175 research outputs found
Neutral beam current drive in a tokamak
Neutral beam current drive (NBCD) on the EAST tokamak is studied by using
Monte-Carlo simulation. The electron shielding effect to the fast ion current
is taken into account by using a fitting formula applicable to general tokamak
equilibria and arbitrary collisionality regime. The net currents driven by the
beam are off-axis although the fast ion currents are on-axis. This is found to
be due to the electron shielding effect being strong near the magnetic axis. We
also investigate the dependence of NBCD efficiency on the plasma density. The
results indicate that the NBCD efficiency decreases with the increase in plasma
density. A simple semi-analytic estimation of the dependence of NBCD efficiency
on the density is proposed and is in reasonable agreement with the results
directly obtained in the simulations
Emerging applications of integrated optical microcombs for analogue RF and microwave photonic signal processing
We review new applications of integrated microcombs in RF and microwave
photonic systems. We demonstrate a wide range of powerful functions including a
photonic intensity high order and fractional differentiators, optical true time
delays, advanced filters, RF channelizer and other functions, based on a Kerr
optical comb generated by a compact integrated microring resonator, or
microcomb. The microcomb is CMOS compatible and contains a large number of comb
lines, which can serve as a high performance multiwavelength source for the
transversal filter, thus greatly reduce the cost, size, and complexity of the
system. The operation principle of these functions is theoretically analyzed,
and experimental demonstrations are presented.Comment: 16 pages, 8 figures, 136 References. Photonics West 2018 invited
paper, expanded version. arXiv admin note: substantial text overlap with
arXiv:1710.00678, arXiv:1710.0861
Photonic RF and microwave reconfigurable filters and true time delays based on an integrated optical Kerr frequency comb source
We demonstrate advanced transversal radio frequency (RF) and microwave
functions based on a Kerr optical comb source generated by an integrated
micro-ring resonator. We achieve extremely high performance for an optical true
time delay aimed at tunable phased array antenna applications, as well as
reconfigurable microwave photonic filters. Our results agree well with theory.
We show that our true time delay would yield a phased array antenna with
features that include high angular resolution and a wide range of beam steering
angles, while the microwave photonic filters feature high Q factors, wideband
tunability, and highly reconfigurable filtering shapes. These results show that
our approach is a competitive solution to implementing reconfigurable, high
performance and potentially low cost RF and microwaveComment: 15 pages, 11 Figures, 60 Reference
Integrated Fabry-Perot cavities as a mechanism for enhancing micro-ring resonator performance
We propose and experimentally demonstrate the enhancement in the filtering
quality (Q) factor of an integrated micro-ring resonator (MRR) by embedding it
in an integrated Fabry-Perot (FP) cavity formed by cascaded Sagnac loop
reflectors (SLRs). By utilizing coherent interference within the FP cavity to
reshape the transmission spectrum of the MRR, both the Q factor and the
extinction ratio (ER) can be significantly improved. The device is
theoretically analyzed, and practically fabricated on a silicon-on-insulator
(SOI) wafer. Experimental results show that up to 11-times improvement in Q
factor, together with an 8-dB increase in ER, can be achieved via our proposed
method. The impact of varying structural parameters on the device performance
is also investigated and verified by the measured spectra of the fabricated
devices with different structural parameters.Comment: 9 pages, 6 figures, 33 Reference
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