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At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2017

Low Energy Nuclear Physics Experiments at Jefferson Lab

Jefferson Lab houses a state-of-the-art 12 GeV accelerator (CEBAF) that may be used to probe nuclear structure. Not all of the experiments at Jefferson Lab are carried out at the GeV scale though. Experiments in the CEBAF injector and in the Low Energy Recirculation Facility (LERF) are capable of doing experiments at low center of mass energy with very high intensities. I will go over some examples of experiments that have been either carried out or have been proposed using these low energy electron sources. The LERF contains an Energy Recovery Linac (ERL) that allows some novel experiments due to the combination of low energy, high current, and thick targets. An example of this, an experiment looking for dark matter candidates, will be described in some detail.

Benson, Stephen↗
DOE OSTI2016

An overview of recent nucleon spin structure measurements at Jefferson Lab

Jefferson Lab have made significant contributions to improve our knowledge of the longitudinal spin structure by measuring polarized structure functions, g1 and g2, down to Q2 = 0.02 GeV2. The low Q2 data is especially useful in testing the Chiral Perturbation theory (cPT) calculations. The spin-dependent sum rules and the spin polarizabilities, constructed from the moments of g1 and g2, provide an important tool to study the longitudinal spin structure. We will present an overview of the experimental program to measure these structure functions at Jefferson Lab, and present some recent results on the neutron polarizabilities, proton g1 at low Q2, and proton and neutron d2 measurement. In addition to this, we will discuss the transverse spin structure of the nucleon which can be accessed using chiral-odd transversity distribution (h1), and show some results from measurements done on polarized 3He target in Hall A.

Allada, Kalyan↗
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

Plasma Processing of SRF Cavities at Jefferson Lab

Jefferson Lab has an ongoing R&D program in plasma processing which is close to going into production pro-cessing in the CEBAF accelerator. Plasma processing is a common technique for removing hydrocarbons from surfaces, which increases the work function and reduces the secondary emission coefficient [1]. The initial focus of the effort is processing C100 cavities by injecting RF power into the HOM coupler ports. The goal will be to improve the operational gradients and the energy margin of the CEBAF linacs by processing cryomodules in situ. Results from processing a cryomodule in the cryomodule test bunker as well as cavity vertical test results will be presented. This work describes the systems and methods used at JLAB for processing cavities using an ar-gon/oxygen gas mixture.

Powers, T.↗
DOE OSTI2014

What is Jefferson Lab

Jefferson Lab is a U.S. Department of Energy national laboratory. Its primary mission is to conduct basic research that builds a comprehensive understanding of the atom's nucleus.

Source record↗
DOE OSTI2015

Superconducting Magnets for the 12 GeV Upgrade at Jefferson Lab

Jefferson Laboratory is embarked on an energy upgrade to its flagship continuous electron beam accelerator in order to expand the scope of its research capabilities and probe further into the structure of nuclear particles. The 12 GeV upgrade includes the design, manufacture, integration, installation and commissioning of eight different superconducting magnets in three separate experimental halls. The effort involves other national laboratories, universities and industry spanning three countries. This paper will summarize the key characteristics of these magnets, ranging in size from 0.2 to 23 MJ in stored energy, and featuring many different types and configurations. The paper will also give an overview of the specific technical challenges for each magnet, and a status report on magnet manufacture and expected delivery dates. The 12GeV upgrade at J-Lab represents the largest superconducting magnet fabrication and installation program currently ongoing in the United States and this paper will present the breadth of collaborations supporting it.

12 GeV upgrade, continuous electron beam accelerat↗
DOE OSTI2018

NMR Measurements for Solid Polarized Targets at Jefferson Lab

Jefferson Lab's solid polarized targets rely on Nuclear Magnetic Resonance techniques to measure the enhanced polarization provided under Dynamic Nuclear Polarization. Upcoming polarized target experiments in JLab's Hall B present challenging conditions which would benefit from improvements to traditional NMR techniques. For decades, JLab has utilized Liverpool Q Meters for NMR measurements, but these are aging and no longer produced. The polarized target group at Bochum has successfully produced replacement Q Meters with modern components, and we are following their example, exploring new designs for both an analog and a digital Q Meter system. Unlike recent experiments in Halls A and C, the new Hall B target will require external NMR coils, resulting in a weaker signal. In addition, two separate target cells will be utilized, each held at different magnetic fields, allowing them to be polarized in opposing directions, but complicating the NMR measurement. We present the challenges presented by the new Hall B target, lay out plans for improvements to our NMR system, and show results of initial tests of our designs.

Maxwell, James↗
DOE OSTI2013

The Jefferson lab FEL driver ERLs

Jefferson Lab has - for over a decade - been operating high power IR and UV FELs using CW energy recovering linacs based on DC photocathode electron sources and CEBAF SRF technology. These machines have unique combinations of beam quality, power, and operational flexibility, and thus offer significant opportunity for experiments that use low and medium energy (several tens - few hundreds of MeV) electron beams. We will describe the systems and detail their present and near-term (potential) performance. Recent internal-target analysis and validation testing will be discussed, and schemes for single- and two-pass fixed target operation described. An introduction to subsequent discussions of beam quality and upgrade paths to polarized operation/higher energy will be given.

43 PARTICLE ACCELERATORS↗
DOE OSTI2014

Jefferson Lab: New opportunities in hadronic physics

Jefferson Lab (JLab) is a fundamental research laboratory located in Newport News (Virginia-USA) whose primary mission is to explore the fundamental nature of confined states of quarks and gluons. It consists of a high-intensity electron accelerator based on continuous wave superconducting radio frequency technology and a sophisticated array of particle detectors. The design features and excellent performance of the accelerator made it possible to plan an upgrade in energy from 6 to 12 GeV without substantially altering the construction scheme of the accelerator. The program includes the construction of major new experimental facilities for the existing three Halls, A, B, C and the construction of the new experimental Hall D. The research program that motivated the upgrade in energy includes: the study of the nucleon 'tomography' through the study of generalized parton distribution functions (GPDs) and transverse momentum dependent parton distribution functions (TMDs), the study of exotics and hybrid mesons to explore the nature of the quarks confinement, precision test of the Standard Model through parity-violating electron scattering experiments. Major highlights of the program at 6 GeV will be presented as well as an overview of the 12 GeV physics program.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2015

Production of Resonances Using CLAS at Jefferson Lab

Measurements of hadronic resonances produced in photoproduction reactions at Jefferson Lab are shown and discussed. Emphasis is placed on the production of the excited hyperon states Sigma(1385), Lambda(1405), and Lambda(1520). Some future prospects for the upcoming Jefferson Lab 12 GeV era are given, where the CLAS12 and GlueX detectors will see unprecedented amounts of data using electromagnetic probes and further our knowledge of hadronic resonances.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2013

The neutron skin in neutron-rich nuclei at Jefferson Lab

The Jefferson Lab program to measure the symmetry energy of neutron-rich nuclear matter, using precision electroweak methods, is progressing well. The initial measurement by the PREX experiment, leading to a 2-sigma determination of the 'neutron skin' in {sup 208}Pb, has been published. Design and preparation for a further, more-precise measurement on {sup 208}Pb is progressing well and there is general acceptance of the great advantage to a further measurement on {sup 48}Ca. The surprising ancillary result that the beam-normal single-spin asymmetry for {sup 208}Pb is consistent with zero is also now in the literature. This paper will discuss the current experimental situation of the program.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2015

Spin physics program in Jefferson Lab’s Hall C

The nucleon spin structure has been studied at Jefferson Lab’s Hall C in experiments RSS (E01-006) and SANE (E07-003), which measured double spin asymmetries using the U. of Virginia solid polarized target and CEBAF’s 6 GeV polarized electrons. The proton longitudinal spin structure g{sub 1} and transverse structure g{sub 2} have been investigated at kinematics extending from the elastic point to DIS, for four-momenta squared ranging from 0.8 to 5 GeV{sup 2}. The neutron structures have been measured in the region of the nucleon resonances at 1.3 GeV{sup 2} on a deuteron target. Results of both experiments will be highlighted. A brief survey of approved experiments for the 12 GeV program will also be presented.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2015

Performance Testing of Jefferson Lab 12 GeV Helium Screw Compressors

Oil injected screw compressors have essentially superseded all other types of compressors in modern helium refrigeration systems due to their large displacement capacity, reliability, minimal vibration, and capability of handling helium's high heat of compression. At the present state of compressor system designs for helium refrigeration systems, typically two-thirds of the lost input power is due to the compression system. It is important to understand the isothermal and volumetric efficiencies of these machines to help properly design the compression system to match the refrigeration process. It is also important to identify those primary compressor skid exergetic loss mechanisms which may be reduced, thereby offering the possibility of significantly reducing the input power to helium refrigeration processes which are extremely energy intensive. This paper summarizes the results collected during the commissioning of the new compressor system for Jefferson Lab?s (JLab?s) 12 GeV upgrade. The compressor skid packages were designed by JLab and built to print by industry. They incorporate a number of modifications not typical of helium screw compressor packages and most importantly allow a very wide range of operation so that JLab?s patented Floating Pressure Process can be fully utilized. This paper also summarizes key features of the skid design that allow this process and facilitate the maintenance and reliability of these helium compressor systems.

Knudsen, P.↗
DOE OSTI2019

Conceptual Design of the Interaction Region Magnets for Future Electron-Ion Collider at Jefferson Lab

The Jefferson Lab Electron Ion Collider (JLEIC) is a proposed new machine for nuclear physics research. As proposed, it will deliver between 15 and 65 GeV center of mass energy collisions between electrons and nuclei. It uses the existing CEBAF accelerator as a full energy injector to deliver 3 to 10 GeV electrons into a new electron collider ring. An all new ion accelerator and collider complex will deliver up to 100 GeV protons, or 40 GeV/nucleon ions. The machine will have luminosity goals of above 1033 cm-2 sec-1 in the whole energy range with a maximum of a few 1034 cm-2 sec-1. The two collider rings use a unique figure-of eight layout to deliver a high degree of polarization in both beams. The machine will include room for two interaction regions with only one initially installed. The crossing angle in the primary interaction region will be 50 mrad. The whole detector region including forward detection covers about 80 meters of the JLEIC complex. This paper will describe the requirements and preliminary designs for both the ion and electron beam magnets in the most complex 32 m long interaction region (IR) around the interaction point (IP). The interaction region has over thirty-seven superconducting magnets operating at 4.5K; these include dipoles, quadrupoles, skew-quadrupoles, solenoids, horizontal and vertical correctors and higher order multipole magnets. The paper will also discuss the electromagnetic interaction between these magnets.

Wiseman, Mark (ORCID:0000000179110306)↗
DOE OSTI2019

LCLS-II cavity higher order modes coupler tuning optimization and challenges at Jefferson Lab

The Thomas Jefferson National Accelerator Facility is currently engaged, along with several other Department of Energy (DOE) national laboratories, in the Linac Coherent Light Source II project (LCLS II) - a new XFEL linac based on 1.3GHz superconducting linear accelerator. Half of the LCLS-II cryomodules are being produced at Jefferson Lab, other half is made at Fermilab. Each cryomodule contains eight 9-cell cavities with two Higher Order Modes (HOM) loop couplers operating at 1.3 GHz. This paper summarizes the HOM filter tuning challenges at Jefferson Lab and describes optimization of the procedure for a 9-cell Tesla type cavity and its integration into a cryomodule production line.

Solopova, Anna D.↗
DOE OSTI2016

Design and Evaluation of joint resistance in SSC Rutherford type cable splices for Torus magnet for the Jefferson Lab 12 GeV Upgrade

The Hall B 3.6-T superconducting torus magnet is being designed and built as part of the Jefferson Lab 12-GeV upgrade. The magnet consists of six trapezoidal coils connected in series, with an operating current of 3770 A. The magnet and the joints (or splices) connecting the coils are all conduction cooled by supercritical 4.6-K helium. This paper studies the design and manufacturing process of the splices made between two SSC Rutherford-type cables and discusses the tests performed to evaluate the performance of the splices under varying incident magnetic fields.

Ghoshal, Probir K.↗
DOE OSTI2014

The proton form factor measurements at Jefferson Lab, past and future

Use of the double-polarization technique to obtain the elastic nucleon form factors has resulted in a dramatic improvement of the quality of two of the four nucleon electromagnetic form factors, G{sub Ep} and G{sub En}. It has also changed our understanding of the proton structure, having resulted in a distinctly different Q{sup 2}-dependence for both G{sub Ep} and G{sub Mp}, contradicting the prevailing wisdom of the 1990’s based on cross section measurements, namely that G{sub Ep} and G{sub Mp} obey a “scaling” relation μG{sub Ep} ∼ G{sub Mp}. A related consequence of the faster decrease of G{sub Ep} revealed by the Jefferson Lab (JLab) polarization results was the disappearance of the early scaling F{sub 2}/F{sub 1} ∼ 1/Q{sup 2} predicted by perturbative QCD. In three experiments, GEp(1), GEp(2) and GEp(3), in Halls A and C at JLab, the ratio of the proton’s electromagnetic elastic form factors, G{sub Ep}/G{sub Mp}, was measured up to four momentum transfer Q{sup 2} of 8.5 GeV{sup 2} with high precision, using the recoil polarization technique. The initial discovery that the proton form factor ratio measured in these three experiments decreases approximately linearly with four-momentum transfer, Q{sup 2}, for values above ∼ 1 GeV{sup 2}, was modified by the GEp(3) results, which suggests a slowing down of this decrease. There is an approved experiment, GEp(5), to continue these measurements to 15 GeV{sup 2}. A dedicated experimental setup, the super bigbite spectrometer (SBS), will be built for this purpose. It will be equipped with a new focal plane polarimeter to measure the polarization of the recoil protons. In this presentation, I will review the status of the proton elastic electromagnetic form factors, mention succinctly a number of theoretical approaches to describe results and show some features required for the future GEp(5) experiment.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2014

Recent results and future direction of the parity-violating electron scattering program in Hall A at Jefferson Lab

Hall A at Jefferson Lab has recently completed three experiments done using the technique of parity-violating electron scattering. Taken together these experiments are a good demonstration of the versatility of this approach. Looking forward, there are two very large scale parity-violation experiments approved to run in Hall A in the 12 GeV era. These experiments represent a significant increase in precision and technical requirements.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗