pC Charge Research Articles

Laser Wakefield Acceleration of Ions with a Transverse Flying Focus.

The extreme electric fields created in high-intensity laser-plasma interactions could generate energetic ions far more compactly than traditional accelerators. Despite this promise, laser-plasma accelerator experiments have been limited to maximum ion energies of ∼100 MeV/nucleon. The central challenge is the low charge-to-mass ratio of ions, which has precluded one of the most successful approaches used for electrons: laser wakefield acceleration. Here, we show that a laser pulse with a focal spot that moves transverse to the laser propagation direction enables wakefield acceleration of ions to GeV energies in underdense plasma. Three-dimensional particle-in-cell simulations demonstrate that this relativistic-intensity "transverse flying focus" can trap ions in a comoving electrostatic pocket, producing a monoenergetic collimated ion beam. With a peak intensity of 10^{20} W/cm^{2} and an acceleration distance of 0.44cm, we observe a proton beam with 23.1pC charge, 1.6GeV peak energy, and 3.7% relative energy spread. This approach allows for compact high-repetition-rate production of high-energy ions, highlighting the capability of more generalized spatiotemporal pulse shaping to address open problems in plasma physics.

Unforeseen advantage of looser focusing in vacuum laser acceleration

Acceleration of electrons in vacuum directly by intense laser fields holds great promise for the generation of high-charge, ultrashort, relativistic electron bunches. While the energy gain is expected to be higher with tighter focusing, this does not account for the reduced acceleration range, which is limited by diffraction. Here, we present the results of an experimental investigation that exposed nanotips to relativistic few-cycle laser pulses. We demonstrate the vacuum laser acceleration of electron beams with 100s pC charge and 15 MeV energy. Two different focusing geometries, with normalized vector potential a0 of 9.8 and 3.8, produced comparable overall charge and electron spectra, despite a factor of almost ten difference in peak intensity. Our results are in good agreement with 3D particle-in-cell simulations, which indicate the importance of dephasing.

Spin-polarized electron beam generation in the colliding-pulse injection scheme

Employing colliding-pulse injection has been shown to enable the generation of high-quality electron beams from laser–plasma accelerators. Here, by using test particle simulations, Hamiltonian analysis, and multidimensional particle-in-cell simulations, we lay the theoretical framework for spin-polarized electron beam generation in the colliding-pulse injection scheme. Furthermore, we show that this scheme enables the production of quasi-monoenergetic electron beams in excess of 80% polarization and tens of pC charge with commercial 10-TW-class laser systems.

Single-shot emittance measurement and optimization of a hybrid photo-cathode gun beam

A unique hybrid photo-cathode S-band gun accelerator is in operation at Ariel University. The accelerator produces an ultra-fast relativistic electron beam with beam characteristics of 6 MeV kinetic energy, 30 pC charge, and 150 fs pulse duration. In this paper, we present a compact transverse emittance measurement system using the multi-slit mask technique. The system is calibrated using a fully automatic calibration routine, and the results are obtained instantaneously. To find the optimal parameters required to obtain the lowest transverse emittance value, we scan the currents in the focusing coils surrounding the gun including a bucking coil current scan to minimize the magnetic field upon the photo-cathode. In the last step, we verify the relation between transverse emittance and electron beam charge in RF guns emitted from a photo-cathode. The verification is done by a beam charge scan.

Design and Testing of a Prototype ASIC for the MTPC Readout at CSNS Back-n White Neutron Source

In this paper, a prototype Application Specific Integrated Circuit (ASIC) for the Multi-purpose Time Projection Chambers (MTPC) at Back-n White Neutron Source is presented. The ASIC integrates 16 readout channels and is fabricated in a 0.18 μm CMOS process. Each channel consists of a Charge Sensitive Amplifier (CSA), a Pole-Zero Cancellation (PZC), two bridged-T shapers, a baseline holder, and a fully differential output buffer. It provides selectable charge ranges of 2 pC and 10 pC, programmable peaking times from 110 ns to 1 μs, and an adjustable output common-mode voltage from 0.7 V to 1.25 V. The ASIC has already been tested and all the results meet the requirements. In the case of 100 pF input capacitance, 2 pC charge range, and 1 μs peaking time, it features a maximum Integral Non-Linearity (INL) of 0.48% and an Equivalent Noise Charge (ENC) of 0.749 fC, which makes the Signal-to-Noise Ratio (SNR) at full-scale input over 2600. In particular, a crosstalk rejection ratio of 63 dB is obtained in this prototype ASIC by using the baseline holder circuit in each channel to generate references for single-ended to differential conversion, isolating noise and crosstalk from the reference path.

Design and Characterization of a Picosecond Timing ASIC in 55-nm CMOS

For more than two decades, amplifier-discriminator ASICs have been demonstrated to be the optimal choice for time measurement in high-energy physics experiments. With the requirement of time resolution further evolving towards the picosecond and sub-picosecond ranges, circuit innovation has become increasingly essential. We present a PIcoSecond Timing (PIST1) ASIC, utilizing the conventional amplifier-discriminator architecture and optimized for the readout of silicon photomultipliers (SiPMs) in the electromagnetic calorimeter (ECAL) for future Higgs factories such as the Circular Electron Positron Collider (CEPC). Further circuit developments are made to enable the ASIC to operate under minimal power with reduced supply voltage. A comprehensive analysis of the noise in the signal link is also conducted and the findings presented. A single-channel prototype is designed in 55 nm CMOS with a single 1.2 V supply voltage. The standalone ASIC testing highlights a time resolution of 4.20±0.04 ps for a minimum ionizing particle (MIP) which is equivalent to 32 pC charge. Additionally, a linear time-over-threshold (ToT) response from 1 to 12 MIP is attained and typical 15 mW power consumption realized.

Simulation of self-modulated laser wakefield acceleration using few TW in downramp injection and ionization injection regimes.

Simulations of transitional self-modulated laser wakefield acceleration driven by laser pulses of a few terawatts are discussed, comparing a downramp-based injection regime with an ionization injection regime. We demonstrate that a configuration using an N 2 gas target and a laser pulse of ∼75m J with ∼2T W peak power is a good alternative as a high repetition rate system that produces electrons of many tens of MeV, pC charge, and emittance of the order of 1mm mrad.

New additive as Li+ source for charge transfer improvement at triple-cation perovskite/Spiro-OMeTAD interface

One of the main obstacles to perovskite solar cells (PSCs) entering the market is the doping-induced degradation of expensive hole transport materials (HTMs), which results in poor device stability. Although lithium bis(trifluoromethanesulfonyl)imide (Li-TFSI) and 4-tert-butylpyridine (4-tBp) as additives are commonly used in HTMs, they often lead to low device stability and reproducibility due to their hygroscopic and volatile nature. In this study, we incorporated the dilithium phthalocyanine (Li 2 Pc) molecule into the Spiro-OMeTAD precursor solution with Li-TFSI and 4-tBp to produce triple-cation PSCs with an n–i–p configuration operating with high efficiency and stability. The addition of the Li 2 Pc molecule not only improves the perovskite/Spiro-OMeTAD interface but also increases the π–π stacking in the thin-film phase according to the absorption and Raman results. Based on space-charge-limited current, photoluminescence, time-resolved photoluminescence and lifetime analysis measurements, charge transfer is improved with the Li 2 Pc molecule and charge recombination losses are reduced. As a result, the control device showed a power conversion efficiency (PCE) of 20.0% with J SC = 24.6 mA/cm 2 and fill factor (FF) = 72.7%, whereas the Li 2 Pc-doped device exhibited an improved PCE of 20.6% with J SC = 25.0 mA/cm 2 and FF = 73.6%. The addition of Li 2 Pc resulted in more stable and high-efficiency solar cells that maintained approximately 90% of the initial efficiency after 40 days. • The addition of the Li 2 Pc molecule can increase the π–π stacking in the thin-film phase. • Li 2 Pc can effectively passivate the defects at the triple-cation perovskite/Spiro-OMeTAD interface. • The efficiency of triple-cation perovskite solar cell is increased from 20.0% to 20.6%. • The device with Li 2 Pc retained about 90% of the initial efficiency after 40 days compared to the control device.

Introduction of Research Work on Laser Proton Acceleration and Its Application Carried out on Compact Laser–Plasma Accelerator at Peking University

Laser plasma acceleration has made remarkable progress in the last few decades, but it also faces many challenges. Although the high gradient is a great potential advantage, the beam quality of the laser accelerator has a certain gap, or it is different from that of traditional accelerators. Therefore, it is important to explore and utilize its own features. In this article, some recent research progress on laser proton acceleration and its irradiation application, which was carried out on the compact laser plasma accelerator (CLAPA) platform at Peking University, have been introduced. By combining a TW laser accelerator and a monoenergetic beamline, proton beams with energies of less than 10 MeV, an energy spread of less than 1%, and with several to tens of pC charge, have been stably produced and transported in CLAPA. The beamline is an object–image point analyzing system, which ensures the transmission efficiency and the energy selection accuracy for proton beams with large initial divergence angle and energy spread. A spread-out Bragg peak (SOBP) is produced with high precision beam control, which preliminarily proved the feasibility of the laser accelerator for radiotherapy. Some application experiments based on laser-accelerated proton beams have also been carried out, such as proton radiograph, preparation of graphene on SiC, ultra-high dose FLASH radiation of cancer cells, and ion-beam trace probes for plasma diagnosis. The above applications take advantage of the unique characteristics of laser-driven protons, such as a micron scale point source, an ultra-short pulse duration, a wide energy spectrum, etc. A new laser-driven proton therapy facility (CLAPA II) is being designed and is under construction at Peking University. The 100 MeV proton beams will be produced via laser–plasma interaction by using a 2-PW laser, which may promote the real-world applications of laser accelerators in malignant tumor treatment soon.

Laser-Induced Graphene Capacitive Killing of Bacteria.

Laser-induced graphene (LIG) is a method of generating a foam-like conformal carbon layer of porous graphene on many types of carbon-based surfaces. This electrically conductive material has been shown to be useful in many applications including environmental technology and includes low fouling and antimicrobial surfaces and can address persistent environmental challenges spawned by bacterial and viral contaminates. Here, we show that a single film of LIG stores charge when an electrical current is applied and dissipates charge when the current is stopped, which results in electricidal surface antibacterial potency. The amount of accumulated and dissipated charge on a single strip of LIG was quantified with an electrometer by generating LIG on both sides of a nonconducting polyimide film, which showed up to 65 pC of charge when the distance between the surfaces was 94 μm corresponding to an areal capacitance of 1.63 pF/cm2. We further corroborate the stored charge decay of a single LIG strip with bacteria death via direct electrical contact. Antimicrobial rates decreased with the same monotonic pattern as the loss of charge from the LIG film (i.e., AR ∼ 97% 0 s after voltage source disconnection vs AR ∼ 21% 90 s after disconnection) showing bacterial death as a function of delayed LIG exposure time after applied voltage disconnection. In terms of energy efficiency, this translates to an increased bacteria potency of ∼170% for the equivalent energy costs as that previously estimated. Finally, we present a mechanistic explanation for the capacitive behavior and the electricidal effects for a single plate of LIG.

Laser Wakefield Photoneutron Generation with Few-Cycle High-Repetition-Rate Laser Systems

Simulations of photoneutron generation are presented for the anticipated experimental campaign at ELI-ALPS using the under-commissioning e-SYLOS beamline. Photoneutron generation is a three-step process starting with the creation of a relativistic electron beam which is converted to gamma radiation, which in turn generates neutrons via the γ,n interaction in high-Z material. Electrons are accelerated to relativistic energies using the laser wakefield acceleration (LWFA) mechanism. The LWFA process is simulated with a three-dimensional particle in cell code to generate an electron bunch of 100s pC charge from a 100 mJ, 9 fs laser interaction with a helium gas jet target. The resultant electron spectrum is transported through a lead sphere with the Monte Carlo N-Particle (MCNP) code to convert electrons to gammas and gammas to neutrons in a single simulation. A neutron yield of 3×107 per shot over 4π is achieved, with a corresponding neutron yield per kW of 6×1011 n/s/kW. The paper concludes with a discussion on the attractiveness of LWFA-driven photoneutron generation on high impact, and societal applications.

Injection induced by coaxial laser interference in laser wakefield accelerators

We propose a new injection scheme that can generate electron beams with simultaneously a few permille energy spread, submillimeter milliradian emittance, and more than a 100 pC charge in laser wakefield accelerators. In this scheme, a relatively loosely focused laser pulse drives the plasma wakefield, and a tightly focused laser pulse with similar intensity triggers an interference ring pattern that creates onion-like multisheaths in the plasma wakefield. Owing to the change in wavefront curvature after the focal position of the tightly focused laser, the innermost sheath of the wakefield expands, which slows down the effective phase velocity of the wakefield and triggers injection of plasma electrons. Both quasicylindrical and fully three-dimensional particle-in-cell simulations confirm the generation of beams with the above mentioned properties.

Radiation Hardening Design of Nonvolatile Hybrid Flip-Flop Based on Spin Orbit Torque MTJ and SRAM

Spin orbit torque magnetic tunnel junction (SOT-MTJ) has been widely used for designing nonvolatile flip-flop (NVFF), thanks to its ultrafast switching speed, zero static power consumption, nearly unlimited endurance, etc. However, in the space environment, the write pulse width of the SOT-MTJ is comparable to radiation-induced current duration. Thus, the SOT-MTJ-based NVFF may suffer from soft error induced by the nonvolatile single event upset (NVSEU) in the backup mode. In this paper, we analyze the sensitive nodes in different work modes and propose the radiation hardening circuits for master–slave NVFF (MS-NVFF) to solve the NVSEUs. Based on a physics-based SOT-MTJ compact model and a 40[Formula: see text]nm CMOS design kit, the reliability of MS-NVFF is verified by simulation with 2[Formula: see text]pC charge, which could be reliably integrated into aerospace and avionics electronics in hostile environments.

Electron beam acceleration using Colliding pulses injection in parabolic plasma channel

optical injection of electrons in laser wakefield accelerator scheme has been shown using the PIC simulation of colliding pulse injection method. Parameter scans like laser polarization, colliding angle, delay and injector pulse intensity have been carried out, to get the optimum values for the injection. To guide the laser pulse over many Rayleigh lengths a parabolic plasma channel is used. For a 45 fs laser pulse of intensity 9 × 1018 W/cm2 focused to spot size of 6 µm inside a plasma of density 4.0 × 1018 cm−3, a highly mono-energetic electron beam with 2.1 pC charge at 337 MeV was obtained.

The Phase Structure of Two Color QCD and Charged Pion Condensation Phenomenon

The phase structure of dense quark matter in the two color case has been investigated with nonzero baryon $${{\mu }_{{\text{B}}}}$$ , isospin $${{\mu }_{{\text{I}}}}$$ and chiral isospin $${{\mu }_{{{\text{I5}}}}}$$ chemical potentials. It has been shown in the mean-field approximation that there exist three dualities, one of them between phases with spontaneous chiral symmetry breaking and condensation of charged pions, found in the three color case. The other two dual symmetries between the phase with condensation of charged pions and the phase with diquark condensation and between chiral symmetry breaking and diquark condensation phenomena. It has been demonstrated that due to the duality properties the phase diagram is extremely symmetric and the whole phase diagram in two color case can be obtained just by dualities from the phase structure of three color case. This shows that the dualities are rather usefull tool. It is shown that chiral imbalance generates charged pion condensation phenomenon in conditions of matter in neutron stars, i. e. electrically neutral and $$\beta $$ -equilibrated dense quark matter. And that diquark condensation does not prohibit the generation of the charged PC phase by chiral imbalance at least in the two color case.

Optimized laser-assisted electron injection into a quasilinear plasma wakefield.

We present an electron injection scheme for plasma wakefield acceleration. The method is based on a recently proposed technique of fast electron generation via laser-solid interaction: a femtosecond laser pulse with the energy of tens of mJ hitting a dense plasma target at 45^{∘} angle expels a well collimated bunch of electrons and accelerates these close to the specular direction up to several MeVs. We study trapping of these fast electrons by a quasilinear wakefield excited by an external beam driver in a surrounding low density plasma. This configuration can be relevant to the AWAKE experiment at CERN. We vary different injection parameters: the phase and angle of injection, the laser pulse energy. An approximate trapping condition is derived for a linear axisymmetric wake. It is used to optimize the trapped charge and is verified by three-dimensional particle-in-cell simulations. It is shown that a quasilinear plasma wave with the accelerating field ∼ 2.5 GV/m can trap electron bunches with ∼ 100 pC charge, ∼60μm transverse normalized emittance and accelerate them to energies of several GeV with the spread ≲ 1% after 10 m..

All-optical quasi-monoenergetic GeV positron bunch generation by twisted laser fields

Generation of energetic electron-positron pairs using multi-petawatt (PW) lasers has recently attracted increasing interest. However, some previous laser-driven positron beams have severe limitations in terms of energy spread, beam duration, density, and collimation. Here we propose a scheme for the generation of dense ultra-short quasi-monoenergetic positron bunches by colliding a twisted laser pulse with a Gaussian laser pulse. In this scheme, abundant γ-photons are first generated via nonlinear Compton scattering and positrons are subsequently generated during the head-on collision of γ-photons with the Gaussian laser pulse. Due to the unique structure of the twisted laser pulse, the positrons are confined by the radial electric fields and experience phase-locked-acceleration by the longitudinal electric field. Three-dimensional simulations demonstrate the generation of dense sub-femtosecond quasi-monoenergetic GeV positron bunches with tens of picocoulomb (pC) charge and extremely high brilliance above 1014 s−1 mm−2 mrad−2 eV−1, making them promising for applications in laboratory physics and high energy physics.

Bumblebee electric charge stimulates floral volatile emissions in Petunia integrifolia but not in Antirrhinum majus

The timing of volatile organic compound (VOC) emission by flowering plants often coincides with pollinator foraging activity. Volatile emission is often considered to be paced by environmental variables, such as light intensity, and/or by circadian rhythmicity. The question arises as to what extent pollinators themselves provide information about their presence, in keeping with their long co-evolution with flowering plants. Bumblebees are electrically charged and provide electrical stimulation when visiting plants, as measured via the depolarisation of electric potential in the stem of flowers. Here we test the hypothesis that the electric charge of foraging bumblebees increases the floral volatile emissions of bee pollinated plants. We investigate the change in VOC emissions of two bee-pollinated plants (Petunia integrifolia and Antirrhinum majus) exposed to the electric charge typical of foraging bumblebees. P. integrifolia slightly increases its emissions of a behaviorally and physiologically active compound in response to visits by foraging bumblebees, presenting on average 121 pC of electric charge. We show that for P. integrifolia, strong electrical stimulation (600–700 pC) promotes increased volatile emissions, but this is not found when using weaker electrical charges more representative of flying pollinators (100 pC). Floral volatile emissions of A. majus were not affected by either strong (600–700 pC) or weak electric charges (100 pC). This study opens a new area of research whereby the electrical charge of flying insects may provide information to plants on the presence and phenology of their pollinators. As a form of electroreception, this sensory process would bear adaptive value, enabling plants to better ensure that their attractive chemical messages are released when a potential recipient is present.

THz-driven split ring resonator undulator

We propose a short period undulator based on the electromagnetic field pattern in a THz-driven split ring resonator structure. An analytical model is developed that allows us to assess the key performance parameters of the undulator and to estimate the emitted radiation spectrum. Different geometric configurations are compared in detail using numerical simulations. A 100 MeV electron bunch with 5 pC charge is shown to emit narrow band 83 eV photon pulses with a peak brightness of approximately ${10}^{19}\text{ }\mathrm{photons}/(\mathrm{s}\text{ }{\mathrm{mrad}}^{2}\text{ }{\mathrm{mm}}^{2}\text{ }\text{ }0.1%\text{ }\text{ }\mathrm{BW})$ when passing through the 100 mm long undulator with a 1 mm period.

Interaction of Ultraintense Radially-Polarized Laser Pulses with Plasma Mirrors

We present experimental results of vacuum laser acceleration (VLA) of electrons using radially polarized laser pulses interacting with a plasma mirror. Tightly focused radially polarized laser pulses have been proposed for electron acceleration because of their strong longitudinal electric field, making them ideal for VLA. However, experimental results have been limited until now because injecting electrons into the laser field has remained a considerable challenge. Here, we demonstrate experimentally that using a plasma mirror as an injector solves this problem and permits to inject electrons at the ideal phase of the laser, resulting in the acceleration of electrons along the laser propagation direction while reducing the electron beam divergence compared to the linear polarization case. We obtain electron bunches with few-MeV energies and a 200 pC charge, thus demonstrating for the first time electron acceleration to relativistic energies using a radially polarized laser. High-harmonic generation from the plasma surface is also measured and provides additional insight into the injection of electrons into the laser field upon its reflection on the plasma mirror. Detailed comparisons between experimental results and full 3D simulations unravel the complex physics of electron injection and acceleration in this new regime: we find that electrons are injected into the radially polarized pulse in the form of two spatially-separated bunches emitted from the p-polarized regions of the focus. Finally, we leverage on the insight brought by this study to propose and validate a more optimal experimental configuration that can lead to extremely peaked electron angular distributions and higher energy beams.