Ultra-low Electron Research Articles

Rate Coefficient of CO<sub>2</sub> Splitting via Vibrational Excited States in Recombining Plasmas with Ultralow Electron Temperatures

Rate Coefficient of CO<sub>2</sub> Splitting via Vibrational Excited States in Recombining Plasmas with Ultralow Electron Temperatures

Rate coefficient of CO2 splitting in recombining H2 and He plasmas with ultralow electron temperatures

We investigated CO2 splitting in recombining H2 and He plasmas with ultralow electron temperatures between 0.1 and 0.4 eV. The conversion from CO2 to CO and O2 was observed in the ultralow-temperature plasmas. Since the rate coefficients of dissociation of CO2 via electronic excited states are negligible at the ultralow electron temperature, the present experimental result gives us corroborative evidence of the CO2 splitting via vibrational excited states. The rate coefficient of the CO2 splitting, which was evaluated from the temporal variation of the CO2 density, decreased clearly with the electron temperature. In addition, the rate coefficient observed in the ionizing H2 plasma with an electron temperature of 4 eV was one order of magnitude smaller than that observed in the recombining plasmas. It has been shown that the CO2 splitting via vibrational excited states has a larger rate coefficient than that via electronic excited states.

Semiclassical Broadening in Quantum Dot Thermometry

We studied the experimental conditions required for the accurate measurement of the electron temperature by using quantum dot (QD) thermometry. The physical requirements were examined by numerically evaluating the QD conductance as a function of QD-reservoir coupling and the electron temperature. An empirical formula for the Coulomb blockade peak at all coupling strengths was suggested. Thereafter, practical limitations set by voltage noise were investigated through a semiclassical treatment of the QD. A noise-broadening, in addition to thermal broadening, was identified, and a noise limit was provided for a given electron temperature. The analysis was applied to a realistic measurement setup by considering a dilution fridge equipped with low-pass RC-filters. We found that careful placements of filters were crucial in order to avoid thermal noise from the filters while measuring ultralow electron temperatures.

Fabrication of 1D long chain-like metal porphyrin-based coordination complexes for high-efficiency hydrogen evolution and photoelectric response

Hydrogen production from electrocatalytic water splitting has aroused extensive attention in many fields recently. Fabrication of low-cost and high-efficiency electrocatalysts are still an urgent and challenging work. Porphyrins as visible-light photosensitizers have been extensively utilized in visible-light photocatalysts and photoelectronic materials. So, fabrication of novel porphyrin-based complexes will be benefited for high-efficiency hydrogen evolution and photoelectric response. Here a series of zirconium porphyrin-based coordination complexes were successfully fabricated via a facile two-step strategy. Due to the unique long chain-like structure and low charge-transfer resistance, the zirconium porphyrin-based coordination complexes displayed excellent electrocatalytic performance for hydrogen evolution reaction. The ZrTPP-PTA-1 showed a low overpotential of 60 mV at the current density 10 mA cm−2 and a Tafel slope of 87 mV dec−1 with an ultralow electron transfer resistance of 17.5 Ω. In addition, a quick photocurrent response occurred for these coordination complexes with a visible-light illumination. The photocurrent of the ZrTPP-OA-2 rised up to 2.5 μA under visible-light irradiation. With this pleasant result, these zirconium porphyrin-based coordination complexes have a great potential to become available alternative of current noble electrocatalysts for photoelectric application.

Piezo-driven sample rotation system with ultra-low electron temperature

Piezo-driven rotator is convenient for tilted magnetic field experiments due to its precise angle control. However, the rotator itself and the sample mounted on it are difficult to be cooled down because of extra heat leaks and presumably bad thermal contacts from the piezo. Here, we report a piezo-driven sample rotation system designed for ultra-low temperature environment. The sample, as well as the rotating sample holder, can be cooled to as low as 25 mK by customized thermal links and thermal contacts. More importantly, the electron temperature in the electrical transport measurements can also be cooled down to 25 mK with the help of home-made filters. To demonstrate the application of our rotation system at ultra-low electron temperature, a measurement revealing tilt-induced localization and delocalization in the second Landau level of two-dimensional electron gas is provided.

Dark Matter Search Results from a One Ton-Year Exposure of XENON1T.

We report on a search for weakly interacting massive particles (WIMPs) using 278.8days of data collected with the XENON1T experiment at LNGS. XENON1T utilizes a liquid xenon time projection chamber with a fiducial mass of (1.30±0.01) ton, resulting in a 1.0ton yr exposure. The energy region of interest, [1.4,10.6] keV_{ee} ([4.9,40.9] keV_{nr}), exhibits an ultralow electron recoil background rate of [82_{-3}^{+5}(syst)±3(stat)] events/(ton yr keV_{ee}). No significant excess over background is found, and a profile likelihood analysis parametrized in spatial and energy dimensions excludes new parameter space for the WIMP-nucleon spin-independent elastic scatter cross section for WIMP masses above 6 GeV/c^{2}, with a minimum of 4.1×10^{-47} cm^{2} at 30 GeV/c^{2} and a 90%confidence level.

Simulating a low-temperature Maxwellian plasma using SH-HtscEBIT

This paper reports an experimental realization of a low-temperature quasi-Maxwell–Boltzmann plasma in an electron beam ion trap (EBIT) by employing a special energy sweep technique. A Maxwellian C IV plasma with electron temperatures in the range 10–40 eV is simulated in the Shanghai high-temperature superconducting EBIT (SH-HtscEBIT), which requires stable performance of the EBIT under the extreme condition of ultralow electron beam energy. The C IV spectra are obtained by an extreme ultraviolet spectrometer in the wavelength region 290–400 Å. The measured spectral line intensity ratios are compared with the results of calculations using a collisional-radiative model. The mean difference between the experimental and theoretical results in the simulated temperature region is about 14%.

Decomposition of carbon dioxide by recombining hydrogen plasma with ultralow electron temperature

We examined the rate coefficient for the decomposition of CO2 in low-pressure recombining hydrogen plasmas with electron temperatures between 0.15 and 0.45 eV, where the electron-impact dissociation was negligible. By using this ultralow-temperature plasma, we clearly observed decomposition processes via vibrational excited states. The rate coefficient of the overall reaction, CO2 + e → products, was 1.5 × 10−17 m3/s in the ultralow-temperature plasma, which was 10 times larger than the decomposition rate coefficient of 2 × 10−18 m3/s in an ionizing plasma with an electron temperature of 4 eV.

Two-color ionization injection using a plasma beatwave accelerator

Two-color laser ionization injection is a method to generate ultra-low emittance (sub-100 nm transverse normalized emittance) beams in a laser-driven plasma accelerator. A plasma beatwave accelerator is proposed to drive the plasma wave for ionization injection, where the beating of the lasers effectively produces a train of long-wavelength pulses. The plasma beatwave accelerator excites a large amplitude plasma wave with low peak laser electric fields, leaving atomically-bound electrons with low ionization potential. A short-wavelength, low-amplitude ionization injection laser pulse (with a small ponderomotive force and large peak electric field) is used to ionize the remaining bound electrons at a wake phase suitable for trapping, generating an ultra-low emittance electron beam that is accelerated in the plasma wave. Using a plasma beatwave accelerator for wakefield excitation, compared to short-pulse wakefield excitation, allows for a lower amplitude injection laser pulse and, hence, a lower emittance beam may be generated.

Probing light mediators at ultralow threshold energies with coherent elastic neutrino-nucleus scattering

Light neutral mediators, with mass $\lesssim 1$ GeV, are common features of extensions to the Standard Model (SM). Current astrophysical and terrestrial experiments have constrained the model parameter space, and planned experiments around the world promise continued improvement in sensitivity. In this paper we study the prospects for probing light neutral mediators using terrestrial stopped pion and reactor sources in combination with ultra-low threshold nuclear and electron recoil detectors. We show that the coherent neutrino-nucleus and neutrino-electron scattering channels provide complementary sensitivity to light mediators. With low threshold detectors, we show that most stringent bounds on models arise from the nuclear scattering process, improving upon previous bounds from electron scattering of solar neutrinos by nearly an order of magnitude for mediator masses $\gtrsim 0.1$ GeV.

Single-stage plasma-based correlated energy spread compensation for ultrahigh 6D brightness electron beams

Plasma photocathode wakefield acceleration combines energy gains of tens of GeV m−1 with generation of ultralow emittance electron bunches, and opens a path towards 5D-brightness orders of magnitude larger than state-of-the-art. This holds great promise for compact accelerator building blocks and advanced light sources. However, an intrinsic by-product of the enormous electric field gradients inherent to plasma accelerators is substantial correlated energy spread—an obstacle for key applications such as free-electron-lasers. Here we show that by releasing an additional tailored escort electron beam at a later phase of the acceleration, when the witness bunch is relativistically stable, the plasma wave can be locally overloaded without compromising the witness bunch normalized emittance. This reverses the effective accelerating gradient, and counter-rotates the accumulated negative longitudinal phase space chirp of the witness bunch. Thereby, the energy spread is reduced by an order of magnitude, thus enabling the production of ultrahigh 6D-brightness beams.

Test Results of the CLIC Damping Wiggler Prototype

The Compact Linear Collider (CLIC) will require ultralow emittance electron and positron beams. Such emittance will be achieved by radiative damping in the CLIC damping rings that will be realized by a use of high-field short-period superconducting damping wigglers. In the course of the CLIC technical feasibility studies, a full-scale damping wiggler prototype was fabricated in BINP. Main parameters of the wiggler are 51 mm of period, 3 T of magnetic field, 1.8 m of magnetic length, 18 mm of the pole gap, and indirect cooling by LHe. Four cryocoolers were used in the wiggler design, which allow its ordinary operation without LHe consumption. Above the magnetic requirements, the main design challenges for this prototype are scalability, particularly of the cooling concept, modularity, and the capability of sustaining a high radiative heat load. The wiggler powering tests and performance of the cryogenic system are described in this paper.

Ultra low emittance electron beams from multi-alkali antimonide photocathode operated with infrared light

The intrinsic emittance of electron beams generated from a multi-alkali photocathode operated in a high voltage DC gun is reported. The photocathode showed sensitivity extending to the infrared part of the spectrum up to 830 nm. The measured intrinsic emittances of electron beams generated with light having wavelength longer than 800 nm are approaching the limit imposed by the thermal energy of electrons at room temperature with quantum efficiencies comparable to metallic photocathodes used in operation of modern photoinjectors.

Large linear magnetoresistance in Dirac semimetalCd3As2with Fermi surfaces close to the Dirac points

We have investigated the magnetoresistive behavior of Dirac semi-metal Cd3As2 down to low temperatures and in high magnetic fields. A positive and linear magnetoresistance (LMR) as large as 3100% is observed in a magnetic field of 14 T, on high-quality single crystals of Cd3As2 with ultra-low electron density and large Lande g factor. Such a large LMR occurs when the magnetic field is applied perpendicular to both the current and the (100) surface, and when the temperature is low such that the thermal energy is smaller than the Zeeman splitting energy. Tilting the magnetic field or raising the temperature all degrade the LMR, leading to a less pronounced quadratic behavior. We propose that the phenomenon of LMR is related to the peculiar field-induced shifting/distortion of the helical electrons' Fermi surfaces in momentum space.

Diffuse Surface Scattering in the Plasmonic Resonances of Ultralow Electron Density Nanospheres.

Localized surface plasmon resonances (LSPRs) have recently been identified in extremely diluted electron systems obtained by doping semiconductor quantum dots. Here, we investigate the role that different surface effects, namely, electronic spill-out and diffuse surface scattering, play in the optical properties of these ultralow electron density nanosystems. Diffuse scattering originates from imperfections or roughness at a microscopic scale on the surface. Using an electromagnetic theory that describes this mechanism in conjunction with a dielectric function including the quantum size effect, we find that the LSPRs show an oscillatory behavior in both position and width for large particles and a strong blue shift in energy and an increased width for smaller radii, consistent with recent experimental results for photodoped ZnO nanocrystals. We thus show that the commonly ignored process of diffuse surface scattering is a more important mechanism affecting the plasmonic properties of ultralow electron density nanoparticles than the spill-out effect.

Beam dynamics of a new low emittance third generation synchrotron light source facility

The Iranian Light Source Facility (ILSF) is a new 3 GeV third generation synchrotron light source facility which is in the design stage. As the main radiation source, design of the ILSF storage ring emphasizes an ultralow electron beam emittance, great brightness, stability and reliability. The storage ring is based on a five-bend achromat lattice providing an ultralow horizontal beam emittance of 0.48 nm rad. In this paper, we present the design feature of the ILSF storage ring, give the linear and nonlinear dynamic properties of the lattice and discuss the related beam dynamic specifications.

Simulation of beam gas coulomb scattering in HALS**Supported by Natural Science Foundation of China (11175182, 11175180)

In conventional research on beam gas coulomb scattering (BGCS), only the related beam lifetime using the analytical method is studied. In this paper, using the particle-in-cell Monte Carlo collisions (PIC-MCC) method, we not only simulated the beam lifetime but also explored the effect of BGCS on the beam distribution. In order to better estimate the effect on particle distribution, we study the ultra-low emittance electron beam. Here we choose the HeFei Advanced Light Source. By counting the lost particles in a certain time, the corresponding beam lifetime we simulated is 4.8482 h/13.8492 h in x/y, which is very close to the theoretic value (5.0555 h /13.7024 h in x/y). By counting the lost particles relative to the collided particles, the simulated value of the loss probability of collided particles is 1.3431e-04, which is also very close to the theoretical value (1.3824e-04). Besides, the simulation shows there is a tail in the transverse distribution due to the BGCS. The close match of the simulation with the theoretic value in beam lifetime and loss probability indicates our simulation is reliable.

Dispersion of two-dimensional plasmons in GaAs quantum well and Ag monolayer

We study theoretically the role of finite temperature, exchange-correlations and finite layer width in explicating experimental findings on dispersion of two-dimensional plasmons in GaAs single quantum well and Ag monolayer. The plasmon energy is obtained from the poles of electron density response function determined by using the finite-temperature self-consistent mean-field theory of Singwi et al. Except for ultra low electron densities (as in GaAs system), our results exhibit a reasonably good agreement with the experimental data. While correlations are found to introduce a noticeable red shift in plasmon frequency, temperature has an opposite effect. Both of these effects become increasingly important with reduction in electron density. At ultra low densities, our predictions agree only for small wave vectors (q<0.6kF), with correlations over-suppressing plasmons into the single electron–hole pair continuum already at a relatively small q. This shortcoming may be arising due to the neglect of the dynamical nature of correlations in our study. Further, it is found that finite layer width gives rise to a red shift in plasmon dispersion, but its effect is significant when average electron-electron spacing is smaller than or comparable with layer width.

Response of the imaging plates to the electron beams from a linear accelerator at ultra-low intensity

The response of the imaging plate (IP) as a two-dimensional irradiation dose monitor of high-energy electrons has been investigated. The Co-60 γ-ray irradiation facilities and the 16 MeV S-band electron linear accelerator (linac) in Radiation Research Center, Osaka Prefecture University have been used for the experiments. From the results of the irradiation experiments with γ-rays uniform response of IP over the plate and linear response to the exposure have been obtained. Thermoluminescence dosimeter has been used to determine the exposure. The ultra-low intensity electron beams developed have been used. The results of the irradiation experiments with the narrow electron beams from the linac at an energy of 8 MeV have shown the linear response of IP to the total electron charge for irradiation. By the broad beam an IP image of a model sample has been obtained showing the characteristic scattering behavior of high-energy electrons. These results have shown the applicability of IP to monitoring two-dimensional dose distribution of electrons.

Bioactive Cellulose Nanofibrils for Specific Human IgG Binding

Bioactive films were produced by conjugation of a short peptide onto modified cellulose nanofibrils (CNF). Specifically, a hydrophilic copolymer, poly(2-aminoethyl methacrylate hydrochloride-co-2-hydroxyethylmethacrylate) (poly(AMA-co-HEMA)), was grafted via surface initiated polymerization from an initiator coupled to CNF. The poly(AMA-co-HEMA) was used as a spacer and support layer for immobilization of the peptide, acetylated-HWRGWVA, which has specific affinity with human immunoglobulin G (hIgG). Two methods for peptide grafting were compared: modification of CNF in aqueous suspension followed by assembly into a bioactive film and peptide grafting on a preformed CNF film. The CNF-based networks were examined on solid supports via atomic force microscopy (AFM) and extreme resolution imaging with ultralow electron landing energies (scanning low energy electron microscopy). The specific binding capability of hIgG and nonspecific protein resistance of the resultant peptide-modified CNF were evaluated by using quartz crystal microgravimetry (QCM). The effects of initiator concentration and thickness of poly(AMA-co-HEMA) layer on hIgG adsorption were investigated in the developed systems, which exhibited high signal-to-noise response.