arXiv subjects

M. Le

Publications and source records attributed to M. Le.

5 recordsLinked to original sources

arXiv2026

Experiments towards a neutron target for measurements in inverse kinematics

Neutron-induced reactions play an important role in fundamental nuclear physics, nuclear astrophysics, and applications. In the case of reactions on rare isotopes, there are limited options for direct experimental measurements. The Neutron Target Demonstrator project at Los Alamos National Laboratory seeks to test the feasibility of moderating spallation neutrons within a 1~m$^3$ graphite cube to create a standing neutron target for neutron-induced reaction measurements in inverse kinematics. This paper presents the results of experimental neutron flux distribution tests using neutron sources (ranging from 1~keV to 50~MeV) created by accelerators at the University of Notre Dame and Texas A\&M University. Measurements were made with both the full graphite cube as well as a ''half cube'' setup in which half of the graphite cube was removed. The measured distributions agree with simulated distributions in the case of the full cube moderator, although there remain discrepancies in certain cases for the half cube moderator. The results shown here will provide useful information for an upcoming experimental campaign to test the neutron target proof-of-principle.

physics.ins-det↗

arXiv2025

Ice Giants Pre-Decadal Survey Mission Study Report

The Ice Giants Study was commissioned by NASA to take a fresh look (as of 2017) at science priorities and concepts for missions to the Uranus and Neptune systems in preparation for the third Planetary Science Decadal Survey. This study was led by a Science Definition Team (SDT) and the Jet Propulsion Laboratory (JPL) with participation from Langley Research Center, Ames Research Center, The Aerospace Corporation, Purdue University, and the European Space Agency. The SDT was appointed by NASA and co-chaired by Mark Hofstadter (JPL) and Amy Simon (Goddard Space Flight Center). The Study Manager was Kim Reh (JPL) and the Study Lead was John Elliott (JPL). The study team assessed and prioritized science objectives taking into account advances since the last Decadal Survey, current and emerging technologies, mission implementation techniques and celestial mechanics. This study examined a wide range of mission architectures, flight elements, and instruments. Six of the prioritized concepts were studied via JPL's Team X process and resulting cost estimates were subjected to independent assessment by The Aerospace Corporation. Results presented herein show that high-value flagship-class mission concepts to either Uranus or Neptune are achievable within ground rule budgetary constraints.

astro-ph.IM↗

arXiv2023

Guided mode evolution and ionization injection in meter-scale multi-GeV laser wakefield accelerators

We show that laser wakefield electron accelerators in meter-scale, low density hydrodynamic plasma waveguides operate in a new nonlinear propagation regime where sustained beating of lowest order modes of the ponderomotively modified channel plays a significant role, whether or not the injected pulse is linearly matched to the guide. For a continuously doped gas jet, this mode beating effect leads to ionization injection and a striated multi-GeV energy spectrum of multiple quasi-monoenergetic peaks; the same process in a locally doped jet produces single multi-GeV peaks with <10% energy spread. A 3-stage model of drive laser pulse evolution and ionization injection characterizes the beating effect and explains our experimental results.

physics.plasm-ph↗

arXiv2022

The POLARBEAR-2 and Simons Array Focal Plane Fabrication Status

We present on the status of POLARBEAR-2 A (PB2-A) focal plane fabrication. The PB2-A is the first of three telescopes in the Simon Array (SA), which is an array of three cosmic microwave background (CMB) polarization sensitive telescopes located at the POLARBEAR (PB) site in Northern Chile. As the successor to the PB experiment, each telescope and receiver combination is named as PB2-A, PB2-B, and PB2-C. PB2-A and -B will have nearly identical receivers operating at 90 and 150 GHz while PB2-C will house a receiver operating at 220 and 270 GHz. Each receiver contains a focal plane consisting of seven close-hex packed lenslet coupled sinuous antenna transition edge sensor bolometer arrays. Each array contains 271 di-chroic optical pixels each of which have four TES bolometers for a total of 7588 detectors per receiver. We have produced a set of two types of candidate arrays for PB2-A. The first we call Version 11 (V11) and uses a silicon oxide (SiOx) for the transmission lines and cross-over process for orthogonal polarizations. The second we call Version 13 (V13) and uses silicon nitride (SiNx) for the transmission lines and cross-under process for orthogonal polarizations. We have produced enough of each type of array to fully populate the focal plane of the PB2-A receiver. The average wirebond yield for V11 and V13 arrays is 93.2% and 95.6% respectively. The V11 arrays had a superconducting transition temperature (Tc) of 452 +/- 15 mK, a normal resistance (Rn) of 1.25 +/- 0.20 Ohms, and saturations powers of 5.2 +/- 1.0 pW and 13 +/- 1.2 pW for the 90 and 150 GHz bands respectively. The V13 arrays had a superconducting transition temperature (Tc) of 456 +/-6 mK, a normal resistance (Rn) of 1.1 +/- 0.2 Ohms, and saturations powers of 10.8 +/- 1.8 pW and 22.9 +/- 2.6 pW for the 90 and 150 GHz bands respectively.

astro-ph.IM↗

arXiv2020

Laser-accelerated, low divergence 15 MeV quasi-monoenergetic electron bunches at 1 kHz

We demonstrate laser wakefield acceleration of quasi-monoenergetic electron bunches up to 15 MeV at 1 kHz repetition rate with 2.5 pC charge per bunch and a core with < 7 mrad beam divergence. Acceleration is driven by 5 fs, < 2.7 mJ laser pulses incident on a thin, near-critical density hydrogen gas jet. Low beam divergence is attributed to reduced sensitivity to laser carrier envelope phase slip, achieved in two ways using laser polarization and gas jet control: (1) electron injection into the wake on the gas jet's plasma density downramp, and (2) use of circularly polarized drive pulses. Under conditions of mild wavebreaking in the downramp, electron beam profiles have a 2D Lorentzian shape consistent with a kappa electron energy distribution. Such distributions had previously been observed only in space or dusty plasmas. We attribute this shape to the strongly correlated collisionless bunch confined by the quadratic wakefield bubble potential, where transverse velocity space diffusion is imparted to the bunch by the red-shifted laser field in the bubble.

physics.plasm-ph↗