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At least 343 records · Page 19

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DOE OSTI2019

Development of FPGA-based multi-sensor excitation low voltage (MSELV) chassis at Jefferson Lab

The design and development of the sensor excitation and read back chassis was driven by the requirements for the monitoring and control of two conduction-cooled superconducting magnets in Hall B for the 12 GeV accelerator upgrade. The torus and solenoid superconducting magnets require extensive instrumentation. Sensor selection was accomplished by applying Jefferson Lab’s (JLab) risk mitigation process, which employed a failure modes and effects analysis approach. The goal was to accommodate all sensor types for monitoring and control and to develop a generic multisensor excitation low voltage chassis that would be used across both magnet systems with a reduced set of functions. As a result, the chassis has been deployed in experimental Hall B at JLab and has been performing successfully since July 2016.

47 OTHER INSTRUMENTATION↗

DOE OSTI2019

A possible low-energy positron source at Jefferson Lab

Jefferson Lab is interested in the production of positrons for nuclear physics applications but also has the capability of producing low energy positrons that could be used for positron annihilation studies. Using the LERF accelerator at the Thomas Jefferson National Accelerator Facility, it is possible to produce a high brightness source of very low-energy positrons. The accelerator requirements are well within the capabilities of the installed hardware. For these experiments, we only need run at up to 100 MeV. A challenge is the production of the positrons. The gamma converter must be able to absorb the 50 kW of beam power that the linac delivers. At this low an energy, the converter, though challenging, is feasible. The transport of the low energy positrons from the production target to the next stage, where the energy is reduced even further, must have a very large acceptance to be able to efficiently transport the flux of positrons from the positron production target to the moderator. We propose to accomplish such a transport by means of a guiding solenoidal field with a novel endcap design. Finally, it is in principle possible to produce a spin polarized beam by filtering the positrons at low energy. The layout of the proposed device will be described in this presentation.

Benson, Stephen↗

DOE OSTI2022

Improving the electrostatic design of the Jefferson Lab 300 kV DC photogun

The 300 kV DC high voltage photogun at Jefferson Lab was redesigned to deliver electron beams with a much higher bunch charge and improved beam properties. The original design provided only a modest longitudinal electric field ( E z ) at the photocathode, which limited the achievable extracted bunch charge. To reach the bunch charge goal of approximately few nC with 75 ps full-width at half-maximum Gaussian laser pulse width, the existing DC high voltage photogun electrodes and anode–cathode gap were modified to increase E z at the photocathode. In addition, the anode aperture was spatially shifted with respect to the beamline longitudinal axis to minimize the beam deflection introduced by the non-symmetric nature of the inverted insulator photogun design. We present the electrostatic design of the original photogun and the modified photogun and beam dynamics simulations that predict vastly improved performance. We also quantify the impact of the photocathode recess on beam quality, where recess describes the actual location of the photocathode inside the photogun cathode electrode relative to the intended location. A photocathode unintentionally recessed/misplaced by sub-millimeter distance can significantly impact the downstream beam size.

47 OTHER INSTRUMENTATION↗

DOE OSTI2017

Performance of Different “Lab-On-Chip” Geometries for Making Double Emulsions to Form Polystyrene Shells

Fluid properties and the geometry of lab-on-chip (LOC) designs together affect the formation of double emulsions for making inertial confinement fusion targets. Critical fluid properties include the fluids’ velocities and interfacial tension—a coupled effect that is best characterized by the capillary number (Ca)—and the relative volumetric flow rates (φ). The important geometry of the LOC is the orientation of the channels where they intersect (junction) and the spacing between successive junctions. T-junctions and focus-flow devices were tested. The latter geometry of a double cross (focus flow) performed better: single-emulsion droplets were formed over a wide range of fluid parameters (0.03 < φ < 0.17 and 0.0003 < Ca < 0.001) at the first junction, and double emulsions were formed over a more limited range (φ > 0.5 and Ca < 0.4) at the second junction. A LOC design using the focus-flow design formed water–oil–water (W/O/W) double emulsions with the oil phase containing polystyrene. The double emulsions yielded shells with an outer dimension ranging from 2.3±0.07 mm to 4.3±0.23 mm and a wall thickness ranging from 30 μm to 1.6 mm. Thus, the value of the flow-rate ratio at the second junction provided the most-effective parameter for controlling the inner diameter, outer diameter, and wall thickness of the shell.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

DOE OSTI2020

Ultrafast molecular frame electronic coherences from lab frame scattering anisotropies

Electronic coherences in molecules are ultrafast charge oscillations on the molecular frame (MF) and their direct observation and separation from electronic population dynamics is challenging. Here we present a valence shell lab frame (LF) scattering method suited to probing electronic coherences in isolated systems. MF electronic coherences lead to LF electronic anisotropies observable by ultrafast angle-resolved scattering. Moment analysis of the LF anisotropy completely separates electronic coherences from population dynamics, demonstrated in excited state NH 3 using ultrafast time-energy-angle-resolved photoelectron spectroscopy. Overall, this general approach applies equally to attosecond/femtosecond electronic coherences in isolated systems.

74 ATOMIC AND MOLECULAR PHYSICS↗

DOE OSTI2012

Density measurement through elastic electron scattering with a gaseous target at the Jefferson Lab

We report the density measurement through e-3He elastic scattering with a 1.23 GeV electron beam in Jefferson Lab experiment E06-010. The extracted 3He density is (9.26 plus-minus 0.06) amagats and the N2/3He ratio is (1:49 plus-minus 0:08)%. In addition, these results are consistent with the deduced target densities based on pressure broadening measurement.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

DOE OSTI2015

Radiation and ionization energy loss simulation for the GDH sum rule experiment in Hall-A at Jefferson Lab

The radiation and ionization energy loss are presented for single arm Monte Carlo simulation for the GDH sum rule experiment in Hall-A at Jefferson Lab. Radiation and ionization energy loss are discussed for $^{12}C$ elastic scattering simulation. The relative momentum ratio $\frac{\Delta p}{p}$ and $^{12}C$ elastic cross section are compared without and with radiation energy loss and a reasonable shape is obtained by the simulation. The total energy loss distribution is obtained, showing a Landau shape for $^{12}C$ elastic scattering. This simulation work will give good support for radiation correction analysis of the GDH sum rule experiment.

43 PARTICLE ACCELERATORS↗

DOE OSTI2012

HDice, Highly-Polarized Low-Background Frozen-Spin HD Targets for CLAS experiments at Jefferson Lab

Large, portable frozen-spin HD (Deuterium-Hydride) targets have been developed for studying nucleon spin properties with low backgrounds. Protons and Deuterons in HD are polarized at low temperatures (~10mK) inside a vertical dilution refrigerator (Oxford Kelvinox-1000) containing a high magnetic field (up to 17T). The targets reach a frozen-spin state within a few months, after which they can be cold transferred to an In-Beam Cryostat (IBC). The IBC, a thin-walled dilution refrigerator operating either horizontally or vertically, is use with quasi-4{pi} detector systems in open geometries with minimal energy loss for exiting reaction products in nucleon structure experiments. The first application of this advanced target system has been used for Spin Sum Rule experiments at the LEGS facility in Brookhaven National Laboratory. An improved target production and handling system has been developed at Jefferson Lab for experiments with the CEBAF Large Acceptance Spectrometer, CLAS.

43 PARTICLE ACCELERATORS↗

DOE OSTI2012

EM Calorimeters for SoLID at Jefferson Lab

Several approved experiments at Jefferson Lab for the 12 GeV era will use the proposed Solenoid Large Intensity Device (SoLID) spectrometer. Two EM calorimeters with a total area of 15 square meters are required for electron identification and electron-pion separation. The challenge is to build calorimeters that can withstand high radiation doses in high magnetic field region and bring photon signals to low field region for readout. Several types of calorimeters were considered and we are favoring Shashlyk type as a result of balancing performance and cost. Our preliminary design and simulation of SoLID EM calorimeters are presented.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗

DOE OSTI2012

The design and performance of the electromagnetic calorimeters in Hall C at Jefferson Lab

The design and performance of the electromagnetic calorimeters in the magnetic spectrometers in Hall C at Jefferson Lab are presented. For the existing HMS and SOS spectrometers, construction information and comparisons of simulated and experimental results are presented. The design and simulated performance for a new calorimeter to be used in the new SHMS spectrometer is also presented. We have developed and constructed electromagnetic calorimeters from TF-1 type lead-glass blocks for the HMS and SOS magnetic spectrometers at JLab Hall C. The HMS/SOS calorimeters are of identical design and construction except for their total size. Blocks of dimension 10 cm × 10 cm × 70 cm are arranged in four planes and stacked 13 and 11 blocks high in the HMS and SOS respectively. The energy resolution of these calorimeters is better than 6%/√E, and pion/electron (π/e) separation of about 100:1 has been achieved in energy range 1–5 GeV. Good agreement has been observed between the experimental and GEANT4 simulated energy resolutions. The HMS/SOS calorimeters have been used nearly in all Hall C experiments, providing good energy resolution and a high pion suppression factor. No significant deterioration in their performance has been observed in the course of use since 1994. For the SHMS spectrometer, presently under construction, details on the calorimeter design and accompanying GEANT4 simulation efforts are given. A Preshower+Shower design was selected as the most cost-effective among several design choices. The preshower will consist of a layer of 28 modules with TF-1 type lead glass radiators, stacked in two columns. The shower part will consist of 224 modules with F-101 type lead glass radiators, stacked in a “fly's eye” configuration of 14 columns and 16 rows. The active area of 120 × 130 cm(2) will encompass the beam envelope at the calorimeter. The anticipated performance of the new calorimeter is simulated over the full momentum range of the SHMS, predicting resolution and yields similar to the HMS calorimeter. Good electron/hadron separation can be achieved by using energy deposition in the Preshower along with total energy deposition in the calorimeter. In this case the PID capability is similar to or better than that attainable with HMS calorimeter, with a pion suppression factor of a few hundreds predicted for 99% electron detection efficiency.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗

DOE OSTI2014

Simulations of a FIR Oscillator with Large Slippage parameter at Jefferson Lab for FIR/UV pump-probe experiments

We previously proposed a dual FEL configuration on the UV Demo FEL at Jefferson Lab that would allow simultaneous lasing at FIR and UV wavelengths. The FIR source would be an FEL oscillator with a short wiggler providing diffraction-limited pulses with pulse energy exceeding 50 microJoules, using the exhaust beam from a UVFEL as the input electron beam. Since the UV FEL requires very short pulses, the input to the FIR FEL is extremely short compared to a slippage length and the usual Slowly Varying Envelope Approximation (SVEA) does not apply. We use a non-SVEA code to simulate this system both with a small energy spread (UV laser off) and with large energy spread (UV laser on).

43 PARTICLE ACCELERATORS↗

DOE OSTI2014

Potential for a Tensor Asymmetry Azz Measurement in the x > 1 Region at Jefferson Lab

The tensor asymmetry A(zz) in the quasi-elastic region through the tensor polarized D(e, e')X channel is sensitive to the nucleon-nucleon potential. Previous measurements of A(zz) have been used to extract b(1) in the DIS region and T(20) in the elastic region. In the quasielastic region, A(zz) can be used to compare light cone calculations with variation nucleon- nucleon calculations, and is an important quantity to determine for understanding tensor effects, such as the dominance of pn correlations in nuclei. In the quasi-elastic region, A(zz) was first calculated in 1988 by Frankfurt and Strikman using the Hamada-Johnstone and Reid soft-core wave functions [1]. Recent calculations by M. Sargsian revisit A(zz) in the x > 1 range using virtual-nucleon and light-cone methods, which differ by up to a factor of two [2]. Discussed in these proceedings, a study has been completed that determines the feasibility of measuring A(zz) in the quasi-elastic x > 1 region at Jefferson Lab's Hall C.

Long, Elena↗

DOE OSTI2025

Fluorescence time profile measurement of LAB based liquid scintillator in response to medium relativistic ion particles

Liquid scintillator is widely used in particle physics experiments due to its high light yield, good timing resolution, scalability and low cost. Certain liquid scintillators exhibit pulse shape discrimination capabilities because of difference in fluorescence timing properties induced by different particles. Its fluoresence timing properties have been measured mostly for radioactive decay sources at MeV energies. Here, we present a novel measurement of fluorescence time properties of Linear Alkyl Benzene (LAB) based liquid scintillator in response to high-energy ions of hydrogen (Z = 1), helium (Z = 2) and krypton at around 200–300 MeV/u for the first time. We compared the results to those from radioactive sources and observed a distinct dE / dX dependence, regardless of the particle type. These findings are essential for physics searches such as the diffuse supernova neutrino background in large liquid scintillator detectors like JUNO, and are also critical towards understanding the underlying scintillation timing mechanism.

Ion identification systems↗

DOE OSTI2026

Cold compressor performance and energy consumption improvements at Jefferson Lab’s Central Helium Liquefiers

Abstract Jefferson Lab operates two central helium liquefiers (CHLs) which both utilize full cold compression from the saturation pressure at operating temperature (approximately 2.1 K) to just over atmospheric pressure. The original plant, CHL1, was recently outfitted with a replacement subatmospheric cold box (SC1R) containing state-of-the-art cold compressor technology, while the newer plant, CHL2, uses an older cold compressor system. In both cases, the heat of compression is absorbed at low temperature at the expense of electrical power consumed by the warm compressors. Due to the superior efficiency and turndown capabilities of SC1R, a new operating mode has been identified for CHL1 in which the required number of operating warm compressors is reduced by one. A cost-based method for optimizing cold compressor stability and efficiency has been developed and applied to CHL2, improving its turndown and lowering the warm compressor discharge pressure. As a result of these efforts, power consumption of the combined CHLs during normal operations has been reduced by nearly 10%, or a total of 650 kW. The observed performance of CHL1 with SC1R, as well as the cold compressor optimization method, leading to this improved energy consumption rate will be discussed in detail.

Mastracci, B [Thomas Jefferson National Accelerato↗

DOE OSTI2021

Measurement of the Ar ( e , e ' p ) and Ti ( e , e ' p ) cross sections in Jefferson Lab Hall A

The E12-14-012 experiment, performed in Jefferson Lab Hall A, has collected exclusive electron-scattering data ( e , e ' p ) in parallel kinematics using natural argon and natural titanium targets. In this study we report the first results of the analysis of the data set corresponding to beam energy 2222 GeV, electron scattering angle 21 . 5 ° , and proton emission angle – 50 ° . The differential cross sections, measured with ≈ 4 % uncertainty, have been studied as a function of missing energy and missing momentum, and compared to the results of Monte Carlo simulations, obtained from a model based on the distorted-wave impulse approximation.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

DOE OSTI2021

Measurement of deeply virtual Compton scattering off 4 He with the CEBAF Large Acceptance Spectrometer at Jefferson Lab

We report on the measurement of the beam spin asymmetry in the deeply virtual Compton scattering off $^4$He using the CEBAF Large Acceptance Spectrometer (CLAS) at Jefferson Lab using a 6 GeV longitudinally polarized electron beam incident on a pressurized $^4$He gaseous target. We detail the method used to ensure the exclusivity of the measured reactions, in particular the upgrade of CLAS with a radial time projection chamber to detect the low-energy recoiling $^4$He nuclei and an inner calorimeter to extend the photon detection acceptance at forward angles. Our results confirm the theoretically predicted enhancement of the coherent ($e^4$He$~\to~e'$$^4$He$'\gamma'$) beam spin asymmetries compared to those observed on the free proton, while the incoherent ($e^4$He$~\to~e'$p$'\gamma'$X$'$) asymmetries exhibit a 30$\%$ suppression. From the coherent data, we were able to extract, in a model-independent way, the real and imaginary parts of the only $^4$He Compton form factor, $\cal H_A$, leading the way toward 3D imaging of the partonic structure of nuclei.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

DOE OSTI2025

Elastic scattering in the 12 N + 197 Au system at 𝐸 lab = 70 MeV

Halo structure is an interesting exotic configuration developed in some light weakly bound nuclei, where a valence particle orbits a nuclear core. Signatures of halo structure can be observed in the angular distributions of the elastic scattering induced by these nuclei at energies around the Coulomb barrier. There are some well-studied reactions with neutron-rich halo nuclei, such as 6 He and 11 Li . However, the information is scarce on the proton-rich side. Recent works confirm the halo structure in the 8B nuclei but still lack more experimental studies for other proton-halo candidates, such as 12 N and 17 F. In this work, we report experimental data for the elastic scattering of 12 N on 197 Au target at 𝐸 lab = 70 MeV. The 12 N is a proton-rich nucleus with proton separation energy 𝑆 𝑝 = 600 keV, which is higher than the 8 B (𝑆 𝑝 = 137 keV) and almost the same as the 17 F (𝑆 𝑝 = 601 keV). Data were obtained at the Cyclotron Institute of Texas A&M University where the 12 N radioactive beam was produced by the momentum achromatic recoil spectrometer. The calculation of the optical model was used to fit the measured angular distribution for the elastic scattering and to obtain the reaction cross section 𝜎 𝑅 . We also performed continuum discretized coupled-channel calculations to compare with the experimental data. The angular distribution of the elastic cross sections exhibits a suppression of the Fresnel peak. From the fitting of the optical model, we obtain the total reaction cross section, 𝜎 𝑅 = 1269 ± 41 mb. The agreement between the CDCC calculation and the experimental elastic scattering data is limited and the breakdown does not exhaust the measured 𝜎 𝑅 . The resulting reduced reaction cross section 𝜎 Red for 12 N + 197 Au is large and comparable to the one obtained for the 8 B + 208 Pb system. This suggests a strong decoupling of the valence proton from the core because of the low binding energy and a dynamic polarization effect. Here, more research is required to estimate the contribution of core excitation.

Elastic scattering reactions↗

DOE OSTI2015

E00-110 experiment at Jefferson Lab Hall A: Deeply virtual Compton scattering off the proton at 6 GeV

We present final results on the photon electroproduction ($\vec{e}p\rightarrow ep\gamma$) cross section in the deeply virtual Compton scattering (DVCS) regime and the valence quark region from Jefferson Lab experiment E00-110. Results from an analysis of a subset of these data were published before, but the analysis has been improved which is described here at length, together with details on the experimental setup. Furthermore, additional data have been analyzed resulting in photon electroproduction cross sections at new kinematic settings, for a total of 588 experimental bins. Results of the $Q^2$- and $x_B$-dependences of both the helicity-dependent and helicity-independent cross sections are discussed. The $Q^2$-dependence illustrates the dominance of the twist-2 handbag amplitude in the kinematics of the experiment, as previously noted. Thanks to the excellent accuracy of this high luminosity experiment, it becomes clear that the unpolarized cross section shows a significant deviation from the Bethe-Heitler process in our kinematics, compatible with a large contribution from the leading twist-2 DVCS$^2$ term to the photon electroproduction cross section. The necessity to include higher-twist corrections in order to fully reproduce the shape of the data is also discussed. The DVCS cross sections in this study represent the final set of experimental results from E00-110, superseding the previous publication.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗