49 Matching Results

Search Results

Advanced search parameters have been applied.

Review of x-ray spectroscopy from laser-produced plasmas

Description: Recent progress in x-ray spectroscopy from laser plasmas is reviewed. Advances in the use of K-shell spectra as a diagnostic tool is discussed. Much activity in understanding complex spectra especially from Ne I and Ni I isoelectronic series have been made. Much of the progress has been due to observation of amplification from ..delta..n = O transitions from these configurations. The spectroscopy will be discussed and examples of spectra of the amplified lines will be shown. Finally, recent work on using x-ray spectroscopy to diagnose high density implosions will be discussed. 33 refs.
Date: September 1, 1987
Creator: Kauffman, R.L.
Partner: UNT Libraries Government Documents Department

Progress Toward Ignition on the National Ignition Facility

Description: The principal approach to ignition on the National Ignition Facility (NIF) is indirect drive. A schematic of an ignition target is shown in Figure 1. The laser beams are focused through laser entrance holes at each end of a high-Z cylindrical case, or hohlraum. The lasers irradiate the hohlraum walls producing x-rays that ablate and compress the fuel capsule in the center of the hohlraum. The hohlraum is made of Au, U, or other high-Z material. For ignition targets, the hohlraum is {approx}0.5 cm diameter by {approx}1 cm in length. The hohlraum absorbs the incident laser energy producing x-rays for symmetrically imploding the capsule. The fuel capsule is a {approx}2-mm-diameter spherical shell of CH, Be, or C filled with DT fuel. The DT fuel is in the form of a cryogenic layer on the inside of the capsule. X-rays ablate the outside of the capsule, producing a spherical implosion. The imploding shell stagnates in the center, igniting the DT fuel. NIC has overseen installation of all of the hardware for performing ignition experiments, including commissioning of approximately 50 diagnostic systems in NIF. The diagnostics measure scattered optical light, x-rays from the hohlraum over the energy range from 100 eV to 500 keV, and x-rays, neutrons, and charged particles from the implosion. An example of a diagnostic is the Magnetic Recoil Spectrometer (MRS) built by a collaboration of scientists from MIT, UR-LLE, and LLNL shown in Figure 2. MRS measures the neutron spectrum from the implosion, providing information on the neutron yield and areal density that are metrics of the quality of the implosion. Experiments on NIF extend ICF research to unexplored regimes in target physics. NIF can produce more than 50 times the laser energy and more than 20 times the power of any previous ICF facility. Ignition scale hohlraum ...
Date: October 17, 2011
Creator: Kauffman, R L
Partner: UNT Libraries Government Documents Department


Description: This memo discusses the analysis of the high-energy x-ray distribution from a laser-induced plasma to determine the superthermal electron distribution. The methods of deconvolution outlined in I are similar to formulae derived in the literature not including and including effects due to electron stopping. In II the methods are applied to an x-ray spectrum from an Au disc irradiated by ARGUS.
Date: December 20, 2007
Creator: Kauffman, R
Partner: UNT Libraries Government Documents Department

Accelerated screening methods for determining chemical and thermal stability of refrigerant-lubricant mixtures, Part II: Experimental comparison and verification of methods. Volume 2, In situ conductivity data

Description: Data are presented for the accelerated screening methods for determining chemical and thermal stability of refrigerant-lubricant mixtures.
Date: September 1, 1995
Creator: Kauffman, R.
Partner: UNT Libraries Government Documents Department

Accelerated screening methods for determining chemical and thermal stability of refreigerant-lubricant mixtures. Part II: Experimental comparison and verification of methods. Final report, volume I

Description: The research reported herein was performed to develop an accelerated screening method for determining the chemical and thermal stabilities of refrigerant/lubricant mixtures. The developed screening method was designed to be safe and to produce accelerated stability rankings that are in agreement with the rankings determined by the current test, Sealed Glass Tube Method to Test the Chemical Stability of Material for Use Within Refrigerant Systems, ANSI/ASHRAE Method 97-1989. The accelerated screening test developed was designed to be independent of refrigerant and lubricant compositions and to be used with a wide variety of construction materials. The studied refrigerants included CFC-11, CFC-12, HCFC-22, HFC-134a, and HFC-32/HFC-134a (zeotrope 30:70 by weight). The studied lubricants were selected from the chemical classes of mineral oil, alkylbenzene oil, polyglycols, and polyolesters. The work reported herein was performed in three phases. In the first phase, previously identified thermal analytical techniques were evaluated for development into an accelerated screening method for refrigerant/lubricant mixtures. The identified thermal analytical techniques used in situ measurements of color, temperature, or conductivity to monitor the degradation of the heated refrigerant/lubricant mixtures. The identified thermal analytical techniques also used catalysts such as ferric fluoride to accelerate the degradation of the heated refrigerant/lubricant mixtures. The thermal analytical technique employing in situ conductivity measurements was determined to be the most suitable for development into an accelerated screening method.
Date: September 1, 1995
Creator: Kauffman, R.
Partner: UNT Libraries Government Documents Department

Review of hohlraum coupling

Description: Extensive experiments have been done to characterize laser-heated hohlraum targets for indirect drive inertial fusion. Scattered light and fast electrons from laser-plasma instabilities have been found not to be significant for short wavelength light. Scaling of radiation temperature with laser power has been studied at several Laboratories and can be represented by a simple power balance scaling for experiments using short wavelength light. Measurements of x-ray production and energy loss in hohlraum walls have been made to study details of the power balance model.
Date: January 30, 1995
Creator: Kauffman, R.L.
Partner: UNT Libraries Government Documents Department

Absolutely calibrated soft-x-ray streak camera for laser-fusion applications

Description: The intensity output of a soft-x-ray streak camera was calibrated (SXRSC) in order to make absolute flux measurements of x rays emitted from laser-produced plasmas. The SXRSC developed at LLNL is used to time-resolve x-ray pulses to better than 20 ps. The SXRSC uses a Au photocathode on a thin carbon substrate which is sensitive to x rays from 100 eV to greater than 10 keV. Calibrations are done in the dynamic mode using a small laser-produced x-ray source. The SXRSC is calibrated by comparing its integrated signal to the output of calibrated x-ray diodes monitoring the source strength. The measured SXRSC response is linear over greater than two orders of magnitude. Using these calibrations, absolute intensities can be measured to an accuracy of +-30%.
Date: January 1, 1982
Creator: Kauffman, R.L.; Medecki, H. & Stradling, G.
Partner: UNT Libraries Government Documents Department

Experiments to study the feasibility of making an x-ray laser at the Novette laser facility

Description: We will discuss a set of experiments which are designed to study approaches to and search for the existence of amplified spontaneous emission at photon energies of 42.3, 53.6, 119.0, and 153.0 eV. The schemes utilize pumping from the Novette laser operated with cylindrical optics at 5 TW/beam and 100 psec.
Date: May 17, 1983
Creator: Matthews, D.L.; Hagelstein, P. & Kauffman, R.
Partner: UNT Libraries Government Documents Department

Time-resolved spectral measurements above 80 A

Description: We have made time-resolved spectral measurements above 80 A from laser-produced plasmas. These are made using a transmission grating spectrograph whose primary components are a cylindrically-curved x-ray mirror for light collection, a transmission grating for spectral dispersions, and an x-ray streak camera for temporal resolution. A description of the instrument and an example of the data are given.
Date: July 1, 1983
Creator: Kauffman, R.L.; Ceglio, N. & Medecki, H.
Partner: UNT Libraries Government Documents Department

X-ray streak crystal spectography

Description: We have built an x-ray streaked crystal spectrograph for making time-resolved x-ray spectral measurements. This instrument can access Bragg angles from 11/sup 0/ to 38/sup 0/ and x-ray spectra from 200 eV to greater than 10 keV. We have demonstrated resolving powers, E/..delta..E > 200 at 1 keV and time resolution less than 20 psec. A description of the instrument and an example of the data is given.
Date: July 1, 1983
Creator: Kauffman, R.L.; Brown, T. & Medecki, H.
Partner: UNT Libraries Government Documents Department

The ICF Status and Plans in the United States

Description: The United States continues to maintain its leadership in ICF as it moves toward the goal of ignition. The flagship of the program is the National Ignition Facility (NIF) presently under construction at LLNL. Experiments had begun on the first four beams of the National Ignition Facility just at the time of the last IFSA Conference. Several new successful campaigns have been conducted since then in planar hydrodynamics and hohlraums as well as activating the VISAR diagnostic for equation of state experiments. Highlights of these results will be reviewed. Presently, the four beam experimental capability has been suspended while the first eight beams are being installed as the first step in building out the project. Meanwhile, much progress has been made in developing ignition designs for using NIF. An array of designs having several ablator materials have been shown computationally to ignite with energies ranging from the design energy to as low as 1 MJ of laser energy. Alternative direct drive designs in the NIF indirect drive configuration have been developed by LLE. This wide array of design choices has increased the chance of achieving ignition sooner on the facility. Plans are now being developed to begin an ignition experimental campaign on NIF in 2010, a little over a year after completion of the facility. Other US facilities are also implementing improved capabilities. Petawatt lasers are now under construction at the University of Rochester and Sandia National Laboratory. The Z pulsed power machine at Sandia National Laboratory is being refurbished to improve its performance. The ongoing research program at the OMEGA laser at the University of Rochester and the Z machine at Sandia National Laboratory as well as at the Nike, Trident and Janus lasers remain strong, performing experiments supporting the NIF ignition plan and direct drive ignition. There also ...
Date: October 12, 2005
Creator: Moses, E; Miller, G & Kauffman, R
Partner: UNT Libraries Government Documents Department

X-ray-transport effects in laser-irradiated disks

Description: X-ray emission spectra are important diagnostics for studying laser-coupling and energy transport. We have begun exploring the sensitivity of such measurements to the plasma density and temperature profiles. The one-dimensional radiation transport equation is solved for various temperature and density profiles. Spectra are calculated in both the LTE and CRE approximations, bracketing the relevant ionization regimes. Their applicability to real plasmas is discussed. The calculated spectra are compared with measurements from different Z targets. This comparison explores the possible temperature and density parameters. Such comparisons can be used to interpret present experimental results as well as guide the design of future experiments.
Date: October 6, 1981
Creator: Kauffman, R.L.; Matthews, D.L. & Lee, R.W.
Partner: UNT Libraries Government Documents Department

Production and decay of heavy top quarks

Description: Experimental evidence indicates that the top quark exists and has a mass between 50 and 200 GeV/c{sup 2}. The decays of a top quark with a mass in this range are studied with emphasis placed on the mass region near the threshold for production of real W bosons. Topics discussed are: (1) possible enhancement of strange quark production when M{sub W} + m{sub s} < m{sub t} < M{sub W} + m{sub b}; (2) exclusive decays of T mesons to B and B{asterisk} mesons using the non-relativistic quark model; (3) polarization of intermediate W's in top quark decay as a source of information on the top quark mass. The production of heavy top quarks in an e{sup +}e{sup {minus}} collider with a center-of-mass energy of 2 TeV is studied. The effective-boson approximation for photons, Z{sup 0}'s and W's is reviewed and an analogous approximation for interfaces between photons and Z{sup 0}'s is developed. The cross sections for top quark pair production from photon-photon, photon-Z{sup 0}, Z{sup 0}Z{sup 0}, and W{sup +}W{sup {minus}} fusion are calculated using the effective-boson approximation. Production of top quarks along with anti-bottom quarks via {gamma}W{sup +} and Z{sup 0}W{sup +} fusion is studied. An exact calculation of {gamma}e{sup +} {yields} {bar {nu}}t{bar b} is made and compared with the effective-W approximation. 31 refs., 46 figs.
Date: August 1, 1989
Creator: Kauffman, R.P.
Partner: UNT Libraries Government Documents Department

Picosecond x-ray measurements from 100 eV to 30 keV

Description: Picosecond x-ray measurements relevant to the Livermore Laser Fusion Program are reviewed. Resolved to 15 picoseconds, streak camera detection capabilities extend from 100 eV to higher than 30 keV, with synchronous capabilities in the visible, near infrared, and ultraviolet. Capabilities include automated data retrieval using charge coupled devices (CCD's), absolute x-ray intensity levels, novel cathodes, x-ray mirror/reflector combinations, and a variety of x-ray imaging devices.
Date: October 15, 1980
Creator: Attwood, D.T.; Kauffman, R.L. & Stradling, G.L.
Partner: UNT Libraries Government Documents Department

Pulsed calibration of the soft x-ray streak camera

Description: In order to better understand laser plasma interactions an effort is being made to obtain quantitative temporally and spectrally resolved measurements in the low energy x-ray region using a soft x-ray streak camera. X-ray mirrors and absorption filters are employed to perform broad band spectroscopy measurements. The components of these systems have now been calibrated and the results of these measurements will be reported. The calibration of the x-ray streak camera, needed to make absolute flux measurements, cannot be measured using the usual x-ray sources because backgrounds interfere with the operation in the D.C. mode. Repetition rates and duty cycles are too low to complete calibration on a D.C. source in a reasonable time using the camera in a pulsed mode. As an alternative the calibrations are being done using a Nd(YAG) laser producing pulses of approx. 1 joule having pulse widths of approx. 150 ps. The x-ray flux is being monitored by three x-ray diodes having Al photocathodes. Absorption filters having the same thicknesses as those used with the streak camera provide x-ray energy responses of the diodes which approximate the channel responses of the streak camera. By comparing the charge from the diode with the integral response of the streak camera, the camera response can be measured. Preliminary results will be discussed.
Date: November 1, 1979
Creator: Kauffman, R.L.; Medecki, H. & Pierce, E.L.
Partner: UNT Libraries Government Documents Department

Improved gas-filled hohlraum performance on Nova with beam smoothing

Description: Gas-filled hohlraums are presently the base line ignition target design for the National Ignition Facility. Initial Nova experiments on gas-filled hohlraums showed that radiation temperature was reduced due to SBS and SRS scattering losses and that implosion symmetry had shifted compared with vacuum hohlraums and calculations. Subsequent single beam experiments imaging thermal x-ray emission showed the shift is due to laser-plasma heating dynamics and filarnentation in a flowing plasma. Experiments using a single beam have shown that scattering losses and effects of filamentation are reduced when the beam is smoothed with an random phase plate (RPP) or kinoform phase plate (KPP). Scattering is further reduced to less than 5% of the incident laser energy when SSD is added.
Date: December 2, 1997
Creator: Kauffman, R.L.; Powers, L.V. & Dixit, S.N.
Partner: UNT Libraries Government Documents Department

Efficient production of 2--10 keV x-rays by laser heated ``underdense radiators``

Description: The next generation of high power lasers offers the prospect of creating multi-kilovolt x-rays with {gt}10% efficiency. Such efficiencies are achieved with ``underdense radiators``, a non- traditional source of laser generated x-rays. Applications of these sources with the proposed National Ignition Facility (NIF) include volume preheating of experiments; bright, multi-keV backlighting; pumps for fluorescent imaging of capsule dopants and Doppler velocimetry; uniform irradiation of large test objects. This paper presents two-dimensional numerical simulations for these high power lasers with unprecedented efficiency.
Date: May 22, 1996
Creator: Suter, L.J.; Kauffman, R.L.; Maxon, M.S. & Davis, J.F.
Partner: UNT Libraries Government Documents Department

Radiation drive in laser heated hohlraums

Description: Nearly 10 years of Nova experiments and analysis have lead to a relatively detailed quantitative and qualitative understanding of radiation drive in laser heated hohlraums. Our most successful quantitative modelling tool is 2D Lasnex numerical simulations. Analysis of the simulations provides us with insight into the details of the hohlraum drive. In particular we find hohlraum radiation conversion efficiency becomes quite high with longer pulses as the accumulated, high Z blow-off plasma begins to radiate. Extensive Nova experiments corroborate our quantitative and qualitative understanding.
Date: November 3, 1995
Creator: Suter, L.J.; Kauffman, R.L. & Darrow, C.B.
Partner: UNT Libraries Government Documents Department

Dynamics of gas-filled hohlraums

Description: In order to prevent high-Z plasma from filling in the hohlraum in indirect drive experiments, a low-Z material, or tamper is introduced into the hohlraum. This material, when fully ionized is typically less than one-tenth of the critical density for the laser light used to illuminate the hohlraum. This tamper absorbs little of the laser light, thus allowing most of the laser energy to be absorbed in the high-Z material. However, the pressure associated with this tamper is sufficient to keep the hohlraum wall material from moving a significant distance into the interior of the hohlraum. In this paper the authors discuss measurements of the motion of the interface between the tamper and the high-Z hohlraum material. They also present measurements of the effect the tamper has on the hohlraum temperature.
Date: April 24, 1995
Creator: Orzechowski, T.J.; Kauffman, R.L. & Kirkwood, R.K.
Partner: UNT Libraries Government Documents Department

Line intensities for diagnosing laser-produced plasmas

Description: We have measured relative line intensities of the K x-ray spectra of Si, Cl, and Ca from laser-produced plasmas to assess their usefulness as a plasma diagnostic. The different elements are added at low concentrations to CH disks which are irradiated at 5 x 10/sup 14/ W/cm/sup 2/ with a 0.53 ..mu..m laser pulse of 20 Joules at 1 nsec. The concentration of each element is kept low in order not to change the Z of the plasma, and therefore the plasma dynamics. The various spectra are measured with a time-resolved spectrograph to obtain line intensities as a function of time over the length of the laser pulse. These relative intensities of various He-like and H-like lines are compared with calculations from a steady-state level population code. The results give good consistency among the various line ratios. Agreement is not as good for analysis of the Li-like satellite lines. Modelling of the Li-like lines need further investigation. 10 references, 9 figures.
Date: October 31, 1983
Creator: Kauffman, R.L.; Matthews, D.L.; Lee, R.W.; Whitten, B.L. & Kilkenny, J.D.
Partner: UNT Libraries Government Documents Department

Time-resolved x-ray line diagnostics of laser-produced plasmas

Description: We have examined the underdense plasma conditions of laser irradiated disks using K x-rays from highly ionized ions. A 900 ps laser pulse of 0.532 ..mu..m light is used to irradiate various Z disks which have been doped with low concentrations of tracer materials. The tracers whose Z's range from 13 to 22 are chosen so that their K x-ray spectrum is sensitive to typical underdense plasma temperatures and densities. Spectra are measured using a time-resolved crystal spectrograph recording the time history of the x-ray spectrum. A spatially-resolved, time-integrated crystal spectrograph also monitors the x-ray lines. Large differences in Al spectra are observed when the host plasma is changed from SiO/sub 2/ to PbO or In. Spectra will be presented along with preliminary analysis of the data.
Date: January 1, 1982
Creator: Kauffman, R.L.; Matthews, D.L.; Kilkenny, J.D. & Lee, R.W.
Partner: UNT Libraries Government Documents Department

Studying electron distributions using the time-resolved free-bound spectra from coronal plasmas

Description: Absorption of laser light in a plasma by inverse bremsstrahlung, I.B., can lead to a non-Maxwellian velocity distribution provided the electron-elecron collision frequency is too low to equilibrate the velocity distribution in the coronal plasma region of a laser heated aluminum disk by measuring the radiation recombination continuum. The experiments are performed using lambda/sub L/ = 0.532 ..mu..m laser light at intensities of approx. 10/sup 16/ W/cm/sup 2/. Such parameters are predicted to produce conditions suitable for a non-thermal electron distribution. The shape of the K-shell recombination radiation has been measured using a time-resolved x-ray spectrograph. The electron distribution can be determined from deconvolution of the recombination continuum shape.
Date: November 1, 1982
Creator: Matthews, D.L.; Kauffman, R.L.; Kilkenny, J.D. & Lee, R.W.
Partner: UNT Libraries Government Documents Department