Laser probing of the plasma in the S-300 facility
Збережено в:
| Дата: | 2002 |
|---|---|
| Автори: | , , , |
| Формат: | Стаття |
| Мова: | English |
| Опубліковано: |
Національний науковий центр «Харківський фізико-технічний інститут» НАН України
2002
|
| Назва видання: | Вопросы атомной науки и техники |
| Теми: | |
| Онлайн доступ: | http://dspace.nbuv.gov.ua/handle/123456789/80301 |
| Теги: |
Додати тег
Немає тегів, Будьте першим, хто поставить тег для цього запису!
|
| Назва журналу: | Digital Library of Periodicals of National Academy of Sciences of Ukraine |
| Цитувати: | Laser probing of the plasma in the S-300 facility / Yu.G. Kalinin, V.A. Korel'skii, E.V. Kravchenko, A.Yu. Shashkov // Вопросы атомной науки и техники. — 2002. — № 4. — С. 193-195. — Бібліогр.: 13 назв. — англ. |
Репозитарії
Digital Library of Periodicals of National Academy of Sciences of Ukraine| id |
irk-123456789-80301 |
|---|---|
| record_format |
dspace |
| spelling |
irk-123456789-803012015-04-15T03:01:49Z Laser probing of the plasma in the S-300 facility Kalinin, Yu.G. Korel'skii, V.A. Kravchenko, E.V. Shashkov, A.Yu. Plasma diagnostics 2002 Article Laser probing of the plasma in the S-300 facility / Yu.G. Kalinin, V.A. Korel'skii, E.V. Kravchenko, A.Yu. Shashkov // Вопросы атомной науки и техники. — 2002. — № 4. — С. 193-195. — Бібліогр.: 13 назв. — англ. 1562-6016 PACS: 52.70.-m http://dspace.nbuv.gov.ua/handle/123456789/80301 en Вопросы атомной науки и техники Національний науковий центр «Харківський фізико-технічний інститут» НАН України |
| institution |
Digital Library of Periodicals of National Academy of Sciences of Ukraine |
| collection |
DSpace DC |
| language |
English |
| topic |
Plasma diagnostics Plasma diagnostics |
| spellingShingle |
Plasma diagnostics Plasma diagnostics Kalinin, Yu.G. Korel'skii, V.A. Kravchenko, E.V. Shashkov, A.Yu. Laser probing of the plasma in the S-300 facility Вопросы атомной науки и техники |
| format |
Article |
| author |
Kalinin, Yu.G. Korel'skii, V.A. Kravchenko, E.V. Shashkov, A.Yu. |
| author_facet |
Kalinin, Yu.G. Korel'skii, V.A. Kravchenko, E.V. Shashkov, A.Yu. |
| author_sort |
Kalinin, Yu.G. |
| title |
Laser probing of the plasma in the S-300 facility |
| title_short |
Laser probing of the plasma in the S-300 facility |
| title_full |
Laser probing of the plasma in the S-300 facility |
| title_fullStr |
Laser probing of the plasma in the S-300 facility |
| title_full_unstemmed |
Laser probing of the plasma in the S-300 facility |
| title_sort |
laser probing of the plasma in the s-300 facility |
| publisher |
Національний науковий центр «Харківський фізико-технічний інститут» НАН України |
| publishDate |
2002 |
| topic_facet |
Plasma diagnostics |
| url |
http://dspace.nbuv.gov.ua/handle/123456789/80301 |
| citation_txt |
Laser probing of the plasma in the S-300 facility / Yu.G. Kalinin, V.A. Korel'skii, E.V. Kravchenko, A.Yu. Shashkov // Вопросы атомной науки и техники. — 2002. — № 4. — С. 193-195. — Бібліогр.: 13 назв. — англ. |
| series |
Вопросы атомной науки и техники |
| work_keys_str_mv |
AT kalininyug laserprobingoftheplasmainthes300facility AT korelskiiva laserprobingoftheplasmainthes300facility AT kravchenkoev laserprobingoftheplasmainthes300facility AT shashkovayu laserprobingoftheplasmainthes300facility |
| first_indexed |
2025-07-06T04:16:06Z |
| last_indexed |
2025-07-06T04:16:06Z |
| _version_ |
1836869607332249600 |
| fulltext |
LASER PROBING OF THE PLASMA IN THE S-300 FACILITY
Yu.G. Kalinin, V.A. Korel'skii, E.V. Kravchenko, and A.Yu. Shashkov
Russian Research Center “Kurchatov Institut”, Kurchatov Square 1,
Moscow 123182, Russia
PACS: 52.70.-m
1. The S-300 eight-module generator, operating at a
current of up to 4 MA with a current rise time of 100 ns
and impedance of 0.15 Ohm, is destined for experiments
with high-temperature pulsed plasmas of light liners and
Z-pinches. Among a number of different diagnostics the
facility has been equipped by laser diagnostic setup too.
Laser probing (interferometry, shadow and the
schlieren photography, etc.) has long been a classic
method for diagnosing imploding plasmas. This method
allows one to study a plasma with a definite density
magnitude and gradients. However, to implement this
diagnostics in pulsed high-current generators, it is
necessary to solve a number of problems related to both
the design of the generators and the specific conditions
under which experiments are carried out: large distances
between the probing radiation source, the object under
study, and the image plane; the relatively small
dimensions of the object; and, finally, rigid requirements
to the synchronization between the probing laser pulse
and the current pulse through the load. In this paper, we
describe a system for the laser probing of the plasma in
the S-300 high-current generator [1]. In our opinion, the
system is fairly well suited for these conditions.
2. The diagnostic setup included the transmitting and
receiving laser components.
The receiving component, which was used to record
the shadow images of the plasma was mounted in the
facility room near the S-300 generator. It consisted of a
lens (f=1600mm) imaging the plasma with a
magnification factor of 2 and a camera equipped with a
set of filters and a photographic cassette. Optical wedges
with an angle of 1˚ were positioned near the focal plane of
the lens in order to separate the beams in the image plane
by a required distance. If needed, different schlieren
masks could be positioned in the focal plane of the lens.
For immobile objects, the resolution of the system in the
object plane was no worse than 35 line/mm.
The transmitting component was located in a separate
room; the distance between the laser system and the target
unit exceeded 18 m.
The first version of the transmitting component (Fig.1)
consisted of a YAG:Nd driving oscillator (DO), a three-
stage second-harmonic generator (SHO), and optical
delay lines. An electrooptical shutter was synchronized
with the current pulse of the S-300 generator. Each SHO
stage consisted of a single-pass amplifier, a LiNbO3
nonlinear crystal with the temperature-sensitive tuning to
the phase matching, and a Glan prism. After passing
through the prism, second-harmonic radiation arrived at
the optical delay line and, then, at a set of mirrors
directing this radiation onto the plasma object. Radiation
at the fundamental frequency, which was polarized
orthogonally to the second-harmonic radiation, passed
through the Glan prism without deflection. Then, it was
amplified and used to generate the second harmonic in the
next stage.
The energy in each probing beam was 20mJ, the
wavelength was 532 nm, the divergence was ~1 mrad, the
pulse duration was 10 ns, and the interval between pulses
was 25 ns.
With this scheme for the probing-beam generation, all
laser and nonlinear optical components operated under
radiation loads that were far below the limiting ones. This
substantially improved the reliability of the diagnostic
setup operation, so that we could adjust the entire
diagnostic system in the pulse-periodic mode with a
repetition rate of about 1Hz. This is particularly important
for experiments with large installations.
Figures 2 and 3 show plasma photographs of different
S-300 loads.
To increase both time and spatial resolution, the
second version laser setup has been elaborated (Fig.4). It
included a Q-switch TEM00 YAG:Nd DO with two laser
amplifiers and a stimulated Brillouin scattering (SBS)
compressor of the DO pulse. Phase conjugation and pulse
compression in various nonlinear media in the course of
SBS were studied in detail by many authors (see, e.g., [2-
7]) and have already been used in plasma diagnostics [8].
The backward scattered beam was deflected by a
polarizing deflector and was directed to a five second-
harmonic generators similar to those mentioned above
with LiNbO3 or KTP non-linear crystals. Second-
harmonic pulse energy was about 3-5 mJ. Five second-
harmonic beams were directed into S-300 output unit after
passing their own delay lines. Thus, this assembly
permitted to obtain five-frame shadow images of plasma
loads with exposure of 1ns and time delay between the
frames of 10 ns.
The diagnostic setup was adjusted in the pulse-periodic
mode at a repetition rate of 0.25-0.5 Hz.
Fig.5 shows shadow photographs of the different Z-
pinchs.
3. There are several reasons that may be responsible
for the formation of a shadow in photographs.
The first reason is the cutoff of the probe radiation in
plasma when the radiation frequency approaches the
plasma frequency ω0:
ω ≈ ω0 = (4πNee2 / m)1/2
For a beam with a wavelength of 532 nm, this occurs
at densities of Ne∼4·1021cm-3.
Problems of Atomic Science and Technology. 2002. № 4. Series: Plasma Physics (7). P. 193-195 193
Second, the probe radiation can be absorbed via
inverse bremsstrahlung (i.e., due to free-free transitions).
In this case, the attenuation of laser radiation is described
by Bouguer's law,
Iν = Iν0 exp(-θ⋅l)
where l is the distance passed by the probing beam and
the absorption coefficient θ is determined by the
expression [9]
θ =((C1Z2gNeNi)/(Te
1/2ν3))⋅(1 - exp(-hν/kTe)).
For kTe >>hν, wich is always satisfied in our
experiments, the absorption coefficient is described by the
formula
θ ≈ (C1h/k)⋅(ZgNi
2/Te
3/2ν2).
Here, C1=3.69∙108 cm-3·K1/2s-3, Z is the ion charge, g is the
Gaunt factor, Ne and Ni are the electron and ion densities,
respectively, ν is the probe-radiation frequency. From this
formula, we obtain the following expression for Ni:
Ni ≈ 7.5ν((θTe
3/2)/(Z3g))1/2
For the plasma under our conditions, we have
Ni>5·1018см-3.
It should be noted that, for a plasma of high Z
materials, the ion density estimated by this formula
depends weakly on the electron temperature. Indeed, we
have Ni ∼ (Te)3/4 / (Z(T))3/2, and the average ion charge
number Z is well approximated by the dependence Z ∼
(T)1/2. Calculations (see, e.g., [10]) show that, as Te
increases from 10 to 100 eV, Z increases from 6 to 20; in
this case, Ni at fixed θ changes by no more that 10%.
The third reason for the formation of a shadow in
photographs is the refraction of the probing beam in
plasma regions where the electron density gradient is so
large that the refracted rays fall outside the aperture angle
of the lens α =d/a, where d is the lens diameter and a is
the distance from the lens to the object. The deflection
angle and the electron-density gradient are related by the
formula [11]
∇Ne = - ε/(4.46⋅10-14λ2l)
where ε is the refraction angle, λ is the probing-radiation
wavelength, and l is the plasma length along the probing
beam. This formula is valid if the probing-wave
frequency is much higher than the frequency of electron
— ion (or electron—neutral) collisions ω>>ωei and much
higher than the electron cyclotron frequency,
ω>>ωe=(e∙H)/(m∙c) (here, H is the magnetic field, and m
is the electron mass), which is always satisfied under
experimental conditions.
For the given geometry of the diagnostic windows, the
plasma density gradient ∇Ne is no less than 3·1020cm-4.
From the characteristic plasma size observed, we can
estimate the electron density as Ne = 1020cm-3.
Consequently, for the tungsten plasma (Fig.4), the ion
density can be estimated as 2·1019cm-3 and, for other
loads, as 5·1019cm-3.
Hence, the formation of a shadow in photographs via
inverse bremsstrahlung absorption seems to be most
probable, at least, for a metal plasma. The appearance of a
shadow due to absorption was previously observed in
experiments on the heating of foils by focused electron
beams [12], as well as in experiments on the implosion of
highly emitting gas puffs [13]. This reason is dominant
under many experimental conditions.
The refraction angles detected by the schlieren method
(Fig.2b) lie in the range from 1 to 6 mrad, which
determines the range of detectable density gradients:
1019сm-4<∇Ne<5·1019сm-4. Taking into account the
characteristic plasma size, the electron density is
estimated at 1019см-3.
4. We thank P.I. Blinov for his help in adjustment of
the components of the diagnostic complex.
This study was supported by the Russian Foundation
for Basic Research (project no. 01-02-17359).
REFERENCES
1. A.S.Chernenko et al., in Proc. of the 11th Int. Conf. on
High-Power Particle Beams, Prague, 1996, p. 154
2. D.V.Vlasov, Zh. Eksp. Teor. Fiz., v.64, p.1986 (1973).
[Sov. Phys. JETP, 37, 1001 (1973)].
3. V.A.Gorbunov et al., Izv. Akad. Nauk SSSR, Ser.
Fiz., v.48, 1580 (1984).
4. R.R.Buzyalis et al., Kvantovaya Elektron. (Moscow),
v.12, 2024 (1985).
5. I.M.Bel'dyuginet al., Kvantovaya Elektron.
(Moscow), v.12, 2394 (1985).
6. V.Kh.Bagdasarov et al., Kvantovaya Elektron.
(Moscow), v.14, 1364 (1987).
7. V N.Belousov and Yu. K. Nizienko, Preprint No.
4707/7 (Inst. Of At. Energy, Moscow, 1988).
8. R.Alliaga-Rossel et al., in Proc. of the 4th Int. Conf. on
Dense Z-pinches, Vancouver, 1997.
9. A.N.Zaydel and G.V.Ostrovskaya, Laser Methods for
Plasma Research (Nauka, Leningrad, 1977).
10. D.Mosher, Phys. Rev. v.10, 2330 (1974).
11. E. P.Kruglyakov, Plasma Diagnostics (Atomizdat,
Moscow, 1973), issue. 3, p. 97.
12. Yu.M.Gorbulin et al., Preprint No. 4042/7 (Institute of
Atomic Energy, Moscow, 1984).
13. S.L.Bogolyubsky et al., in Proc. of the 7th Int.
Conf.on High-Power Beams, Karlsruhe, 1988,
p.1255.
FIGURE CAPTIONS
Fig.1. Optical scheme for generating three probing
beams (I, II, and III) with 25 ns delays between the
pulses:
1) DO, 2) amplifier, 3) nonlinear crystal for the
frequency doubling, and 4) Glan prism for separating the
beams at the fundamental and second harmonics. The
latter pass through the optical delay lines and are
directed into the S-300 generator.
194
Fig.2. (a) shadow photograph of the implosion of an
aluminum wire 110µm in diameter and 1cm in length at a
current through the load of 2MA. (b) schlieren
photographs of the implosion of a C2D4 fiber 30 µm in
diameter and 1.5 cm in length at a current of 1.7MA.
Schlieren masks allow the detection of the deflection
angles of the probing beams in the range from 1 to 6
mrad in all directions. Here and in subsequent figures,
numerals on the right from photographs show the delay
time (in ns) between the exposure and the current start.
Fig.3. Shadow photographs of two imploding wire arrays
composed of eighty tungsten wires 6µm in diameter. The
array diameter is 1 cm, its length is 1 cm, the current
through the load is 2.6 MA, and the current rise time is
~100 ns.
Fig.4. Optical scheme of the transmitting component of
the laser diagnostic setup for five-frame plasma probing:
1) YAG:Nd DO, 2), 8) isolators, 3) YAG:Nd amplifiers, 4)
lens (f = 0.9 m), 5) scattering CCl4 cell (l = 1.5 m), 6)
SHOs (LiNbO3), 7) Glan prisms, 9) mirror with a
reflection coefficient of 30%, 10) SHOs (KTP) and B)
Faraday rotator. Five beams pass through the optical
delay lines and are directed into the S-300 generator.
Fig.5. Five-frame shadow photographs of agar-agar Z-
pinches 5mm in diameter and 1cm in length. The current
through the load is 1.9MA (left frames) and 1.65MA
(right frames).
Fig.6. Five-frame shadow photographs of copper wire
120µm in diameter and 0.8cm in length at a current
through the load of 1.75MA (left frames) and 2.7MA
(right frames).
Problems of Atomic Science and Technology. 2002. № 4. Series: Plasma Physics (7). P. 193-195 195
Russian Research Center “Kurchatov Institut”, Kurchatov Square 1,
Moscow 123182, Russia
|