1,281 research outputs found
Center for Momentum Transport and Flow Organization in Plasmas and Magnetofluids (CMTFO)
The CMTFO funding partially supports a junior researcher and a graduate student at UCI. During this project, we have further developed the global gyrokinetic particle code GTC to study the momentum transport in tokamak driven by electrostatic ion temperature gradient (ITG) turbulence [1] with kinetic electrons and by collisionless trapped electron mode (CTEM) turbulence [2]. We have also upgraded GTC for fully electromagnetic simulation and for linear plasma configuration with verification and validation of the electron temperature gradient (ETG) turbulence in Columbia Linear Machine. The followings are the highlights on the physics results reported in the key publications of this project
SciDAC Center for Gyrokinetic Particle Simulation of Turbulent Transport in Burning Plasmas
During the first year of the SciDAC gyrokinetic particle simulation (GPS) project, the GPS team (Zhihong Lin, Liu Chen, Yasutaro Nishimura, and Igor Holod) at the University of California, Irvine (UCI) studied the tokamak electron transport driven by electron temperature gradient (ETG) turbulence, and by trapped electron mode (TEM) turbulence and ion temperature gradient (ITG) turbulence with kinetic electron effects, extended our studies of ITG turbulence spreading to core-edge coupling. We have developed and optimized an elliptic solver using finite element method (FEM), which enables the implementation of advanced kinetic electron models (split-weight scheme and hybrid model) in the SciDAC GPS production code GTC. The GTC code has been ported and optimized on both scalar and vector parallel computer architectures, and is being transformed into objected-oriented style to facilitate collaborative code development. During this period, the UCI team members presented 11 invited talks at major national and international conferences, published 22 papers in peer-reviewed journals and 10 papers in conference proceedings. The UCI hosted the annual SciDAC Workshop on Plasma Turbulence sponsored by the GPS Center, 2005-2007. The workshop was attended by about fifties US and foreign researchers and financially sponsored several gradual students from MIT, Princeton University, Germany, Switzerland, and Finland. A new SciDAC postdoc, Igor Holod, has arrived at UCI to initiate global particle simulation of magnetohydrodynamics turbulence driven by energetic particle modes. The PI, Z. Lin, has been promoted to the Associate Professor with tenure at UCI
Graphene Nano-Ribbon Electronics
We have fabricated graphene nano-ribbon field-effect transistor devices and
investigated their electrical properties as a function of ribbon width. Our
experiments show that the resistivity of a ribbon increases as its width
decreases, indicating the impact of edge states. Analysis of temperature
dependent measurements suggests a finite quantum confinement gap opening in
narrow ribbons. The electrical current noise of the graphene ribbon devices at
low frequency is found to be dominated by the 1/f noise.Comment: 6 pages, 7 figure
Numerical model for geothermal energy utilization from double pipe heat exchanger in abandoned oil wells
The number of abandonded wells are increasing in the late period of oilfield development. The utilization of these abandonded oil wells is promising and environment-friendly for geothermal development. In this study, a numerical model for geothermal heating is derived from a double pipe heat exchanger in abandoned oil wells. The main influencing factors of injection rate, injection time, and the types of filler in casing annulus on temperature profiles and outlet temperature have been considered in this model. The influences of injection rate on heat-mining rate are then discussed. Results show that the double pipe heat exchanger can gain higher temperature at the outlet when the casing annulus is filled by liquid other than dry cement under the given parameter combination. The outlet temperature decreases with the increase in injection rate and injection time. The temperature rapidly decreases in the first 40 days during the injection process. The balance between heat mining rate and outlet temperature is important for evaluating a double pipe heat exchanger in abandoned oil wells. This work may provide a useful tool for a field engineer to estimate the temperature of liquid in wellhead and evaluate the heat transfer efficiency for double pipe heat exchanger in abandoned oil wells.Cited as: Lin, Z., Liu, K., Liu, J., Geng, D., Ren, K., Zheng, Z. Numerical model for geothermal energy utilization from double pipe heat exchanger in abandoned oil wells. Advances in Geo-Energy Research, 2021, 5(2): 212-221, doi: 10.46690/ager.2021.02.1
Reconstruction of tokamak plasma safety factor profile using deep learning
In tokamak operations, accurate equilibrium reconstruction is essential for
reliable real-time control and realistic post-shot instability analysis. The
safety factor (q) profile defines the magnetic field line pitch angle, which is
the central element in equilibrium reconstruction. The motional Stark effect
(MSE) diagnostic has been a standard measurement for the magnetic field line
pitch angle in tokamaks that are equipped with neutral beams. However, the MSE
data are not always available due to experimental constraints, especially in
future devices without neutral beams. Here we develop a deep learning-based
surrogate model of the gyrokinetic toroidal code for q profile reconstruction
(SGTC-QR) that can reconstruct the q profile with the measurements without MSE
to mimic the traditional equilibrium reconstruction with the MSE constraint.
The model demonstrates promising performance, and the sub-millisecond inference
time is compatible with the real-time plasma control system
Conductance Quantization in Graphene Nanoribbons
We report the experimental observation of conductance quantization in
graphene nanoribbons, where 1D transport subbands are formed due to the lateral
quantum confinement. We show that this quantization in graphene nanoribbons can
be observed at temperatures as high as 80 K and channel lengths as long as 1.7
m. The observed quantization is in agreement with that predicted by
theoretical calculations
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