Experimental study of secondary emission mode in RF gun with thermionic cathode
The paper deals with the problems concerning the influence of secondary emission on the operation of radio frequency (RF) gun with thermionic cathode. The characteristics of particles bombarding the cathode are investigated
 by the numerical simulation. The experiments on the study of second...
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| Опубліковано в: : | Вопросы атомной науки и техники |
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| Дата: | 2004 |
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| Мова: | Англійська |
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Національний науковий центр «Харківський фізико-технічний інститут» НАН України
2004
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| Цитувати: | Experimental study of secondary emission mode in RF gun with thermionic cathode
 / I.V. Khodak, V.A. Kushnir, V.V. Mitrochenko, S.A. Perezogin, D.L. Stepin // Вопросы атомной науки и техники. — 2004. — № 1. — С. 218-220. — Бібліогр.: 6 назв. — англ. |
Репозитарії
Digital Library of Periodicals of National Academy of Sciences of Ukraine| _version_ | 1860204226386329600 |
|---|---|
| author | Khodak, I.V. Kushnir, V.A. Mitrochenko, V.V. Perezogin, S.A. Stepin, D.L. |
| author_facet | Khodak, I.V. Kushnir, V.A. Mitrochenko, V.V. Perezogin, S.A. Stepin, D.L. |
| citation_txt | Experimental study of secondary emission mode in RF gun with thermionic cathode
 / I.V. Khodak, V.A. Kushnir, V.V. Mitrochenko, S.A. Perezogin, D.L. Stepin // Вопросы атомной науки и техники. — 2004. — № 1. — С. 218-220. — Бібліогр.: 6 назв. — англ. |
| collection | DSpace DC |
| container_title | Вопросы атомной науки и техники |
| description | The paper deals with the problems concerning the influence of secondary emission on the operation of radio frequency (RF) gun with thermionic cathode. The characteristics of particles bombarding the cathode are investigated
by the numerical simulation. The experiments on the study of secondary emission have been carried out on two-resonant thermionic RF gun, set as an injector of linac LIC. The results of measurements, their treatment and discussion are presented.
Розглянуті питання пов’язані з впливом вторинної емісії на роботу високочастотної електронної гармати
з термокатодом. Методом чисельного моделювання досліджено характеристики часток, що бомбардують
поверхню катода. Експерименти по дослідженню вторинної емісії проведено на дворезонаторної
термоемісійної гарматі. Наведено результати вимірювань та їх обговорення.
Рассмотрены вопросы, связанные с влиянием вторичной эмиссии на работу высокочастотной электронной пушки с термокатодом. Методом численного моделирования исследованы характеристики частиц, бомбардирующих поверхность катода. Эксперименты по изучению вторичной эмиссии проведены на двухрезонаторной термоэмиссионной ВЧ-пушке. Приведены результаты измерений и их обсуждение.
|
| first_indexed | 2025-12-07T18:11:39Z |
| format | Article |
| fulltext |
EXPERIMENTAL STUDY OF SECONDARY EMISSION MODE
IN RF GUN WITH THERMIONIC CATHODE
I.V. Khodak, V.A. Kushnir, V.V. Mitrochenko, S.A. Perezogin, D.L. Stepin
National Science Center “Kharkov Institute of Physics and Technology”, Kharkov, Ukraine
E-mail: kushnir@kipt.kharkov.ua
The paper deals with the problems concerning the influence of secondary emission on the operation of radio fre-
quency (RF) gun with thermionic cathode. The characteristics of particles bombarding the cathode are investigated
by the numerical simulation. The experiments on the study of secondary emission have been carried out on two-res-
onant thermionic RF gun, set as an injector of linac LIC. The results of measurements, their treatment and discus-
sion are presented.
PACS:29.25.Bx,41.75.Lx
1. INTRODUCTION
The using in linacs of RF gun-based injectors [1] al-
lows the significant improvement of accelerated beam
parameters. A RF gun is in general a RF cavity tuned on
the operating linac frequency. On the cavity wall a cath-
ode is installed. The emitted surface is placed in a high-
strength RF field (more than 105V/m). Photoinjectors
and thermionic RF guns are commonly used for genera-
tion of the high-quality electron beams. Besides, the RF
guns based on other emission mechanisms are designed.
Among them are, in particular, field emission RF gun,
plasma RF gun [2] and secondary emission RF gun [3].
For future RF gun improvement it is of great interest the
study of electron emission from the cathode exposed si-
multaneously to the action of a high strength RF field,
optical and X-radiation, temperature and electron bom-
bardment. The present work deals with the study of sec-
ondary emission processes which occur in the RF gun
with a thermionic cathode.
2. THE BACK BOMBARDMENT EFFECT
AND SECONDARY EMISSION IN THE
THERMIONIC RF GUN
In thermionic RF guns the electron emission from
the cathode takes place during the accelerating positive
half-cycles of RF field. The part of electrons emitted
from the cathode does not leave the cavity. When the
field sign is changing electrons are accelerated in the
back direction and bombard the cathode. This effect is
named as "backbombardment effect". It leads to the fol-
lowing consequences.
1. The electrons bombarding the emitter pass their
kinetic energy to the cathode. It leads to the change of
the cathode temperature during the RF pulse. It is
known that the emission current density in a thermionic
RF gun is limited only by the emission possibility of the
cathode but not the space charge (Chaild-Lengmur limi-
tation). Therefore due to backbombardment the output
current is changed during RF pulse too. If the cathode
surface does not cool down to initial temperature during
the time between pulses, the average temperature is in-
creased. The bombardment in thermionic RF guns limits
the range of the possible current pulse length (less than
10 µs) and pulse repetition-rate (less than 25 pps). This
effect is studied well, and some methods to reduce the
cathode heating up and to increase its influence on beam
characteristics are developed. Thus, the use of a trans-
verse dc magnetic field at the cathode allows one signif-
icantly decrease the bombardment. The number of back
electrons and their average power are also reduced in
the RF gun with optimal resonance system, containing
some coupled cavities.
2. The incidence of electrons on the surface of the
cathode causes the secondary electron emission. The
number of secondary electrons is defined by the sec-
ondary electron yield δ and depends on the surface
properties and impact electron energy. The destiny of
secondary electrons depends on the impact time (we
will neglect the time difference between the impact mo-
ment and the moment of secondary electron
occurrence). Secondary electrons, as well as, thermo-
electrons emitted during the accelerating positive half-
cycles of RF field (π>ϕ>0) are accelerated, but some
part of them can be accelerated in the opposite direction
and again impact the cathode surface. Evidently the sec-
ondary emission will exert the influence on beam pa-
rameters at the thermionic RF gun exit, if δ ≥ 1 and the
impact time (RF phase) is favorable.
We study the characteristics of bombarding elec-
trons for the 1.5 cell 2797 MHz thermionic RF gun us-
ing PARMELA code. This RF gun is installed and oper-
ated in the linac LIC [4, 5]. The operating field on the
cavity axes is of 35...40 MV/m. The dependence of the
thermionic electron energy on the phase is shown
in Fig.1. The sign plus corresponds to electrons leaving
the cavity and the sign minus corresponds to surface
electrons impacting the cathode.
One can see that electrons emitted in the phase ranges
85...95° and 160...180° can impact the cathode with a
low energy that is preferable for secondary emission
180°. Analysis of the electron trajectory shows that
electrons of the first phase range execute a complex mo-
tion during long time. The particles emitted in the phase
range 160...180° come back on the cathode for time less
than half-period. The number of back electrons increas-
es and their energy decreases as the RF field in the cavi-
ty decreases.
___________________________________________________________
PROBLEMS OF ATOMIC SIENCE AND TECHNOLOGY. 2004. № 1.
Series: Nuclear Physics Investigations (42), p.218-220.218
The phase of electrons that corresponds to the mo-
ment of their coming back to the cathode versus the
phase of their leaving is shown in Fig.2.
-1
-0.75
-0.5
-0.25
0
0.25
0.5
0.75
1
1.25
0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180
Phase, (degree)
W
(M
eV
)
Fig.1. Thermionic electron energy versus RF
phase
0
200
400
600
800
1000
1200
1400
1600
1800
2000
80 100 120 140 160 180 200
ϕ °
ϕ
ba
ck
°
Fig.2. Phase of electrons corresponding to the
moment of their coming back to the cathode
versus the phase of their leaving
It follows from simulation results that the main
source of secondary electrons is electrons emitted from
the cathode in the phase range 80...100°. They come
back to the cathode in the wide phase band and part of
them has a low energy. It should be noted that due to the
Shottky effect the number of thermionic electrons emit-
ted in the field maximum (ϕ=90°, E ∼105 V/m) can be
on the order of magnitude greater than that of electrons
emitted under ϕ=0°. The LaB6 and dispenser cathodes
are most frequently used in thermionic RF guns. The
secondary electron yield δmax of LaB6 does not exceed 1,
but for dispenser cathodes δmax it can be significant. For
instance, for the oxide-nickel pressed cathode [6], that
we use, the secondary electron yield δmax is more than 4
under some conditions.
3. EXPERIMENTAL RESULTS
The experimental study of the secondary emission in
a thermionic RF gun was carried out in the linac LIC
[5], that contains the universal 1.5 cell RF gun [4] as an
electron injector. During the experiments the gun oper-
ated in a thermionic mode with the oxide-nickel
thermionic cathode [6]. The typical oscillograms are
shown in Fig. 3. The growth of the output current during
the pulse is a feature of thermionic RF guns and it can
be explained by the existence of backbombardment ef-
fect and the temperature increase.
It is possible to observe the secondary emission in
the RF gun being studied, when the thermionic emission
is suppressed by the cathode temperature decrease or by
the increase of the work function. It is known that the
secondary emission yield is weakly dependent on these
parameters. This approach has been used in our experi-
ments.
0
20
40
60
80
100
120
0 1000 2000 3000 4000 5000 6000
t (ns)
A
rb
. u
ni
ts
.
1
2
3
4
Fig.3. 1 - the envelope of RF pulse at the entrance of
cavity, 2 –output current, 3 – the envelope of RF pulse
reflected from the cavity, 4 –RF field in the cavity
The change in the beam pulse current with the heater
current change is shown in Fig.4. The corresponding
temperature change of the cathode surface is of (∆
Т ≈ 150°...200°). This temperature variation leads to the
significant decrease of the thermionic current density.
0
0.5
1
1.5
2
0 2000 4000 6000
t (ns)
Iп
(A
) 1
2
3
4
Fig.4. The output current versus the cathode heater
current: 1 – I=4.5 A, 2 – I=4.1 A, 3 – I=3.8 A,
4 – I=3.5 A
The growth of the output current occurs at the mo-
ments of the leading edge and the trailing edge of the
RF pulse. Under subsequent temperature decrease the
thermionic current disappears, but the current on the
pulse edges is does not disappear. If the field strength in
a cavity decreases in such a temperature regime, the cur-
rent pulse of rectangular form is observed at the exit of
the gun. The current amplitude in this case is of
100...150 mA and the electron energy does not exceed
300 keV. It is evidently that the current observed is not
caused by the thermionic or field emission of electrons.
We suppose that the secondary electrons are the source
of this current. The electrons of thermionic or field
emission and secondary “back” electrons also can play
the role of the primary electrons.
Secondary emission mode has been observed, when
some samples of oxide-nickel cathodes with anomalous
properties were investigated. The ordinary dependences
of a thermionic current on the temperature and the field
strength have not been obtained for these cathodes. Ap-
parently these cathodes have anomalous high work
function. Probably, the cause of significant growth of
the secondary emission yield was creation in these cath-
___________________________________________________________
PROBLEMS OF ATOMIC SIENCE AND TECHNOLOGY. 2004. № 1.
Series: Nuclear Physics Investigations (42), p.218-220.219
odes of a non-conducting film on their nickel substrate.
In this case the pulse current does not practically depend
on the temperature of the cathode surface under its
change by 200...300°. As a result, the increase of the
current amplitude during the pulse typical for thermion-
ic RF gun was not observed. The oscillograms for this
operation mode are presented in Fig.5.
0
1000
2000
3000
4000
5000
0
20
40
60
80
100
120
t ( µ s)
A
rb
. u
ni
ts
1
2
3
4
Fig.5. 1 – the envelope of RF pulse at the entrance of
cavity, 2 – output current (I=1.4 A), 3 - current at
the linac exit (I=0.75 A), 4 – RF field in the cavity
The described mode has been observed at a field of
30 МV/m. The electron energy exceeded 300 keV with
a current up to 1.4 А at the exit of the gun. Instability of
the leading current pulse edge was observed at the exit
of the accelerating section (see Fig.5.) This instability
can be caused by the significant phase- or energy insta-
bility in the initial part of the current pulse injected into
the section. The pulse current at the exit of the gun de-
creases in the range of 20...30% with the decrease of the
field strength up to ≈ 20 МV/m. However, a further de-
crease of the field to some limit value resulted in disap-
pearance of the current at the exit, in decrease of the
field in the cavity up to zero and the cavity detuning.
We suppose that such a behavior corresponds to the ap-
pearance of a multipactor discharge.
CONCLUSION
Thus, we can make the following conclusions:
1. It has been shown, that there are all the neces-
sary conditions in the thermionic RF gun for ap-
pearance of the current caused by the secondary
emission. The mode with the intensive sec-
ondary emission in the RF gun with oxide-im-
pregnated or pressed cathode is the most proba-
ble.
2. The anomalous operation modes of the
thermionic RF gun have been observed during
experiment. These modes can be explained by
only secondary emission processes on the oxide
cathode surface.
3. The results of preliminary measurements give
the possibility for the background of further ex-
perimental investigation to study in detail the
secondary emission in RF guns. Of great inter-
est is the study of the following problems such
as: stability; conditions of appearance of single-
wall multipactor discharge and the mechanism
of its saturation; dependences of bunch parame-
ters on secondary emission properties of the sur-
face and so on.
The authors are very grateful to the staff of "Accel-
erator" of NSC KIPT for their help in experiment real-
ization.
REFERENCES
1. V.A. Kushnir. RF guns for resonance linacs //
Zarubezhay radioelektronika. Uspekhi sovremen-
noy radioelectroniki. 2001, №12, p.19-34 (in Rus-
sian).
2. M.I. Ayzatsky, V.A. Kushnir, V.V. Mitrochenko et
al. The metallic-dielectric cathode in the RF gun //
Pisma v Zh. Tekh. Fiz. 1998, v.24, №19, p.36-39 (in
Russian).
3. L.K. Len, Frederic M. Mako. Self-bunching elec-
tron guns. Proc. of the 1999 PAC, New York, 1999,
p.70-74.
4. N.I.Aizatsky, E.Z.Biller, A.N.Dovbnya et al. Two-
cell RF gun for a high-brightness linac. Proc. of the
1996 EPAC, 1996, v.2, p.1553-1555.
5. M.I. Ayzatsky, E.Z. Biller, A.N.Dovbnya et al. Op-
erating performances and current status of the
Laser Injector Complex facility (LIC). Proc. of the
1996 EPAC, 1996, v.1, p.795-797.
6. Yu.V. Alekseev, N.R. Kanicheva, V.V. Korablyov
et al. The investigation of oxide-nickel thermo cath-
ode surface: Preprint NIIEFA. П-б-0753, L., 1987,
p.19.
ЭКСПЕРИМЕНТАЛЬНОЕ ИССЛЕДОВАНИЕ ВТОРИЧНО-ЭМИССИОННОГО РЕЖИМА
РАБОТЫ ВЧ-ПУШКИ С ТЕРМОЭМИССИОННЫМ КАТОДОМ
И.В. Ходак, В.А. Кушнир, В.В. Митроченко, С.А. Пережогин, Д.Л. Степин
Рассмотрены вопросы, связанные с влиянием вторичной эмиссии на работу высокочастотной электрон-
ной пушки с термокатодом. Методом численного моделирования исследованы характеристики частиц, бом-
бардирующих поверхность катода. Эксперименты по изучению вторичной эмиссии проведены на двухрезо-
наторной термоэмиссионной ВЧ-пушке. Приведены результаты измерений и их обсуждение.
ЕКСПЕРИМЕНТАЛЬНЕ ДОСЛІДЖЕННЯ ВТОРИННО-ЕМІСІЙНОГО РЕЖИМУ
РАБОТИ ВЧ-ГАРМАТИ З ТЕРМОЕМИССІЙНИМ КАТОДОМ
І.В. Ходак, В.А. Кушнір, В.В. Митроченко, С.А. Пережогін, Д.Л. Стьопін
Розглянуті питання пов’язані з впливом вторинної емісії на роботу високочастотної електронної гармати
з термокатодом. Методом чисельного моделювання досліджено характеристики часток, що бомбардують
поверхню катода. Експерименти по дослідженню вторинної емісії проведено на дворезонаторної
термоемісійної гарматі. Наведено результати вимірювань та їх обговорення.
220
I.V. Khodak, V.A. Kushnir, V.V. Mitrochenko, S.A. Perezogin, D.L. Stepin
National Science Center “Kharkov Institute of Physics and Technology”, Kharkov, Ukraine
1. INTRODUCTION
|
| id | nasplib_isofts_kiev_ua-123456789-79079 |
| institution | Digital Library of Periodicals of National Academy of Sciences of Ukraine |
| issn | 1562-6016 |
| language | English |
| last_indexed | 2025-12-07T18:11:39Z |
| publishDate | 2004 |
| publisher | Національний науковий центр «Харківський фізико-технічний інститут» НАН України |
| record_format | dspace |
| spelling | Khodak, I.V. Kushnir, V.A. Mitrochenko, V.V. Perezogin, S.A. Stepin, D.L. 2015-03-25T20:49:34Z 2015-03-25T20:49:34Z 2004 Experimental study of secondary emission mode in RF gun with thermionic cathode
 / I.V. Khodak, V.A. Kushnir, V.V. Mitrochenko, S.A. Perezogin, D.L. Stepin // Вопросы атомной науки и техники. — 2004. — № 1. — С. 218-220. — Бібліогр.: 6 назв. — англ. 1562-6016 PACS:29.25.Bx,41.75.Lx https://nasplib.isofts.kiev.ua/handle/123456789/79079 The paper deals with the problems concerning the influence of secondary emission on the operation of radio frequency (RF) gun with thermionic cathode. The characteristics of particles bombarding the cathode are investigated
 by the numerical simulation. The experiments on the study of secondary emission have been carried out on two-resonant thermionic RF gun, set as an injector of linac LIC. The results of measurements, their treatment and discussion are presented. Розглянуті питання пов’язані з впливом вторинної емісії на роботу високочастотної електронної гармати
 з термокатодом. Методом чисельного моделювання досліджено характеристики часток, що бомбардують
 поверхню катода. Експерименти по дослідженню вторинної емісії проведено на дворезонаторної
 термоемісійної гарматі. Наведено результати вимірювань та їх обговорення. Рассмотрены вопросы, связанные с влиянием вторичной эмиссии на работу высокочастотной электронной пушки с термокатодом. Методом численного моделирования исследованы характеристики частиц, бомбардирующих поверхность катода. Эксперименты по изучению вторичной эмиссии проведены на двухрезонаторной термоэмиссионной ВЧ-пушке. Приведены результаты измерений и их обсуждение. The authors are very grateful to the staff of "Accelerator" of NSC KIPT for their help in experiment realization. en Національний науковий центр «Харківський фізико-технічний інститут» НАН України Вопросы атомной науки и техники Применение ускоренных пучков Experimental study of secondary emission mode in RF gun with thermionic cathode Експериментальне дослідження вторинно-емісійного режиму работи ВЧ-гармати з термоемиссійним катодом Экспериментальное исследование вторично-эмиссионного режима работы ВЧ-пушки с термоэмиссионным катодом Article published earlier |
| spellingShingle | Experimental study of secondary emission mode in RF gun with thermionic cathode Khodak, I.V. Kushnir, V.A. Mitrochenko, V.V. Perezogin, S.A. Stepin, D.L. Применение ускоренных пучков |
| title | Experimental study of secondary emission mode in RF gun with thermionic cathode |
| title_alt | Експериментальне дослідження вторинно-емісійного режиму работи ВЧ-гармати з термоемиссійним катодом Экспериментальное исследование вторично-эмиссионного режима работы ВЧ-пушки с термоэмиссионным катодом |
| title_full | Experimental study of secondary emission mode in RF gun with thermionic cathode |
| title_fullStr | Experimental study of secondary emission mode in RF gun with thermionic cathode |
| title_full_unstemmed | Experimental study of secondary emission mode in RF gun with thermionic cathode |
| title_short | Experimental study of secondary emission mode in RF gun with thermionic cathode |
| title_sort | experimental study of secondary emission mode in rf gun with thermionic cathode |
| topic | Применение ускоренных пучков |
| topic_facet | Применение ускоренных пучков |
| url | https://nasplib.isofts.kiev.ua/handle/123456789/79079 |
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