Methods for Extremely Sparse-Angle Proton Tomography

Proton radiography is a widely-fielded diagnostic used to measure magnetic structures in plasma. The deflection of protons with multi-MeV kinetic energy by the magnetic fields is used to infer their path-integrated field strength. Here, the use of tomographic methods is proposed for the first time to lift the degeneracy inherent in these path-integrated measurements, allowing full reconstruction of spatially resolved magnetic field structures in three dimensions. Two techniques are proposed which improve the performance of tomographic reconstruction algorithms in cases with severely limited numbers of available probe beams, as is the case in laser-plasma interaction experiments where the probes are created by short, high-power laser pulse irradiation of secondary foil targets. The methods are equally applicable to optical probes such as shadowgraphy and interferometry [M. Kasim et al. Phys. Rev. E 95, 023306 (2017)], thereby providing a disruptive new approach to three dimensional imaging across the physical sciences and engineering disciplines.Comment: 11 pages, 6 figures, companion article to arXiv:2103.1126

Advantages to a diverging Raman amplifier

The plasma Raman instability can efficiently compress a nanosecond long high-power laser pulse to sub-picosecond duration. Although, many authors envisaged a converging beam geometry for Raman amplification, here we propose the exact opposite geometry; the amplification should start at the intense focus of the seed. We generalise the coupled laser envelope equations to include this non-collimated case. The new geometry completely eradicates the usual trailing secondary peaks of the output pulse, which typically lower the efficiency by half. It also reduces, by orders of magnitude, the initial seed pulse energy required for efficient operation. As in the collimated case, the evolution is self similar, although the temporal pulse envelope is different. A two-dimensional particle-in-cell simulation demonstrates efficient amplification of a diverging seed with only 0.3 mJ energy. The pulse has no secondary peaks and almost constant intensity as it amplifies and diverges

The 2018 European heatwave led to stem dehydration but not to consistent growth reductions in forests

Heatwaves exert disproportionately strong and sometimes irreversible impacts on forest ecosystems. These impacts remain poorly understood at the tree and species level and across large spatial scales. Here, we investigate the effects of the record-breaking 2018 European heatwave on tree growth and tree water status using a collection of high-temporal resolution dendrometer data from 21 species across 53 sites. Relative to the two preceding years, annual stem growth was not consistently reduced by the 2018 heatwave but stems experienced twice the temporary shrinkage due to depletion of water reserves. Conifer species were less capable of rehydrating overnight than broadleaves across gradients of soil and atmospheric drought, suggesting less resilience toward transient stress. In particular, Norway spruce and Scots pine experienced extensive stem dehydration. Our high-resolution dendrometer network was suitable to disentangle the effects of a severe heatwave on tree growth and desiccation at large-spatial scales in situ, and provided insights on which species may be more vulnerable to climate extremes

Dependence of tokamak confinement on ELM power loss

Zusammenfassung in deutscher SpracheDie Energie-Einschlusszeit TE ist eine Messgröße, die beschreibt, wie lange Energie in einem Plasma eingeschlossen bleibt. Studien für die Tokamak-Einschlusszeit mit mehreren Tokamaks wurden verwendet um Skalierungen abzuleiten, die auf sogenannten Engineering-Parametern beruhen. Der Vergleich zwischen gemessener und errechneter Einschlusszeit resultiert in dem sogenannten H-Faktor, welcher den Wert eins annimmt, wenn die Skalierung perfekt ist. Ein H-Faktor, der niedriger als eins ist beschreibt ein Szenario, in welchem das Plasma für den Teilcheneinschluss schlechtere Eigenschaften aufweist als berechnet. Das Auftreten von sogenannten Edge Localised Modes (ELMs), also von lokalisierten Moden im Plasmarand, in der High Confinement Mode eines Tokamaks beschränkt die Größe der Randtransportbarriere, welche auch Pedestal (Podest) genannt wird. Ein Zusammenbruch wegen einer ELM ist mit Teilchen- und Energietransport aus dem Plasma hinaus assoziiert und passiert, wenn ein kritischer Pedestaldruckgradient erreicht wird. Den Messungen und Skalierungen zufolge hat die Erhöhung der Heizleistung einen negativen Effekt auf TE. Jedoch wurde bislang noch nicht evaluiert, in welcher Form die durch ELMs verlorene Leistung Skalierungen der Einschlusszeit beeinflusst. In dieser Masterarbeit wurde die Skalierung der Energie-Einschlusszeit durch das Einbeziehen ebendieser Leistung recharakterisiert. Es wird mithilfe von ASDEX-Upgrade Messungen gezeigt, dass keine Verbesserung der Skalierung erreicht wird. Eine höhere Standardabweichung im H-Faktor für Preduced = Pheat - PELM verglichen mit dem H-Faktor für die Pheat-Skalierung unterstützen diese Beobachtung. Um die Skalierungen interpretieren zu können, wurden Parameterkorrelationen - zum Beispiel für Pheat oder die Verlustleistung durch ELMs - berechnet. Des Weiteren wurde versucht Skalierungen für die ELM-Verluste, welche in die Anteile der ELM-Frequenz und des Energieverlusts aufgeteilt wurden, zu finden. Jedoch war die Interpretation dieser Skalierungen problematisch, da sie, wie durch einen hohen RMS-Fehlerwert beschrieben wird, unpräzise zu sein scheinen. Hinweise für einen positiven Trend zwischen den ELM-Verlusten und dem Pedestaldruck werden jedoch gezeigt.The energy confinement time TE is a measure of how long energy remains in a plasma. Multi-machine studies of TE have been used to derive a scaling law for tokamak confinement based on engineering parameters. Comparing the measured confinement time to the predicted confinement time results in the H-factor, which is equal to one if the scaling is perfect. An H-factor of less than one describes a scenario where the plasma does not perform as well as predicted. The occurence of Edge Localised Modes (ELMs) in the high confinement mode of a tokamak limits the height of the edge transport barrier, known as the pedestal. A crash due to an ELM is associated with particle and energy transport outwards of the confined region and occurs when a critical pedestal pressure gradient is reached. According to measurements and scalings, increasing the input power has a negative effect on E. But the effect of the power lost due to ELMs on the confinement time has so far not been taken into account for scalings of the energy confinement time. In this thesis, the energy confinement time scaling is recharacterised by including the power losses due to ELMs and it is shown, using data from ASDEX Upgrade, that no improvement can be seen by doing so. A higher deviation in the H-Factor for Preduced = Pheat -PELM compared with the H-factor of the Pheat scaling attest to this finding. In order to be able to interpret the scalings, parameter correlations, e.g. for the heating power and the ELM loss power, have been computed. It was also tried to find scaling laws for ELM losses, which were split into scalings for the ELM frequency and for the energy loss due to ELMs. These scalings however were more difficult to interpret and were found to be more inaccurate resulting in a high root-mean-square error. Indications will be presented which show a positive trend between ELM losses and the pedestal pressure.6

Complication rate after cystectomy following pelvic radiotherapy: an international, multicenter, retrospective series of 682 cases

PURPOSE: Conflicting evidence exists on the complication rates after cystectomy following previous radiation (pRTC) with only a few available series. We aim to assess the complication rate of pRTC for abdominal-pelvic malignancies. METHODS: Patients treated with radical cystectomy following any previous history of RT and with available information on complications for a minimum of 1 year were included. Univariable and multivariable logistic regression models were used to assess the relationship between the variable parameters and the risk of any complication. RESULTS: 682 patients underwent pRTC after a previous RT (80.5% EBRT) for prostate, bladder (BC), gynecological or other cancers in 49.1%, 27.4%, 9.8% and 12.9%, respectively. Overall, 512 (75.1%) had at least one post-surgical complication, classified as Clavien ≥ 3 in 29.6% and Clavien V in 2.9%. At least one surgical complication occurred in 350 (51.3%), including bowel leakage in 6.2% and ureteric stricture in 9.4%. A medical complication was observed in 359 (52.6%) patients, with UTI/pyelonephritis being the most common (19%), followed by renal failure (12%). The majority of patients (86%) received an incontinent urinary diversion. In multivariable analysis adjusted for age, gender and type of RT, patients treated with RT for bladder cancer had a 1.7 times increased relative risk of experiencing any complication after RC compared to those with RT for prostate cancer (p = 0.023). The type of diversion (continent vs non-continent) did not influence the risk of complications. CONCLUSION: pRTC carries a high rate of major complications that dramatically exceeds the rates reported in RT-naïve RCs. status: publishe

Complication rate after cystectomy following pelvic radiotherapy: an international, multicenter, retrospective series of 682 cases

PURPOSE: Conflicting evidence exists on the complication rates after cystectomy following previous radiation (pRTC) with only a few available series. We aim to assess the complication rate of pRTC for abdominal-pelvic malignancies. METHODS: Patients treated with radical cystectomy following any previous history of RT and with available information on complications for a minimum of 1 year were included. Univariable and multivariable logistic regression models were used to assess the relationship between the variable parameters and the risk of any complication. RESULTS: 682 patients underwent pRTC after a previous RT (80.5% EBRT) for prostate, bladder (BC), gynecological or other cancers in 49.1%, 27.4%, 9.8% and 12.9%, respectively. Overall, 512 (75.1%) had at least one post-surgical complication, classified as Clavien ≥ 3 in 29.6% and Clavien V in 2.9%. At least one surgical complication occurred in 350 (51.3%), including bowel leakage in 6.2% and ureteric stricture in 9.4%. A medical complication was observed in 359 (52.6%) patients, with UTI/pyelonephritis being the most common (19%), followed by renal failure (12%). The majority of patients (86%) received an incontinent urinary diversion. In multivariable analysis adjusted for age, gender and type of RT, patients treated with RT for bladder cancer had a 1.7 times increased relative risk of experiencing any complication after RC compared to those with RT for prostate cancer (p = 0.023). The type of diversion (continent vs non-continent) did not influence the risk of complications. CONCLUSION: pRTC carries a high rate of major complications that dramatically exceeds the rates reported in RT-naïve RCs.status: publishe