12 research outputs found
Generation of coherent two-color pulses at the two adjacent harmonics in a seeded free-electron laser
The growing requirements of pump-probe techniques and nonlinear optics
experiments greatly promote the studies of two-color free-electron lasers
(FELs). We propose a new method to generate coherent two-color pulses in a
high-gain harmonic generation (HGHG) FEL. In this scheme, an initial tilted
electron beam is sent though the modulator and dispersive section of an HGHG
FEL to generate the bunching at harmonics of the seed laser. Then a transverse
gradient undulator (TGU) is adopted as the radiator and in such radiator, only
two separated fractions of the tilted beam will resonate at two adjacent
harmonics of the seed laser and are enabled to emit the coherent two-color
pulses simultaneously. The time separation between the two pulses are on the
order of hundreds of femtoseconds, and can be precisely controlled by varying
the tilted amplitude of the electron beam and/or the transverse gradient of the
TGU radiator. Numerical simulations confirm the validity and feasibility of
this scheme in the EUV waveband
Normal planar undulators doubling as transverse gradient undulators
The transverse gradient undulator (TGU) has important application in the short-wavelength high-gain free electron lasers (FELs) driven by laser-plasma accelerators. However, the usual transversely tapered TGUs need special design and manufacture, and the transverse gradient cannot be tuned arbitrarily. In this paper we explore a new and simple method of using the natural transverse gradient of a normal planar undulator to compensate the beam energy spread effect. In this method, a vertical dispersion on the electron beam is introduced, then the dispersed beam passes through a normal undulator with a vertical off-axis orbit where the vertical field gradient is selected properly related to the dispersion strength and the beam energy spread. Theoretical analysis and numerical simulations for self-amplified spontaneous emission FELs based on laser plasma accelerators are presented, and indicate that this method can greatly reduce the effect of the beam energy spread, leading to a similar enhancement on FEL performance as the usual transversely tapered TGU, but with the advantages of economy, tunable transverse gradient and no demand of extra field for correcting the orbit deflection induced by the field gradient
Understanding the Role of Extracellular Polymeric Substances on Ciprofloxacin Adsorption in Aerobic Sludge, Anaerobic Sludge, and Sulfate-Reducing Bacteria Sludge Systems
Extracellular polymeric substances
(EPS) of microbial sludge play
a crucial role in removal of organic micropollutants during biological
wastewater treatment. In this study, we examined ciprofloxacin (CIP)
removal in three parallel bench-scale reactors using aerobic sludge
(AS), anaerobic sludge (AnS), and sulfate-reducing bacteria (SRB)
sludge. The results showed that the SRB sludge had the highest specific
CIP removal rate via adsorption and biodegradation. CIP removal by
EPS accounted up to 35. 6 ± 1.4%, 23.7 ± 0.6%, and 25.5
± 0.4% of total removal in AS, AnS, and SRB sludge systems, respectively,
at influent CIP concentration of 1000 μg/L, which implied that
EPS played a critical role in CIP removal. The binding mechanism of
EPS on CIP adsorption in three sludge systems were further investigated
using a series of batch tests. The results suggested that EPS of SRB
sludge possessed stronger hydrophobicity (proteins/polysaccharides
(PN/PS) ratio), higher availability of adsorption sites (binding sites
(<i>n</i>)), and higher binding strength (binding constant
(<i>K</i><sub>b</sub>)) between EPS and CIP compared to
those of AS and AnS. The findings of this study provide an insight
into the role of EPS in biological process for treating CIP-laden
wastewaters