Aggregate breakdown is an important process which controls infiltration rate (IR) and the availability of fine materials necessary for structural sealing under rainfall. The purpose of this study was ...to investigate the effects of different slope gradients, rain intensities and particle size distributions on aggregate breakdown and IR to describe the formation of surface seal. To address this issue, 60 experiments were carried out in a 35 × 30 × 10 cm detachment tray using a rainfall simulator. By sieving a sandy loam soil, two sub-samples with different maximum aggregate sizes of 2 mm (Dmax2 mm) and 4.75 mm (Dmax4.75 mm) were prepared. The soils were exposed to two different rain intensities (57 and 80 mm h−1) on several slopes (0.5, 2.5, 5, 10 and 20%) each at three replicates. The result showed that for all slope gradients and rain intensities, the most fraction percentages in soils Dmax2 and Dmax4.75 mm were in the finest size classes of 0.02 and 0.043 mm, respectively. The soil containing finer aggregates exhibited higher transportability of pre-detached material than the soil containing larger aggregates. Also, IR increased with increasing slope gradient, rain intensity and aggregate size under unsteady state conditions because of less development of surface seal. However, under steady state conditions, no significant relationship was found between slope and IR. The findings of this study revealed the importance of rain intensity, slope steepness and soil aggregate size on aggregate breakdown and seal formation, which can control infiltration rate and the consequent runoff and erosion rates.
The possibility to accelerate electron beams to ultra-relativistic velocities over short distances by using plasma-based technology holds the potential for a revolution in the field of particle ...accelerators
. The compact nature of plasma-based accelerators would allow the realization of table-top machines capable of driving a free-electron laser (FEL)
, a formidable tool to investigate matter at the sub-atomic level by generating coherent light pulses with sub-ångström wavelengths and sub-femtosecond durations
. So far, however, the high-energy electron beams required to operate FELs had to be obtained through the use of conventional large-size radio-frequency (RF) accelerators, bound to a sizeable footprint as a result of their limited accelerating fields. Here we report the experimental evidence of FEL lasing by a compact (3-cm) particle-beam-driven plasma accelerator. The accelerated beams are completely characterized in the six-dimensional phase space and have high quality, comparable with state-of-the-art accelerators
. This allowed the observation of narrow-band amplified radiation in the infrared range with typical exponential growth of its intensity over six consecutive undulators. This proof-of-principle experiment represents a fundamental milestone in the use of plasma-based accelerators, contributing to the development of next-generation compact facilities for user-oriented applications
.
Abstract
The core purpose of this research is to use optical emission spectroscopy to determine the electron temperature (
T
e
) of a hydrogen plasma generated in a capillary discharge plasma, with a ...focus on its temporal variation. The plasma density (
n
e
) is first determined using the Stark broadening technique, which measures the broadening of spectral lines as a result of the electric field in the plasma. Subsequently, a passive spectroscopic technique is employed to estimate the electron plasma temperature by detecting the emitted light from the plasma. This spectral detection is performed using a visible range spectrometer. In this study, two elements, oxygen and nitrogen, are specifically selected based on the chemical composition of the capillary. The electron plasma temperature is estimated using the line ratio method, which involves comparing the intensities of two specific spectral lines emitted by the selected elements. By analyzing these line ratios, the electron plasma temperature can be inferred. The combination of the Stark broadening technique and line ratio method provides valuable insights into the plasma's physical characteristics, specifically its density and temperature.
Abstract
One of the most important features of plasma-based accelerators is their compactness because plasma modules can have dimensions of the order of mm
cm
−
1
, providing very high-accelerating ...fields up to hundreds of GV
m
−
1
. The main challenge regarding this type of acceleration lies in controlling and characterising the plasma itself, which then determines its synchronisation with the particle beam to be accelerated in an external injection stage in the laser wakefield acceleration (LWFA) scheme. This issue has a major influence on the quality of the accelerated bunches. In this work, a complete characterisation and optimisation of plasma targets available at the SPARC_LAB laboratories is presented. Two plasma-based devices are considered: supersonic nozzles for experiments adopting the self-injection scheme of laser wakefield acceleration and plasma capillary discharge for both particle and laser-driven experiments. In the second case, a wide range of plasma channels, gas injection geometries and discharge voltages were extensively investigated as well as studies of the plasma plumes exiting the channels, to control the plasma density ramps. Plasma density measurements were carried out for all the different designed plasma channels using interferometric methods in the case of gas jets, spectroscopic methods in the case of capillaries.
The breakthrough provided by plasma-based accelerators enabled unprecedented accelerating fields by boosting electron beams to gigaelectronvolt energies within a few centimeters 1-4. This, in turn, ...allows the realization of ultracompact light sources based on free-electron lasers (FELs) 5, as demonstrated by two pioneering experiments that reported the observation of self-amplified spontaneous emission (SASE) driven by plasma-accelerated beams 6,7. However, the lack of stability and reproducibility due to the intrinsic nature of the SASE process (whose amplification starts from the shot noise of the electron beam) may hinder their effective implementation for user purposes. Here, we report a proof-of-principle experiment using plasma-accelerated beams to generate stable and reproducible FEL light seeded by an external laser. FEL radiation is emitted in the infrared range, showing the typical exponential growth of its energy over six consecutive undulators. Compared to SASE, the seeded FEL pulses have energies 2 orders of magnitude larger and stability that is 3 times higher.
Abstract
Plasma technology offers revolutionary potential for particle accelerators by enabling the
acceleration of electron beams to ultra-relativistic velocities in a small-scale dimension. The
...compact nature of plasma-based accelerators permits the creation of accelerating gradients on the
GV scale. Plasma acceleration structures are created by utilizing either ultra-short laser pulses
(Laser Wakefield Acceleration, LWFA) or energetic particle beams (Particle Wakefield Acceleration,
PWFA), which need to be tailored to the plasma parameters. However, both methods face the
challenge of limited acceleration length, which is currently only a few centimeters. To overcome
this challenge, one approach is to generate plasma within a capillary tube, which can extend the
acceleration length up to approximately forty centimeters or more. Consequently, it is crucial to
characterize the produced plasma in terms of density and geometric structure. Optical emission
spectroscopy (EOS) methods can be employed to measure and characterize the plasma electron density
by analyzing the emitted plasma light. This paper presents measurements of the plasma electron
density distribution for a hydrogen-filled capillary tube using both Balmer alpha
(H
α
) and Balmer beta (H
β
) lines. Comparing the
intensities of H
α
and H
β
emissions enables more precise
measurements of the plasma electron density and provides additional information about other plasma
properties.
Abstract
Compact accelerator machines are capable of producing accelerating gradients in the GV/m
scale, which is significantly higher than the MV/m scale of conventional machines. As accelerators
...are widely used in many fields, such as industrial, research institutes, and medical applications,
the development of these machines will undoubtedly have a profound impact on people's daily
lives. SPARC_LAB, a test facility at INFN-LNF (Laboratori Nazionali di Frascati), is focused on
enhancing particle accelerator research infrastructure using innovative plasma acceleration
concepts. Within SPARC_LAB, we utilize plasma-filled capillaries with lengths of up to tens of
centimeters. However, the plasma formation process is critical to ensure proper oversight of the
plasma properties, which subsequently affects the dynamics of the electron bunch to be
accelerated. One of the most critical points that significantly affects the properties of the
electron beam passing through the plasma source is the shot-by-shot stability of the plasma
density along the longitudinal dimension of the plasma-discharge capillary. Therefore, this paper
aims to investigate the shot-by-shot stability of the plasma density during discharge,
contributing to further advancements in the field of plasma acceleration.
Abstract
We report the experimental activity on the plasma-discharge capillary tubes suitable for plasma-based accelerators (PBAs) carried out at the SPARC LAB (sources for plasma accelerators and ...compton with laser and beam) test-facility. A high-voltage discharge is produced inside a Hydrogen-filled capillary tube. Through spectroscopic techniques, the density of the plasma thus produced is monitored either spatially or temporally through the line Stark broadening profiles.
This work is concerned with both theoretical studies and the experimental developments of a plasma device to be used in plasma-based accelerators. In the field of the particle accelerators is growing ...the interest in the development of compact accelerator machines that also have to be able to exceed the current limits of the conventional accelerator structures. This research activity is leading towards plasma-based devices able to produce accelerating gradients in the GV/m scale. The activity of the SPARC_LAB test-facility concerns the development of this kind of plasma devices, as the gas-filled capillary plasma sources. In these devices, to create the plasma, one or more gas inlets feed the channel with a neutral gas (hydrogen, argon, nitrogen, etc.), which will be ionized by using a high-voltage discharge. The plasma plumes produced at the ends of such a capillary can affect the beam, due to the stability and uniformity of the electron density in which in these areas decrease strongly and, consequently, the beam emittance can degrade. A study on the plasma plumes formation presented here, where also a possible solution based on the capillary shape modifications proposed to optimize the density profile at the ends.
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