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The Radio Frequency Quadrupole (RFQ) was conditioned at the European Spallation Source during spring 2021. We used part of the conditioning time to estimate the accelerating potential within the RFQ analyzing the x-rays bremsstrahlung radiation emitted by the electrons released and accelerated in the RFQ. The results of these measurements are in good agreement with the theoretical prediction.

Bremsstrahlung X-ray yield of 204Tl (0.76MeV) and 147Pm (0.225MeV) in in Barium compounds such as BaF2, BaI2, BaS, Ba3N2, BaSe and BaH2 has been measured using NaI(Tl) crystal and is compared with theory. The Z dependence of Bremsstrahlung is also measured and compared with the theory.

The interaction between intense 30 fs laser pulses and foam-coated 1.5 μ m-thick Al foils in the relativistic regime (up to 5 × 10 20  W cm −2 ) is studied to optimize the laser energy conversion into laser-accelerated protons. A significant enhancement is observed for foam targets in terms of proton cut-off energy (18.5 MeV) and number of protons above 4.7 MeV (4 × 10 9 protons/shot) with respect to uncoated foils (9.5 MeV, 1 × 10 9 protons/shot), together with a sixfold increase in the bremsstrahlung yield. This enhancement is attributed to increased laser absorption and electron generation in the foam meso- and nanostructure.

The charge contained in an electron bunch is one of the most important parameters in accelerator physics. Several techniques to measure the electron bunch charge exist. However, many conventional charge diagnostics face serious drawbacks when applied to plasma accelerators. For example, integrating current transformers (ICTs or toroids) have been shown to be sensitive to the electromagnetic pulses (EMP) originating from the plasma, whereas scintillating screens are sensitive to background radiation such as betatron radiation or bremsstrahlung and only allow for a destructive measurement of the bunch charge. We show measurements with a noninvasive, cavity-based charge diagnostic (the DaMon), which demonstrate its high sensitivity, high dynamic range and resistance towards EMP. The measurements are compared to both an ICT and an absolutely calibrated scintillating screen.

remsstrahlung in rays is significant factor for high vitality electrons. At medium to high laser intensities absorption by the classical inverse bremsstrahlung process decreases rapidly and this mechanism alone is insufficient to explain the levels of absorption measured in recent experiments. Bremsstrahlung radiation measurement is one of the most commonly used plasma diagnostics methods. Most of the bremsstrahlung measurements with electron cyclotron resonance ion sources have been performed in continuous operation mode yielding information only on the steady-state bremsstrahlung emission. The processes of absorption of laser energy are fundamental to the study of laser-heated thermonuclear plasmas and have received considerable attention from theorists and in experiments. This paper describes results of bremsstrahlung. An algorithm for the simulation of bremsstrahlung emission by fast electrons using numerical cross sections is described

Terrestrial gamma‐ray flashes are linked to growth of long bidirectional lightning leader system consisting of positive and stepping negative leaders. The spatial extent of streamer zones of a typical lightning leader with tip potential exceeding several tens of megavolts is on the order of 10–100 m. The photoelectric absorption of bremsstrahlung radiation generated by avalanching relativistic runaway electrons occurs efficiently on the same spatial scales. The intense multiplication of these electrons is triggered when the size of the negative leader streamer zone crosses a threshold of approximately 100 m (for sea‐level air pressure conditions) allowing self‐replication of these avalanches due to the upstream relativistic electron seeds generated by the photoelectric absorption. The model results also highlight importance of electrode effects in interpretation of X‐ray emissions from centimeter to meter long laboratory discharges, in particular, a similar feedback effect produced by generation of runaway electrons from the cathode material. Plain Language Summary We propose a physical mechanism that explains spectacular naturally occurring bursts of X‐rays that are observed in association with lightning activity in the Earth’s atmosphere. These events are commonly referred to as terrestrial gamma ray flashes (TGFs). The mechanism is based on a feedback process allowing amplification of relativistic electron avalanches when X‐rays emitted by these electrons travel backwards with respect to the electron motion and generate new relativistic electron seeds due to the photoelectric absorption in air. The presented model results agree with the observational and experimental evidence indicating that TGFs are associated with steps of negative lightning leaders and originate from relatively compact regions of space with spatial extent on the order of 10–100 m. The mechanism is not sensitive to the origin and amount of the initial runaway electrons and identical results are obtained whether the initial seeds are provided by the natural background as cosmic ray secondaries or generated by the streamer discharges. We also provide quantitative evidence that in the presence of electrodes the same amplification mechanism and X‐ray production may involve generation of runaway electrons from the cathode material. These effects may be relevant to development of new X‐ray sources. Key Points The onset of terrestrial gamma ray flashes is linked to the spatial extent of the lightning leader streamer zone The photoelectric absorption is the dominant feedback factor defining inception of relativistic runaway discharges in air The photoelectric absorption generated runaway electrons from the cathode facilitate X‐rays from laboratory sparks

A bstract Using a heavy-mass effective field theory (HEFT), we study gravitational-wave emission in the scattering of two spinless black holes or neutron stars of arbitrary masses at next-to-leading order in the Post-Minkowskian expansion. We compute the contributions to the one-loop scattering amplitude with four scalars and one graviton which are relevant to the calculation of the waveforms, also presenting expressions of classical tree-level amplitudes with four scalars and up to two radiated gravitons. The latter are obtained using a novel on-shell recursion relation for classical amplitudes with four scalars and an arbitrary number of gravitons. Our one-loop five-point amplitude is expressed in terms of a single family of master integrals with the principal value prescription for linearised massive propagators, which we evaluate using differential equations. In our HEFT approach, soft/heavy-mass expansions of complete integrands are avoided, and all hyper-classical iterations and quantum corrections are dropped at the diagrammatic level, thereby computing directly contributions to classical physics. Our result exhibits the expected factorisation of infrared divergences, the correct soft limits, and highly nontrivial cancellations of spurious poles. Finally, using our amplitude result we compute numerically the corresponding next-to-leading corrections to the spectral waveforms and the far-field time-domain waveforms using the Newman-Penrose scalar Ψ 4 .

Real-time evaluation of laser-driven byproducts is crucial for state-of-the-art facilities operating at high repetition rates. This work presents real-time measurements of hard X-rays (bremsstrahlung radiation) generated from the interaction of high-intensity laser pulses with solid targets in the target normal sheath acceleration regime using a scintillator stack detector. The detector offers insights into the effectiveness of laser–plasma interaction through measured fluctuations in bremsstrahlung radiation temperature and scintillation light yield on a shot-to-shot basis. Moreover, a strong correlation of the bremsstrahlung measurements (i.e., temperature and yield) with the cutoff energy of laser-driven protons was observed. The scintillator stack detector serves not only as a diagnostic for online monitoring of the laser–plasma interaction but also as a promising tool for estimating proton energy fluctuations in a non-disruptive manner, which is particularly important when direct proton source characterization is impractical, for example, during experiments aimed at irradiating user samples with the accelerated proton beam.

Prompt photons are important yet challenging to observe in relativistic heavy-ion collisions, as they are produced in the early stages and traverse almost the entire QGP medium without interaction. Experimental analyses typically employ isolation cuts, in the hope to identify prompt photons. Most theoretical studies consider only events with actual prompt photons, assuming no contribution from isolated non-prompt photons to reduce computational cost. For the first time, we present a study that compares simulation results generated using inclusive (bremsstrahlung) and prompt-photon events with multiple experimental observables for both p − p and Pb − Pb collisions at 5.02 TeV. Simulations are carried out using the multi-stage JETSCAPE framework tuned to describe the quenching of jets and hadrons. Isolated non-prompt photons are generated in hard photon bremsstrahlung, where the photon is radiated at a sufficient angle to the jet. Several photon triggered jet and jet substructure observables show significant contributions from inclusive photons, yielding an improvement in comparison with experimental data. Novel photon triggered jet substructure observables are also expected to show new structures, yet to be detected in experiment. This effort examines the significance of isolated nonprompt photons using parameters tuned for a simultaneous description of the leading hadron and jet spectrum, and thus provides an independent verification of the multistage evolution framework.

Theoretically predicted fundamental features in the process of resonant spontaneous bremsstrahlung radiation during the scattering of ultrarelativistic electrons with energies of the order ∼ 100 GeV by the nuclei in strong laser fields with intensities up to I ∼ 10 24  W cm −2 . Under resonant conditions, an intermediate electron in the wave field enters the mass shell. As a result, the initial second-order process by the fine structure constant is effectively reduced to two first-order processes: laser-stimulated Compton effect and laser-assisted Mott process. The resonant kinematics for two reaction channels (A and B) is studied in detail. An analytical resonant differential cross-section with simultaneous registration of the frequency and the outgoing angle of a spontaneous gamma-quantum for channels A and B is obtained. The resonant differential cross section takes the largest value with a small number of absorbed laser photons. In this case, the resonant cross-section is determined by one parameter, depending on the small transmitted momenta, as well as the resonance width. In strong fields, spontaneous gamma quanta of small energies are most likely to be emitted compared to the energy of the initial electrons. At the same time, the angular width of the radiation of such gamma quanta is the largest. With an increase in the number of absorbed laser photons, the resonant cross-section decreases quite quickly, and the resonant frequency of spontaneous gamma quanta increases. It is shown that the resonant differential cross-section has the largest value in the region of average laser fields ( I ∼ 10 18  W cm −2 ) and can be of the order of ∼ 1 0 19 in units Z 2 α r e 2 . With an increase in the intensity of the laser wave, the value of the resonant differential cross-section R r e s max decreases and for the intensity I ∼ 10 24  W cm −2 is R r e s max ≲ 1 0 7 in units Z 2 α r e 2 . The obtained results reveal new features of spontaneous emission of ultrarelativistic electrons on nuclei in strong laser fields and can be tested at international laser installations.