Effect of negative shift of metalhydride cathode on the emission of H⁻ ions from penning discharge
On the basis of numerical calculations, the experimental results obtained by the authors in the study of the source of negative hydrogen ions of the Penning type with a metal hydride cathode are explained. It was shown that the yield of negative ions depends on the potential at the metal hydride cat...
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Національний науковий центр «Харківський фізико-технічний інститут» НАН України
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Sereda, I. Tseluyko, A. Hrechko, Ya. 2023-12-03T14:50:24Z 2023-12-03T14:50:24Z 2019 Effect of negative shift of metalhydride cathode on the emission of H⁻ ions from penning discharge / I. Sereda, A. Tseluyko, Ya. Hrechko // Problems of atomic science and technology. — 2019. — № 4. — С. 113-115. — Бібліогр.: 12 назв. — англ. 1562-6016 PACS: 52.80.Sm https://nasplib.isofts.kiev.ua/handle/123456789/195191 On the basis of numerical calculations, the experimental results obtained by the authors in the study of the source of negative hydrogen ions of the Penning type with a metal hydride cathode are explained. It was shown that the yield of negative ions depends on the potential at the metal hydride cathode and is determined by the temperature of the plasma electrons. The dependence of this potential on the electron temperature is calculated numerically to ensure the maximum current of negative ions. На основі чисельних розрахунків пояснені експериментальні результати, які отримані авторами при дослідженні джерела негативних іонів водню типу Пеннінга з металогідридним катодом. Показано, що вихід негативних іонів залежить від потенціалу на металогідридному катоді і визначається температурою електронів плазми. Залежність цього потенціалу від температури електронів розраховується чисельно для забезпечення максимального струму негативних іонів. На основе численных расчетов объяснены экспериментальные результаты, полученные авторами при исследовании источника отрицательных ионов водорода типа Пеннинга с металлогидридным катодом. Показано, что выход отрицательных ионов зависит от потенциала на металлогидридном катоде и определяется температурой электронов плазмы. Зависимость этого потенциала от температуры электронов рассчитывается численно для обеспечения максимального тока отрицательных ионов. en Національний науковий центр «Харківський фізико-технічний інститут» НАН України Вопросы атомной науки и техники Gas and plasma-beam discharges and their applications Effect of negative shift of metalhydride cathode on the emission of H⁻ ions from penning discharge Вплив від’ємного зсуву металогідридного катода на емісію іонів Н⁻ з розряду пеннінга Влияние отрицательного смещения металлогидридного катода на эмиссию ионов Н⁻ из разряда пеннинга Article published earlier |
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Digital Library of Periodicals of National Academy of Sciences of Ukraine |
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DSpace DC |
| title |
Effect of negative shift of metalhydride cathode on the emission of H⁻ ions from penning discharge |
| spellingShingle |
Effect of negative shift of metalhydride cathode on the emission of H⁻ ions from penning discharge Sereda, I. Tseluyko, A. Hrechko, Ya. Gas and plasma-beam discharges and their applications |
| title_short |
Effect of negative shift of metalhydride cathode on the emission of H⁻ ions from penning discharge |
| title_full |
Effect of negative shift of metalhydride cathode on the emission of H⁻ ions from penning discharge |
| title_fullStr |
Effect of negative shift of metalhydride cathode on the emission of H⁻ ions from penning discharge |
| title_full_unstemmed |
Effect of negative shift of metalhydride cathode on the emission of H⁻ ions from penning discharge |
| title_sort |
effect of negative shift of metalhydride cathode on the emission of h⁻ ions from penning discharge |
| author |
Sereda, I. Tseluyko, A. Hrechko, Ya. |
| author_facet |
Sereda, I. Tseluyko, A. Hrechko, Ya. |
| topic |
Gas and plasma-beam discharges and their applications |
| topic_facet |
Gas and plasma-beam discharges and their applications |
| publishDate |
2019 |
| language |
English |
| container_title |
Вопросы атомной науки и техники |
| publisher |
Національний науковий центр «Харківський фізико-технічний інститут» НАН України |
| format |
Article |
| title_alt |
Вплив від’ємного зсуву металогідридного катода на емісію іонів Н⁻ з розряду пеннінга Влияние отрицательного смещения металлогидридного катода на эмиссию ионов Н⁻ из разряда пеннинга |
| description |
On the basis of numerical calculations, the experimental results obtained by the authors in the study of the source of negative hydrogen ions of the Penning type with a metal hydride cathode are explained. It was shown that the yield of negative ions depends on the potential at the metal hydride cathode and is determined by the temperature of the plasma electrons. The dependence of this potential on the electron temperature is calculated numerically to ensure the maximum current of negative ions.
На основі чисельних розрахунків пояснені експериментальні результати, які отримані авторами при дослідженні джерела негативних іонів водню типу Пеннінга з металогідридним катодом. Показано, що вихід негативних іонів залежить від потенціалу на металогідридному катоді і визначається температурою електронів плазми. Залежність цього потенціалу від температури електронів розраховується чисельно для забезпечення максимального струму негативних іонів.
На основе численных расчетов объяснены экспериментальные результаты, полученные авторами при исследовании источника отрицательных ионов водорода типа Пеннинга с металлогидридным катодом. Показано, что выход отрицательных ионов зависит от потенциала на металлогидридном катоде и определяется температурой электронов плазмы. Зависимость этого потенциала от температуры электронов рассчитывается численно для обеспечения максимального тока отрицательных ионов.
|
| issn |
1562-6016 |
| url |
https://nasplib.isofts.kiev.ua/handle/123456789/195191 |
| citation_txt |
Effect of negative shift of metalhydride cathode on the emission of H⁻ ions from penning discharge / I. Sereda, A. Tseluyko, Ya. Hrechko // Problems of atomic science and technology. — 2019. — № 4. — С. 113-115. — Бібліогр.: 12 назв. — англ. |
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| fulltext |
ISSN 1562-6016. ВАНТ. 2019. №4(122) 113
EFFECT OF NEGATIVE SHIFT OF METALHYDRIDE CATHODE
ON THE EMISSION OF H– IONS FROM PENNING DISCHARGE
I. Sereda, A. Tseluyko, Ya. Hrechko
V.N. Karazin Kharkiv National University, Kharkiv, Ukraine
E-mail: igorsereda@karazin.ua
On the basis of numerical calculations, the experimental results obtained by the authors in the study of the source
of negative hydrogen ions of the Penning type with a metal hydride cathode are explained. It was shown that the
yield of negative ions depends on the potential at the metal hydride cathode and is determined by the temperature of
the plasma electrons. The dependence of this potential on the electron temperature is calculated numerically to en-
sure the maximum current of negative ions.
PACS: 52.80.Sm
INTRODUCTION
The development of negative ion sources for high-
power ion beams is a significant challenge for world
science and are pursued in fusion research institutes
worldwide, e.g., IPP Garching [1] (Germany), Consor-
zio RFX [2] (Padova, Italy), JAEA [3, 4] and NIFS [5]
(Japan). This is due to the neutralization efficiency of
negative hydrogen ions, that remains acceptable at high-
er kinetic energy and is nearly independent on beam
energy above 100 keV/nucleon. Since high heating
power (up to 33 MW) of atomic beams are required in
fusion research, the need for producing intense negative
ion beams becomes urgent. The main problem that aris-
es here is the insufficient current of negative ion beams
for heating the plasma in tokamaks up to the burning
temperature. For instance, in ITER, negative ion current
should be more than 40 A to produce intense neutral
beam with reasonable pulse duration for effective plas-
ma heating.
Another application area of negative ions beams is
producing a number of medical radionuclides used in
diagnosis and contact radiation therapy [6]. Beams of
high energy (hundreds MeV) and small average current
(from 20 µA to several A) are used here depending on
the type of therapy [6]. All these force the intensive
development of negative hydrogen ion sources, which
are traditionally based on two types of processes: H–
formation in the plasma volume [7], and on surfaces [8].
In the first case negative ions are formed by dissociative
attachment of slow electrons to vibrational-
ly/ rotationally excited hydrogen molecules H2
* and H–
current usually does not exceed tens mA at several kW
of a discharge power in a pulse. In the second one – by
the interaction between hydrogen plasma and caesiated
surface facing the plasma. Using cesium sufficiently
increases the intensity of negative ions, but complicates
ion source operation and requires a careful stabilization
of cesium injection and discharge parameters [8]. These
sources are usually set separately from acceleration
complexes to avoid operational risks associated with
cesium flow. Maximum H– current on the level of 2 A
has been achieved there. On the contrary, volume
sources possess much low intensity of H– beam (tens
mA), but they are more reliable, compact and environ-
mentally friendly (cesium free). They could be inserted
inside an acceleration complex that sufficiently reduces
dimensions and cost of the equipment. Achieved low
current of negative ions is caused by hydrogen pressure
limitation in the source volume, because raising it more
than 10-2 Torr increases the destruction processes of
negative ions [7]. So, if one could increase the intensity
of H– beam from volume source, it would be the best
way to produce high-power negative ion beams for fu-
sion and accelerators.
In our previous work we obtained the H– ion current
of 10 μA at an input power of 6 W from Penning type
ion source with metal-hydride cathode [12]. Maximum
extracted current was observed at electrical bias of met-
al-hydride cathode. The purpose of the paper is to ex-
plain carried out results and to giveadvices on increas-
ing the extracted current.
1. EXPERIMENTAL SETUP
Experimental results [12] were obtained on a device
shown in Fig. 1. It shows a schematic illustration of the
Penning type H– ion source with metal hydride cathode
and electromagnetic filter.
Fig. 1. The scheme of the Penning type H– ion source:
1 – metal hydride cathode; 2 – cathode-holder with wa-
ter-cool; 3 – thermocouple; 4 – anode; 5 – copper cath-
ode-reflector with an aperture; 6 – reflecting grid;
7 – electrons collector; 8 – filter magnetic coil;
9 – H– ion collector, Hzo0 – main axial Penning magnet-
ic field (Hzo0 = 0…1000 Oe)
Hydrogen plasma was formed inside a tubular an-
ode 4 and between a metal hydride cathode 1 and a cop-
per cathode-reflector 5. Behind the central aperture in
the cathode-reflector 5 an electromagnetic filter was set.
It consists of a grid 6 for positive ions reflecting, a mag-
netic coil 8 for electrons diverting, a collector of divert-
ed electrons 7 and a collector of extracted axial beam of
H– ions 9.
The metal hydride cathode 1 was produced from hy-
dride-forming alloy Zr50V50. The quantity of hydrogen
stored in the cathode is ~ 9×10-3 m-3 under normal at-
Ud
+3kV
1
4 5
6
7
8
9
Icol
z
Hz0
Hzo0
z,cm 0 1 2 3
4 5 6 7 8 9
Hcoil
-UMH
+UC
water
2
3
ISSN 1562-6016. ВАНТ. 2019. №4(122) 114
mospheric conditions. For pressure being stabilized, the
metal hydride cathode had got a water-cool and its tem-
perature was not exceed 20°С, that much lower than the
temperature of thermal destruction of hydride phases.
Therefore, H2
* desorption was determined only by a dis-
charge current and is provided mainly by ion-stimulated
processes from the surface of metal hydride [11].
2. RESULTS AND DISCUSSION
Fig. 2 shows the experimental results [12] of the to-
tal collector current (Icol) of outgoing particles behavior
depending on the value of metal hydride cathode bias.
The growth of axial total current with an increase in
negative bias on the metal hydride cathode (UMH) may
be attributed to the repulsive force to the electrons by
the extra cathode potential.
0 50 100 150 200 250
-100
-80
-60
-40
-20
0
I co
l ,
µ
A
-UMH, V
Fig. 2. The dependence of total current on negative
electric bias on the metal hydride cathode at Ud = 4 kV,
Hzo0 = 1000 Oe, p = 5×10-6 Torr
On the other hand, an increase in the H– ion current
(
H
I − ) (Fig. 3) is observed only to the values of UMH of
-50 V.
0 50 100 150 200 250
-10
-9
-8
-7
-6
-5
-4
-3
-2
-1
0
Ifit
IH -
I H
-- ,
µ
A
-UMH , V
Fig. 3. The dependence of H– ion current on negative
electric bias on the metal hydride cathode at Ud = 4 kV,
Hzo0 = 1000 Oe, p = 5×10-6 Torr
To explain this behavior, we assume that the elec-
tron concentration near the cathode is described by the
Boltzmann distribution. Thus, the dependence of
H
I −
current on UMH can be approximately described as:
( )MHUb
H eaII −=− 0 , (1)
where I0 is the current of outgoing charged particles,
which we do not associate here with any particular
physical process, but simply approximate it up to a con-
stant i to fit the experimental curve Icol in Fig. 2.
( )2
0 0fit MHI I i c U U= − = − + . (2)
This additional term i is related to the initial current
of negatively charged particles from the whole cell vol-
ume at UMH = 0 and was not included in the equation
(1) because it concerns only the cathode region.
Substituting the following values of a = 3.85,
b = 0.0237, c = 0.001, i = 25, and U0 = 40 one can be
sure of the good match of calculations (dot curve) with
experiment (solid curve) in Fig. 3 at |UMH| ≤ 50 V. So,
an increase in the H– ion current is due to the growth of
the total collector current.
The coincidence of the H– yield maximum with the
calculated curve is a result of the parameter a in Eq. (1)
fit and does not help as physical interpretation. But the
factor b is responsible for the inflection point of the
curve
H
I − in Fig. 3 and depends on the temperature of
plasma electrons (Te). If the factor eb
kTe
= , one could
see, that Te should be 42 eV, which is in good agree-
ment with experiments carried out in [11]. Higher val-
ues of b correspond to a decrease in Te and a shift of the
inflection point towards smaller values of |UMH|. One
can see this dependence from Fig. 4, which is calculated
from Eq. (2).
0 50 100 150
0
20
40
60
80
100
T e ,
e
V
-UMH, V
Fig. 4. The dependence of metal-hydride electric bias
on temperature of plasma electrons
A further significant decline in the calculated
H
I −
curve (dot curve) is obviously due to electrons depletion
in the cathode region reducing the rate of the dissocia-
tive electron attachment. Since in our experiments the
reduction of H– current (solid line) is not so strong, as it
predicted by Boltzmann distribution, we suppose that at
least three more physical phenomena are responsible for
the
H
I − curve behavior in Fig. 3. These are secondary
ion-electron emission, which slows down the depletion
of electrons, reduction in the efficiency of accelerated
electron dissociative attachment to H2
* molecules and
the destructive impact of energetic electrons on H– ions.
The dissociative attachment rate coefficients can be
as high as 10-8 cm3⋅s-1 at Te ≈ 1…2 eV when the mole-
cules are in the highest vibrational states [7]. But an
ISSN 1562-6016. ВАНТ. 2019. №4(122) 115
increase in the electron temperature even to 5 eV leads
to a decrease in the rate coefficients by 4 orders of mag-
nitude. So, high bias supply on metal hydride UMH can
sufficiently reduce the efficiency of electron dissocia-
tive attachment to H2
* molecules. Destructive impact of
accelerated electrons on H– ions appears only at high
plasma density ne > 1017m-3 [7] that much higher, than
in our experiments (ne = 3×1015 m-3) [17]. Thus, the
maximum H– yield is apparently due to the effect of
these competing processes.
CONCLUSIONS
Thus, the current of negative ions depends on the
potential at the metal-hydride cathode and is determined
by the temperature of the plasma electrons. To increase
the H– current one should supply a negative potential on
metal hydride cathode, with sufficient values to deflect
plasma electrons. In our experiments Te ≈ 40 eV, and
the maximum value of H– current is achieved by apply-
ing a negative bias to 50 V. The higher values of electric
bias leads to decreasing in the efficiency of H– ions
formation due to electrons depletion in the cathode re-
gion and reduction in the dissociative attachment rate
coefficients.
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Article received 17.05.2019
ВЛИЯНИЕ ОТРИЦАТЕЛЬНОГО СМЕЩЕНИЯ МЕТАЛЛОГИДРИДНОГО КАТОДА
НА ЭМИССИЮ ИОНОВ Н– ИЗ РАЗРЯДА ПЕННИНГА
И. Середа, А. Целуйко, Я. Гречко
На основе численных расчетов объяснены экспериментальные результаты, полученные авторами при ис-
следовании источника отрицательных ионов водорода типа Пеннинга с металлогидридным катодом. Пока-
зано, что выход отрицательных ионов зависит от потенциала на металлогидридном катоде и определяется
температурой электронов плазмы. Зависимость этого потенциала от температуры электронов рассчитывает-
ся численно для обеспечения максимального тока отрицательных ионов.
ВПЛИВ ВІД’ЄМНОГО ЗСУВУ МЕТАЛОГІДРИДНОГО КАТОДА
НА ЕМІСІЮ ІОНІВ Н– З РОЗРЯДУ ПЕННІНГА
І. Середа, О. Целуйко, Я. Гречко
На основі чисельних розрахунків пояснені експериментальні результати, які отримані авторами при дос-
лідженні джерела негативних іонів водню типу Пеннінга з металогідридним катодом. Показано, що вихід
негативних іонів залежить від потенціалу на металогідридному катоді і визначається температурою елект-
ронів плазми. Залежність цього потенціалу від температури електронів розраховується чисельно для забез-
печення максимального струму негативних іонів.
1. EXPERIMENTAL SETUP
2. RESULTS AND DISCUSSION
|