We present the results of electron generation experiments conducted at the Advanced Photon Research Center, Japan Atomic Energy Research Institute, using 23-fs relativistically intense 20-TW tightly focused laser pulses with underdense plasma. We observed electron energies up to 40 MeV characterized by a two-temperature Maxwell distribution. With the help of particle-in-cell simulations, we found that these are due to different plasma wave-breaking processes. A charge of 5 nC/shot was obtained at a small solid angle, which corresponds to high peak current generation.
A new regime of relativistic high-order harmonic generation has been discovered (Pirozhkov 2012 Phys. Rev. Lett. 108 135004). Multi-terawatt relativistic-irradiance (>1018 W cm−2) femtosecond (∼30–50 fs) lasers focused to underdense (few × 1019 cm−3) plasma formed in gas jet targets produce comb-like spectra with hundreds of even and odd harmonic orders reaching the photon energy of 360 eV, including the 'water window' spectral range. Harmonics are generated either by linearly or circularly polarized pulses from the J-KAREN (KPSI, JAEA) and Astra Gemini (CLF, RAL, UK) lasers. The photon number scalability has been demonstrated with a 120 TW laser, producing 40 μJ sr−1 per harmonic at 120 eV. The experimental results are explained using particle-in-cell simulations and catastrophe theory. A new mechanism of harmonic generation by sharp, structurally stable, oscillating electron spikes at the joint of the boundaries of the wake and bow waves excited by a laser pulse is introduced. In this paper, detailed descriptions of the experiments, simulations and model are provided and new features are shown, including data obtained with a two-channel spectrograph, harmonic generation by circularly polarized laser pulses and angular distribution.
The results of experiments are presented for the laser electron acceleration in the ablative capillary discharge plasma. The plasma channel is formed by the discharge inside the ablative capillary. The intense short laser pulse is guided over a 4 cm length. The generated relativistic electrons show both the quasimonoenergetic and quasi-Maxwellian energy spectra, depending on laser and plasma parameters. The analysis of the inner walls of the capillaries that underwent several tens of shots shows that the wall deformation and blistering resulted from the discharge and laser pulse effects.
In Japan, fetal growth restriction (FGR) has been diagnosed when the estimated fetal weight (EFW) below -1.5SD. On the other hand, the definition of FGR by ISUOG defines FGR and small for gestational age (SGA) by using the ultrasound Doppler in addition to the EFW. FGR is further classified into early FGR, and late FGR. The purpose of this study was to reclassify FGR fetus by Japanese criteria according to ISUOG criteria and investigate perinatal outcomes. This was retrospective study in our hospital from 2017 to 2021. Fetus diagnosed with FGR by Japanese criteria were reclassified retrospectively into early FGR group, late FGR group, and SGA group according to the ISUOG definition. Perinatal outcomes were statistically examined. The mothers were guaranteed the opportunity to decline participation. (Ethical committee approved number M21259). One hundred eighty-five fetuses were reclassified according to the ISUOG definition. Twenty-four fetuses were excluded due to malformations, 43 were in the early FGR, 39 in the late FGR, and 79 in the SGA. The data are presented below in the order of early FGR/late FGR/SGA groups with medians or percentages. Before pregnancy maternal weight was 53/48/50Kg, weight gain during pregnancy was 6.8/7.3/9.1Kg, gestational age (GA) at delivery was 36.4/38.3/39.3week, preterm birth rate was 53/20/10%, vaginal delivery rate was 23/64/65%, 1-min Apgar score was 8/8/8, 5-min Apgar score was 9/9/9, birthweight was 1.4/3.7/6.4%ile, birth height was 2.6/4.0/6.5%ile, and birth head circumference was 13.6/13.2/25.9%ile. Statistically, early FGR had significantly higher rates of preterm delivery, earlier GA at delivery, and lower rates of vaginal delivery compared to late FGR and SGA. Late FGR significantly lower maternal weight gain during pregnancy, earlier GA at delivery compared to SGA. Fetus diagnosed with FGR by Japanese criteria were reclassified using ISUOG definition. This study shows that prenatal outcomes were statistically different.
A new method of optical guidance by the implosion phase of a fast Z-pinch discharge in a gas-filled capillary is proposed. An imploding plasma column has a concave electron-density profile in the radial direction, just before a stagnation phase driven by a converging current sheet and a shock wave. The feasibility of optical guidance of a high-intensity (>1 x 10(17) W/cm(2)) Ti:sapphire laser pulse by use of this method over a distance of 2 cm, corresponding to 12.5 times the Rayleigh length, has been experimentally demonstrated. The guiding-channel formation process was directly probed with a He-Ne laser beam. The electron density in the fully ionized channel was estimated to be 2.0 x 10(17) cm(-3) on the axis and 7.0 x 10(17) cm(-3) on the peaks of the channel edge, with a diameter of 70 mum, as indicated by the experimental results, which were corroborated by a magnetohydrodynamics simulation.
Laser wakefi eld acceleration, based on the effect of plasma waves excitation in the wake of an intense laser pulse, is now regarded as a basis for the next generation of charged particle accelerators.In order to generate a bunch with high quality and stability, required for applications, the electrons should be duly injected into the wakefi eld and this injection should be controllable.This paper reviews optical injection of electrons into the wakefi eld for a stable and a controllable electron beam generation.The wakefi eld is generated by a laser pulse.The second laser pulse collides with the fi rst pulse at 180 and at 135 degrees realizing optical injection of an electron bunch.The electron bunch has high stability and high reproducibility compared with single pulse electron generation.
The results of experiments are presented for the single laser pulse interaction with a very low density gas target, under the conditions when the generated wake wave is below the wave-breaking threshold and the laser pulse power is lower than the critical power for relativistic self-focusing. A quasi-monoenergetic electron beam is found to be stably generated for various laser pulse intensity values by controlling the acceleration length. The results of two-dimensional particle-in-cell simulations show that for the electron acceleration an additional mechanism of electron injection into the acceleration phase is required. It is demonstrated that the longitudinal inhomogeneity of the plasma density leads to the electron injection.
We studied the cause of cracking of a clinically used polyurethane (PU) catheter during the constant infusion of etoposide (VP-16) injection (Lastet), administered without dilution to patients as a part of combination high-dose chemotherapy. After VP-16 injection was infused into the PU catheter at a constant infusion rate (30 ml/h) for 24 h, a decrease in the elasticity (36% of untreated) and on increase in the length of the catheter (3.7%) were observed. These changes were significantly higher than those treated with the control saline. The similar changes of the PU catheter were observed after treatment with a basal solution containing polyethylene glycol 400 (PEG 400), polysorbate 80 and ethanol, which is the vehicle of the VP-16 injection, and with ethanol alone. Moreover, obvious degeneration of the internal wall (occurrence of spots like melting) and cutting face (micro-cracking) of the catheter was observed with an electron microscope after treatment with the vehicle. On the other hand, the elasticity or extension of the PU catheter were not changed after treatment with saline or PEG 400. From these findings, it was suggested that the degeneration and subsequent cracking of the PU catheter during the infusion of VP-16 injection was caused by ethanol contained in its injection solution. No cracking or morphological changes of polyvinyl chloride (PVC) and silicone catheters were found after treatment with the vehicle solution. However, since it has been reported in previous reports that di(2-ethylhexyl)phthalate was leached from PVC bags, the high dose chemotherapy with the dilution-free VP-16 injection should be achieved safely and effectively using a silicon catheter, rather than the PU catheter.
An intense isotropic source of multicharged carbon and oxygen ions with energy above 300 keV and particle number >108 per shot was obtained by femtosecond Ti:Sa laser irradiation of submicron clusters. The source was employed for high-contrast contact ionography images with 600 nm spatial resolution. A variation in object thickness of 100 nm was well resolved for both Zr and polymer foils.
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