Physics Opportunities with the 12 GeV Upgrade at Jefferson Lab

This white paper summarizes the scientific opportunities for utilization of the upgraded 12 GeV Continuous Electron Beam Accelerator Facility (CEBAF) and associated experimental equipment at Jefferson Lab. It is based on the 52 proposals recommended for approval by the Jefferson Lab Program Advisory Committee.The upgraded facility will enable a new experimental program with substantial discovery potential to address important topics in nuclear, hadronic, and electroweak physics.Comment: 64 page

Laser-produced MeV electrons and hard X-ray spectroscopic diagnostics

A new spectroscopic technique for the measurement of the sizes of hard X-ray sources produced by the irradiation of solid-density targets by intense laser radiation is discussed. The technique is based on the source broadening of K shell spectral lines from targets irradiated by intense picosecond laser pulses. The spectra are recorded by a modified Cauchois type spectrometer, where the detector is placed far behind the Rowland circle where source broadening dominates instrumental resolution. The laser irradiation with focused intensity greater than 1018 W/cm2 produces relativistic electrons that propagate from the focal spot in to the surrounding target material with mm range. The energetic electrons produce 1 s electron ionization and K shell radiation with picosecond duration that can be utilized for transient radiography of dense objects including evolving dense plasmas. However, the hard X-ray source has mm lateral size when extended targets are utilized while a much smaller source size (of order 10 μm) is necessary for high-resolution point projection radiography. The lateral source size can be greatly reduced by using targets with limited aspect to the radiography object such as thin foils and wires, but the brightness of these sources is greatly reduced compared to thick planar targets. Studies indicate that the electron range and source size can also be reduced by utilizing an electrically resistive target material such as Teflon

Normal-incidence multilayer mirror X-ray microscope. Final report

An x-ray multilayer mirror microscope was designed constructed, and implemented to record images at a wavelength of 33.8 {Angstrom} of laser-irradiated targets. The morphology of the 33.8 {Angstrom} emission from a variety of targets was studied at the Livermore Nova laser 2-beam facility. Imaged were radiatively heated, low-density plastic and silica foams targets, x-ray laser targets, and gas-filled hohlraums. The absolute x-ray flux was determined. A two-mirror microscope and a CCD x-ray detector have been designed and constructed that will provided images with improved spatial resolution and dynamic range. The two-mirror microscope is designed to fit SIM4 on the Livermore 10-beam target chamber or any other comparably sized instrument module

High-resolution imaging of early-time imprinting using normal-incidence multilayer mirrors. Final report

A normal-incidence multilayer mirror telescope was designed, fabricated, and tested. The telescope consisted of a primary mirror and a secondary mirror in a Cassegrain optical configuration. The mirrors had multilayer coatings that efficiently reflected the soft x-ray radiation in a narrow bandpass centered at a wavelength of 48 {angstrom}. The telescope was taken to the Laboratory for Laser Energetics (LLE) on October 28, 1996. The telescope was mounted in a TIM instrument module on the OMEGA target chamber. The focusing and alignment of the mirrors were checked and optimized. Images were recorded on x-ray film on October 30. Images were recorded on a gated framing camera on October 31 and November 1. On each laser shot, hard x-ray images were recorded by a pinhole camera and a gated framing camera. The soft and hard x-ray images were returned to NRL for analysis. The images were digitized and compared. The major result of the study was that the soft x-ray emission from plasmas generated by 6 to 8 overlapping OMEGA beams is quite uniform, even for the case when beam smoothing techniques were not implemented. This implies that the soft x-ray emission can be used for backlighter applications and for the study of absorption by CH foils in the 48 {angstrom} wavelength region, at slightly longer wavelengths than the carbon K absorption edge where carbon is relatively transmissive. These backlighter techniques are now being implemented at LLE

Normal-incidence multilayer mirror X-ray microscope. Final report

An x-ray multilayer mirror microscope was designed constructed, and implemented to record images at a wavelength of 33.8 {Angstrom} of laser-irradiated targets. The morphology of the 33.8 {Angstrom} emission from a variety of targets was studied at the Livermore Nova laser 2-beam facility. Imaged were radiatively heated, low-density plastic and silica foams targets, x-ray laser targets, and gas-filled hohlraums. The absolute x-ray flux was determined. A two-mirror microscope and a CCD x-ray detector have been designed and constructed that will provided images with improved spatial resolution and dynamic range. The two-mirror microscope is designed to fit SIM4 on the Livermore 10-beam target chamber or any other comparably sized instrument module

SHORT WAVELENGTH LASER CALCULATIONS IN THE Be I, B I AND C I ISOELECTRONIC SEQUENCES

Short Wavelength Laser Calculations in the Beryllium, Boron and Carbon Isoelectronic Sequences - Level populations of the 2s3p, 2s23p 2 and 2s22p3p configurations in ions of the Be I, B I and C I isoelectronic 2 sequences can be inverted with respect to populations of the 2s3s, 2s23s, and 2s22p3s configurations by electron collisional pumping. In the case of B I and C I ions, the process is analogous to the process for Ne-like ions which has lately received considerable attention. In the case of Be I ions, the inversion is a consequence of the slow radiative decay of the 2s3p 3P2 and 2s3p 3P0 levels. Level populations are calculated for Be-like, B-like and C-like ions with atomic number Z between 18 and 36 and for electron densities from 1015 to 1022 cm-3. For each of the Be I and B I isoelectronic sequences, 20 levels are involved with principal quantum number n equal either to 2 or 3. For the CI isoelectronic sequence 46 levels are involved. Using the level populations, gain coefficients are calculated for transitions of the type 2s3s - 2s3p, 2s23s - 2s23p and 2s22p3s - 2s22p3p. The calculated gain coefficients are compared to previous calculations. At high electron densities where collisional mixing of the excited levels becomes important, the intensities of the X-ray transitions from the 2sk2pm3p levels decrease relative to the X-ray transitions from the 2sk2pm3s and 2sk2pm3d levels where k=1, m=0 or k=2, m=0,1. The density dependence of these X-ray line ratios is calculated elsewhere /16, 17/. These line ratios represent a promising diagnostic for electron density. Finally, the opacities of the 2s2p - 2s3s, 2s22p - 2s23s and 2s22p2 - 2s22p3s transitions are discussed for plasma parameters for which a reasonable gain can be achieved

High-resolution K-shell spectra from laser excited molybdenum plasmas

X-ray spectra from Molybdenum plasmas were recorded by a Cauchois-type cylindrically bent Transmission Crystal Spectrometer (TCS). The absolutely calibrated spectrometer provides an unprecedented resolution of inner shell transitions (K x-ray radiation). This tool allows us to resolve individual lines from different charge states existing inside the laser-produced plasma. The inner shell transitions from highly charged Molybdenum shown in this report have never been resolved before in such detail in a laser-produced plasma

High-resolution K-shell spectra from laser excited molybdenum plasmas

X-ray spectra from Molybdenum plasmas were recorded by a Cauchois-type cylindrically bent Transmission Crystal Spectrometer (TCS). The absolutely calibrated spectrometer provides an unprecedented resolution of inner shell transitions (K x-ray radiation). This tool allows us to resolve individual lines from different charge states existing inside the laser-produced plasma. The inner shell transitions from highly charged Molybdenum shown in this report have never been resolved before in such detail in a laser-produced plasma

Використання вольфраму як бар’єрного шару у багатошарових рентгенівських дзеркалах Sc/Si

Методами рентгеновской дифракции (ƛ = 0,154 нм), просвечивающей электронной микроскопии поперечных срезов и рефлектометрии в мягкой рентгеновской области (ƛ = 25-50 нм) исследованы барьерные свойства слоев вольфрама толщиной 0,1-2,1 нм в многослойных рентгеновских зеркалах (МРЗ) Sc/W/Si, изготовленных методом прямоточного магнетронного распыления. Показано, что слои вольфрама толщиной 0,6-0,8 нм отделяют слои Sc и Si и препятствуют образованию перемешанной зоны ScSi. Вольфрам, взаимодействуя со слоями Si, формирует аморфную прослойку, толщина которой меньше толщины перемешанных зон ScSi, образующихся в МРЗ Sc/Si без барьеров. При tw < 0,5 нм вольфрам на скандии не образует сплошную пленку. Введение барьерных слоев толщиной t = 0,3-0,8 нм приводит к росту отражательной способности в мягкой рентгеновской области (ƛ ~ 38 нм), по меньшей мере, в 2,5 раза по сравнению с МРЗ Sc/Si. Максимальный коэффициент отражения (R ~ 25%, ƛ ~ 38 нм) наблюдается при введении барьерных слоев толщиной tw ~ 0,54 нм. Обсуждаются пути дальнейшего усовершенствования технологии нанесения барьерных слоев и повышения отражательной способности МРЗ Sc/Si.By methods of hard X-ray diffraction (ƛ = 0.154 nm), cross-sectional transmission electron microscopy and soft X-ray (ƛ = 25-50 nm) reflectometry the barrier characteristics of tungsten layers of tw = 0.1-2.1 nm thick in Sc/W/Si multilayer X-ray mirrors (MXMs) fabricated with DC magnetron sputtering are studied. Tungsten layers of 0.6-0.8 nm thick are shown to separate Sc and Si layers and prevent formation of ScSi intermixed zones. Tungsten interacts with silicon forming thinner silicide layers in comparison with original ScSi interlayers in Sc/Si MXMs without barriers. Barrier layers are not continuous at tw < 0,5 nm when deposited on Sc layers. Introduction of W-layers 0.3-0.8 nm thick increases reflectivity (ƛ ~ 38 nm) of Sc/W/Si MXMs at least by factor of 2.5 maximizing at R ~ 25 % at normal incidence (α = 5°). Further improvements in technology and reflectivity are discussed.Методами рентгенівської дифракції (ƛ = 0,154 нм), просвічувальної електронної мікроскопії поперечних зрізів і рефлектометрії в м'якій рентгенівської області (ƛ = 25-50 нм) досліджені бар'єрні властивості шарів вольфраму товщиною 0,1-2,1 нм в багатошарових рентгенівських дзеркалах (БРД) Sc/W/Si, виготовлених методом прямоточного магнетронного розпилення. Показано, що шари вольфраму товщиною 0,6-0,8 нм відокремлюють шари Sc і Si і перешкоджають утворенню перемішаної зони ScSi. Вольфрам, взаємодіючи з шарами Si, формує аморфний прошарок, товщина якого менше товщини перемішаних зон ScSi, що утворюються в МРЗ Sc/Si без бар’єрів. При tw < 0,5 нм вольфрам на скандії не утворює суцільну плівку. Введення бар'єрних шарів товщиною t = 0,3-0,8 нм призводить до зростання відбивної здатності в м'якій рентгенівської області (ƛ ~ 38 нм), щонайменше, в 2,5 рази в порівнянні з МРЗ Sc/Si. Максимальний коефіцієнт відбиття (R ~ 25%, ƛ ~ 38 нм) спостерігається при введенні бар'єрних шарів товщиною tw ~ 0,54 нм. Обговорюються шляхи подальшого удосконалення технології нанесення бар'єрних шарів і підвищення відбивної здатності БРД Sc/Si