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Radiation Sources
Published in Harry E. Martz, Clint M. Logan, Daniel J. Schneberk, Peter J. Shull, X-Ray Imaging, 2016
Harry E. Martz, Clint M. Logan, Daniel J. Schneberk, Peter J. Shull
Fundamentally, the efficiency of laser Thomson scattering is limited by the small magnitude of the Thomson cross section (~0.6 barns) and the inability of electron beams to be focused to spots on par with minimum laser spot dimensions. In 1994, LLNL scientists recognized (Barty and Hartemann 2004) that the Thomson scattering brilliance should increase rapidly as a function of electron beam energy and beam quality. To the first order, this occurs because at higher electron beam energy, it is possible to overcome electrostatic repulsion and focus the electron to smaller spot dimensions. Roughly, the electron spot dimension is proportional to its beam energy, and thus, the peak brilliance (photons s−1 0.1% band width [BW] mrad−2 mm−2) of the laser Thomson source increases as a function of electron beam energy somewhere between the second and fourth power. This rapid increase in peak brilliance is in stark contrast to the trends of alternative sources, such as large-scale synchrotrons. In the nuclear excitation region above 100 keV, the peak brilliance of third-generation synchrotrons decreases faster than exponentially. Above 2 MeV, the peak brilliance of a monoenergetic γ-ray (MEGa-ray) source produced via laser–Thomson scattering can exceed that of the largest synchrotrons by more than 15 orders of magnitude. It is important to note that for many nuclear applications and especially for those related to management of nuclear materials, it is the bandwidth of the Compton source and not the pulse duration that is of foremost importance.
Laser-Accelerated Electrons as X-Ray/γ-Ray Sources
Published in Paul R. Bolton, Katia Parodi, Jörg Schreiber, Applications of Laser-Driven Particle Acceleration, 2018
Stefan Karsch, Konstantin Khrennikov
In Thomson scattering, a light pulse scatters off a moving electron, and for simplicity, we will focus on a backscattering geometry. The wiggling force on the electron is now provided by a light pulse with spatially varying E and B-field instead of a constant-amplitude undulator. Its shorter wavelength creates harder X-rays for a given electron energy. Since even few fs LWFA electron bunches are much longer than the scattered radiation period, the process is incoherent1 and can be treated as an incoherent sum of the radiation generated by all electrons in the bunch. Therefore, we will first discuss the radiation of a single electron. Most of this section follows Esarey et al. [1] and Ride et al. [27].
Origins of Quantum Theory
Published in Vinod Kumar Khanna, Introductory Nanoelectronics, 2020
In the low-energy limit, Compton scattering is observed in the form of classical Thomson scattering, which therefore signifies its low-energy boundary. Thomson scattering represents the elastic scattering experienced by electromagnetic waves under the influence of a free charged particle. In this scattering, the charged particle itself is accelerated. The acceleration is caused by the electric field of the incident wave. The charge thus accelerated emits dipolar electromagnetic radiation at the same frequency as the incident wave. In this way, the wave undergoes scattering. Thus there is no change in frequency or wavelength of the wave.
Temporal Profiling of Electron Temperatures Using the Hα–Hβ Line Emission and Triple Langmuir Probe Array in the Pre-Ionization Discharge of the MT-I Spherical Tokamak
Published in Fusion Science and Technology, 2020
M. Usman Naseer, F. Deeba, S. I. W. Shah, S. Hussain, A. Qayyum
The MT-I is the modified version of the GLAST-II Spherical Tokamak wherein the glass vacuum vessel has been replaced by a metallic (stainless steel 304) one, while keeping other subsystems the same as those of the GLAST-II. Plasma characterization is one of the important aspects of device optimization to understand the physical features and issues related to fusion plasmas, such as radiation losses, impurities, and particle transport. Various diagnostic methods have been used to characterize the plasma, such as electric probes, optical emission spectroscopy, interferometry, and Thomson scattering.1–7 The electric probes have an advantage over other plasma diagnostics due to their ability to acquire measurement at a specific point, usually at the edge plasma region. Their ability to measure the parameters in the core region gets limited due to very high plasma temperatures and the perturbations caused due to the physical insertion of probes. The optical diagnostics don’t have such issues as the perturbation of plasma, but the resultant measurements provide the averaged values over a specific volume and line of sight.
Development of Real-Time Software for Thomson Scattering Analysis at NSTX-U
Published in Fusion Science and Technology, 2019
Roman Rozenblat, Egemen Kolemen, Florian M. Laggner, Christopher Freeman, Greg Tchilinguirian, Paul Sichta, Gretchen Zimmer
Thomson scattering (TS) is a known and widely applied tool used to diagnose hot plasma. Its underlying fundamental principle is the interaction of a high-energy laser beam with free electrons of the plasma. Especially in applications for magnetic confinement fusion, it is one of the main profile diagnostic tools since it provides a noninvasive, localized measurement of electron density and temperature.1 For this reason TS diagnostics are very common and installed on multiple fusion devices. Some of the experiments that use the TS diagnostics method include the Joint European Torus experiment,2 TFTR (Ref. 3), DIII-D (Ref. 4), Alcator C-Mod tokamak,5 ADEX Upgrade,6 MAST (Ref. 7), Large Helical Device8 (LHD), Helical Symmetry Experiment9 (HSX), and Wendelstein 7-X (Ref. 10). The goal of the presented project is to build a real-time analysis prototype for the TS diagnostic tool at National Spherical Tokamak eXperiment Upgrade (NSTX-U) that can calculate plasma parameters. These parameters can then be used by the NSTX-U plasma control system (PCS) to feedback the plasma density and temperature during a shot. This diagnostic tool consists of several lasers, which fire in a predefined sequence.11–14 In addition, this project demonstrates the real-time performance that can be achieved using present-day commercial off-the-shelf hardware and software technologies.
VITALS: A Surrogate-Based Optimization Framework for the Accelerated Validation of Plasma Transport Codes
Published in Fusion Science and Technology, 2018
P. Rodriguez-Fernandez, A. E. White, A. J. Creely, M. J. Greenwald, N. T. Howard, F. Sciortino, J. C. Wright
The Alcator C-Mod tokamak29 is a diverted, high-field, compact, experimental fusion device with major radius m and typical minor radius m. Electron temperature traces are measured with a fast time resolution electron cyclotron emission (ECE) grating polychromator with nine spatial channels.30 Average electron densities are determined from line-integrated measurements of a ten-channel two-color interferometer.31 The electron density and temperature profiles are measured using a Thomson scattering system.32 Plasma toroidal rotation and ion temperature profiles are measured with a high-resolution imaging X-ray spectrometer system.33,34 Experimental heat fluxes are obtained through power balance analysis using TRANSP (Refs. 35 and 36). Electron incremental thermal diffusivity measurements are obtained via the partial sawtooth heat pulse propagation method.22 Long-wavelength () electron temperature fluctuations are measured with a correlation ECE (CECE) radiometer.37,38 The error bars on the plasma parameters were determined by the instrumental uncertainty of the diagnostics as well as fitting errors of the profiles.23