The effects of generating pulsed radiation by a long spark discharge are important for the development of lightning models and applications related to lightning protection. In experiments with a Marx ...generator simulating a lightning discharge, we detected the radiation in the form of a single ultrawideband electromagnetic pulse (UWB EMP) about 200 ps in duration, and rising time about 100 ps. UWB EMP generation occurs during the breakdown of a “rod–rod” 4 m long gap. Pulses of almost unipolar shape are observed in more than half of all positive discharges. EMP emission occurs before the main stage, and corresponds to the start of the upward leader from a grounded electrode. In negative discharges, pulses are also observed, but less frequently and with a smaller amplitude. The UWB EMPs, given their large amplitude (more than 100 V/m at a distance of 90 m from the discharge), can be considered as possible new lightning damage factors.
Plain Language Summary
A Marx generator with an operating voltage of several megavolts is used to simulate a lightning stroke of a grounded object. The generation of a short electromagnetic pulse (several hundreds of picoseconds long) has been detected during a breakdown of a long air gap using special electromagnetic probes. Such a pulse is observed in the majority of positive discharges in the “rod–rod” gap. Subnanosecond pulse can be regarded as possible new damage factor of lightning strokes.
Key Points
Marx generator allows studying generation of ultra‐wideband electromagnetic pulses (EMPs) by long spark discharges that model lightning
Single EMP about 200 ps duration is generated by 4‐m long spark discharge in a rod‐rod geometry
Pulses of almost unipolar shape with up to 200 V/m amplitude are observed at 90 m distance from more than half of all positive discharges
A precision measurement of the ratio RK of the rates of kaon leptonic decays K±→e±ν and K±→μ±ν with the full data sample collected by the NA62 experiment at CERN in 2007–2008 is reported. The result, ...obtained by analysing ∼150000 reconstructed K±→e±ν candidates with 11% background contamination, is RK=(2.488±0.010)×10−5, in agreement with the Standard Model expectation.
Laboratory modeling of ionospheric heating experiments Starodubtsev, M. V.; Nazarov, V. V.; Gushchin, M. E. ...
Journal of geophysical research. Space physics,
October 2016, 2016-10-00, 20161001, Letnik:
121, Številka:
10
Journal Article
Recenzirano
Turbulent plasma processes, such as those which occur in the Earth's ionosphere during ionospheric heating by powerful radio waves, were studied under laboratory conditions, and new physical models ...of small‐scale ionospheric turbulence are proposed as a result of these studies. It is shown here that the mechanism of small‐scale plasma filamentation can be connected with the thermal self‐channeling of Langmuir waves. During this process, Langmuir waves are guided by a plasma channel, which in turn is formed by the guided waves through a thermal plasma nonlinearity. The spectrum of the self‐guided Langmuir waves exhibits sidebands whose features are similar to stimulated electromagnetic emission. We present two mechanisms of sideband generation. The first mechanism can be observed during the formation of the plasma channel and is connected with the parametric shift in the frequency of the self‐channeling wave. The second mechanism is connected with the scattering of the self‐channeling wave on the low‐frequency eigenmodes of the plasma irregularity.
Key Points
Thermal self‐channeling of Langmuir waves is the main mechanism of small‐scale plasma filamentation
The spectrum of the self‐guided Langmuir waves exhibits spectral satellites similar to SEE features
The satellites are generated due to the parametric effects and due to the guided wave scattering
Observation of K+→π+π0π0γ decay Artamonov, A. V.; Bychkov, V. N.; Donskov, S. V. ...
The European physical journal. C, Particles and fields,
04/2024, Letnik:
84, Številka:
4
Journal Article
Recenzirano
Odprti dostop
The
K
+
→
π
+
π
0
π
0
γ
decay is observed by the OKA collaboration. About 60 events of the decay observed with signal:noise
≈
1
. The branching ratio obtained by normalization to
K
+
→
π
+
π
0
π
0
is ...measured to be
(
3.7
±
0.9
(
s
t
a
t
)
±
0.3
(
s
y
s
t
)
)
×
10
-
6
for
E
γ
∗
>
10
MeV
. The branching ratio,
γ
energy spectrum and angular distribution are consistent with ChPT prediction.
A high-statistics data sample of the
K
+
decays is recorded by the OKA collaboration. A missing mass analysis is performed to search for a light invisible pseudoscalar axion-like particle (ALP)
a
in ...the decay
K
+
→
π
+
π
0
a
. No signal is observed, and the upper limits for the branching ratio of the decay are calculated. The
90
%
confidence level upper limit changes from
2.5
·
10
-
6
to
2
·
10
-
7
for the ALP mass from 0 to 200 MeV/
c
2
, except for the region of
π
0
mass, where the upper limit is
4.4
·
10
-
6
.
The ducting of whistler waves by systems of small‐scale field‐aligned plasma density depletions is studied. Similarly to our previous paper (Zudin et al., 2019, https://doi.org/10.1029/2019ja026637), ...we carry out analytical calculations and numerical simulations for the parameters of an active experiment in which very low frequency whistler waves emitted by a ground‐based transmitter at a frequency of 18 kHz were received onboard the DEMETER satellite at 700 km above the SURA heating facility. Random‐sized density depletions with a level around 10%–20% and perpendicular sizes ranging from 10 m up to about 300 m are considered. The properties of ducted waves are determined by the perpendicular size of individual depletions. Particularly, depletions with a width of more then d0 ∼ 100 m form separate ducting structures, that is, coupled waveguides capable of exchanging energy by means of mode overlap. Depletions with a width of less than d0 ∼ 100 m form a common waveguide structure, whose properties are equivalent to those of a wider irregularity with a smoothed density profile. Two important differences are revealed in ducting properties of density depletions compared to density enhancements considered in Zudin et al. (2019, https://doi.org/10.1029/2019ja026637). First, depletions support highly oblique Gendrin mode waves, rather than quasi‐longitudinal whistlers as in the case of density enhancements. Second, the characteristic perpendicular size d0 ∼ 100 m of density depletions separating the regimes of “coupled waveguides” and of “equivalent ducting structure” with smoothed density profile is by an order of magnitude smaller than for density enhancements of the same 10–20% relative level.
Key Points
Small‐scale field‐aligned ionospheric plasma density depletions can serve as specific ducting structures for very low frequency whistlers
The ducting properties of systems from multiple small‐scale density depletions are studied both analytically and numerically
The ducting properties of density depletions and enhancements are compared
The transformation of a subnanosecond ultrawideband electromagnetic pulse (UWB EMP) in a large-volume transparent plasma has been demonstrated experimentally using a large-scale KROT plasma device. ...The column of the plasma generated in the device chamber has a length of more than 4 m and a diameter of more than 1 m. This allows one to implement the regime of quasiuniform ionization, which is necessary to simulate UWB EMP propagation through the ionosphere. It is shown that the length of the wave propagation path in the plasma is sufficient for dispersion transformation of the pulse retaining the envelope of its frequency spectrum.
Study of K+→π0e+νγ decay with OKA setup Polyarush, A. Yu; Akimenko, S. A.; Artamonov, A. V. ...
The European physical journal. C, Particles and fields,
02/2021, Letnik:
81, Številka:
2
Journal Article
Recenzirano
Odprti dostop
Results of a study of the
K
+
→
π
0
e
+
ν
γ
decay at OKA setup are presented. More than 32,000 events of this decay are observed. The differential spectra over the photon energy and the ...photon–electron opening angle in kaon rest frame are presented. The branching ratios, normalized to that of
K
e
3
decay are calculated for different cuts on
E
γ
∗
and
c
o
s
Θ
e
γ
∗
. In particular, the branching ratio for
E
γ
∗
>
30
MeV and
Θ
e
γ
∗
>
20
∘
is measured R =
B
r
(
K
+
→
π
0
e
+
ν
e
γ
)
B
r
(
K
+
→
π
0
e
+
ν
e
)
= = (0.587±0.010(
stat
.)±0.015(
syst
.))
×
10
-
2
, which is in a good agreement with ChPT
O
(
p
4
)
calculations.
The
T
-odd correlation
, which is the mixed product of the momenta of
,
, and γ in the system of rest of the kaon divided by
, has been measured in the
K
+
→ π
0
e
+
ν
e
γ radiative decay among 101 ...200 candidate events detected at the OKA setup. The asymmetry of the distribution in
is characterized by the ratio
, where
is the number of events with positive (negative) ξ. The value
= (+0.1 ± 3.9(stat.) ± 1.7(syst.)) × 10
–3
or
(90% C.L.) has been obtained.
A method for creating a pressure gradient by pulsed injection of air into a large vacuum chamber for laboratory simulation of plasma phenomena in a vertically nonuniform atmosphere is proposed. The ...dynamics of subsonic and transonic air flows at different background chamber pressures is studied. The feasibility of creating and detecting instantaneous pressure drops by more than two orders of magnitude on a scale of about one meter is shown. Features of the operation of the PMI-10-2 ionization gauge used for pressure measurements in a pulsed gas flow are discussed.
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