12 Matching Results

Search Results

Advanced search parameters have been applied.

Measuring the absolute DT neutron yield using the Magnetic Recoil Spectrometer at OMEGA and the NIF

Description: A Magnetic Recoil Spectrometer (MRS) has been installed and extensively used on OMEGA and the National Ignition Facility (NIF) for measurements of the absolute neutron spectrum from inertial confinement fusion (ICF) implosions. From the neutron spectrum measured with the MRS, many critical implosion parameters are determined including the primary DT neutron yield, the ion temperature, and the down-scattered neutron yield. As the MRS detection efficiency is determined from first principles, the absolute DT neutron yield is obtained without cross-calibration to other techniques. The MRS primary DT neutron measurements at OMEGA and the NIF are shown to be in excellent agreement with previously established yield diagnostics on OMEGA, and with the newly commissioned nuclear activation diagnostics on the NIF.
Date: May 3, 2012
Creator: Mackinnon, A; Casey, D; Frenje, J A; Johnson, M G; Seguin, F H; Li, C K et al.
Partner: UNT Libraries Government Documents Department

A novel particle Time Of Flight (pTOF) diagnostic for measurements of shock- and compression-bang times in D3He and DT implosions at the NIF

Description: The particle-time-of-flight (pTOF) diagnostic, fielded alongside a Wedge Range-Filter (WRF) proton spectrometer, will provide an absolute timing for the shock-burn weighted {rho}R measurements that will validate the modeling of implosion dynamics at the National Ignition Facility (NIF). In the first phase of the project, pTOF has recorded accurate bang times in cryogenic DT, DT-Exploding Pusher and D{sup 3}He implosions using DD or DT neutrons with an accuracy better than {+-}70 ps. In the second phase of the project, a deflecting magnet will be incorporated into the pTOF design for simultaneous measurements of shock- and compression-bang times in D{sup 3}He-filled surrogate implosions using D{sup 3}He protons and DD-neutrons, respectively.
Date: May 2, 2012
Creator: Mackinnon, A; Rinderknecht, H G; Johnson, M G; Zylstra, A B; Sinenian, N; Rosenbergh, M J et al.
Partner: UNT Libraries Government Documents Department

Compact proton spectrometers for measurements of shock

Description: The compact Wedge Range Filter (WRF) proton spectrometer was developed for OMEGA and transferred to the National Ignition Facility (NIF) as a National Ignition Campaign (NIC) diagnostic. The WRF measures the spectrum of protons from D-{sup 3}He reactions in tuning-campaign implosions containing D and {sup 3}He gas; in this work we report on the first proton spectroscopy measurement on the NIF using WRFs. The energy downshift of the 14.7-MeV proton is directly related to the total {rho}R through the plasma stopping power. Additionally, the shock proton yield is measured, which is a metric of the final merged shock strength.
Date: May 2, 2012
Creator: Mackinnon, A; Zylstra, A; Frenje, J A; Seguin, F H; Rosenberg, M J; Rinderknecht, H G et al.
Partner: UNT Libraries Government Documents Department

Nuclear Diagnostics of ICF

Description: In inertial confinement fusion (ICF), a high temperature and high density plasma is produced by the spherical implosion of a small capsule. A spherical target capsule is irradiated uniformly by a laser beam (direct irradiation) or x-rays from a high Z enclosure (hohlraum) that is irradiated by laser or ion beams (indirect irradiation). Then high-pressure ablation of the surface causes the fuel to be accelerated inward. Thermonuclear fusion reactions begin in the center region of the capsule as it is heated to sufficient temperature (10 keV) by the converging shocks (hot spot formation). During the stagnation of the imploded shell, the fuel in the shell region is compressed to high density ({approx} 10{sup 3} times solid density in fuel region). When these conditions are established, energy released by the initial nuclear reactions in center ''hot-spot'' region can heat up the cold ''fuel'' region and cause ignition. They are developing advanced nuclear diagnostics for imploding plasmas of the ignition campaign on the National Ignition Facility (NIF). The NIF is a 1.8MJ, 192-beam glass laser system that is under construction at Lawrence Livermore National Laboratory. One objective of the NIF is to demonstrate ignition and gain in an inertial confinement fusion plasma. Extreme physical conditions characterize the imploded plasmas on the NIF. First, the thickness of the plasma, expressed by areal density (plasma density times radius), is large, up to {approx} 1 g/cm{sup 2}. Highly penetrating probes such as energetic neutrons, hard x-rays, or {gamma} rays are required to see deep inside the plasma. Second, the implosion time is quite short. The implosion process takes {approx} 20 ns and the duration of the fusion reaction is on the order of 100 picoseconds. To observe the time history of the nuclear reactions, time resolution better than 10 ps is required. Third, the size ...
Date: October 18, 2001
Creator: Izumi, N; Ierche, R A; Moran, M J; Phillips, T W; Sangster, T C; Schmid, G J et al.
Partner: UNT Libraries Government Documents Department

Cryogneic-Target Performance and Implosion Physics Studies on OMEGA

Description: Recent progress in direct-drive cryogenic implosions on the OMEGA Laser Facility [T. R. Boehly et al., Opt. Commun. 133, 495 (1997)] is reviewed. Ignition-relevant areal densities of ~200 mg/cm^2 in cryogenic D2 implosions with peak laser-drive intensities of ~5 x 10^14 W/cm^2 were previously reported [T. C. Sangster et al., Phys. Rev. Lett. 100, 185006 (2008)]. The laser intensity is increased to ~10^15 W/cm^2 to demonstrate ignition-relevant implosion velocities of 3–4 x 10^7 cm/ s, providing an understanding of the relevant target physics. Planar-target acceleration experiments show the importance of the nonlocal electron-thermal-transport effects for modeling the laser drive. Nonlocal and hot-electron preheat is observed to stabilize the Rayleigh–Taylor growth at a peak drive intensity of ~10^15 W/cm^2. The shell preheat caused by hot electrons generated by two-plasmon-decay instability was reduced by using Si-doped ablators. The measured compressibility of planar plastic targets driven with high-compression shaped pulses agrees well with one-dimensional simulations at these intensities. Shock mistiming has contributed to compression degradation of recent cryogenic implosions driven with continuous pulses. Multiple-picket (shock-wave) target designs make it possible for a more robust tuning of the shock-wave arrival times. Cryogenic implosions driven with double-picket pulses demonstrate somewhat improved compression performance at a peak drive intensity of ~10^15 W/cm^2.
Date: March 6, 2009
Creator: Smalyuk, V.A.; Betti, R.; Boehly, T.R.; Craxton, R.S.; Delettrez, J.A.; Edgell, D.H. et al.
Partner: UNT Libraries Government Documents Department

Neutron spectrometry - An essential tool for diagnosing implosions at the National Ignition Facility

Description: DT neutron yield (Y{sub n}), ion temperature (T{sub i}) and down-scatter ratio (dsr) determined from measured neutron spectra are essential metrics for diagnosing the performance of Inertial Confinement Fusion (ICF) implosions at the National Ignition Facility (NIF). A suite of neutron-Time-Of-Flight (nTOF) spectrometers and a Magnetic Recoil Spectrometer (MRS) have been implemented in different locations around the NIF target chamber, providing good implosion coverage and the redundancy required for reliable measurements of Yn, Ti and dsr. From the measured dsr value, an areal density ({rho}R) is determined from the relationship {rho}R{sub tot} (g/cm{sup 2}) = (20.4 {+-} 0.6) x dsr{sub 10-12 MeV}. The proportionality constant is determined considering implosion geometry, neutron attenuation and energy range used for the dsr measurement. To ensure high accuracy in the measurements, a series of commissioning experiments using exploding pushers have been used for in situ calibration. The spectrometers are now performing to the required accuracy, as indicated by the good agreement between the different measurements over several commissioning shots. In addition, recent data obtained with the MRS and nTOFs indicate that the implosion performance of cryogenically layered DT implosions, characterized by the experimental Ignition Threshold Factor (ITFx) which is a function of dsr (or fuel {rho}R) and Y{sub n}, has improved almost two orders of magnitude since the first shot in September, 2010.
Date: May 2, 2012
Creator: Mackinnon, A J; Johnson, M G; Frenje, J A; Casey, D T; Li, C K; Seguin, F H et al.
Partner: UNT Libraries Government Documents Department

Direct-Drive Inertial Fusion Research at the University of Rochester's Laboratory for Laser Energetics: A Review

Description: This paper reviews the status of direct-drive inertial confinement fusion (ICF) research at the University of Rochester's Laboratory for Laser Energetics (LLE). LLE's goal is to demonstrate direct-drive ignition on the National Ignition Facility (NIF) by 2014. Baseline "all-DT" NIF direct-drive ignition target designs have been developed that have a predicted gain of 45 (1-D) at a NIF drive energy of ~1.6 MJ. Significantly higher gains are calculated for targets that include a DT-wicked foam ablator. This paper also reviews the results of both warm fuel and initial cryogenic-fuel spherical target implosion experiments carried out on the OMEGA UV laser. The results of these experiments and design calculations increase confidence that the NIF direct-drive ICF ignition goal will be achieved.
Date: April 16, 2010
Creator: McCrory, R.L.; Meyerhofer, D.D.; Loucks, S.J.; Skupsky, S.; Bahr, R.E.; Betti, R. et al.
Partner: UNT Libraries Government Documents Department