Parameters of electron beam generated by RF gun with ferroelectric cathode
RF guns with thermoemission and photoemission cathodes generate an electron beam pulse current and current pulse duration of 10⁻¹…10³ A and 10⁻⁶…10⁻¹² s, respectively. It is proposed to apply a ferroelectric cathode in RF gun. S-band RF gun with the cathode has been researched experimentally. Maxi...
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| Zitieren: | Parameters of electron beam generated by RF gun with ferroelectric cathode / I.V. Khodak, V.A. Kushnir, V.P. Romas’ko, V.V. Zakutin // Вопросы атомной науки и техники. — 2006. — № 3. — С. 66-68. — Бібліогр.: 8 назв. — англ. |
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Digital Library of Periodicals of National Academy of Sciences of Ukraine| _version_ | 1860129445845663744 |
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| author | Khodak, I.V. Kushnir, V.A. Romas’ko, V.P. Zakutin, V.V. |
| author_facet | Khodak, I.V. Kushnir, V.A. Romas’ko, V.P. Zakutin, V.V. |
| citation_txt | Parameters of electron beam generated by RF gun with ferroelectric cathode / I.V. Khodak, V.A. Kushnir, V.P. Romas’ko, V.V. Zakutin // Вопросы атомной науки и техники. — 2006. — № 3. — С. 66-68. — Бібліогр.: 8 назв. — англ. |
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| container_title | Вопросы атомной науки и техники |
| description | RF guns with thermoemission and photoemission cathodes generate an electron beam pulse current and current pulse duration of 10⁻¹…10³ A and 10⁻⁶…10⁻¹² s, respectively. It is proposed to apply a ferroelectric cathode in RF gun. S-band RF gun with the cathode has been researched experimentally. Maximum beam pulse current is 9 A with current pulse duration of 40…90 ns and particle energy of 500 keV.
ВЧ-пушки с термо- и фотоэмиссионными катодами генерируют электронные пучки с импульсным током 10⁻¹…10³ A и длительностью импульса 10⁻⁶…10⁻¹² с. Предлагается применение в ВЧ-пушке ферроэлектрического катода. ВЧ-пушка S-диапазона с таким катодом была исследована экспериментально. Максимальный импульсный ток пучка составляет 9 А при длительности импульса 40…90 нс и энергии частиц 500 кэВ.
ВЧ-гармати з термо- та фотоемісійними катодами генерують електронні пучки з імпульсним струмом 10⁻¹…10³ A і тривалістю імпульсу 10⁻⁶…10⁻¹² с. Пропонується застосування у ВЧ-гарматі фероелектричного катода. ВЧ-гармата S-діапазону з таким катодом була досліджена експериментально. Максимальний імпульсний струм пучка складає 9 А при тривалості імпульсу 40…90 нс та енергії частинок 500 кеВ.
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PARAMETERS OF ELECTRON BEAM GENERATED BY RF GUN WITH
FERROELECTRIC CATHODE
I.V. Khodak, V.A. Kushnir, V.P. Romas’ko, V.V. Zakutin
NSC KIPT, Kharkov, Ukraine
E-mail: khiv@kipt.kharkov.ua
RF guns with thermoemission and photoemission cathodes generate an electron beam pulse current and current
pulse duration of 10-1…103 A and 10-6…10-12 s, respectively. It is proposed to apply a ferroelectric cathode in RF
gun. S-band RF gun with the cathode has been researched experimentally. Maximum beam pulse current is 9 A with
current pulse duration of 40…90 ns and particle energy of 500 keV.
PACS: 29.25.Bx, 41.75.Lx, 77.22.Jp, 85.80.-n
1. INTRODUCTION
The main advantage of RF guns is the generation of
intense and high brightness electron beams. This is pos-
sible due to employing of thermionic cathodes with typ-
ical emission current density of 10…30 A/cm2 or pho-
tocathodes with emission current density up to
102 A/cm2 within a laser pulse duration of 10-8…10-11 s.
RF gun operates in a storage energy mode if the beam
current pulse duration τb follows the condition: 1<<τb⋅
f0<<Q0/π⋅f0, where ⋅f0 is the gun operating frequency, Q0
is unloaded quality factor. According to estimations
made in paper [1], S-band photo-RF gun may be the
source of nanosecond pulse beam with the maximum
charge in a bunch > 10 nC. However, the producing of
the charge is limited by high power flow density of laser
pulse that is quite close to the cathode damage to be
caused.
The alternative way the high charge can be achieved
in RF gun is application of the cathodes with plasma-as-
sisted electron emission. The cathodes are featured both
by the high emission current density (≥ 102 А/cm2) and
by the ability to provide the duration of a beam current
pulse of few tens nanoseconds. We propose to apply fer-
roelectric cathodes [2] in RF gun. The emission current
density in the cathodes may be up to 103 A/cm2.
The features of the ferroelectric cathode in the con-
text of RF gun and results of the experimental research
of S-band RF gun operation with driven ferroelectric
cathode are considered in the paper. There are provided
and analysed results of operation of experimental
sample of the cathode and parameters of generated elec-
tron beam.
2. FERROЕLECTRIC CATHODE FOR RF
GUN
An RF gun with ferroelectric cathode follows the
conventional RF gun concept. The cathode is featured
by the developing of plasma sheath due to conventional
dielectric surface flashover in the region of triple point
junctions of metal-dielectric structure of the cathode [3].
In the RF gun the flashover may be both self-excited by
exposed RF electric field and triggered by external elec-
tric field. The self-excited flashover is risen up during
the transient of RF gun feeling up by RF power [4].
Therefore, the electric field strength and, hence, the
stored energy is not optimal, for instance, to the electron
capture ratio. It means that the flashover on a ferroelec-
tric cathode in RF gun should be triggered by the ex-
ternal electric field during the time intervals of RF
power pulse duration corresponding to the maximum
stored electromagnetic energy.
The design of the driven ferroelectric cathode for the
RF gun follows the principle of spatial separation of
plasma sheath development on the cathode and after-ac-
celeration of electrons. The base of the cathode is the
ferroelectric disc 2 (Fig.1).
Fig.1. Cross-section of ferroelectric cathode for RF gun
The front side of the disc contacts with the patterned
electrode 1, and the rear side is deposited by the solid
electrode 3 that is supplied by a triggering pulse. The
disc with area of ≅ 0.8 cm2 and thickness 0.5 mm is
made of BaTiO3 with εr = 2150. The aperture in the pat-
terned electrode is prolonged by a cylindrical surface of
finite length h and diameter d making the cut of a cyl-
indrical waveguide. The free end face of the cavity con-
tacts with ferroelectric disc and the opposite end face is
the interface for plasma extraction. The RF electric field
strength in the waveguide of the patterned electrode de-
cays exponentially. According to results of the comput-
ing of the axial RF electric field distribution using SU-
PERFISH code [5], the attenuation of the RF electric
field strength near the surface of the ferroelectric disc is
104 times for sizes d = 1 mm and h = 1 mm. It is much
lower of the threshold magnitude of the self-excited and
uncontrolled flashover [4]. The end face of the wave-
guide contacting with the ferroelectric disc has a
sharpen ridge (Fig.1). The ridge implements tangential
electrostatic field and induces the electric field strength
in the region of triple point junctions up to ~109 V/m
within the driving voltage of 1-3 kV. The computing of
electrostatic field distribution using POISSON code [5]
has shown up that the ridge with sizes 0.15×0.15 mm
decreases tangential and radial electrostatic field two
times.
3. EXPERIMENTAL EQUIPMENT
RF gun operation was investigated using a single-
cell S-band RF gun with pillbox-like cavity [6]. Some
parameters of the gun cavity are summarized in Table.
____________________________________________________________
PROBLEMS OF ATOMIC SCIENCE AND TECHNOLOGY. 2006. № 3.
Series: Nuclear Physics Investigations (47), p.66-68.66
mailto:khiv@kipt.kharkov.ua
RF gun cavity main parameters
Operating frequency, f0 (MHz) 2797.15
Feeding RF power, Pc (MW) ≤ 1.5
Unloaded Q-factor, Q0 11000
Coupling coefficient, β 1.05
The maximum axial electric field strength in the gun
cavity is determined by the following expression evalu-
ated from resonant perturbation measurements of the
field:
0)(470)/( QWPmVE c= . (2)
The gun has been installed in the special facility pur-
posed for pilot tests of injectors for electron linacs. The
measuring equipment of the facility permits measuring
the parameters of electron beams with particle energy
from 104 to 106 eV. The gun output pulse current was
measured by beam current transformer having time res-
olution of 0.5 ns. Electron energy of the beam was
measured using dipole magnetic spectrometer and
Faraday cup (FC). The beam profile was measured with
a spatial resolution 0.2 mm by actuator-driven slits and
FC. The distance between the slits and the gun output is
0.8 m. Beam transport through this beam-line interval is
supplied by unit axial lens and unit quadrupole lens. RF
power is supplied by klystron RF amplifier operating in
self-excited mode with operating frequency of
2797.15 MHz. Tunable directional coupler in the feed-
ing waveguide supplied RF feeding power Pc in 0.08…
1 MW range. The RF pulse duration was 2 µs.
The source of the triggering pulse is based on the
scheme with transmission line. Its length supplies gener-
ation of voltage pulses with flattop duration 60 ns. The
magnitude of the pulse voltage may be adjusted in 0.1…
3 kV range. The output resistance of the source of ≅
5 Ohm is matched with 50-Ohm wave impedance of the
transmission line by a three-stepped voltage-dividing
transformer. The transformer is made from cut-offs of
coaxial lines that minimizes the rise time of the pulse
down to 10 ns.
4. PARAMETERS OF ELECTRON BEAM
The ferroelectric cathode used in the experiments
has one aperture in the patterned electrode. The pat-
terned electrode has been grounded while the rear elec-
trode has been supplied by the triggering pulse Utr both
of positive and negative polarity. The generated electron
beam had maximum pulse current up to 8.9 A within the
both polarity of the pulse Utr. The current pulse duration
(FWHM) is different and complies 90 ns for positive Utr
and 40 ns for negative Utr. Electron energy in the max-
imum of energy spread for negative Utr is ≅ 500 keV.
The RF gun output current Ig may be varied by the
voltage change of the pulse Utr. Besides this variation,
the current Ig also depends on the RF electric field
strength. The current Ig is close to saturation in the mode
of RF gun operation with Utr=2 kV and Eav> 20 MV/m
(Fig.2).
However, within the higher voltage Utr the current Ig
is not saturated, that can be explained by the virtual
cathode existence under electric field up to 35 MV/m. It
follows from the dependences there is the high current
Fig.2. Beam current vs. the electric field strength
density of the emission from the ferroelectric cathode.
Comparative analysis of measured results with results of
numerical simulation of particle dynamics using
PARMELA code [7] has shown that emission current
density is approximately ≈9⋅ 102 А/cm2 for the RF gun
operation with triggering voltage Utr=-2 kV (Fig.3). The
particle energy estimated after the results of the analysis
is ≅500 keV that fits the measured results.
Fig.3. PARMELA simulation and measurements
The beam current pulses Ig are differed by duration,
by the time delay of the pulse rising and by the pulse
shapes. The positive Utr triggering makes the electrostat-
ic field to be accelerating for electrons during the total
time of plasma inducing and enhancement in the wave-
guide of the patterned electrode. All electrons are ex-
tracted into the gun cavity just after the rise time of the
pulse Utr and continuously within its duration. The dura-
tion of the pulse Ig is 90 ns in this case.
The negative pulse Utr makes the electrostatic field
of the cathode to be decelerating for electrons during the
same time of plasma inducing and enhancement. There
are no extracted electrons that could be accelerated by
the RF electric field within the duration of the pulse Utr.
The most of electrons are accelerated in this case after
the electrostatic field strength becomes lower than RF
electric field strength in the plasma extraction interface.
As a result, the in-pulse temporal beam current distribu-
tion has intervals with flat and sharp slopes differed
considerably by the value of the instantaneous current.
The duration of the pulse Ig is 50 ns in this case.
The different polarity of the pulse Utr gives rise to
different initial transverse and longitudinal momentum
spreads of electrons in the plasma extraction interface of
the cathode that should cause the difference of spatial
and angular parameters of the beam at RF gun output.
This statement was validated by the results of the beam
profile and beam emittance measurements. Thus, the
measured beam profile for the negative Utr has shown
up the correlation of the temporal beam structure with
____________________________________________________________
PROBLEMS OF ATOMIC SCIENCE AND TECHNOLOGY. 2006. № 3.
Series: Nuclear Physics Investigations (47), p.66-68.67
the spatial distribution of the beam current. Fig.4
demonstrates the plane projection of the beam deduced
from the profile measurements.
Fig.4. Plane projection of the beam current distribution
It is assumed that particles being inside the dashed
line (FWHM level of the distribution) compose the core
of the beam with diameter 6.5 mm. The beam emittance
was measured using a ‘pepper-pot’ technique [8]. The
measured normalised beam emittance is 20 mm⋅mrad
for 40 % of particles. The normalised beam emittance
measured for positive pulse Utr is much larger. There is
the large beam size in this case (σx,y (FWHM) =10 mm).
The lifetime (~105 shots) of two experimental
samples of the cathode during the RF gun operation in a
single pulse repetition rate mode was limited by the
breakdown of the ferroelectric disk after increasing of
the triggering voltage value by design. The same break-
down and lifetime reducing has been observed after the
cathode operation without RF field.
5. CONCLUSION
RF guns with the plasma ferroelectric cathode can
generate pulse electron beams with pulse current up to
10 A and with pulse duration few tens nanoseconds. The
pulse polarity of the cathode is triggered and defines
two modes of the beam generation.
Within the phase length of electron bunch in RF gun
∆ϕ the peak current in a bunch is Ib=Ip⋅(2⋅π)/∆ϕ. For a
typical bunch length about 0.7 rad the peak current may
be up to 102 A with particle energy ≅500 keV.
Despite the high plasma electron temperature, the
beam emittance is comparable with the same parameter
of thermionic RF guns.
ACKNOWLEDGMENTS
The authors are exceedingly grateful to the staff of
R&D "Accelerator" of NSC KIPT for their help
throughout the experiment period. Special thanks are to
Prof. A.N. Dovbnya and Prof. M.I. Aizatsky for the sup-
port of the work, to Dr. V.V. Mitrochenko and
Dr. V.F. Zhiglo for useful discussions of the results.
REFERENCES
1. N.I. Ayzatskiy, A.N. Dovbnya, V.A. Kushnir et al.
Photoemission from the surface of oxide Ba-Ni
cathode by action of intense ultraviolet laser radi-
ation // Gazette KhNU. Series Physical "Nuclei,
Particles, Fields". 2001, v.3/15/, №529, p.83 (in
Russian).
2. G. Rosenman, D. Shur, Ya. E. Krasik and
A. Dunaevsky. Electron emission from ferroelec-
trics // J. Appl. Phys. 2000, №88, p.6109-6161.
3. G. A. Mesyatz, D. I. Proskurovskiy. Pulse electric
discharge in vacuum. Novosibirsk: “Nauka”, 1984,
256 p. (in Russian).
4. I.V. Khodak, V.A. Kushnir. Performances of the
beam generated by metal-dielectric cathodes in RF
electron guns. Proc. of EPAC’04, Lucerne,
Switzerland. 2004, p.767-768.
5. J.H. Billen, L.M. Young. POISSON/SUPERFISH
group of codes. LA-UR-96-1834, Ver. 7.02 for PC,
Los Alamos, 2003.
6. N.I. Ayzatsky, E.Z. Biller, V.N. Boriskin et al.
Electron resonance high-current accelerator for in-
vestigation of collective methods of acceleration //
Plasma physics. 20. 1994, v.20, №(7,8), p.671-673
(in Russian).
7. L.M. Young. PARMELA. LA-UR-96-1835,
Ver.3.21 for PC, Los Alamos, 2002.
8. S.G. Anderson, J.B. Rosenzweig. Space-charge ef-
fects in high brightness electron beam emittance
measurements // Phys. Rev. Special Topics – Accel.
and Beams. 2002, №5(014201), p.1-12.
ПАРАМЕТРЫ ЭЛЕКТРОННОГО ПУЧКА, ФОРМИРУЕМОГО ВЧ-ПУШКОЙ
С ФЕРРОЭЛЕКТРИЧЕСКИМ КАТОДОМ
И.В. Ходак, В.А. Кушнир, В.П. Ромасько, В.В. Закутин
ВЧ-пушки с термо- и фотоэмиссионными катодами генерируют электронные пучки с импульсным током
10-1…103 A и длительностью импульса 10-6…10-12 с. Предлагается применение в ВЧ-пушке ферроэлектриче-
ского катода. ВЧ-пушка S-диапазона с таким катодом была исследована экспериментально. Максимальный
импульсный ток пучка составляет 9 А при длительности импульса 40…90 нс и энергии частиц 500 кэВ.
ПАРАМЕТРИ ЕЛЕКТРОННОГО ПУЧКА, ЩО ФОРМУЄТЬСЯ ВЧ-ГАРМАТОЮ
З ФЕРРОЕЛЕКТРИЧНИМ КАТОДОМ
І.В. Ходак, В.А. Кушнір, В.П. Ромасько, В.В. Закутін
ВЧ-гармати з термо- та фотоемісійними катодами генерують електронні пучки з імпульсним струмом
101…103 A і тривалістю імпульсу 10-6…10-12 с. Пропонується застосування у ВЧ-гарматі фероелектричного
катода. ВЧ-гармата S-діапазону з таким катодом була досліджена експериментально. Максимальний
імпульсний струм пучка складає 9 А при тривалості імпульсу 40…90 нс та енергії частинок 500 кеВ.
68
ПАРАМЕТРЫ ЭЛЕКТРОННОГО ПУЧКА, ФОРМИРУЕМОГО ВЧ-ПУШКОЙ
С ФЕРРОЭЛЕКТРИЧЕСКИМ КАТОДОМ
ПАРАМЕТРИ ЕЛЕКТРОННОГО ПУЧКА, що ФОРМується ВЧ-гарматою
з ФЕРРОеЛЕКТРИЧнИМ КАТОДОМ
|
| id | nasplib_isofts_kiev_ua-123456789-79304 |
| institution | Digital Library of Periodicals of National Academy of Sciences of Ukraine |
| issn | 1562-6016 |
| language | English |
| last_indexed | 2025-12-07T17:43:45Z |
| publishDate | 2006 |
| publisher | Національний науковий центр «Харківський фізико-технічний інститут» НАН України |
| record_format | dspace |
| spelling | Khodak, I.V. Kushnir, V.A. Romas’ko, V.P. Zakutin, V.V. 2015-03-30T18:51:12Z 2015-03-30T18:51:12Z 2006 Parameters of electron beam generated by RF gun with ferroelectric cathode / I.V. Khodak, V.A. Kushnir, V.P. Romas’ko, V.V. Zakutin // Вопросы атомной науки и техники. — 2006. — № 3. — С. 66-68. — Бібліогр.: 8 назв. — англ. 1562-6016 PACS: 29.25.Bx, 41.75.Lx, 77.22.Jp, 85.80.-n https://nasplib.isofts.kiev.ua/handle/123456789/79304 RF guns with thermoemission and photoemission cathodes generate an electron beam pulse current and current pulse duration of 10⁻¹…10³ A and 10⁻⁶…10⁻¹² s, respectively. It is proposed to apply a ferroelectric cathode in RF gun. S-band RF gun with the cathode has been researched experimentally. Maximum beam pulse current is 9 A with current pulse duration of 40…90 ns and particle energy of 500 keV. ВЧ-пушки с термо- и фотоэмиссионными катодами генерируют электронные пучки с импульсным током 10⁻¹…10³ A и длительностью импульса 10⁻⁶…10⁻¹² с. Предлагается применение в ВЧ-пушке ферроэлектрического катода. ВЧ-пушка S-диапазона с таким катодом была исследована экспериментально. Максимальный импульсный ток пучка составляет 9 А при длительности импульса 40…90 нс и энергии частиц 500 кэВ. ВЧ-гармати з термо- та фотоемісійними катодами генерують електронні пучки з імпульсним струмом 10⁻¹…10³ A і тривалістю імпульсу 10⁻⁶…10⁻¹² с. Пропонується застосування у ВЧ-гарматі фероелектричного катода. ВЧ-гармата S-діапазону з таким катодом була досліджена експериментально. Максимальний імпульсний струм пучка складає 9 А при тривалості імпульсу 40…90 нс та енергії частинок 500 кеВ. The authors are exceedingly grateful to the staff of
 R&D "Accelerator" of NSC KIPT for their help
 throughout the experiment period. Special thanks are to
 Prof. A.N. Dovbnya and Prof. M.I. Aizatsky for the support
 of the work, to Dr. V.V. Mitrochenko and
 Dr. V.F. Zhiglo for useful discussions of the results. en Національний науковий центр «Харківський фізико-технічний інститут» НАН України Вопросы атомной науки и техники Ускорители заряженных частиц Parameters of electron beam generated by RF gun with ferroelectric cathode Параметры электронного пучка, формируемого ВЧ-пушкой с ферроэлектрическим катодом Параметри електронного пучка, що формується ВЧ-гарматою з ферроелектричним катодом Article published earlier |
| spellingShingle | Parameters of electron beam generated by RF gun with ferroelectric cathode Khodak, I.V. Kushnir, V.A. Romas’ko, V.P. Zakutin, V.V. Ускорители заряженных частиц |
| title | Parameters of electron beam generated by RF gun with ferroelectric cathode |
| title_alt | Параметры электронного пучка, формируемого ВЧ-пушкой с ферроэлектрическим катодом Параметри електронного пучка, що формується ВЧ-гарматою з ферроелектричним катодом |
| title_full | Parameters of electron beam generated by RF gun with ferroelectric cathode |
| title_fullStr | Parameters of electron beam generated by RF gun with ferroelectric cathode |
| title_full_unstemmed | Parameters of electron beam generated by RF gun with ferroelectric cathode |
| title_short | Parameters of electron beam generated by RF gun with ferroelectric cathode |
| title_sort | parameters of electron beam generated by rf gun with ferroelectric cathode |
| topic | Ускорители заряженных частиц |
| topic_facet | Ускорители заряженных частиц |
| url | https://nasplib.isofts.kiev.ua/handle/123456789/79304 |
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