechanism. (C) 2014 AIP Publishing LLC.
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| 7. |
- Gallardo González, I., et al.
(author)
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Effects of the dopant concentration in laser wakefield and direct laser acceleration of electrons
- 2018
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In: New Journal of Physics. - : IOP Publishing. - 1367-2630. ; 20:5
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Journal article (peer-reviewed)abstract
- In this work, we experimentally study the effects of the nitrogen concentration in laser wakefield acceleration of electrons in a gas mixture of hydrogen and nitrogen. A 15 TW peak power laser pulse is focused to ionize the gas, excite a plasma wave and accelerate electrons up to 230 MeV. We find that at dopant concentrations above 2% the total divergence of the electrons is increased and the high energy electrons are emitted preferentially with an angle of ±6 mrad, leading to a forked spatio-spectral distribution associated to direct laser acceleration (DLA). However, electrons can gain more energy and have a divergence lower than 4 mrad for concentrations below 0.5% and the same laser and plasma conditions. Particle-in-cell simulations show that for dopant concentrations above 2%, the amount of trapped charge is large enough to significantly perturb the plasma wave, reducing the amplitude of the longitudinal wakefield and suppressing other trapping mechanisms. At high concentrations the number of trapped electrons overlapping with the laser fields is increased, which rises the amount of charge affected by DLA. We conclude that the dopant concentration affects the quantity of electrons that experience significant DLA and the beam loading of the plasma wave driven by the laser pulse. These two mechanisms influence the electrons final energy, and thus the dopant concentration should be considered as a factor for the optimization of the electron beam parameters.
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| 8. |
- Hansson, M., et al.
(author)
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Localization of ionization-induced trapping in a laser wakefield accelerator using a density down-ramp
- 2016
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In: Plasma Physics and Controlled Fusion. - : IOP Publishing. - 0741-3335 .- 1361-6587. ; 58:5
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Journal article (peer-reviewed)abstract
- We report on a study on controlled trapping of electrons, by field ionization of nitrogen ions, in laser wakefield accelerators in variable length gas cells. In addition to ionization-induced trapping in the density plateau inside the cells, which results in wide, but stable, electron energy spectra, a regime of ionization-induced trapping localized in the density down-ramp at the exit of the gas cells, is found. The resulting electron energy spectra are peaked, with 10% shot-to-shot fluctuations in peak energy. Ionization-induced trapping of electrons in the density down-ramp is a way to trap and accelerate a large number of electrons, thus improving the efficiency of the laser-driven wakefield acceleration.
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| 9. |
- Ju, J., et al.
(author)
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Analysis of x-ray emission and electron dynamics in a capillary-guided laser wakefield accelerator
- 2014
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In: Physical Review Special Topics. Accelerators and Beams. - 1098-4402. ; 17:5
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Journal article (peer-reviewed)abstract
- The dynamics of electron acceleration driven by laser wakefield inside a 30.5 mm long dielectric capillary tube is analyzed using radiation emitted in the x-ray range. 3D particle-in-cell simulations, performed with parameters close to the experimental ones, show that in long plasmas, the accelerated electrons catch up and finally overrun the driving laser owing to a higher velocity of the electrons in the plasma. The electrons are then transversely scattered by the laser pulse, and penetrate the capillary wall where they generate bremsstrahlung radiation, modeled using geant4 simulations. The signature of bremsstrahlung radiation is detected using an x-ray camera, together with the betatron radiation emitted during electron acceleration in the plasma bubble. The reflection of betatron radiation from the inner capillary surface also accounts for a fraction of the observed signal on the x-ray camera. The simulation results are in agreement with the experimental ones and provide a detailed description of the electron and radiation properties, useful for the design of laser wakefield accelerators or radiation sources using long plasma media.
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| 10. |
- Krynitz, B., et al.
(author)
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Risk of basal cell carcinoma in Swedish organ transplant recipients: a population-based study
- 2016
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In: British Journal of Dermatology. - : WILEY-BLACKWELL. - 0007-0963 .- 1365-2133. ; 174:1, s. 95-103
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Journal article (peer-reviewed)abstract
- Background Risk of basal cell carcinoma (BCC) has been reported to be several-fold increased among organ transplant recipients (OTRs). However, due to lack of reliable BCC registration, population-based risk estimates are scarce. Objectives To characterize risk of BCC among OTRs compared with the general population, and contrast with risk of cutaneous squamous cell carcinoma (SCC). Subjects and methods OTRs transplanted during 2004-2011 were identified through national healthcare registers and linked with the nationwide Swedish BCC Register initialized in 2004. Relative risk of BCC was expressed as standardized incidence ratios (SIR) with 95% confidence intervals (CI). Results Altogether, 4023 transplanted patients developed 341 BCCs during follow-up. Compared with the general population, the relative risk of BCC was increased sixfold (SIR 6.1, 95% CI 5.4-6.9). The risk was higher in kidney and heart/lung than in liver recipients (SIRkidney 7.2, 6.3-8.3; SIRheart/lung 5.8, 4.0-8.2; SIRliver 2.6, 1.7-4.0), and risk increased with time since transplantation (P-trend < 0.01). The SCC to BCC ratio was 1 : 1.7 and BCC developed earlier after transplantation than SCC. Distribution of anatomical sites and histological types did not differ substantially between OTR- and population-BCCs. Conclusions Risk of BCC was strikingly elevated in OTRs compared with the general population. Risk was higher in kidney recipients and increased with follow-up time. These findings support a tumour-promoting effect of immunosuppressive drugs in BCC development. The low SCC to BCC ratio was possibly attributed to short follow-up time.
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| 11. |
- Lindqvist, Olav, et al.
(author)
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Complexity in Non-Pharmacological Caregiving Activities at the End of Life : An International Qualitative Study
- 2012
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In: PLoS Medicine. - San Francisco : Public Library of Science. - 1549-1277 .- 1549-1676. ; 9:2, s. e1001173-
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Journal article (peer-reviewed)abstract
- Background: In late-stage palliative cancer care, relief of distress and optimized well-being become primary treatment goals. Great strides have been made in improving and researching pharmacological treatments for symptom relief; however, little systematic knowledge exists about the range of non-pharmacological caregiving activities (NPCAs) staff use in the last days of a patient's life. Methods and Findings: Within a European Commission Seventh Framework Programme project to optimize research and clinical care in the last days of life for patients with cancer, OPCARE9, we used a free-listing technique to identify the variety of NPCAs performed in the last days of life. Palliative care staff at 16 units in nine countries listed in detail NPCAs they performed over several weeks. In total, 914 statements were analyzed in relation to (a) the character of the statement and (b) the recipient of the NPCA. A substantial portion of NPCAs addressed bodily care and contact with patients and family members, with refraining from bodily care also described as a purposeful caregiving activity. Several forms for communication were described; information and advice was at one end of a continuum, and communicating through nonverbal presence and bodily contact at the other. Rituals surrounding death and dying included not only spiritual/religious issues, but also more subtle existential, legal, and professional rituals. An unexpected and hitherto under-researched area of focus was on creating an aesthetic, safe, and pleasing environment, both at home and in institutional care settings. Conclusions: Based on these data, we argue that palliative care in the last days of life is multifaceted, with physical, psychological, social, spiritual, and existential care interwoven in caregiving activities. Providing for fundamental human needs close to death appears complex and sophisticated; it is necessary to better distinguish nuances in such caregiving to acknowledge, respect, and further develop end-of-life care.
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| 12. |
- Maitrallain, A., et al.
(author)
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Parametric study of high-energy ring-shaped electron beams from a laser wakefield accelerator
- 2022
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In: New Journal of Physics. - : IOP Publishing. - 1367-2630. ; 24:1
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Journal article (peer-reviewed)abstract
- Laser wakefield accelerators commonly produce on-axis, low-divergence, high-energy electron beams. However, a high charge, annular shaped beam can be trapped outside the bubble and accelerated to high energies. Here we present a parametric study on the production of low-energy-spread, ultra-relativistic electron ring beams in a two-stage gas cell. Ring-shaped beams with energies higher than 750 MeV are observed simultaneously with on axis, continuously injected electrons. Often multiple ring shaped beams with different energies are produced and parametric studies to control the generation and properties of these structures were conducted. Particle tracking and particle-in-cell simulations are used to determine properties of these beams and investigate how they are formed and trapped outside the bubble by the wake produced by on-axis injected electrons. These unusual femtosecond duration, high-charge, high-energy, ring electron beams may find use in beam driven plasma wakefield accelerators and radiation sources.
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| 13. |
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| 14. |
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| 15. |
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| 16. |
- Spesyvtsev, R., et al.
(author)
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Generation of electron high energy beams with a ring-like structure by a dual stage laser wakefield accelerator
- 2019
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In: Relativistic Plasma Waves and Particle Beams as Coherent and Incoherent Radiation Sources III. - : SPIE. - 9781510627383 ; 11036
-
Conference paper (peer-reviewed)abstract
- The laser wake-field accelerator (LWFA) traditionally produces high brightness, quasi-monoenergetic electron beams with Gaussian-like spatial and angular distributions. In the present work we investigate the generation of ultra-relativistic beams with ring-like structures in the blowout regime of the LWFA using a dual stage accelerator. A density down-ramp triggers injection after the first stage and is used to produce ring-like electron spectra in the 300 - 600 MeV energy range. These well defined, annular beams are observed simultaneously with the on-axis, high energy electron beams, with a divergence of a few milliradians. The rings have quasi-monoenergetic energy spectra with an RMS spread estimated to be less than 5%. Particle-in-cell simulations confirm that off-axis injection provides the electrons with the initial transverse momentum necessary to undertake distinct betatron oscillations within the plasma bubble during their acceleration process.
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| 17. |
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| 18. |
- Andreev, N. E., et al.
(author)
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Analysis of laser wakefield dynamics in capillary tubes
- 2010
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In: New Journal of Physics. - : IOP Publishing. - 1367-2630. ; 12
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Journal article (peer-reviewed)abstract
- A general approach to the modifications of the spectrum of a laser pulse interacting with matter is elaborated and used for spectral diagnostics of laser wakefield generation in guiding structures. Analytical predictions of the laser frequency red shift due to the wakefield excited in a capillary waveguide are confirmed by self-consistent modeling results. The role of ionization blue shift, and nonlinear laser pulse and wakefield dynamics on the spectrum modification, is analyzed for recent experiments on plasma wave excitation by an intense laser pulse guided in hydrogen-filled glass capillary tubes up to 8 cm long. The dependence of the spectral frequency shift, measured as a function of filling pressure, capillary tube length and incident laser energy, is in excellent agreement with the simulation results, and the associated longitudinal accelerating field is in the range 1-10 GV m(-1).
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| 19. |
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| 20. |
- Audet, T. L., et al.
(author)
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Investigation of ionization-induced electron injection in a wakefield driven by laser inside a gas cell
- 2016
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In: Physics of Plasmas. - : AIP Publishing. - 1070-664X .- 1089-7674. ; 23:2
-
Journal article (peer-reviewed)abstract
- Ionization-induced electron injection was investigated experimentally by focusing a driving laser pulse with a maximum normalized potential of 1.2 at different positions along the plasma density profile inside a gas cell, filled with a gas mixture composed of 99%H2+1%N2. Changing the laser focus position relative to the gas cell entrance controls the accelerated electron bunch properties, such as the spectrum width, maximum energy, and accelerated charge. Simulations performed using the 3D particle-in-cell code WARP with a realistic density profile give results that are in good agreement with the experimental ones. The interest of this regime for optimizing the bunch charge in a selected energy window is discussed.
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| 21. |
- Aurand, B., et al.
(author)
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Manipulation of the spatial distribution of laser-accelerated proton beams by varying the laser intensity distribution
- 2016
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In: Physics of Plasmas. - : AIP Publishing. - 1089-7674 .- 1070-664X. ; 23:2
-
Journal article (peer-reviewed)abstract
- We report on a study of the spatial profile of proton beams produced through target normal sheath acceleration using flat target foils and changing the laser intensity distribution on the target front surface. This is done by either defocusing a single laser pulse or by using a split-pulse setup and irradiating the target with two identical laser pulses with variable spatial separation. The resulting proton beam profile and the energy spectrum are recorded as functions of the focal spot size of the single laser pulse and of the separation between the two pulses. A shaping of the resulting proton beam profile, related to both an increase in flux of low-energy protons in the target normal direction and a decrease in their divergence, in one or two dimensions, is observed. The results are explained by simple modelling of rear surface sheath field expansion, ionization, and projection of the resulting proton beam.
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| 22. |
- Axelsson, K. F., et al.
(author)
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Fracture Risk After Gastric Bypass Surgery : A Retrospective Cohort Study
- 2018
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In: Osteoporosis International. - : Springer London. - 0937-941X .- 1433-2965. ; 29:Suppl. 1, s. S491-S491
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Journal article (other academic/artistic)abstract
- Objectives: Gastric bypass surgery constitutes the most common and effective bariatric surgery to treat obesity. Gastric bypass leads to bone oss but fracture risk following surgery has been insufficiently studied. Our objective was to investigate if gastric bypass surgery in obese patients, with and without diabetes, was associated with fracture risk, and if the fracture risk was associated with post-surgery weight loss or insufficient calcium and vitamin D supplementation.Methods: Using large databases, 38 971 obese patients undergoing gastric bypass were identified, 7758 with diabetes and 31 213 without. Through multivariable 1:1 propensity score matching, well-balanced controls were identified. The risk of fracture and fall injury was investigated using Cox proportional hazards and flexible parameter models. Fracture risk according to weight loss and degree of calcium and vitamin D supplementation one year post-surgery was investigated.Results: 77 942 patients had a median and total follow-up time of 3.1 (IQR 1.7-4.6) and 251 310 person-years, respectively. Gastric bypass was associated with increased risk of any fracture, in patients with diabetes and without diabetes using a multivariable Cox model (HR 1.26, 95%CI 1.05-1.53 and HR 1.32, 95%CI 1.18-1.47, respectively). The risk of fall injury without fracture was also increased after gastric bypass, both in patients with (HR 1.26 95%CI 1.04-1.52) and without diabetes (HR 1.24 95%CI 1.12-1.38). Weight loss or degree of calcium and vitamin D supplementation after gastric bypass were not associated with fracture risk.Conclusions: Gastric bypass was associated with an increased risk of fracture and fall injury. Weight loss or calcium and vitamin D supplementation following surgery were not associated with fracture risk. These findings indicate that gastric bypass increases fracture risk, which could at least partly be due to increased susceptibility to falls.
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| 23. |
- Berg, J, et al.
(author)
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CAVIAR : a tool to improve serial analysis of the 12-lead electrocardiogram
- 1995
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In: Clinical Physiology and Functional Imaging. - : Wiley. - 0144-5979. ; 15:5, s. 435-445
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Journal article (peer-reviewed)abstract
- An important part of an electrocardiogram (ECG) interpretation is the comparison between the present ECG and earlier recordings. The purpose of the present study was to evaluate a combination of two computer-based methods, synthesized vectorcardiogram (VCG) and CAVIAR, in this comparison. The methods were applied to a group of 38 normal subjects and to a group of 36 patients treated with anthracyclines. A fraction of these patients are likely to develop cardiac injury during or after the treatment, since anthracyclines are known to cause heart failure and cardiomyopathy. Two ECGs were recorded on each patient, one before and one after the treatment. On each normal subject, two ECGs were recorded with an interval of 8-9 years. A synthesized VCG was calculated from each ECG and the two synthesized VCGs from each subject were analysed with the CAVIAR method. The CAVIAR analysis is a quantitative method and normal limits for four measurements were established using the normal group. Values above these limits were more frequent in the patient group than in the normal group. The conventional ECGs were also analysed visually by an experience ECG interpreter without knowledge of the result of the CAVIAR analysis. No significant serial changes were found in 10 of the patients with high CAVIAR values. Changes in the ECGs were found in two patients with normal CAVIAR values. In summary, synthesized VCG and CAVIAR could be used to highlight small serial changes that are difficult to find in a visual analysis of ECGs.
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| 24. |
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| 25. |
- Cassou, K., et al.
(author)
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Optimization toward a high-average-brightness soft-x-ray laser pumped at grazing incidence
- 2007
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In: Optics Letters. - 0146-9592. ; 32:2, s. 139-141
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Journal article (peer-reviewed)abstract
- We report the near-field imaging characterization of a 10 Hz Ni-like 18.9 nm molybdenum soft-x-ray laser pumped in a grazing incidence pumping (GRIP) geometry with a table-top laser driver. We investigate the effect of varying the GRIP angle on the spatial behavior of the soft-x-ray laser source. After multiparameter optimization, we were able to find conditions to generate routinely a high-repetition-rate soft-x-ray laser with an energy level of up to 3 mu J/pulse and to 6 x 10(17) photons/s/mm(2)/mrad(2)/(0.1% bandwidth) average brightness and 1 x 10(28) photons/s/mm(2)/mrad(2)/(0.1% bandwidth) peak brightness. (c) 2006 Optical Society of America.
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| 26. |
- Cvijovic, Marija, 1977, et al.
(author)
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Strategies for structuring interdisciplinary education in systems biology: An European perspective
- 2016
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In: npj Systems Biology and Applications. - : Springer Science and Business Media LLC. - 2056-7189. ; 2
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Journal article (peer-reviewed)abstract
- Systems Biology is an approach to biology and medicine that has the potential to lead to a better understanding of how biological properties emerge from the interaction of genes, proteins, molecules, cells and organisms. The approach aims at elucidating how these interactions govern biological function by employing experimental data, mathematical models and computational simulations. As Systems Biology is inherently multidisciplinary, education within this field meets numerous hurdles including departmental barriers, availability of all required expertise locally, appropriate teaching material and example curricula. As university education at the Bachelor’s level is traditionally built upon disciplinary degrees, we believe that the most effective way to implement education in Systems Biology would be at the Master’s level, as it offers a more flexible framework. Our team of experts and active performers of Systems Biology education suggest here (i) a definition of the skills that students should acquire within a Master’s programme in Systems Biology, (ii) a possible basic educational curriculum with flexibility to adjust to different application areas and local research strengths, (iii) a description of possible career paths for students who undergo such an education, (iv) conditions that should improve the recruitment of students to such programmes and (v) mechanisms for collaboration and excellence spreading among education professionals. With the growing interest of industry in applying Systems Biology approaches in their fields, a concerted action between academia and industry is needed to build this expertise. Here we present a reflection of the European situation and expertise, where most of the challenges we discuss are universal, anticipating that our suggestions will be useful internationally. We believe that one of the overriding goals of any Systems Biology education should be a student’s ability to phrase and communicate research questions in such a manner that they can be solved by the integration of experiments and modelling, as well as to communicate and collaborate productively across different experimental and theoretical disciplines in research and development.
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| 27. |
- Desforges, F. G., et al.
(author)
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Reproducibility of electron beams from laser wakefield acceleration in capillary tubes
- 2014
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In: Nuclear Instruments & Methods in Physics Research. Section A: Accelerators, Spectrometers, Detectors, and Associated Equipment. - : Elsevier BV. - 0167-5087 .- 0168-9002. ; 740, s. 54-59
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Journal article (peer-reviewed)abstract
- The stability of accelerated electron beams produced by self injection of plasma electrons into the wakefield driven by a laser pulse guided inside capillary tubes is analyzed statistically in relation to laser and plasma parameters, and compared to results obtained in a gas jet. The analysis shows that reproducible electron beams are achieved with a charge of 66 pC +/- 11%, a FWHM beam divergence of 9 mrad +/- 14%, a maximum energy of 120 MeV +/- 10% and pointing fluctuations of 2.3 mrad using 10 mm long, 178 mu m diameter capillary tubes at an electron density of (10.0 +/- 1.5) x 10(18) cm(-3). Active stabilization of the laser pointing was used and laser parameters were recorded on each shot. Although the shot-to-shot laser energy fluctuations can account for a fraction of the electrons fluctuations, gas density fluctuations are suspected to be a more important source of instability. (C) 2013 Elsevier B.V. All rights reserved.
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| 28. |
- Dickson, L. T., et al.
(author)
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Mechanisms to control laser-plasma coupling in laser wakefield electron acceleration
- 2022
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In: Physical Review Accelerators and Beams. - 2469-9888. ; 25:10
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Journal article (peer-reviewed)abstract
- Experimental results, supported by precise modeling, demonstrate optimization of a plasma-based injector with intermediate laser pulse energy (<1 J), corresponding to a normalized vector potential a0=2.15, using ionization injection in a tailored plasma density profile. An increase in electron bunch quality and energy is achieved experimentally with the extension of the density downramp at the plasma exit. Optimization of the focal position of the laser pulse in the tailored plasma density profile is shown to efficiently reduce electron bunch angular deviation, leading to a better alignment of the electron bunch with the laser axis. Single peak electron spectra are produced in a previously unexplored regime by combining an early focal position and adaptive optic control of the laser wavefront by optimizing the symmetry of the prefocal laser energy distribution. Experimental results have been validated through particle-in-cell simulations using realistic laser energy, phase distribution, and temporal envelope, allowing for accurate predictions of difficult to model parameters, such as total charge and spatial properties of the electron bunches, opening the way for more accurate modeling for the design of plasma-based accelerators.
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| 29. |
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| 30. |
- Ferri, Julien, 1990, et al.
(author)
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Proton acceleration by a pair of successive ultraintense femtosecond laser pulses
- 2018
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In: Physics of Plasmas. - : AIP Publishing. - 1070-664X .- 1089-7674. ; 25
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Journal article (peer-reviewed)abstract
- © 2018 Author(s). We investigate the target normal sheath acceleration of protons in thin aluminum targets irradiated at a relativistic intensity by two time-separated ultrashort (35 fs) laser pulses. When the full-energy laser pulse is temporally split into two identical half-energy pulses, and using target thicknesses of 3 and 6 μm, we observe experimentally that the second half-pulse boosts the maximum energy and charge of the proton beam produced by the first half-pulse for time delays below ∼0.6-1 ps. Using two-dimensional particle-in-cell simulations, we examine the variation of the proton energy spectra with respect to the time-delay between the two pulses. We demonstrate that the expansion of the target front surface caused by the first pulse significantly enhances the hot-electron generation by the second pulse arriving after a few hundreds of fs time delay. This enhancement, however, does not suffice to further accelerate the fastest protons driven by the first pulse once three-dimensional quenching effects have set in. This implies a limit to the maximum time delay that leads to proton energy enhancement, which we theoretically determine.
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| 31. |
- Filippi, F., et al.
(author)
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Plasma density profile reconstruction of a gas cell for Ionization Induced Laser Wakefield Acceleration
- 2023
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In: Journal of Instrumentation. - 1748-0221. ; 18:5
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Journal article (peer-reviewed)abstract
- Laser-driven plasma wakefields can provide hundreds of MeV electron beam in mm-range distances potentially shrinking the dimension of the actual particle accelerators. The plasma density plays a fundamental role in the control and stability of the acceleration process, which is a key development for the future electron injector proposed by EuPRAXIA. A gas cell was designed by LPGP and LIDYL teams, with variable length and backing pressure, to confine the gas and tailor the gas density profile before the arrival of the laser. This cell was used during an experimental campaign with the multi TW-class laser at the Lund Laser Centre. Ionization assisted injection in a tailored density profile is used to tune the electron beam properties. During the experiment, we filled the gas cell with hydrogen mixed with different concentration of nitrogen. We also varied the backing pressure of the gas and the geometrical length of the gas cell. We used a transverse probe to acquire shadowgraphic images of the plasma and to measure the plasma electron density. Methods and results of the analysis with comparisons between shadowgraphic and interferometric images will be discussed.
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| 32. |
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| 33. |
- Frank, J., et al.
(author)
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Dietary flavonoids with a catechol structure increase alpha-tocopherol in rats and protect the vitamin from oxidation in vitro
- 2006
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In: Journal of Lipid Research. - 0022-2275 .- 1539-7262. ; 47:12, s. 2718-2725
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Journal article (peer-reviewed)abstract
- To identify dietary phenolic compounds capable of improving vitamin E status, male Sprague-Dawleyrats were fed for 4 weeks either a basal diet ( control) with 2 g/kg cholesterol and an adequate content of vitamin E or the basal diet fortified with quercetin ( Q), (2)-epicatechin (EC), or (1)-catechin ( C) at concentrations of 2 g/kg. All three catechol derivatives substantially increased concentrations of alpha-tocopherol (alpha-T) in blood plasma and liver. To study potential mechanisms underlying the observed increase of alpha-T, the capacities of the Flavonoids to i) protect alpha-T from oxidation in LDL exposed to peroxyl radicals, ii) reduce alpha-tocopheroxyl radicals (alpha-T-.) in SDS micelles, and iii) inhibit the metabolism of tocopherols in HepG2 cells were determined. All flavonoids protected alpha-T from oxidation in human LDL ex vivo and dose-dependently reduced the concentrations of alpha-T-.. None of the test compounds affected vitamin E metabolism in the hepatocyte cultures. In conclusion, fortification of the diet of Sprague-Dawley rats with Q, EC, or C considerably improved their vitamin E status. The underlying mechanism does not appear to involve vitamin E metabolism but may involve direct quenching of free radicals or reduction of the alpha-T-. by the flavonoids.
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| 34. |
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| 35. |
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| 36. |
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| 37. |
- Gerlee, Philip, 1980, et al.
(author)
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Gene divergence and pathway duplication in the metabolic network of yeast and digital organisms
- 2009
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In: Journal of the Royal Society Interface. - : The Royal Society. - 1742-5689 .- 1742-5662. ; 6, s. 1233-1245
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Journal article (peer-reviewed)abstract
- We have studied the metabolic gene–function network in yeast and digital organisms evolved in the artificial life platform Avida. The gene–function network is a bipartite network in which a link exists between a gene and a function (pathway) if that function depends on that gene, and can also be viewed as a decomposition of the more traditional functional gene networks, where two genes are linked if they share any function. We show that the gene–function network exhibits two distinct degree distributions: the gene degree distribution is scale-free while the pathway distribution is exponential. This is true for both yeast and digital organisms, which suggests that this is a general property of evolving systems, and we propose that the scale-free gene degree distribution is due to pathway duplication, i.e. the development of a new pathway where the original function is still retained. Pathway duplication would serve as preferential attachment for the genes, and the experiments with Avida revealed precisely this; genes involved in many pathways are more likely to increase their connectivity. Measuring the overlap between different pathways, in terms of the genes that constitute them, showed that pathway duplication also is a likely mechanism in yeast evolution. This analysis sheds new light on the evolution of genes and functionality, and suggests that function duplication could be an important mechanism in evolution.
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| 38. |
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| 39. |
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| 40. |
- Hansson, Martin, et al.
(author)
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Enhanced stability of laser wakefield acceleration using dielectric capillary tubes
- 2014
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In: Physical Review Special Topics. Accelerators and Beams. - 1098-4402. ; 17:3
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Journal article (peer-reviewed)abstract
- The stability of beams of laser wakefield accelerated electrons in dielectric capillary tubes is experimentally investigated. These beams are found to be more stable in charge and pointing than the corresponding beams of electrons accelerated in a gas jet. Electron beams with an average charge of 43 pC and a standard deviation of 14% are generated. The fluctuations in charge are partly correlated to fluctuations in laser pulse energy. The pointing scatter of the electron beams is measured to be as low as 0.8 mrad (rms). High laser beam pointing stability improved the stability of the electron beams.
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| 41. |
- Hansson, M., et al.
(author)
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Injection of electrons by colliding laser pulses in a laser wakefield accelerator
- 2015
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In: Nuclear Instruments & Methods in Physics Research. Section A: Accelerators, Spectrometers, Detectors, and Associated Equipment. - : Elsevier BV. - 0168-9002. ; 829, s. 99-103
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Journal article (peer-reviewed)abstract
- To improve the stability and reproducibility of laser wakefield accelerators and to allow for future applications, controlling the injection of electrons is of great importance. This allows us to control the amount of charge in the beams of accelerated electrons and final energy of the electrons. Results are presented from a recent experiment on controlled injection using the scheme of colliding pulses and performed using the Lund multi-terawatt laser. Each laser pulse is split into two parts close to the interaction point. The main pulse is focused on a 2. mm diameter gas jet to drive a nonlinear plasma wave below threshold for self-trapping. The second pulse, containing only a fraction of the total laser energy, is focused to collide with the main pulse in the gas jet under an angle of 150°. Beams of accelerated electrons with low divergence and small energy spread are produced using this set-up. Control over the amount of accelerated charge is achieved by rotating the plane of polarization of the second pulse in relation to the main pulse. Furthermore, the peak energy of the electrons in the beams is controlled by moving the collision point along the optical axis of the main pulse, and thereby changing the acceleration length in the plasma.
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| 42. |
- Hussein, A. E., et al.
(author)
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Laser-wakefield accelerators for high-resolution X-ray imaging of complex microstructures
- 2019
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In: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 9:1
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Journal article (peer-reviewed)abstract
- Laser-wakefield accelerators (LWFAs) are high acceleration-gradient plasma-based particle accelerators capable of producing ultra-relativistic electron beams. Within the strong focusing fields of the wakefield, accelerated electrons undergo betatron oscillations, emitting a bright pulse of X-rays with a micrometer-scale source size that may be used for imaging applications. Non-destructive X-ray phase contrast imaging and tomography of heterogeneous materials can provide insight into their processing, structure, and performance. To demonstrate the imaging capability of X-rays from an LWFA we have examined an irregular eutectic in the aluminum-silicon (Al-Si) system. The lamellar spacing of the Al-Si eutectic microstructure is on the order of a few micrometers, thus requiring high spatial resolution. We present comparisons between the sharpness and spatial resolution in phase contrast images of this eutectic alloy obtained via X-ray phase contrast imaging at the Swiss Light Source (SLS) synchrotron and X-ray projection microscopy via an LWFA source. An upper bound on the resolving power of 2.7 ± 0.3 μm of the LWFA source in this experiment was measured. These results indicate that betatron X-rays from laser wakefield acceleration can provide an alternative to conventional synchrotron sources for high resolution imaging of eutectics and, more broadly, complex microstructures.
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| 43. |
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| 44. |
- Ju, J., et al.
(author)
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Enhancement of x-rays generated by a guided laser wakefield accelerator inside capillary tubes
- 2012
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In: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 100:19
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Journal article (peer-reviewed)abstract
- Abstract in UndeterminedElectrons accelerated in the nonlinear regime in a laser wakefield accelerator experience transverse oscillations inside the plasma cavity, giving rise to ultra-short pulsed x-rays, also called the betatron radiation. We show that the fluence of x-ray can be enhanced by more than one order of magnitude when the laser is guided by a 10 mm long capillary tube instead of interacting with a 2 mm gas jet. X-rays with a synchrotron-like spectrum and associated critical energy ∼ 5 keV, with a peak brightness of ∼ 1×1021 ph/s/mm2/mrad2/0.1%BW, were achieved by employing 16 TW laser pulses.
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| 45. |
- Ju, J., et al.
(author)
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Study of electron acceleration and x-ray radiation as a function of plasma density in capillary-guided laser wakefield accelerators
- 2013
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In: Physics of Plasmas. - : AIP Publishing. - 1070-664X .- 1089-7674. ; 20:8
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Journal article (peer-reviewed)abstract
- Laser wakefield electron acceleration in the blow-out regime and the associated betatron X-ray radiation were investigated experimentally as a function of the plasma density in a configuration where the laser is guided. Dielectric capillary tubes were employed to assist the laser keeping self-focused over a long distance by collecting the laser energy around its central focal spot. With a 40 fs, 16 TW pulsed laser, electron bunches with tens of pC charge were measured to be accelerated to an energy up to 300 MeV, accompanied by X-ray emission with a peak brightness of the order of 10 21 ph/s/mm(2)/mrad(2)/0.1%BW. Electron trapping and acceleration were studied using the emitted X-ray beam distribution to map the acceleration process; the number of betatron oscillations performed by the electrons was inferred from the correlation between measured X-ray fluence and beam charge. A study of the stability of electron and X-ray generation suggests that the fluctuation of X-ray emission can be reduced by stabilizing the beam charge. The experimental results are in good agreement with 3D particle-in-cell (PIC) simulation. (C) 2013 AIP Publishing LLC.
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| 46. |
- Kazamias, S, et al.
(author)
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Characterization of a transient collisional Ni-like molybdenum soft x-ray laser pumped in grazing incidence
- 2008
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In: Physical Review A (Atomic, Molecular and Optical Physics). - 1050-2947. ; 77:3
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Journal article (peer-reviewed)abstract
- We present experimental results from an extensive investigation of a Ni-like Mo X-ray laser pumped in the transient regime and GRIP configuration (GRazing Incidence Pumping). The pump laser is a 10 Hz, 1 J, Ti:Sa laser system. The main diagnostic is a monochromatic near-field imaging system with a 1.7 micron spatial resolution that shows the soft x-ray laser source size and position relative to the target surface. Changes of those characteristics are observed for different GRIP angles, varied between 15◦ and 21◦, while keeping all other parameters constant. Intense lasing is observed routinely at 18.9 nm with up to 3 microjoule output energy and stable operation is demonstrated at 10 Hz. We have investigated the role of several pumping parameters, in particular the relative energy and delay between the long and short pulse. We show that this multi-parameter scan leads to a well-defined optimal regime of operation and better understanding of the GRIP configuration. Finally, as the GRIP scheme requires careful tailoring of the plasma conditions to the specific soft x-ray laser under investigation, we add a prepulse before the plasma producing long pulse to generate large-scale preplasmas. This increases the brightness of the soft x-ray beam and leads to an almost gaussian near-field spatial profile.
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| 47. |
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| 48. |
- Kettle, B., et al.
(author)
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Single-Shot Multi-keV X-Ray Absorption Spectroscopy Using an Ultrashort Laser-Wakefield Accelerator Source
- 2019
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In: Physical Review Letters. - 0031-9007. ; 123:25
-
Journal article (peer-reviewed)abstract
- Single-shot absorption measurements have been performed using the multi-keV x rays generated by a laser-wakefield accelerator. A 200 TW laser was used to drive a laser-wakefield accelerator in a mode which produced broadband electron beams with a maximum energy above 1 GeV and a broad divergence of ≈15 mrad FWHM. Betatron oscillations of these electrons generated 1.2±0.2×106 photons/eV in the 5 keV region, with a signal-to-noise ratio of approximately 300 1. This was sufficient to allow high-resolution x-ray absorption near-edge structure measurements at the K edge of a titanium sample in a single shot. We demonstrate that this source is capable of single-shot, simultaneous measurements of both the electron and ion distributions in matter heated to eV temperatures by comparison with density functional theory simulations. The unique combination of a high-flux, large bandwidth, few femtosecond duration x-ray pulse synchronized to a high-power laser will enable key advances in the study of ultrafast energetic processes such as electron-ion equilibration.
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| 49. |
- Landegren, N, et al.
(author)
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AIREing out autoimmunity
- 2015
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In: SCIENCE TRANSLATIONAL MEDICINE. - 1946-6234. ; 7:292
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Journal article (other academic/artistic)
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| 50. |
- Lindau, Filip, et al.
(author)
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Quantitative study of 10 Hz operation of a soft x-ray laser-energy stability and target considerations
- 2007
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In: Optics Express. - 1094-4087. ; 15:15, s. 9486-9493
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Journal article (peer-reviewed)abstract
- A soft x- ray laser from Ni- like Mo, pumped in grazing incidence ( GRIP), is analyzed with regard to high repetition rate operation. Reliable lasing is obtained, but with significant energy fluctuations attributed mainly to beam pointing jitter from the pump laser. Two modes of operation are compared: continuously moving target and stationary target. With a moving target the soft X- ray output is constant on average, whereas the repeated use of the same target position leads to a pulse energy which increases for several tens of shots. This effect might be caused by improved guiding of the pump laser in the formed groove and the removal, through laser ablation, of the oxide layer on the target surface. (c) 2007 Optical Society of America.
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