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At least 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Nb 3 Sn multicell cavity coating system at Jefferson Lab

Superconducting radio frequency niobium cavities are the building blocks of modern accelerators for scientific applications. Lower surface resistance, higher fields, and high operating temperatures advance the reach of the future accelerators for scientific discovery as well as potentially enabling cost-effective industrial solutions. We describe the design and performance of an Nb 3 Sn coating system that converts the inner surface of niobium cavities to an Nb 3 Sn film. The niobium surface, heated by radiation from the niobium retort, is exposed to Sn and SnCl 2 vapor during the heat cycle, which results in about 2 μm Nb 3 Sn film on the niobium surface. Film composition and structure as well as radio frequency properties with 1-cell R&D cavities and 5-cell practical accelerator cavities are presented.

47 OTHER INSTRUMENTATION↗
DOE OSTI2021

Redesigning the Jefferson Lab Hall A beam line for high precision parity experiments

The Continuous Electron Beam Accelerator Facility (CEBAF) was built with a thermionic electron source and the three original experimental hall lines reflected this. A few years after beam delivery began a parity violation experiment was approved and two polarimeters were installed in the Hall A beam line. The beam raster system was placed after the new Compton polarimeter, before one accelerator quadrupole and four quadrupoles in the new Moller polarimeter. It was very difficult to meet experimental requirements on envelope functions and raster shape with this arrangement so a sixth quadrupole was installed downstream of the Moller polarimeter to provide an additional degree of freedome. All of the parity experiments in Hall A have been run with this still-unsatisfactory configuration. The MOLLER experiment is predicated on achieving a 2% error on a 32 ppb asymmetry. Beam line changes are required to meet the systematic error budget. This work documents the existing beam line, an interim change which can be accomplished during a annual maintenance down, and the final configuration for MOLLER and subsequent experiments.

47 OTHER INSTRUMENTATION↗
DOE OSTI2021

Deeply Virtual Compton Scattering Using a Positron Beam in Hall-C at Jefferson Lab

In this study we propose to use the High Momentum Spectrometer of Hall C combined with the Neutral Particle Spectrometer (NPS) to perform high precision measurements of the Deeply Virtual Compton Scattering (DVCS) cross section using a beam of positrons. The combination of measurements with oppositely charged incident beams is the only unambiguous way to disentangle the contribution of the DVCS 2 term in the photon electroproduction cross section from its interference with the Bethe-Heitler amplitude. This provides a stronger way to constrain the Generalized Parton Distributions of the nucleon. A wide range of kinematics accessible with an 11 GeV beam off an unpolarized proton target will be covered. The $\mathcal{Q}^2$-dependence of each contribution will be measured independently.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2022

Evaluation of Single-Cell Cavities Made of Forged Ingot Niobium at Jefferson Lab

Currently, fine grain niobium (Nb) (grain size ~ 50 um) and large grain Nb (grain size of a few cm) are being used for the fabrication of superconducting radio frequency (SRF) cavities. Medium grain forged ingot with grain size of a few hundred um may be beneficial for cost-effectiveness as well as providing better performance for future SRF-based accelerators. Forged ingot Nb with medium grain size is a novel production method to obtain Nb discs used for the fabrication of superconducting radio frequency cavities. We have fabricated two 1.5 GHz single cell cavities made from forged Nb ingot with a residual resistivity ratio of ~100. The cavities were chemically and mechanically polished and heat-treated in the temperature range of 650-1000 C before the rf test. One of the cavities reached an accelerating gradient of 34 MV/m with a quality factor Q > 1e10, while the second cavity was limited at 14 MV/m, likely due to a weld defect at the equator.

Dhakal, P.↗
DOE OSTI2022

In Situ Plasma Processing of Superconducting Cavities at Jefferson Lab

Jef­fer­son Lab began a plasma pro­cess­ing pro­gram start­ing in the spring of 2019. Plasma pro­cess­ing is a com­mon tech­nique for re­mov­ing hy­dro­car­bons from sur­faces, which in­creases the work func­tion and re­duces the sec­ondary emis­sion co­ef­fi­cient. Un­like he­lium pro­cess­ing which re­lies on ion bom­bard­ment of the field emit­ters, plasma pro­cess­ing uses free oxy­gen pro­duced in the plasma to break down the hy­dro­car­bons on the sur­face of the cav­ity. The resid­u­als of the hy­dro­car­bons in the form of water, car­bon monox­ide and car­bon diox­ide are re­moved from the cry­omod­ule as part of the process gas flow. The ini­tial focus of the ef­fort is pro­cess­ing C100 cav­i­ties by in­ject­ing RF power into the HOM cou­pler ports. We will then start in­ves­ti­gat­ing pro­cess­ing of C50 cav­i­ties by in­tro­duc­ing RF into the fun­da­men­tal power cou­pler. The plan is to start pro­cess­ing cry­omod­ules in the CEBAF tun­nel in the mid-term fu­ture, with a goal of im­prov­ing the op­er­a­tional gra­di­ents and the en­ergy mar­gin of the linacs. This work will de­scribe the sys­tems and meth­ods used at JLAB for pro­cess­ing cav­i­ties using an argon oxy­gen gas mix­ture. Be­fore and after plasma pro­cess­ing re­sults will also be pre­sented.

Powers, T.↗
DOE OSTI2023

Geometry Optimization for a Quadrupole Resonator at Jefferson Lab

The quadrupole resonator (QPR) is a sample characterization tool to measure the RF properties of superconducting materials using the calorime-try method at different temperatures, magnetic fields, and frequencies. Such resonators are cur-rently operating at CERN and HZB but suffer from Lorentz force detuning and modes overlap-ping, resulting in higher uncertainties in surface resistance measurement. Using the two CERN's QPR model iterations, the geometry was opti-mized via electromagnetic and mechanical simu-lations to eliminate these issues. The new QPR version was modelled for an increasing range of magnetic fields. The magnetic field is concentrat-ed at the center of the sample to reduce the un-certainty in surface resistance measurements sig-nificantly. This paper discusses the QPR geome-try optimization for the new version of QPR, which is now progressing toward fabrication.

Bira, S.↗
DOE OSTI2020

Deeply Virtual Compton Scattering on the Proton in Hall A at Jefferson Lab

The structure of nucleons as they are composed of quarks and gluons is not well understood. Non-perturbative methods (such as lattice-QCD) describing quark/gluon interactions are ongoing in development, but still cannot fully reproduce the structure of hadrons. Among the observables which describe longitudinal momentum and transverse position of partons, generalized parton distributions (GPDs) describe the correlations between the two, and are accessible through p(right-arrow e;e'y)p scattering experiments in the Bjorken limit when factorization holds. A complete understanding of these functions will help us to better understand the structure of nucleons. Experiment E12-06-114 was performed by JLab's DVCS Hall A Collaboration in 2014 and 2016. Using a polarized electron beam and a liquid hydrogen target, the collaboration measured cross sections for the exclusive reaction p(right-arrow e;e'y)p at xB=0.36, 0.48, and 0.60,3 .2 lte Q2 lte 9.00, and -1.28 lte t lte -0.69. This dissertation details the analysis and results of measuring the p(right-arrow e;e'y)p cross section at xB=0.48. The measured cross section results allow us to demonstrate the validity of factorization in our kinematic regime, and extract Compton Form Factor combinations important for understanding GPDs. Additionally, the cross section results are used to test existing GPD models, KM10a and KM15.

Johnson, Alexa N.↗
DOE OSTI2021

Isotope Production at the Jefferson Lab LERF Facility (Final Report)

The project initially proceeded well, meeting all of the Milestones. However, the need to create a new irradiation area in the LERF (the initial proposal was to use the CEBAF Injector) used up a larger fraction of the budget than foreseen. A further problem arose when the hot-cell became unavailable at VCU, followed by VCU dropping out of the collaboration. This meant that we were unable to separate the 67 Cu from the gallium. We replaced this by carrying out detailed gamma spectroscopy to determine the quantity of 67 Cu produced.

07 ISOTOPE AND RADIATION SOURCES↗
DOE OSTI2021

Isotope Production at the Jefferson Lab LERF Facility

The project initially proceeded well, meeting all of the Milestones. However, the need to create a new irradiation area in the LERF (the initial proposal was to use the CEBAF Injector) used up a larger fraction of the budget than foreseen. A further problem arose when the hot-cell became unavailable at VCU, followed by VCU dropping out of the collaboration. This meant that we were unable to separate the 67 Cu from the gallium. We replaced this by carrying out detailed gamma spectroscopy to determine the quantity of 67 Cu produced. This work was published as presentations in November of 2021 by the two doctoral students (Geno Santistevan and Robert Bentley) and proceedings articles for American Nuclear Society’s topical meeting AccApp21 (https://www.ans.org/pubs/proceedings/issue-3206/), as well as in invited, expanded versions in the peer-reviewed journal “Nuclear Science and Engineering”. Geno and Robert have subsequently successfully leveraged this research to achieve “doctoral candidacy” status and are expected to defend their dissertations in the Fall of 2023.

07 ISOTOPE AND RADIATION SOURCES↗
DOE OSTI2022

Development of Large Area µRWELL Detectors for CLAS12 High Luminosity Upgrade at Jefferson Lab

The high-luminosity upgrade of the CEBAF Large Acceptance Spectrometer (CLAS12) will significantly enhance the physics reach of experiments in Hall B at JLab. However, at the current luminosity of L = 1 × 1035 cm-2 s-1, the reconstruction efficiency of charged particles in the forward region of the CEBAF Large Acceptance Spectrometer (CLAS12) is at the level of 85% and limited in part by the drift chambers inability to handle high occupancy, in the first tracking region (DC-R1) of the Forward Detector. The reconstruction efficiency is expected to drop even lower at higher luminosities with the current tracking technology. Various options under consideration to achieve the desired performance at a higher luminosity of L = 2 × 1035 cm-2 s-1 include the addition of fast tracking layers to complement DC-R1 or the replacement of DC-R1 with a different tracking detector technology altogether. In either case, a novel generation of compact, simple and robust Micro-Pattern Gaseous Detector (MPGD) known as the Resistive Micro-Well detector (µRWELL) is the ideal candidate to satisfy the requirements in terms of timing O (10 ns) and position O (100 µm) resolutions. A large µRWELL prototype, combined with a two-dimensional U-V strip readout layer based on the novel concept of capacitive-sharing approach has been developed as a proof of principle for fast tracking capabilities in the forward region of CLAS12 high-luminosity upgrade. In this talk, we will present the technical aspects of the design choices of the large µRWELL prototype under development and report on the detector assembly process and preliminary performance characteristic tests. We will also discuss the plans for the test and characterization of the prototype in beam during spring 2023 CEBAF run. Finally, we will report on ongoing R&D efforts on small prototypes with the goal to improve rate capability, spatial resolution performance and minimize material thickness.

Gnanvo, Kondo↗
DOE OSTI2023

Spin Structure Program at Jefferson Lab

High performance polarized beam and targets at JLab enabled an extensive program to measure nucleon spin structure functions with high precision. This talk will highlight the recent JLab spin experiments, including the measurement of the neutron spin asymmetry (A1n) in the valance quark (high-x) region and the measurement of the neutron spin moment d2 in medium-high Q2 region to study quark-gluon correlations. Recent results on spin moments at low Q2 (spin sum rules and spin polarizabilities) for both the proton and neutron will also be presented

Chen, Jian-Ping↗