Vincent Tang

Vincent Tang
Lawrence Livermore National Laboratory | LLNL

About

63
Publications
3,977
Reads
How we measure 'reads'
A 'read' is counted each time someone views a publication summary (such as the title, abstract, and list of authors), clicks on a figure, or views or downloads the full-text. Learn more
604
Citations

Publications

Publications (63)
Article
Full-text available
An overview of the diagnostics installed on the Al-cator C-Mod tokamak is presented. Approximately 25 diagnostic systems are being operated on C-Mod. The compact design of the machine and the cryostat enclos-ing the vacuum vessel and magnetic field coils make access challenging. Diagnostics are used to study four focus areas: transport, plasma boun...
Article
This paper reviews the physics and technology of wave-particle - interaction experiments in the ion cyclotron range of frequencies (ICRF) and the lower hybrid (LH) range of frequencies (LHRF) on the Alcator C-Mod tokamak. Operation of fixed frequency (80 MHz) and tunable (40- to 80-MHz) ICRF transmitters and the associated transmission system is de...
Article
The Z-pinch phase of a dense plasma focus (DPF) emits multiple-MeV ions from a ∼cm length interaction. The mechanisms through which these physically simple devices generate such high-energy beams in a relatively short distance are not fully understood. We are exploring the mechanisms behind these large accelerating gradients using fully kinetic sim...
Article
We are seeking to gain a better fundamental understanding of the ion beam acceleration and neutron production dense plasma focus (DPF) device. Experiments were performed on a kilojoule level, fast rise time DPF located at LLNL. Ion beam spectra and neutron yield were measured for deuterium pinches. Visible light images of the pinch are used to d...
Article
The Z-pinch phase of a dense plasma focus (DPF) emits multiple-MeV ions in a ∼cm length. The mechanisms through which these physically simple devices generate such high energy beams in a relatively short distance are not fully understood. We are exploring the origins of these large gradients using measurements of an ion probe beam injected into a...
Article
Full-text available
Active interrogation using neutrons is an effective method for detecting shielded nuclear material. A lightweight, lunch-box-sized, battery-operated neutron source would enable new concepts of operation in the field. We have developed at-scale components for a highly portable, completely self-contained, pulsed Deuterium-Tritium (DT) neutron source...
Article
Full-text available
The object of this review is to summarize the achievements of research on the Alcator C-Mod tokamak [Hutchinson et al., Phys. Plasmas 1, 1511 (1994) and Marmar, Fusion Sci. Technol. 51, 261 (2007)] and to place that research in the context of the quest for practical fusion energy. C-Mod is a compact, high-field tokamak, whose unique design and oper...
Article
Dense plasma focus (DPF) Z-pinch devices are sources of copious high energy electrons and ions, x-rays, and neutrons. Megajoule-scale DPFs can generate 10(12) neutrons per pulse in deuterium gas through a combination of thermonuclear and beam-target fusion. However, the details of the neutron production are not fully understood and past optimizatio...
Article
Dense-plasma-focus (DPF) Z-pinch devices are sources of copious high-energy electrons and ions, x rays, and neutrons. The mechanisms through which these physically simple devices generate such high-energy beams in a relatively short distance are not fully understood and past optimization efforts of these devices have been largely empirical. Previou...
Article
We have designed and built a Dense Plasma Focus (DPF) Z-pinch device using a kJ-level capacitor bank and a hollow anode, and fueled by a cylindrically symmetric gas puff. Using this device, we have measured peak deuteron beam energies of up to 400 keV at 0.8 kJ capacitor bank energy and pinch lengths of ∼6 mm, indicating accelerating fields greater...
Article
We have developed a thin-film coating for neutron generator targets that can be loaded with deuterium or tritium at low temperatures (100 °C), and at gas/Ti ratios greater than 1.7. The key to this improvement is the addition of a thin palladium overcoat at the end of the titanium deposition. This overcoat prevents the oxidation of the titanium fil...
Article
We report a study of materials recovered from a uranium-containing plasma generated by an electric arc. The device used to generate the arc is capable of sustaining temperatures of an eV or higher for up to 100 μs. Samples took the form of a 4 μm-thick 238U film deposited onto 8 pairs of 17 μm-thick Cu electrodes supported on a 25 μm-thick Kapton b...
Article
We present a Hybrid Monte-Carlo method (HMCM) for simulating neutron and photon radiographs. HMCM utilizes the combination of a Monte-Carlo particle simulation for calculating incident film radiation and a statistical post-processing routine to simulate film noise. Since the method relies on MCNP for transport calculations, it is easily generalized...
Article
A palm sized, portable neutron source would be useful for widespread implementation of detection systems for shielded, special nuclear material. We present progress towards the development of the components for an ultracompact neutron generator using a pulsed, meso-scale field ionization source, a deuterated (or tritiated) titanium target driven...
Article
Accelerator driven fusion gammas and fast neutrons could provide unique radiography capabilities due to their ability to produce both high and low energy mono-energetic gammas and neutrons compared with broadband bremsstrahlung based x-ray sources. The possibility of simultaneously obtaining both gamma and neutron radiographs using one source could...
Article
Dense plasma focus Z-pinch devices are sources of copious high energy electrons and ions, x rays, and neutrons. The mechanisms through which these physically simple devices generate such high-energy beams in a relatively short distance are not fully understood. We now have, for the first time, demonstrated a capability to model these plasmas fully...
Article
A new inversion algorithm based on the maximum entropy method (MEM) is proposed to remove unwanted effects in fast neutron imaging which result from an uncollimated source interacting with a finitely thick scintillator. The algorithm takes as an input the image from the thick scintillator (TS) and the radiography setup geometry. The algorithm then...
Article
In this talk, we discuss planned experiments on acceleration of an injected ion beam in a Z-pinch plasma with MV/cm gradients and the first fully kinetic simulations of such beam-plasma systems. Multi-MeV, kilo-Ampere ion beams have been produced by 100 kJ class, centimeter scale, Dense Plasma Focus (DPF) Z-pinches. We have now demonstrated similar...
Article
Dense plasma focus (DPF) z-pinch plasmas are known to produce abundant neutrons and particle beams, but the mechanisms behind the high gradient fields in DPFs are not well understood. We have a 4 MeV deuteron beam that can be used to probe the electric field gradients produced by the DPF experiment at LLNL. This information can be used in conjuncti...
Article
A broadband experimental study of Alfvén eigenmode (AE) damping and excitation examines both low-n and high-n AEs (0 < |n| < 9) with a single diagnostic. Direct measurements of the damping rate of stable AEs with the active MHD system, in conjunction with analytic and numerical calculation, indicate that AE stabilization in Alcator C-Mod is largely...
Article
Full-text available
A flashover arc source that delivered up to 200 mJ on the 100s-of-ns time-scale to the arc and a user-selected dielectric surface was characterized for studying high-explosive kinetics under plasma conditions. The flashover was driven over thin pentaerythritol tetranitrate (PETN) and poly(methyl methacrylate) (PMMA) dielectric films and the resulta...
Article
Full-text available
We have characterized an arc source that delivers up to 200 mJ to the arc and dielectric surface on the 100s of ns time-scale for the goal of creating a platform to study high explosive kinetics under plasma conditions. The arc was driven over PETN and PMMA films with temperatures and electron densities characterized spatiotemporally using atomic e...
Article
Dense Plasma Focus (DPF) Z-pinches are abundant sources of radiation, including neutrons, x-rays, and energetic electron and ion beams. Energetic protons and deuterons up to 10 MeV have been observed from cm-scale-length pinches, implying average acceleration gradients up to 1 GV/m. Gradients of this magnitude could potentially be exploited in the...
Article
Dense Plasma Focus (DPF) Z-pinches are copious sources of neutrons and MeV level particle beams. Deuterons up to 10 MeV have been observed from centimeter-scale long pinches indicating gradients up to 1 GV/m. These beams contribute significantly to the DPF's radiation output. The mechanisms behind these gradients are not understood and a true predi...
Article
form only given. Dense Plasma Focus (DPF) Z-pinches are copious sources of radiation including neutrons, x-rays, and MeV level electron and ion beams. Energetic protons and deuterons up to 10 MeV have been observed from ~cm long pinches indicating average acceleration gradients up to 1 GV/m. Corresponding electron beams with lower particle energy a...
Article
Initiation of high explosives (HE) is the process of transitioning the HE from a quiescent state to one containing a propagating release of chemical energy. Plasma arc initiation is driven by a discharge across the surface on or through the HE. Experiments have found that at least one conventional high explosive (pentaerythritol tetranitrate, PETN)...
Article
A new granular two-phase mixed media insulator consisting of packed polypropylene beads and silicone oil is found to have up to 10 times greater resistivity and nearly 2 times greater breakdown strength compared with the same silicone oil when operated in DC mode.
Article
The final Z -pinch stage of a dense plasma focus (DPF) could be used as a simple, compact, and potentially rugged plasma-based high-gradient accelerator with fields at the 100-MV/m level. In this paper, we review previously published experimental beam data that indicate the feasibility of such a DPF-based accelerator, qualitatively discuss the phys...
Article
We present a thorough characterization of a capacitor driven arc source that can deliver up to 200 mJ of energy to the arc and high explosive in a well-controlled, repeatable manner on the hundreds of nanoseconds time-scale. Our ultimate purpose is to create a platform to study high explosive kinetics under extreme conditions of high-temperature. I...
Article
Neutron interrogation techniques have specific advantages for detection of hidden, shielded, or buried threats over other detection modalities in that neutrons readily penetrate most materials providing backscattered gammas indicative of the elemental composition of the potential threat. Such techniques have broad application to military and homela...
Article
As a step towards developing an ultra compact D-D neutron source for various defense and homeland security applications, a compact, low average power ion source is needed. Towards that end, we are testing a high current, pulsed surface flashover ion source, with deuterated titanium as the spark contacts. Neutron yield and source lifetime data will...
Article
As a step towards developing an ultra compact D-D neutron source for various defense and homeland security applications, a compact ion source is needed. Towards that end, we are testing a pulsed, surface flashover source, with deuterated titanium films deposited on alumina substrates as the electrodes. An electrochemically-etched mask was used to d...
Article
Full-text available
Intense pulsed D–D neutron emission with rates of ≫10<sup>10</sup> n / s during the pulse, pulse widths of approximately hundreds of nanoseconds and neutron yields of greater than 10 000 per pulse, are demonstrated in a compact pyroelectric accelerator. The accelerator consists of a small pyroelectric LiTaO <sub>3</sub> crystal that provides the ac...
Article
We developed and tested a compact collimated 16 channel fiber optic array diagnostic for studying the light emission of railgun armature plasmas with approximately millimeter spatial and submicrosecond temporal resolution. The design and operational details of the diagnostic are described. Plasma velocities, oscillation, and dimension data from the...
Article
This document summarizes the Flash X-Ray accelerator (FXR) optical transition radiation (OTR) spot-size diagnostics efforts in FY07. During this year, new analysis, simulation, and experimental approaches were utilized to interpret OTR spot data from both dielectric foils such as Kapton (VN type) and metal coated foils. Significant new findings of...
Article
Full-text available
We have developed and tested a compact collimated sixteen channel fiber optic array diagnostic for studying the light emission of railgun armature plasmas with mm spatial and sub-s temporal resolution. The design and operational details of the diagnostic are described. Plasma velocities, oscillation, and dimension data from the diagnostic for the L...
Article
The LLNL Crystal Driven Neutron Source is operational and has produced record ion currents of approximately 10 nA and neutron output of 1.9(+/-0.3)x10(5) per thermal cycle using a crystal heating rate of 0.2 degrees C/s from 10 to 110 degrees C. A 3 cm diameter by 1 cm thick LiTaO(3) crystal with a socket secured field emitter tip is thermally cycl...
Article
Full-text available
\Alcator C-MOD has compared plasma performance with plasma-facing components (PFCs) coated with boron to all-metal PFCs to assess projections of energy confinement from current experiments to next-generation burning tokamak plasmas. Low-Z coatings reduce metallic impurity influx and diminish radiative losses leading to higher H-mode pedestal pressu...
Article
Full-text available
Progress is reviewed on the simulation of wave-particle interactions in the ion cyclotron range of frequencies (ICRF). Two important aspects of this problem are described. First, mode conversion from a long wavelength fast magnetosonic wave to short wavelength ion Bernstein waves (IBW) and ion cyclotron waves (ICW) is simulated and validation tests...
Article
Energetic minority protons with ~100 keV effective temperature are routinely created in Alcator C-Mod plasmas with the application of ion-cyclotron-range-of-frequency (ICRF) heating. A multichannel compact neutral particle analyzer (CNPA) is used to make measurements of these distributions in Alcator C-Mod's unique and reactor-relevant operating sp...
Article
Full-text available
Energetic particle physics is studied in Alcator C-Mod in reactor relevant regimes with high density and equilibrated electron and ion temperatures. Stable Alfven eigenmodes are excited with low-power active magnetohydrodynamic antennas in the absence of a significant energetic particle tail to directly measure the damping rate of the modes. Stable...
Article
Traditionally, thin metal foils are employed for optical transition radiation (OTR) beam diagnostics but the possibility of shorting accelerator insulating surfaces and modifying accelerating fields are concerns. The successful utilization of dielectric foils in place of metal ones could alleviate these issues but necessitates more understanding of...
Article
Full-text available
Alcator C-Mod's lower hybrid current drive (LHCD) system allows the exploration of advanced tokamak (AT) regimes at densities relevant to ITER and fusion reactors. The location of the LHCD is critical to AT performance and may be inferred by measuring the nonthermal bremsstrahlung emission in the hard x-ray (HXR) region. A pinhole camera using an a...
Article
The AORSA global-wave solver is combined with the CQL3D bounce-averaged Fokker-Planck code to simulate the quasilinear evolution of non-thermal distributions in ion cyclotron resonance heating of tokamak plasmas. A novel re-formulation of the quasilinear operator enables calculation of the velocity space diffusion coefficients directly from the glo...
Article
A four-channel compact neutral particle analyzer CNPA based on operating small Si diode detectors in pulse-height analysis PHA mode is used to measure energetic hydrogen minority ions with energies between 50 and 350 keV stemming from ion-cyclotron range-of-frequency heated DH Alcator C-Mod plasmas with both active and passive charge exchange CX. F...
Article
Introduction Stable Toroidal Alfvén Eigenmodes (TAEs) with a broad spectrum of moderate toroidal mode numbers (3 � |n| � 14) are excited on Alcator C-Mod with a pair of antennas at one toroidal location (1). This is in the range of mode numbers expected to be unstable in ITER (2,3), at the same toroidal field and density as ITER. By sweeping the fr...
Article
Full-text available
Research on the Alcator C-Mod tokamak has emphasized RF heating, self-generated flows, momentum transport, scrape-off layer (SOL) turbulence and transport and the physics of transport barrier transitions, stability and control. The machine operates with P-RF up to 6 MW corresponding to power densities on the antenna of 10 MW m(-2). Analysis of rota...
Article
Full-text available
To simulate the resonant interaction of fast Alfvén wave (FW) heating and Coulomb collisions on energetic ions, including finite orbit effects, a Monte‐Carlo code ORBIT‐RF has been coupled with a 2D full wave code TORIC4. ORBIT‐RF solves Hamiltonian guiding center drift equations to follow trajectories of test ions in 2D axisymmetric numerical magn...
Article
Full-text available
Alfvén eigenmodes (AEs) are studied to assess their stability in high density reactor relevant regimes where Ti ≈ Te and as a diagnostic tool. Stable AEs are excited with active magnetohydrodynamics antennas in the range of the expected AE frequency. Toroidal Alfvén eigenmode (TAE) damping rates between 0.5%<γ/ω<4.5% have been observed in diverted...
Article
The absorption of ion cyclotron radio frequency (ICRF) waves by resonant ions at ion cyclotron harmonics has been observed experimentally in existing tokamaks such as DIII-D and C-Mod. From NPA energy spectrum measurements, strong enhancement of the tail energy spectrum was observed due to the acceleration of resonant ions by ICRF waves. In this pa...
Article
Recent experimental results from the new Compact Neutral Particle Analyzer (CNPA) and a completed multi-detector upgrade of the diagnostic are presented. The CNPA uses Si diodes to detect charge-exchanged (CX) induced energetic (>20keV) neutral particles for ICRF hydrogen minority tail temperature diagnosis. A diagnostic neutral beam (DNB) provides...
Article
A Lower Hybrid Current Drive (LHCD) system is being installed on C-Mod, allowing exploration of advanced tokamak (AT) regimes. The location of the LHCD is critical to AT performance and may be dynamically adjusted through n| spectral control. The current deposition profile may be inferred by measuring the non-thermal Bremsstrahlung emission in the...
Article
In this preliminary scoping study, post-accident temperature transients of several fusion–fission designs utilizing ITER-FEAT-like parameters and fission pebble bed fuel technology are examined using a 1-D cylindrical matlab heat transfer code along with conventional fission decay heat approximations. Scenarios studied include systems with no addit...
Article
A new tail temperature diagnostic based on detection and pulse-height analysis of energetic charged-exchanged (CX) neutral particles has been constructed for minority-heated ICRF discharges in Alcator C-Mod. The diagnostic consists of a silicon diode detector viewing the diagnostic neutral beam from a top port. The detector system is capable of thr...
Article
A goal of advanced tokamak scenarios on C-Mod is to achieve high bootstrap fraction. One promising regime uses internal transport barriers (ITB) produced by off-axis ICRH.(S. Wukitch et al., Physics of Plasma 9, 2149 (2002).) Transient simulations of such high bootstrap current fraction plasmas are performed using TRANSP. These simulations are used...
Article
Advanced Tokamak (AT) plasmas appear to be a promising approach to fusion and can be characterized by steady-state operation and enhanced confinement through control of pressure and current density profiles. A Lower Hybrid Current Drive (LHCD) system is being fabricated for C-Mod, allowing the exploration of AT regimes. In preparation for LHCD oper...
Article
Toroidal Alfvén Eigenmodes (TAEs) are weakly damped MHD waves in tokamak plasmas. Interaction with fast particles such as fusion-born alphas can overcome the damping and lead to the spontaneous appearance of unstable TAEs. The Active MHD diagnostic on Alcator C-Mod is used to investigate the relationship between the TAE margin to instability and co...
Article
Unstable Alfvén eigenmodes are observed in Enhanced D-alpha (EDA) H-mode in Alcator C-Mod at least up to densities of ne˜2.5x10^20m-3 with strong H-minority ICRF heating. The mode frequencies are typically in the range 400 - 800 kHz. The largest amplitude modes (Btheta/Btheta˜5x10-5 at the wall) often agree in frequency with the expected Toroidal A...
Article
Recent experimental results from the upgraded multi-channel Compact Neutral Particle Analyzer (CNPA) system are presented and compared with numerical simulations. The CNPA system consists of Si diode detectors and measures charge exchange (CX) induced energetic (>40 keV) neutral particles for ICRF hydrogen minority tail temperature diagnosis. A new...
Article
Energetic minority protons with ˜100keV effective temperature are routinely created in C-Mod plasmas with the application of ICRF. A new multi-channel Compact Neutral Particle Analyzer is used to make measurements of these distributions via an active charge-exchange (CX) technique. Using a detailed model that accounts for beam, halo, and impurity C...
Article
Correct interpretation of lower hybrid current drive experiments requires detailed modeling of coupling, power deposition, and hard x-ray emission. Results from a LH coupling code are used to calculate expected n || spectra and waveguide reflection coefficients. The spectral results from the coupling code are then used in Fokker-Planck simulations...

Network

Cited By

Projects

Projects (3)
Archived project
Turbulence measurements (phase contrast imaging and reflectometry) Lower hybrid control system