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The Berkeley Lab IT Department sponsored a community outreach program aimed at teaching young children about computers and networks. Second graders from LeConte Elementary School joined Lab IT Staff for a day of in-depth exercises and fun.
Two new high gradient C100 cryomodules with a total of 16 new cavities were installed at the end of the CEBAF south linac during the 2011 summer shutdown as part of the 12-GeV upgrade project at Jefferson Lab. We surveyed the higher order modes (HOMs) of these cavities in the Jefferson Lab cryomodule test facility and CEBAF tunnel. We then studied recirculating beam breakup (BBU) in November 2011 to evaluate CEBAF low energy performance, measure transport optics, and evaluate BBU thresholds due to these HOMs. This paper discusses the experiment setup, cavity measurements, machine setup, optics measurements, and lower bounds on BBU thresholds by new cryomodules.
A 499 MHz parallel bar superconducting deflecting cavity has been designed and optimized for a possible implementation at the Jefferson Lab. Previously the mechanical analysis, mainly stress, was performed. Since then pressure sensitivity was studied further and the cavity parts were fabricated. The prototype cavity is not completed due to the renovation at Jefferson Lab which resulted in the temporary shutdown of the electron beam welding facility. This paper will present the analysis results and facts encountered during fabrication. The unique geometry of the cavity and its required mechanical strength present interesting manufacturing challenges.
On Saturday, June 22, 2013, a 50-foot-wide, circular electromagnet began its 3,200-mile land and sea voyage from Brookhaven National Laboratory in New York to a new home at Fermilab in Illinois. There, scientists will use it to study the properties of muons, subatomic particles that live only 2.2 millionths of a second, and the results could open the door to new realms of particle physics. In the first part of the move, Emmert International and a team of Fermilab and Brookhaven Lab scientists and engineers transported the electromagnet across the Brookhaven Lab site to a staging area by its main gate.
Solid, frozen-spin targets of molecular HD were rst developed for nuclear physics by a collaboration between Syracuse University and Brookhaven National Lab. They have been successfully used in measurements with photon beams, rst at the Laser-Electron-Gamma-Source [1] and most recently at Je erson Lab during the running of the E06-101 (g14) experiment [2]. Preparations are underway to utilize the targets in future electron experiments after the completion of the 12 GeV JLab upgrade [3]. HD is an attractive target since all of the material is polarizable, of low Z, and requires only modest holding elds. At the same time, the small contributions from the target cell can be subtracted from direct measurements. Reaching the frozen-spin state with both high polarization and a signi cant spin relaxation time requires careful control of H2 and D2 impurities. Commercially available HD contains 0.5 - 2% concentrations of H2 and D2. Low-temperature distillation is required to reduce these concentrations to the 104 level to enable useful target production. This distillation is done using a column lled with heli-pack C [4] to give good separation e ciency. Approximately 12 moles of commercial HD is condensed into the mechanically refrigerated system at the base temperature of 11K. The system is then isolated and the temperature stabilized at 18K producing liquid HD, which is boiled by a resistive heater. The circulation established by the boil-o condensing throughout the column then ltering back down produces a steady-state isotopic separation permitting the extraction of HD gas with very low H2 and D2 content. A residual gas analyzer initially monitors distillation. Once the H2 concentration falls below its useful operating range, samples are periodically collected for analysis using gas chromatography [5] and Raman scattering. Where the measurement techniques overlap, good agreement is obtained. The operation of the distillery and results of gas analysis will be discussed. References [1] Phy. Rev. Lett. 101 (2009) 172002. [2] www.jlab.org/exp_prog/proposals/06/PR-06-101.pdf [3] www.jlab.org/exp_prog/proposals/12/PR12-12-009.pdf, www.jlab.org/exp_prog/proposals/12/PR12-12-010.pdf, and www.jlab.org/exp_prog/proposals/11/PR12-11-111.pdf [4] Nucl. Inst. Meth. 664 (2012) 347, www.wilmad-labglass.com/Products/LG-6730-104/ [5] Rev. Sci. Instrum. 82, 024101 (2011).
Solid HDice targets are polarized by bringing the HD crystal to thermal equilibrium at low temperature and high magnetic field, typically 10-20 mK and 15 Tesla, at Jefferson Lab. In this regime, due to its smaller magnetic moment, the resulting polarization for D is always at least three times smaller than for H. The controlled amount of polarizing catalysts, o-H2 and p-D2, used in the process of reaching a frozen-spin state, further limit the maximum achievable D polarization. Nonetheless, H and D polarizations can be transferred from one to the other by connecting the H and D sub-states of the HD system with RF. In a large target, the RF power needed for such transitions is effectively limited by non-uniformities in the RF field. High efficiency transfers can require substantial RF power levels, and a tuned-RF circuit is needed to prevent large temperature excursions of the holding cryostat. In this paper, we compare the advantages and limitations of two different RF transfer methods to increase D polarization, Forbidden Adiabatic and Saturated Forbidden RF Transitions. The experience with the HD targets used during the recently completed E06-101 experiment in Hall-B of Jefferson Lab is discussed.
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.
The U.S. and international nuclear physics community uses Jefferson Lab's state-of-the-art Continuous Electron Beam Accelerator Facility or CEBAF to conduct world-class fundamental research. The Lab supports more than 1,250 visiting researchers from more than 200 institutions.
(July 12, 2018) - Our favorite goats from Goats R Us are spending time in area 2 just above Buildings 55, 60, & 64. We bring goats to the lab each year to aid in efforts around fire prevention and fire safety. They help us manage vegetation and reduce potential wildfire fuels. (Video: Kelly J. Owen / Berkeley Lab)
(July 12, 2018) Our favorite goats from Goats R Us are herded from Area 5 to Area 2 this morning to spend time just above Buildings 55, 60, & 64. We bring goats to the lab each year to aid in efforts around fire prevention and fire safety. They help us manage vegetation and reduce potential wildfire fuels. (Video: Kelly J. Owen / Berkeley Lab)
The goats from "Goats R Us" make a meal of the Lab's grassy hillsides to reduce fire risk. More info » http://ps.lbl.gov/fire.html (Video: Kelly J. Owen / Berkeley Lab)
This research is part of the Je?erson Lab MARATHON experiment (MeAsurement of the Fn 2 /Fp 2 , d/u RAtios and A = 3 EMC E?ect in Deep Inelastic Electron Scattering Off the Tritium and Helium MirrOr Nuclei). MARATHON is an experiment on electron deep inelastic scattering off the 3H, 3He mirror nuclei. It has extracted, from the measured deep inelastic scattering cross section ratio o? 3H and 3He, the ratio of the neutron to proton inelastic structure functions Fn 2 /Fp 2 . The extraction has taken advantage of the isospin symmetry of the A = 3 mirror nuclei within a novel technique, which avoids the theoretical uncertainties that are present in the SLAC experiments of the 1970s, which used hydrogen and deuterium targets. The experiment was performed using the upgraded 11 GeV beam of the Jefferson Lab electron accelerator, the Hall A Experimental Facility, and a newly designed cryogenic, high-pressure gas target system containing 3H and 3He cells. Electrons scattered o? the gas targets were detected in the two superconducting, high-resolution magnetic spectrometers of Hall A. The cross section data cover the four-momentum transfer squared range 2.0 < Q2 < 14.0 (GeV/c)2, and the Bjorken x scaling variable range 0.19 < x < 0.83. The experiment also measured, for calibration purposes, electron deep inelastic scattering off hydrogen and deuterium at selected kinematics.
Recirculating linear accelerators (linacs) provide a compact and efficient way of accelerating particle beams to medium and high energies by reusing the same linac for multiple passes. In recirculating linacs, maximum current can be limited by multipass beam breakup (BBU), which occurs when an electron beam interacts with the higher order modes (HOMs) of accelerating cavities during multipass recirculations. The average current of the CEBAF 12 GeV Upgrade accelerator at Jefferson Lab, a 5-pass recirculating linac, may be limited by multipass BBU. This disserta- tion work was performed as part of the 12 GeV Upgrade project at Jefferson Lab to investigate limits on average beam currents from the BBU instability. Exper- imental and simulation studies were carried out, and revealed that the multipass BBU will not be a limiting factor to the average beam current in the 12 GeV Upgrade of the CEBAF accelerator. This dissertation includes the theoretical calculation for longitudinal BBU, which revealed that the maximum current limit from longitudinal BBU is much higher than the transverse one. Therefore, longitudinal BBU will not become a problem, as long as transverse BBU does not cause instability. A cumulative BBU simulation study for a new injector in the 12 GeV accelerator also was conducted. The results showed that the transient behavior of cumulative BBU in the injector is not problematic.
The electron beam polarization in experimental Hall C at Jefferson Lab has been measured with a total uncertainty of dP/P<0.7\% at a beam energy of ≈ 1~GeV. This was accomplished using two, high-precision electron beam polarimeters. The first device makes use of M\o ller scattering from atomic electrons polarized in a pure iron foil driven to magnetic saturation. The second uses polarized electron-photon (Compton) scattering from laser light stored in a low gain Fabry-Perot cavity. Data from both devices, as well as a direct comparison of the two will be shown. The polarization data that will be described were taken as part of the Qweak experiment in Hall C, which aimed to measure the polarization to better than 1\%. Future experiments at Jefferson Lab will require knowledge of the polarization to 0.4\% or better. In this talk, I will describe the lessons learned during the Qweak running and discuss prospects for improving the beam polarimetry precision to the 0.4\% level.
Protons and neutrons, are the building blocks of atomic nuclei. They constitute over 99 percent of the mass of the matter in the visible universe. A fundamental challenge of modern nuclear physics is to understand the structure of these constituents. The 12 GeV Upgrade of the Continuous Electron Beam Accelerator Facility (CEBAF) at Jefferson Lab and the construction of state-of-the-art detector systems make it a unique facility in the world to address this challenge. Electron scattering is a superb experimental tool to study the internal structure of nucleons at differing distance scales, as the resolving power of the probe can be varied. The CEBAF Upgrade was completed in September 2017 and the new generation of experiments has started. These experiments will enable a collaboration of scientists from around the world to perform precise experiments of exclusive processes covering a large range in kinematics to effectively engage in nuclear imaging, revealing hidden aspects of its internal structure, and providing insight into quark confinement forces in the nucleon, one of the greatest mysteries of modern physics. The Generalized Parton Distributions (GPDs) provide the theoretical framework to interpret the experimental data in terms of 3-dimensional imaging. In addition, recent development demonstrated that the GPD formalism enables access to the nucleon's Gravitational Form Factors that encode its mechanical properties. We will focus on the study of the Deeply Virtual Compton Scattering (DVCS), the most effective way to access GPDs. We will review the landscape of both theory and experiment, and discuss the latest results from Jefferson Lab at 6 GeV in comparison with results from other facilities, and present a first look at the new experiments with the 12 GeV Upgrade.
The electron beam polarization in experimental Hall C at Jefferson Lab is measured using two devices. The Hall-C/Basel M\o ller polarimeter measures the beam polarization via electron-electron scattering and utilizes a novel target system in which a pure iron foil is driven to magnetic saturation (out of plane) using a superconducting solenoid. A Compton polarimeter measures the polarization via electron-photon scattering, where the photons are provided by a high-power, CW laser coupled to a low gain Fabry-Perot cavity. In this case, both the Compton-scattered electrons and backscattered photons provide measurements of the beam polarization. Results from both polarimeters, acquired during the Q-Weak experiment in Hall C, will be presented. In particular, the results of a test in which the M\o ller and Compton polarimeters made interleaving measurements at identical beam currents will be shown. In addition, plans for operation of both devices after completion of the Jefferson Lab 12 GeV Upgrade will also be discussed.
Over thirty years after the first experiments probed the spin structure of the nucleon, the pace of experimental and theoretical exploration of this subject keeps increasing. During its fifteen-year run with beam energies up to 6 GeV, Jefferson Lab has made many important contributions to this field - from measurements of the inclusive spin structure functions of the proton and the neutron over a wide kinematic range to seminal experiments accessing the three-dimensional nucleon spin structure through Generalized Parton Distributions and Transverse Momentum Dependent structure functions. An even brighter future lies ahead - after the 12 GeV upgrade, Jefferson Lab will completely map the spin-dependent parton distribution functions for all quark flavors in the valence region. In this talk, I will present an overview of this program, with special emphasis on recent and forthcoming results from the 6 GeV run and a glimpse of the future program with 12 GeV.
The force which holds the nucleus together has been under intense study for many decades. The nuclear shell model, which plays a central role in these investigations, has been very successful in reproducing low energy measurements, but is insufficient to predict medium energy results. The discrepancy is believed to originate from short range correlations, i.e. overlapping nucleons in the nucleus which briefly create densities close to those in neutron stars. Using an electron beam, these features of the nucleus can be isolated and studied at kinematics where xbj>1. In order to present the new results from Jefferson Lab, we will first highlight what has happened in the field over the last decade. We will also discuss the goals of the future related measurements scheduled to run at Jefferson Lab after the 12 GeV upgrade.