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Summary Background The benefit and safety of laparoscopic pancreatoduodenectomy (LPD) for the treatment of pancreatic or periampullary tumours remain controversial. Studies have shown that the learning curve plays an important role in LPD, yet there are no randomised studies on LPD after the surgeons have surmounted the learning curve. The aim of this trial was to compare the outcomes of open pancreatoduodenectomy (OPD) with those of LPD, when performed by experienced surgeons. Methods In this multicentre, open-label, randomised controlled trial done in 14 Chinese medical centres, we recruited patients aged 18–75 years with a benign, premalignant, or malignant indication for pancreatoduodenectomy. Eligible patients were randomly assigned (1:1) to undergo either LPD or OPD. Randomisation was centralised via a computer-generated system that used a block size of four. The patients and surgeons were unmasked to study group, whereas the data collectors, outcome assessors, and data analysts were masked. LPD and OPD were performed by experienced surgeons who had already done at least 104 LPD operations. The primary outcome was the postoperative length of stay. The criteria for discharge were based on functional recovery, and analyses were done on a modified intention-to-treat basis (ie, including patients who had a pancreatoduodenectomy regardless of whether the operation was the one they were assigned to). This trial is registered with Clinicaltrials.gov , number NCT03138213 . Findings Between May 18, 2018, and Dec 19, 2019, we assessed 762 patients for eligibility, of whom 656 were randomly assigned to either the LPD group (n=328) or the OPD group (n=328). 31 patients in each group were excluded and 80 patients crossed over (33 from LPD to OPD, 47 from OPD to LPD). In the modified intention-to-treat analysis (297 patients in the LPD group and 297 patients in the OPD group), the postoperative length of stay was significantly shorter for patients in the LPD group than for patients in the OPD group (median 15·0 days [95% CI 14·0–16·0] vs 16·0 days [15·0–17·0]; p=0·02). 90-day mortality was similar in both groups (five [2%] of 297 patients in the LPD group vs six [2%] of 297 in the OPD group, risk ratio [RR] 0·83 [95% CI 0·26–2·70]; p=0·76). The incidence rate of serious postoperative morbidities (Clavien-Dindo grade of at least 3) was not significantly different in the two groups (85 [29%] of 297 patients in the LPD group vs 69 [23%] of 297 patients in OPD group, RR 1·23 [95% CI 0·94–1·62]; p=0·13). The comprehensive complication index score was not significantly different between the two groups (median score 8·7 [IQR 0·0–26·2] vs 0·0 [0·0–20·9]; p=0·06). Interpretation In highly experienced hands, LPD is a safe and feasible procedure. It was associated with a shorter length of stay and similar short-term morbidity and mortality rates to OPD. Nonetheless, the clinical benefit of LPD compared with OPD was marginal despite extensive procedural expertise. Future research should focus on identifying the populations that will benefit from LPD. Funding National Natural Science Foundation of China and Tongji Hospital, Huazhong University of Science and Technology, China.

IntroductionPancreatoduodenectomy (PD) is one of the most complex abdominal operations to perform, and it is usually conducted for tumours of the periampullary region and chronic pancreatitis. Minimally invasive surgery has been progressively being developed for pancreatic surgery, first with the advent of hybrid-laparoscopy and recently with total laparoscopic surgery. Issues including the safety and efficacy of total laparoscopic pancreaticoduodenectomy (TLPD) and open pancreaticoduodenectomy (OPD) are currently being debated. Studies comparing these two surgical techniques are emerging, and large randomised controlled trials (RCTs) are lacking but are clearly required.Methods and analysisTJDBPS01 is a multicentre, prospective, randomised controlled, parallel-group, superiority trial in 14 centres with pancreatic surgery experts who have performed ≥104 TLPDs and OPDs. A total of 656 patients who will undergo PD are randomly allocated to the TLPD group or OPD group in a 1:1 ratio. The trial hypothesis is that TLPD has superior or equivalent safety and advantages in postoperative recovery compared with OPD. The primary outcome is the postoperative length of stay.Ethics and disseminationThe Instituitional Review Board Approval of Tongji Hospital, Tongji Medical College, Huazhong University of Science and Technology has approved this trial and will be routinely monitoring the trial at frequent intervals, as will an independent third-party organisation. Any results from this trial (publications, conference presentations) will be published in peer-reviewed journals and conference proceedings.Trial registration numberNCT03138213

In our previous work, a plasma approach for single attosecond pulse (AP) generation was proposed. A few-cycle relativistic circularly polarized laser pulse will induce a single drastic oscillation of plasma boundary, from which high-order harmonics and furthermore an ultra-intense single AP can be generated naturally after it is reflected. Analytical model and simulations both demonstrate that the process is mostly efficient as the pulse duration is close to the plasma responding time. The effects of plasma density ramp are analyzed here, suggesting that the proposal is still quite efficient with appropriate density gradient in the ramp. At last, a combined approach is employed to obtain single AP with 30 fs incident laser. The relatively large-duration pulse is firstly shortened by a density dropping thin foil, and then reflected from an overdense plasma target. One-dimensional simulation shows that a 600 as single light pulse is generated with peak intensity of 3×1020 W/cm2.

We propose a new method of obtaining a compact ultra-bright, ultra-broadband hard X-ray source. This X-ray source has a high peak brightness in the order of 1022 photons/(s mm2 mrad2 0.1\%BW), an ultrashort duration (10 fs), and a broadband spectrum (flat distribution from 0.1 MeV to 4 MeV), and thus has wide-ranging potential applications, such as in ultrafast Laue diffraction experiments. In our scheme, laser-plasma accelerators (LPAs) provide driven electron beams. A foil target is placed oblique to the beam direction so that the target normal sheath field (TNSF) is used to provide a bending force. Using this TNSF-kick scheme, we can fully utilize the advantages of current LPAs, including their high charge, high energy, and low emittance.

This study investigates the dynamics of a compressed electron layer (CEL) when a circularly polarized laser pulse with a sharp front irradiates a high-density foil. A time-dependent model for CEL motion during the hole-boring stage is proposed to describe details of the interaction for any shape of laser pulse. The opacity case, where the laser pulse is totally reflected, is investigated using this model. The results obtained are consistent with the results from particle-in-cell (PIC) simulations. A relaxation distance determined by the laser-front steepness is necessary to build a stable CEL state before ions rejoin into the CEL. For the transparent case, the laser-front steepness is important for the formation of the stable CEL state at the back surface of the target. Considering the motion of ions, both the CEL and ion dynamics are important to rebalance the laser pressure and electrostatic charge-separation force as the hole-boring stage changes to the light-sail stage.

In plasma-based accelerators, electrons are accelerated by ultrahigh gradient of $1--100\text{ }\text{ }\mathrm{GV}/\mathrm{m}$ and undergo the focusing force with the same order as the accelerating force. Heated electrons are injected in a plasma wake and exhibit the betatron oscillation that generates synchrotron radiation. Intense betatron radiation from laser-plasma accelerators is attractive x-ray/gamma-ray sources, while it produces radiation loss and significant effects on energy spread and transverse emittance via the radiation reaction force. In this article, electron beam dynamics on transverse emittance and energy spread with considering radiation reaction effects are studied numerically. It is found that the emittance growth and the energy spread damping initially dominate and balance with radiative damping due to the betatron radiation. Afterward the emittance turns to decrease at a constant rate and leads to the equilibrium at a nanometer radian level with growth due to Coulomb scattering at PeV-level energies. A constant radiation loss rate ${R}_{T}=2/3$ is found without regard to the electron beam and plasma conditions. Self-cooling of electron beams due to betatron radiation may guarantee TeV-range linear colliders and give hints on astrophysical ultrahigh-energy phenomena.

By particle-in-cell simulation and analysis, we propose a plasma approach to generate a relativistic chirped pulse based on a laser-foil interaction. When two counterpropagating circularly polarized pulses interact with an overdense foil, the driving pulse (with a larger laser field amplitude) will accelerate the whole foil to form a double-layer structure, and the scattered pulse (with a smaller laser field amplitude) is reflected by this flying layer. Because of the Doppler effect and the varying velocity of the layer, the reflected pulse is up-shifted for frequency and chirped; thus, it could be compressed to a nearly single-cycled relativistic laser pulse with a short wavelength. Simulations show that a nearly single-cycled subfemtosecond relativistic pulse can be generated with a wavelength of 0.2 μm after dispersion compensation.

Light pressure acceleration of ions in the interaction of the frequency-tripled (3ω) laser pulse and foil target is studied, and a promising method to increase accelerated ion energy is shown. Results show that at a constant laser energy, much higher ion energy peak value is obtained for 3ω laser compared with that using the fundamental frequency laser. The effect of energy loss during frequency conversion on ion acceleration is considered, which may slightly decrease the acceleration effect.

An interesting layered structure of multiple high density layers are formed when two counter-propagating circularly polarized laser pulses with the same polarization direction irradiate on an ultra-thin foil. This structure changes periodically. For light atoms most of which electrons may be fully ionized, this layered structure can keep for dozens of laser periods after the laser-foil interaction. This interesting structure may have potential applications.

A cascaded target normal sheath acceleration (TNSA) scheme is proposed to simultaneously increase energy and improve energy spread of a laser-produced mono-energetic proton beam. An optimum condition that uses the maximum sheath field to accelerate the center of the proton beam is theoretically found and verified by two-dimensional particle-in-cell simulations. An initial 10 MeV proton beam is accelerated to 21 MeV with energy spread decreased from 5% to 2% under the optimum condition during the process of the cascaded TNSA. The scheme opens a way to scale proton energy lineally with laser energy.

High harmonic generation (HHG) from relativistic laser-foil interaction is investigated analytically and through particle-in-cell simulations. Previous work has shown that when two counter-propagating circularly polarized (CP) laser pulses interact with a thin foil, electrons can be well confined spatially to form a high density layer. The layer electrons oscillate in certain transversal direction and radiate intense high order harmonics. It is demonstrated here that there is a critical foil thickness, only below which can high harmonics be generated efficiently. Furthermore, to enhance the intensity in higher order region, the third linearly polarized (LP) short-wavelength laser pulse with much lower intensity is introduced. Analysis and simulations both show that the enhancement is determined by the relative phase δϕ between the driving CP laser pulses and LP pulse. The enhancement at high order is quite considerable and very sensitive to the relative phase δϕ, thus offering not only a way to efficientl...

A laser wakefield driven by an asymmetric laser pulse with/without chirp is investigated analytically and through two-dimensional particle-in-cell simulations. For a laser pulse with an appropriate pulse length compared with the plasma wavelength, the wakefield amplitude can be enhanced by using an asymmetric un-chirped laser pulse with a fast rise time; however, the growth is small. On the other hand, the wakefield can be greatly enhanced for both positively chirped laser pulse having a fast rise time and negatively chirped laser pulse having a slow rise time. Simulations show that at the early laser-plasma interaction stage, due to the influence of the fast rise time the wakefield driven by the positively chirped laser pulse is more intense than that driven by the negatively chirped laser pulse, which is in good agreement with analytical results. At a later time, since the laser pulse with positive chirp exhibits opposite evolution to the one with negative chirp when propagating in plasma, the wakefield in the latter case grows more intensely. These effects should be useful in laser wakefield acceleration experiments operating at low plasma densities.

Few-cycle relativistic circularly polarized (CP) laser pulse reflected from overdense plasma is investigated by analysis and particle-in-cell simulations. It is found that through the laser-induced one-time drastic oscillation of the plasma boundary, an ultra-intense single attosecond light pulse can be generated naturally. An analytical model is proposed to describe the interaction and it agrees well with simulation results. They both indicate that peak intensity of the generated attosecond pulse is higher when the plasma density is closer to the relativistic transparency threshold and/or the pulse duration is closer to plasma oscillating period. Two dimensional simulation shows that a two-cycle 1021 W/cm2 CP laser can generate a single 230 attosecond 2 × 1021 W/cm2 pulse of light at a conversion efficiency greater than 10-2.

Instabilities in the interaction of a normal intensity circularly polarized pulse and an overdense foil are investigated with two and three dimensional particle-in-cell simulations. Two typical instabilities were shown during the interaction. One is the Weibel-like instability induced by the current far above the Alfven limit, and the other is the boundary instability with ring structures spreading to the center from the boundary which is induced by the transverse boundaries of the target or the laser pulse. These instabilities are important to the proton acceleration by using moderate laser pulses at intensities accessible experimentally with existing laser systems.

Stable acceleration of relativistic ions by the radiation pressure of a superintense, circularly polarized laser pulse with sharp front is investigated by analytical modeling and particle-in-cell simulation. For foils with given density and thickness, the suitable steepness of the laser front is found to suppress instabilities and efficiently drive a stable monoenergetic ion beam. With a laser pulse of peak amplitude a{sub 0}=200, a proton beam of energy about 10 GeV can be generated. The dynamics of the laser-compressed electron layer and the ions in the hole-boring stage are investigated. In the case studied, the ions initially in the middle of the target are found to be accelerated to the back surface of the target ahead of the other ions.

Protons in a microtarget embedded in an underdense high-mass plasma can be accelerated sequentially by the radiation pressure of a short circularly polarized laser pulse and the induced wake bubble field in the background plasma, which has been shown in detail by two-dimensional particle in cell simulations. It has been found that instead of using transverse Gaussian pulses proton energy can be increased dramatically by using a transverse super-Gaussian laser pulse. With a 2.14x10{sup 23} W/cm{sup 2} laser pulse in a tritium plasma of density 1.5x10{sup 20}/cm{sup 3}, 76 GeV high-quality quasimonoenergetic protons have been obtained. The scaling relations between the obtainable proton energy and the laser amplitude as well as the background plasma density have been shown.

The overloading effect of self-injected high-charge electron bunch in the bubble regime of laser wakefield acceleration is studied. When too many electrons are trapped by the bubble, the wakefield can be strongly modified, preventing further injection of the background electrons. This process is directly observed in two-dimensional particle-in-cell simulation and is explained using a one-dimensional wake model. For obtaining significantly more energetic electrons, the use of a decreasing plasma density profile is proposed.

Large amount of energetic electrons generated in laser wake fields driven by multiparallel laser pulses is investigated with three-dimensional particle-in-cell simulations. By adjusting the distance between the pulses, bubbles with different structure are formed, which results in different injection efficiency. Compared with the single-pulse case, the charge of the energetic electrons could be doubled when the distance between the two pulses is large enough. A characteristic distance between the pulses is obtained, above which the total amount of the energetic electrons increases linearly by applying more laser pulses. There is no limit for the charge increase in our scheme as long as the plasma is wide enough so that more pulses can be applied.

The influence of laser pulse duration and areal density of target in the interaction of a circularly polarized pulse with an ultrathin overdense foil is investigated. One-dimensional particle-in-cell simulation shows that with an appropriate laser-pulse rising front, the light pressure acceleration regime is effective even though the thin foil is transparent. As the laser intensity evolves, three stages in the acceleration process can be identified: at first the total reflection of the laser pulse, followed by partial reflection, and then near total reflection again due to the Doppler effect. The influences of the rising front of laser pulse and areal density of the ultrathin foil are investigated. It is found that an optimal laser pulse rising front exists for obtaining high (saturation) ion energy with the same laser energy within a short time. An optimal areal density also exists for obtaining the highest energy. For the same laser pulse, a higher areal density or a higher density with same areal density is more appropriate for obtaining a stationary state for making light pressure acceleration mechanism more effective.

By means of particle-in-cell (PIC) simulations, we found that when the focus size of a laser pulse is much larger than the plasma wavelength and when the laser power is hundreds of times larger than the critical power required for relativistic self-focusing, a large complex bubble is formed. The transversal size of the bubble depends on the laser spot size. Owing to the large bubble size, a bunch of electrons with the total charge in the range of a few tens of nano- Coulombs is trapped and accelerated in the bubble. When the plasma density is 2◊10 19 cm 3 , the charge of the energetic electron bunch with energy above 5MeV exceeds 45nC with a laser spot size of 60µm. Electrons continuously self-injected into such a complex bubble serve as an effective source of high- charge electron bunches.