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Lu, W.

Publications and source records attributed to Lu, W..

At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Ultrabright Electron Bunch Injection in a Plasma Wakefield Driven by a Superluminal Flying Focus Electron Beam

Here, we propose a new method for self-injection of high-quality electron bunches in the plasma wakefield structure in the blowout regime utilizing a “flying focus” produced by a drive beam with an energy chirp. In a flying focus the speed of the density centroid of the drive bunch can be superluminal or subluminal by utilizing the chromatic dependence of the focusing optics. We first derive the focal velocity and the characteristic length of the focal spot in terms of the focal length and an energy chirp. We then demonstrate using multidimensional particle-in-cell simulations that a wake driven by a superluminally propagating flying focus of an electron beam can generate GeV-level electron bunches with ultralow normalized slice emittance (~30 nm rad), high current (~17 kA), low slice energy spread (~0.1%), and therefore high normalized brightness (> 10 19 A/ m 2 /rad 2 ) in a plasma of density ~10 19 cm –3 . The injection process is highly controllable and tunable by changing the focal velocity and shaping the drive beam current. Nearterm experiments at FACET II where the capabilities to generate tens of kA, < 10 fs drivers are planned, could potentially produce beams with brightness near 10 20 A / m 2 / rad 2 .

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2021

Investigating the Impact of Thickness, Calendering and Channel Structures of Printed Electrodes on the Energy Density of LIBs - 3D Simulation and Validation

Current lithium ion batteries (LIBs) are expensive and bulky, limited by relatively low charging rates. To increase the rate of charging and reduce weight, thin electrodes with high energy density are required. The increase in energy density can be achieved by several techniques including boosting electrolyte transport, high loading/utilization of active material, employing high conductive electrolytes and electrodes with advanced architectures, and increasing cell temperature. In this paper, a 3D physics-based electrochemical model of LIBs is developed in COMSOL simulation software for different thickness, calendering steps as well as channel structures (conical, cylindrical) to optimize the electrode design and in turn maximize volumetric energy density. The simulation results demonstrated that calendering the electrodes with high initial porosity increases the volumetric energy density of the cell. In addition, cylindrical channel structures with relatively lower edge-to-edge distance also results in increased volumetric energy density. The simulation results of the 3D model was validated by comparing it with experimental results.

improving volumetric energy density↗
DOE OSTI2020

Using Diffuse Scattering to Observe X-Ray-Driven Nonthermal Melting

We present results from the SPring-8 Angstrom Compact free electron LAser (SACLA) XFEL facility, using a high intensity ($\sim\!10^{20}\,$W/cm$^2$) X-ray pump X-ray probe scheme to observe changes in the ionic structure of silicon induced by X-ray heating of the electrons. By avoiding Laue spots in the scattering signal from a single crystalline sample, we observe a rapid rise in diffuse scattering, which we attribute to a loss of lattice order and a transition to a liquid state within 100 fs of irradiation, a timescale which agrees well with first principles simulations, but is faster than that predicted by purely inertial behavior. This method is capable of observing liquid scattering without masking or filtering of signal from the ambient solid, allowing the liquid structure to be measured throughout and beyond the phase change.

Hartley, Nicholas J.↗
DOE OSTI2020

Study of CMOS strip sensor for future silicon tracker

Monolithic silicon sensors developed with High-Voltage CMOS (HV-CMOS) processes have become highly attractive for charged particle tracking. Compared with the standard CMOS sensors, HV-CMOS sensors can provide larger and deeper depletion regions that lead to larger signals and faster charge collection. They can provide high position resolution, low material budget, high radiation hardness and low cost that are desirable for high performance tracking in harsh collision environment. Various studies have been conducted to explore the technology feasibility for the large-area tracking systems at future collider experiments. CHESS (CMOS HV/HR Evaluation for Strip Sensor) sensor series have been developed as an alternative solution to the conventional silicon micro-strip detectors for the ATLAS inner tracker upgrade. The first prototype (named CHESS1) was to evaluate the diode geometry and the in-pixel analog electronics. Obtained test results were used to optimize the second prototype (named CHESS2). CHESS2 was implemented with a full digital readout architecture and realized as a full reticle sized monolithic sensor. Here, the basic characteristics of the CHESS2 prototype sensors and their performance in response to different input signals are presented.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2019

Betatron radiation and emittance growth in plasma wakefield accelerators

Beam-driven plasma wakefield acceleration (PWFA) has demonstrated great progress during the past two decades of research. The novel Facility for Advanced Accelerator Experimental Tests (FACET) II, currently under construction, will provide 10 GeV electron beams with unprecedented parameters for the next generation of PWFA experiments. In the context of the FACET II facility, we introduce simulation results on expected betatron radiation and its potential application to diagnose emittance preservation and hosing instability in the upcoming PWFA experiments.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2019

Producing multi-coloured bunches through beam-induced ionization injection in plasma wakefield accelerator

Our work discusses the properties of electron beams formed in plasma wakefield accelerators through ionization injection. Specifically, the potential for generating a beam composed of co-located multi-colour beamlets is demonstrated in the case where the ionization is initiated by the evolving charge field of the drive beam itself. The physics of the processes of ionization and injection are explored through OSIRIS simulations. Experimental evidence showing similar features are presented from the data obtained in the E217 experiment at the FACET facility of the SLAC National Laboratory.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Phase Space Dynamics of a Plasma Wakefield Dechirper for Energy Spread Reduction

Plasma-based accelerators have made impressive progress in recent years. However, the beam energy spread obtained in these accelerators is still at the ~1% level, nearly one order of magnitude larger than what is needed for challenging applications like coherent light sources or colliders. In plasma accelerators, the beam energy spread is mainly dominated by its energy chirp (longitudinally correlated energy spread). Furthermore, we demonstrate that when an initially chirped electron beam from a linac with a proper current profile is sent through a low-density plasma structure, the self-wake of the beam can significantly reduce its energy chirp and the overall energy spread. The resolution-limited energy spectrum measurements show at least a threefold reduction of the beam energy spread from 1.28% to 0.41% FWHM with a dechirping strength of ~1 (MV/m)/(mm pC). Refined time-resolved phase space measurements, combined with high-fidelity three-dimensional particle-in-cell simulations, further indicate the real energy spread after the dechirper is only about 0.13% (FWHM), a factor of 10 reduction of the initial energy spread.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2019

Signal Processing for Beam Loss Monitor System at Jefferson Lab

Ion Chamber and Photomultiplier Tube (PMT) are both used for beam loss monitor in the Machine Protection System (MPS) at Jefferson Lab. The requirements of signal processing of these detectors are different, so two VME-based signal processing boards, Beam Loss Monitor (BLM) board and Ion-Chamber board, were developed. The BLM board has fast response (< 1us) and 5 decades dynamic range from 10nA to 1 mA, while the Ion-Chamber board has 8 decades dynamic range from 100 pA to 10 mA and slower response. Both of boards provide functions of machine protection and beam diagnostics, and features of fast shutdown (FSD) interface, beam sync interface, built-in-self-test, remotely controlled bias signals, and on-board memory buffer.

Yan, J.↗
DOE OSTI2018

Tri-stage quasimonoenergetic proton acceleration from a multi-species thick target

We show that quasimonoenergetic proton beams can be generated through a multi-ion thick target irradiated by a circularly polarized laser pulse. After disrupted by the transverse instabilities in the laser pressure acceleration process, heavy ions as majority species can still provide a co-moving electric field. Different from the dynamics using ultrathin foil, protons with small doped rates can experience a full tri-stage quasimonoenergetic acceleration (hole boring, sheath boosting, and free expansion stages) in this scenario. A theoretical model is developed to explain the proton energy evolution in detail and verified by two-dimensional particle-in-cell simulations. Finally, the scaling of proton energy with laser intensity indicates that the 200 MeV proton beam with narrow energy spread (3%–10%) and sufficiently large charges (10 10 –10 11 ) required for medical applications can be obtained using 100s TW class laser systems in near future.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2018

Superconducting ECR ion source: From 24-28 GHz SECRAL to 45 GHz fourth generation ECR

The development of superconducting ECR source with higher magnetic fields and higher microwave frequency is the most straight forward path to achieve higher beam intensity and higher charge state performance. SECRAL, a superconducting third generation ECR ion source, is designed for 24-28 GHz microwave frequency operation with an innovative magnet configuration of sextupole coils located outside the three solenoids. SECRAL at 24 GHz has already produced a number of record beam intensities, such as 40 Ar 12+ 1.4 emA, 129 Xe 26+ 1.1 emA, 129 Xe 30+ 0.36 emA, and 209 Bi 31+ 0.68 emA. SECRAL-II, an upgraded version of SECRAL, was built successfully in less than 3 years and has recently been commissioned at full power of a 28 GHz gyrotron and three-frequency heating (28 + 45 + 18 GHz). New record beam intensities for highly charged ion production have been achieved, such as 620 eμA 40 Ar 16+ , 15 eμA 40 Ar 18+ , 146 eμA 86 Kr 28+ , 0.5 eμA 86 Kr 33+ , 53 eμA 129 Xe 38+ , and 17 eμA 129 Xe 42+ . Recent beam test results at SECRAL and SECRAL II have demonstrated that the production of more intense highly charged heavy ion beams needs higher microwave power and higher frequency, as the scaling law predicted. A 45 GHz superconducting ECR ion source FECR (a first fourth generation ECR ion source) is being built at IMP. FECR will be the world's first Nb 3 Sn superconducting-magnet-based ECR ion source with 6.5 T axial mirror field, 3.5 T sextupole field on the plasma chamber inner wall, and 20 kW at a 45 GHz microwave coupling system. This paper will focus on SECRAL performance studies at 24-28 GHz and technical design of 45 GHz FECR, which demonstrates a technical path for highly charged ion beam production from 24 to 28 GHz SECRAL to 45 GHz FECR.

47 OTHER INSTRUMENTATION↗
DOE OSTI2018

Neutron poison burnout and effects on SNS moderator performance

Detailed neutron absorber burnup calculations were performed for the poison plate and decoupler layers of the decoupled ambient water and liquid hydrogen moderators of SNS. Although local poison burnout was identified for the water moderator at 32 GWh and local decoupler burnout was becomes apparent at the hydrogen moderator at 37 GWh delivered proton beam energy, both moderators see major impacts to the moderator performance by increases of pulse widths and spectral changes only past the stated burnout energies.

Gallmeier, Franz X.↗
DOE OSTI2018

Options for a very cold neutron source for the second target station at SNS

Simulation work is underway to identify a very cold neutron source solution that would provide an order of magnitude higher neutron output than the conventional moderator suite. Moderator candidates such as water ice, beryllium, ortho-D2, CH4, and neon all solid at temperatures of 4-6 K were investigated. At present no moderator option was able to achieve the set goal; ortho-D2 and CH4 seem to be the most promising options.

Gallmeier, Franz X.↗
DOE OSTI2018

Phase locked multiple rings in the radiation pressure ion acceleration process

Laser contrast plays a crucial role for obtaining high quality ion beams in the radiation pressure ion acceleration (RPA) process. Through one- and two-dimensional particle-in-cell (PIC) simulations, we show that a plasma with a bi-peak density profile can be produced from a thin foil on the effects of a picosecond prepulse, and it can then lead to distinctive modulations in the ion phase space (phase locked double rings) when the main pulse interacts with the target. These fascinating ion dynamics are mainly due to the trapping effect from the ponderomotive potential well of a formed moving standing wave (i.e. the interference between the incoming pulse and the pulse reflected by a slowly moving surface) at nodes, quite different from the standard RPA process. Here, a theoretical model is derived to explain the underlying mechanism, and good agreements have been achieved with PIC simulations.

43 PARTICLE ACCELERATORS↗