Experimental studies of some features of beam-plasma discharge initial stage
In case of gas pressure increasing, the plasma density rapidly increases at p=(1-2)*10⁻⁴ Torr, due to the beam-plasma discharge start (BPD). For fixed pressure above 2*10⁻⁴ Torr, the BPD start depends from the interaction length L and beam current I, with relation I∝ L⁻¹ . Measurements of the electr...
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| Опубліковано в: : | Вопросы атомной науки и техники |
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| Дата: | 2005 |
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Національний науковий центр «Харківський фізико-технічний інститут» НАН України
2005
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| Цитувати: | Experimental studies of some features of beam-plasma discharge initial stage / V.I. Butenko, B.I. Ivanov, V.P. Prishchepov // Вопросы атомной науки и техники. — 2005. — № 1. — С. 149-151. — Бібліогр.: 8 назв. — англ. |
Репозитарії
Digital Library of Periodicals of National Academy of Sciences of Ukraine| _version_ | 1859469946418888704 |
|---|---|
| author | Butenko, V.I. Ivanov, B.I. Prishchepov, V.P. |
| author_facet | Butenko, V.I. Ivanov, B.I. Prishchepov, V.P. |
| citation_txt | Experimental studies of some features of beam-plasma discharge initial stage / V.I. Butenko, B.I. Ivanov, V.P. Prishchepov // Вопросы атомной науки и техники. — 2005. — № 1. — С. 149-151. — Бібліогр.: 8 назв. — англ. |
| collection | DSpace DC |
| container_title | Вопросы атомной науки и техники |
| description | In case of gas pressure increasing, the plasma density rapidly increases at p=(1-2)*10⁻⁴ Torr, due to the beam-plasma discharge start (BPD). For fixed pressure above 2*10⁻⁴ Torr, the BPD start depends from the interaction length L and beam current I, with relation I∝ L⁻¹ . Measurements of the electron velocity distribution were performed using an UHF method and a multi-electrode probe. The start conditions are agreed with theoretical estimations.
При збільшенні тиску газу до (1-2)*10⁻⁴ Торр щільність плазми різко підвищуется завдяки пучково-плазмовому розряду (ППР). При фіксованому тиску вище 2*10⁻⁴ Торр початок ППР залежить від довжини взаємодії L та струму пучка I: I∝L⁻¹. Були проведені вимірювання розподілу електронів по швидкостям СВЧ методом та багатосітковим зондом. Умови старту ППР узгоджуються із теоретичними оцінками.
При увеличении давления газа до (1-2)*10⁻⁴ Торр плотность плазмы резко возрастает благодаря пучково- плазменному разряду (ППР). При фиксированном давлении выше 2*10⁻⁴ Торр начало ППР зависит от длины взаимодействия L и тока пучка I: I∝ L⁻¹. Проведены измерения распределения электронов по скоростям СВЧ методом и многосеточным зондом. Условия старта ППР согласуются с теоретическими оценками.
|
| first_indexed | 2025-11-24T08:18:09Z |
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| fulltext |
EXPERIMENTAL STUDIES OF SOME FEATURES OF BEAM-PLASMA
DISCHARGE INITIAL STAGE
V.I. Butenko, B.I. Ivanov, V.P. Prishchepov
NSC KIPT, Kharkov, 61108, Ukraine (E-mail: ivanovbi@kipt.kharkov.ua)
In case of gas pressure increasing, the plasma density rapidly increases at p=(1-2)*10-4 Torr, due to the beam-plasma
discharge start (BPD). For fixed pressure above 2*10-4 Torr, the BPD start depends from the interaction length L and
beam current I, with relation I∝ L-1. Measurements of the electron velocity distribution were performed using an UHF
method and a multi-electrode probe. The start conditions are agreed with theoretical estimations.
PACS: 52.40.Mj
1. EXPERIMENTS
Beam-plasma studies were described in many papers
and reviews (e. g., see [1]). Our paper is devoted to a par
ticular problem, namely, to the start conditions of beam-
plasma discharges (BPG). This problem was investigated
in [-]. In [2,3] BPD was studied for the cyclotron branch.
In this case the BPD start (for hydrogen gas) take place at
the pressure of (1-2)*10-4 Torr [2]; in [3] the BPD start
(for nitrogen and argon) take place at the pressure ~1*10-4
Torr. In [4-6], where BPD was studied for the plasma
branch, the discharge also starts at the pressure of (1-
2)*10-4 Torr. Our studies were performed on three differ
ent installations. It is interesting to note that all these ex
periments demonstrate the BPD start at the same critical
pressure, pcr=(1-2)*10-4 Torr. This phenomenon requires
further investigations and explanations.
Parameters of our first installation (see Fig. 1): a
pulsed axial electron beam of 0-12 keV, 0-3 A, 10 mm di
ameter; pulse duration 25 mks, a longitudinal magnetic
field of 0,1-1 kOe; an interaction length is 40 cm.
Fig. 1. 1-15 kV rectifier, 2-pulse forming line, 3-start de
vice, 4-400 V rectifier...7-HF oscillator…12-cathode, 13-
anode, 14-collector, 15-quartz tube, 16-HF cavity
In case of increasing gas pressure (air) up to 10-4 Torr,
the BPG starts, and the electron density quickly rises from
2.7*109 cm-3 to 1.1*1010 cm-3 (Fig. 2).
Fig. 2. Frequency shift for a HF-cavity vs. pressure for
10 keV beam (∆f=1 MHz corresponds to n=2.7*109 cm-3)
The electron distribution function of BPD was mea
sured at 2nd installation, see Fig. 3. The electron beam was
created by a gun consisting of a LaB6 cathode (11) and a
mesh anode (12), with the following parameters:
Fig. 3. Setup of 2nd installation
DC beam voltage U~10-1000 V, current I~1-100 mA,
beam diameter 2a =10 mm, magnetic field H variable
between 0 and 1 kOe , magnetic field inhomogenity 1 %.
The beam was shot down the axis of a quartz tube 30 mm
in diameter, which was evacuated down to pressures of
the order of 10-6 Torr. A cavity operated in the E010 mode
(13) was mounted coaxial with the tube and served to
measure electron density, together with an axially
overmode helical resonator (14) which was used for the
measurement of the distribution of electrons over axial
velocity. The parameters of the helical resonator are: I.D.
of metallic screen 2b=102 mm, height h=300 mm,; helix
I.D. 2c=33 mm, helix pitch 17 mm. The resonator was
excited via a coupling loop from a generator (2)
delivering 10 mW at the resonant frequency f=1750 MHz,
vph/c=0.4, and k3=0.8 cm-1. The microwave power
transmitted through the resonator was registered with a
receiver (5) and oscilloscope (9). The magnetic field was
varied linearly in time, by means of a sawtooth generator
(6). The microwave power transmitted through the
resonator was displayed on the scope screen vs. magnetic
field.
We have simultaneously measured the distribution
function by means of the multi-electrode probe. To
measure the energy distribution by means of the retarding
potential method we have to differentiate collector current
with respect to analyzing grid voltage: f(W||)∝ dIk /dUe.
We have used a setup permitting to carry out such
differentiation and to display the distribution function on
the scope screen. Fig. 4 (oscillograms 2,4,6) shows these
electron energy distribution function in the beam-plasma
discharge (lower trace). The upper trace is the variation of
voltage on the analyzing grid. On the left are the oscil
lograms (1, 3, 5) of microwave power transmitted through
the resonator vs. magnetic field (lower trace). The upper
Problems of Atomic Science and Technology. 2005. № 1. Series: Plasma Physics (10). P. 149-151 149
mailto:ivanovbi@kipt.kharkov.ua
trace is the variation of magnetic field strength. The
parameter is the residual gas pressure. As the pressure is
increased the beam cyclotron absorption peak merges
with the plasma peak, and a characteristic plateau is
formed in the distribution function (see oscillograms 5,6).
Fig. 5 a,b is a comparison of electron distribution
measurements in the initial stage of the beam-plasma
discharge, by the microwave method and the retarding
potential method. The oscillograms (1) are [P(H)]1/2
curves used to calculate f(v||) curves (2) and the
oscillograms (3) are distribution functions f(W||) obtained
by the retarding potential method. In the initial stage of
the discharge both methods give like results.
Fig. 4. Dependence of
transmitted microwave power
on magnetic field strength, and
the electron distribution
function, measured with the
retarding potential method
(U = 300 V, I = 10 mA,
H = 400 - 700 Oe;
1,2 - n = 2.8*108 cm-3;
3,4 -n=4.6*108 cm-3;
5,6-n=8.3*108 cm-3)
Fig. 5. The function [P(H)]1/2 (1) and the electron
distribution function, measured with the microwave
method (2) and the retarding potential method (3).
(U=300 V, I=10 mA, H = 400-700 Oe, U3= -(0-600) V.
a) n =108 cm-3 ; b) n = 3.7*108 cm-3)
The scheme of the 3rd experimental set is presented in
Fig. 6. Electron beam was created by electron gun with
LaB6 cathode (1) of 3 cm diameter and anode grid (2).
The DC energy and current of the beam were changed
in the interval 0-10 keV, 0-60 mA. Through the pipe (3)
providing pressure jump, electron beam was injected into
interaction chamber (4) of 150 cm length and 15 cm
diameter. Inside of it there are placed: an open 8 mm
resonator (5) for plasma density measurement, HF-probes
(6),
a movable metallic screen beam collector (7). Interaction
chamber was placed in solenoid creating magnetic field
up to 1500 Oe. The HF-probes were two double-wound
magnetic loops, oriented on azimuthal and longitudinal
components of HF magnetic field. Movable copper screen
of 13 cm diameter provides the length changing of the
beam-plasma interaction region. Plasma was produced
during interaction of electron beam with neutral gas.
H0
12345 6 7
to pump
Fig. 6. 3rd experimental set (1, 2 - cathode and anode of
electron gun, 3-pressure jump pipe, 4-interaction chamber,
5-resonator, 6-HF-probes, 7-movable beam collector
2 4 6 8
0
4
8
12
16
n,
1
09 c
m
-3
p, 10-4 Torr
Fig. 7. Plasma density dependence vs. gas pressure
(bottom - collision ionization, top – ionization by BPD)
In Fig. 7 the plasma density on dependence of gas
pressure is presented. Here the BPD starts at p=2*10-4 Torr.
The start current Ist dependence on the interaction
length L is shown in Fig. 8; as it is follows, Ist∝AL-1.
1 2 3
0
10
20
30
40
I,
m
A
1/L, m-1
Fig. 8. Start current vs. interaction length in form of L-1
The growth rates of excited oscillations were found
near the plasma frequency: ω ≤ωp and the cyclotron
frequency: ω ≥ ωH. In Fig. 9 series of spectra are
presented for the beam current values. Magnetic field is
700 Oe, beam energy 2 keV, interaction length 122 cm,
gas pressure 5⋅10-4 Torr. It is seen that spectrum has two
maxima corresponding to frequency bands for case of ωp
< ωH.
150
Fig. 9. Oscillations spectra vs. beam current I (mA)=
12 (1), 15 (2), 20 (3), 30 (4), 40 (5), 50 (6), 60 (7)
These pictures are shown that single mode generation
near ωp starts at I1=12 mA, several frequencies start at
I2=15 mA, the continuous spectrum near ωp appears at
I3=30 mA, a frequency near ωH arises at I4=40 mA and
continuous spectrum near ωH is formed at I5=50 mA.
2. DISCUSSION
As is known, at the gas pressure of 10-6-10-5 Torr, the
neutralization of the electron beam by the ions (created by
gas ionization) can occur. At increasing the gas pressure
up to (1-2)*10-4 Torr, the secondary electrons are suffi
ciently accumulated and the BPD starts, see Figs. 1, 4, 5,
7. In 3rd experiment it was shown (Fig. 9) that the BPD
starts at the plasma branch, as in [4-7] also.
We had measured the electron distribution function
for longitudinal velocities and energies. From common
notions, it is evident that dispersion of longitudinal veloc
ities of secondary electrons can be large. By measure
ments, it was determined that, before starting BPD, the
secondary electrons have the longitudinal mean energy
~10 eV, see Fig. 5a. This indicates possibility for kinetic
type of beam-plasma instability at the BPD start. Really,
the BPD starts such a way that the beam current magni
tude is vice versa to the length of interaction distance: I∝
L-1, see Fig. 8. There is an evidence that the instability has
the kinetic increment γ ∝ nb ∝ I. In fact, the BPD start de
pends on EM field amplitude increase along the system
length to reach the critical value Ecr for the discharge:
Ecr=E0expγL. So, if γL and IL are const, then γ ∝ I∝ nb.
The advanced BPD stage was theoretically studied in
[8] where particle balance condition takes in account the
secondary electrons accumulation (due to gas ionization
by the electron beam), and their losses due to ambipolar
diffusion (seen as main losses) and recombination. Unfor
tunately, at the BPD start conditions, for pressure of 10-
4 Torr and low plasma density, the diffusion equation is
invalid because the electron free path is sufficiently more
then lengths of experimental systems, and the ion free
path is sufficiently more then their transverse sizes.. In
this case, for calculation of critical pressure pcr we pro
pose the balance equation for ions created by the electron
beam and ones going away across the magnetic field
through the lateral electron beam surface, whereas sec
ondary electrons going away along the magnetic field:
πa2nbvbσin0L=2πaLniv⊥i , (1)
where a – beam radius, nb – electron beam density, vb –
beam velocity, σi – ionization cross-section, n0 – neutral
particle density, L – interaction length, ni – ion concentra
tion, v⊥i – ion transverse velocity. Supposing that ni=ne
(the quasi-neutrality condition), ne=nb (the condition of
maximum of the instability increment), and
n0=3.5*1016 p Torr, we receive relation for pcr in the form:
pcr=2v⊥i / 3.5*1016avbσi (2)
The results of calculations are shown in the Table
(here we use W⊥i≈1 eV). The amount of calculated pcr
(pcr~10-4 Torr) coincides with experimental data for the
plasma branch but not coincides for the cyclotron one
[2,3]. Latter may be explained as if ionization efficiency
at the cyclotron branch is sufficiently increased.
Refer
ences
Gas Wb,
keV
a,
cm
σi,
cm2
pcr. exp.
mTorr
pcr..calc.
mTorr
[2] H2 0.58 0.13 3.9*10-17 0.2 7.8
[3] H2 4.5 0.20 7.3*10-18 2.0 9.2
[3] N2 4.5 0.20 2.5*10-17 ~0.1 0.59
[4] Ar 0.50 0.15 1.8*10-16 0.2 0.36
[5] Air 1.2 0.65 8.1*10-17 0.2 0.19
[6] Ar 4.0 1.15 3.4*10-17 0.1 0.09
1 exp Air 10 0.50 1.4*10-17 0.1 0.46
2 exp Air 0.30 0.50 2.2*10-16 0.2 0.12
3 exp Air 2.0 1.50 5.3*10-17 0.2 0.10
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ЭКСПЕРИМЕНТАЛЬНОЕ ИССЛЕДОВАНИЕ НЕКОТОРЫХ СВОЙСТВ НАЧАЛЬНОЙ СТАДИИ ПУЧ
КОВО-ПЛАЗМЕННОГО РАЗРЯДА
В.И. Бутенко, Б.И. Иванов, В.П. Прищепов
При увеличении давления газа до (1-2)*10-4 Торр плотность плазмы резко возрастает благодаря пучково-
плазменному разряду (ППР). При фиксированном давлении выше 2*10-4 Торр начало ППР зависит от длины
взаимодействия L и тока пучка I: I∝L-1. Проведены измерения распределения электронов по скоростям СВЧ ме
тодом и многосеточным зондом. Условия старта ППР согласуются с теоретическими оценками.
151
ЕКСПЕРИМЕНТАЛЬНЕ ДОСЛІДЖЕННЯ ДЕЯКИХ ВЛАСТИВОСТЕЙ ПОЧАТКОВОЇ СТАДІЇ ПУЧ
КОВО-ПЛАЗМОВОГО РОЗРЯДУ
В.І. Бутенко, Б.І. Іванов, В.П. Прищепов
При збільшенні тиску газу до (1-2)*10-4 Торр щільність плазми різко підвищуется завдяки пучково-пла
змовому розряду (ППР). При фіксованому тиску вище 2*10-4 Торр початок ППР залежить від довжини взаємодії
L та струму пучка I: I∝L-1. Були проведені вимірювання розподілу електронів по швидкостям СВЧ методом та
багатосітковим зондом. Умови старту ППР узгоджуються із теоретичними оцінками.
152
|
| id | nasplib_isofts_kiev_ua-123456789-78947 |
| institution | Digital Library of Periodicals of National Academy of Sciences of Ukraine |
| issn | 1562-6016 |
| language | English |
| last_indexed | 2025-11-24T08:18:09Z |
| publishDate | 2005 |
| publisher | Національний науковий центр «Харківський фізико-технічний інститут» НАН України |
| record_format | dspace |
| spelling | Butenko, V.I. Ivanov, B.I. Prishchepov, V.P. 2015-03-24T08:22:26Z 2015-03-24T08:22:26Z 2005 Experimental studies of some features of beam-plasma discharge initial stage / V.I. Butenko, B.I. Ivanov, V.P. Prishchepov // Вопросы атомной науки и техники. — 2005. — № 1. — С. 149-151. — Бібліогр.: 8 назв. — англ. 1562-6016 PACS: 52.40.Mj https://nasplib.isofts.kiev.ua/handle/123456789/78947 In case of gas pressure increasing, the plasma density rapidly increases at p=(1-2)*10⁻⁴ Torr, due to the beam-plasma discharge start (BPD). For fixed pressure above 2*10⁻⁴ Torr, the BPD start depends from the interaction length L and beam current I, with relation I∝ L⁻¹ . Measurements of the electron velocity distribution were performed using an UHF method and a multi-electrode probe. The start conditions are agreed with theoretical estimations. При збільшенні тиску газу до (1-2)*10⁻⁴ Торр щільність плазми різко підвищуется завдяки пучково-плазмовому розряду (ППР). При фіксованому тиску вище 2*10⁻⁴ Торр початок ППР залежить від довжини взаємодії L та струму пучка I: I∝L⁻¹. Були проведені вимірювання розподілу електронів по швидкостям СВЧ методом та багатосітковим зондом. Умови старту ППР узгоджуються із теоретичними оцінками. При увеличении давления газа до (1-2)*10⁻⁴ Торр плотность плазмы резко возрастает благодаря пучково- плазменному разряду (ППР). При фиксированном давлении выше 2*10⁻⁴ Торр начало ППР зависит от длины взаимодействия L и тока пучка I: I∝ L⁻¹. Проведены измерения распределения электронов по скоростям СВЧ методом и многосеточным зондом. Условия старта ППР согласуются с теоретическими оценками. en Національний науковий центр «Харківський фізико-технічний інститут» НАН України Вопросы атомной науки и техники Plasma electronics Experimental studies of some features of beam-plasma discharge initial stage Експериментальне дослідження деяких властивостей початкової стадії пучково-плазмового розряду Экспериментальное исследование некоторых свойств начальной стадии пучково-плазменного разряда Article published earlier |
| spellingShingle | Experimental studies of some features of beam-plasma discharge initial stage Butenko, V.I. Ivanov, B.I. Prishchepov, V.P. Plasma electronics |
| title | Experimental studies of some features of beam-plasma discharge initial stage |
| title_alt | Експериментальне дослідження деяких властивостей початкової стадії пучково-плазмового розряду Экспериментальное исследование некоторых свойств начальной стадии пучково-плазменного разряда |
| title_full | Experimental studies of some features of beam-plasma discharge initial stage |
| title_fullStr | Experimental studies of some features of beam-plasma discharge initial stage |
| title_full_unstemmed | Experimental studies of some features of beam-plasma discharge initial stage |
| title_short | Experimental studies of some features of beam-plasma discharge initial stage |
| title_sort | experimental studies of some features of beam-plasma discharge initial stage |
| topic | Plasma electronics |
| topic_facet | Plasma electronics |
| url | https://nasplib.isofts.kiev.ua/handle/123456789/78947 |
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