Emittance measurement of electron beam of RF gun with plasma ferroelectric cathode
An RF gun with a plasma ferroelectric cathode can generate intense electron beams with peak current in a bunch up to 10² A. The space charge forces of the beam increase errors of the beam emittance measurement using a ‘quadrupole’ technique. The errors of the measurements and the implementation...
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| Опубліковано в: : | Вопросы атомной науки и техники |
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| Дата: | 2006 |
| Автори: | , |
| Формат: | Стаття |
| Мова: | Англійська |
| Опубліковано: |
Національний науковий центр «Харківський фізико-технічний інститут» НАН України
2006
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| Цитувати: | Emittance measurement of electron beam of RF gun with plasma ferroelectric cathode / I.V. Khodak, V.A. Kushnir // Вопросы атомной науки и техники. — 2006. — № 3. — С. 104-106. — Бібліогр.: 11 назв. — англ. |
Репозитарії
Digital Library of Periodicals of National Academy of Sciences of Ukraine| _version_ | 1859984742183600128 |
|---|---|
| author | Khodak, I.V. Kushnir, V.A. |
| author_facet | Khodak, I.V. Kushnir, V.A. |
| citation_txt | Emittance measurement of electron beam of RF gun with plasma ferroelectric cathode / I.V. Khodak, V.A. Kushnir // Вопросы атомной науки и техники. — 2006. — № 3. — С. 104-106. — Бібліогр.: 11 назв. — англ. |
| collection | DSpace DC |
| container_title | Вопросы атомной науки и техники |
| description | An RF gun with a plasma ferroelectric cathode can generate intense electron beams with peak current in a bunch
up to 10² A. The space charge forces of the beam increase errors of the beam emittance measurement using a
‘quadrupole’ technique. The errors of the measurements and the implementation of the ‘pepper-pot’ technique are
referred in the paper. Studied is the beam emittance generated by a single-cell S-band RF gun with the plasma
ferroelectric cathode. The beam pulse current is 6 A (current in a bunch is 60 A) with pulse duration 40…90 ns and
particle energy ≅ 500 keV.
ВЧ-пушка с плазменным ферроэлектрическим катодом может генерировать интенсивные электронные пучки с током в сгустке до 10² A. Силы пространственного заряда такого пучка увеличивают погрешности измерения эмиттанса с использованием квадруполей. В работе рассмотрены погрешности измерений и реализован ‘pepper-pot’-метод измерения эмиттанса. Был исследован эмиттанс пучка, генерируемого однорезонаторной ВЧ-пушкой S-диапазона с плазменным ферроэлектрическим катодом. Импульсный ток пучка составляет 6 A (ток в сгустке до 60 А) при длительности импульса 40…90 нс и энергии электронов ≅ 500 кэВ.
ВЧ-гармата з плазмовим фероелектричним катодом може генерувати інтенсивні електронні пучки зі
струмом у згустку до 10² A. Сили просторового заряду такого пучка завищують погрішності вимірювання
емітансу з використанням квадруполів. В роботі розглянуті погрішності вимірювань та реалізований
‘pepper-pot’-метод вимірювання емітансу. Було досліджено емітанс пучка, що генерується
однорезонаторною ВЧ-гарматою S-діапазону з плазмовим фероелектричним катодом. Імпульсний струм
пучка дорівнює 6 A (струм в згустку до 60 А) при тривалості імпульсу 40…90 нс та енергії електронів
≅ 500 кеВ.
|
| first_indexed | 2025-12-07T16:28:17Z |
| format | Article |
| fulltext |
EMITTANCE MEASUREMENT OF ELECTRON BEAM OF RF GUN
WITH PLASMA FERROELECTRIC CATHODE
I.V. Khodak, V.A. Kushnir
NSC KIPT, Kharkov, Ukraine
E-mail: khiv@kipt.kharkov.ua
An RF gun with a plasma ferroelectric cathode can generate intense electron beams with peak current in a bunch
up to 102 A. The space charge forces of the beam increase errors of the beam emittance measurement using a
‘quadrupole’ technique. The errors of the measurements and the implementation of the ‘pepper-pot’ technique are
referred in the paper. Studied is the beam emittance generated by a single-cell S-band RF gun with the plasma
ferroelectric cathode. The beam pulse current is 6 A (current in a bunch is 60 A) with pulse duration 40…90 ns and
particle energy ≅ 500 keV.
PACS: 29.25.Bx, 41.75.-i, 52.59.Sa, 06.90.+v
1. INTRODUCTION
An RF gun is a source of electron beam that is guid-
ed and shaped by the RF electric field of high strength
(~107 V/m) [1,2]. The RF gun can be the source of a
nanosecond pulse beam with the maximum charge in a
bunch > 102 nC [3]. One of the ways the charge can be
achieved is the application of the cathodes that are fea-
tured 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. The
experimental operation of the plasma ferroelectric cathode
in the RF gun [4] has resulted in the generation of an elec-
tron beam with pulse current pulse 4…9 A, with the cur-
rent pulse duration 40…90 ns and particle energy
≅ 500 keV [5]. Within the RF power pulse duration >10-
6 s, the RF gun with the ferroelectric cathode operates in
the storage energy mode and generates the intense elec-
tron beam.
Considerable impact of the space charge forces on
the spatial particle movement in an intense beam gives
rise to errors in intense beam emittance measurements
using the conventional ‘profile scan’ technique. The
beam emittance will be defined highly accurate if meas-
urement technique used has minimum errors. In the pa-
per considered are the estimations of the errors risen
from the emittance measurement of the beam generated
by the RF gun with the plasma ferroelectric cathode.
The ‘pepper-pot’ technique minimises the effect of the
space charge forces on the measurement results. This
technique has been implemented into emittance meas-
urements of the beam studied. The results of the meas-
urements are also summarized in.
2. BEAM INTENSITY ESTIMATION
The intensity rate of the researched beam has been
pre-estimated from results of analysis of the beam enve-
lope equation for the one of transverse direction with
space charge forces taken into account [6]:
( )
2
2 3 3
0
4n
x
x x y
I
I
εσ
γ σ γ σ σ
⋅′′ = +
⋅ ⋅ + , (1)
where I is the beam pulse current, А, I0 – the Alfen cur-
rent, А (17 kA), γ – the Lorenz factor, εn – the normal-
ized emittance, mm⋅mrad, σх, σу – the beam transverse
sizes, mm. The ratio of the second term in the right-
hand side of the Eq. (1) to the first term is a coefficient
K defining the dominant rate of space charge forces in a
beam. In an axisymetric beam assumption (σх=σу≡σо):
2
0
2
0
2
n
IK
I
σ
γ ε
⋅ ⋅=
⋅ ⋅ . (2)
A beam is treated as an intensive one with domina-
tion of the space charge forces, if K > 1. The substitu-
tion of numerical values (I=60 A, γ=1.7, σ0=10 mm, ε
n=180 mm⋅mrad) into the Eq.(2) results in K ≈ 10. This
value defines the beam generated by the RF gun with
the plasma ferroelectric cathode as an intense space
charge dominated beam. In this case, the space charge
forces affect the electron dynamics dominantly and sub-
stantially affect the results of beam parameters measure-
ment.
3. PROFILE SCAN TECHNIQUE TEST
The space charge forces effect on the experimental
beam emittance measurement has been pre-checked us-
ing a wide-usable in accelerator technology technique of
the beam emittance measurement by the definition of a
σ – matrix of a beam passing transport element with a
priory defined transfer matrix R [7]. In the experiment
[5] the beam was generated in the single-cavity RF gun
with the plasma ferroelectric cathode which emitting
surface is ≅ 1 mm2. The beam pulse current and particle
energy is 4.5 A and 500 keV, respectively. For the beam
emittance measurement, there was used an axial lens
with maximum axial magnetic field 2 kOe installed at
the gun exit. According to the technique, the beam emit-
tance is derived as detε σ ′=
uur
, where σ ′
uur
is the beam
matrix at the end of interval ‘lens-drift’. The initial
beam matrix 0σ is derived by the equation 0 TR Rσ σ′ = .
The element 11σ ′ is a beam profile that applying axial
lens is derived as 11 1 /L fσ ў = − , where L is the drift
length, ( ) 22
01/ / 8f aB Bπ ρ= is the focal length of the lens,
a is the lens aperture, Bρ is the magnetic rigidity, В0 is
the maximum axial field of the length. The beam profile
has been measured for three different values of magnet-
ic field by the system of actuator-driven slits with
0.2 mm slit width. The drift length was 230 mm. The
measured normalized beam emittance in horizontal
plane is εх=109 mm⋅mrad.
The space charge forces effect on the measurement
result has been estimated using computer simulation of
____________________________________________________________
PROBLEMS OF ATOMIC SCIENCE AND TECHNOLOGY. 2006. № 3.
Series: Nuclear Physics Investigations (47), p.104-106.104
mailto:khiv@kipt.kharkov.ua
the measurement procedure. An electron beam with cor-
responding pulse current was simulated with
PARMELA code [8]. Twiss parameters of the beam α,
β, γ were the input data for the program TRACE3D [9],
which computes beam particle trajectories in a defined
transport channel using the matrix instrumentation with
the space charge forces both taken and not taken into ac-
count. The normalized beam emittance computed with
the space charge forces taken into account is εx=117 mm
⋅mrad that corresponds to the measured value with rela-
tive error 1%. The value of the normalized emittance
computed without space charge forces is εx=27 mm⋅
mrad that is approximately four times smaller than the
value computed with the space charge forces taken into
account. Therefore, the emittance measurement of the
researched beam using the outlined above technique is
featured by a high (> 100%) relative error.
4. ‘PEPPER-POT’ MEASUREMENTS
The beam emittance of the RF gun with the plasma
ferroelectric cathode has been measured using the ‘pep-
per-pot’ technique. The main idea of the technique is the
collimation of a beam into beamlets with the space
charge forces effect neglected. This permits elimination
of the space charge forces effect from the error estimation
of the measuring procedure that makes the high accuracy
measurement of intense beams with K∼102 to be possible
[10]. Particle density distribution and total beam emit-
tance is deduced from the measured angular divergence
and particle density distribution in the beamlets according
to the corresponding analytical relations [6].
The beam in a transport channel is collimated by the
plate P (Fig.1) with apertures that are disposed with the
definite step d across the probable beam cross-section.
The detecting plane M is disposed on the distance L
from the plate P. Each beamlet width in the detecting
plane is the direct measure of the width of the transverse
momentum distribution in the collimating plane. The to-
tal beam emittance is deduced directly from the beam
intensity distribution under the approximation of the
Gauss beam particle distribution [11].
Fig.1. «Pepper-pot» layout
For the experimental emittance measurement all ele-
ments of the two-plate system has been calculated in the
definite order according to the technique requirements
[6]. Initial data for the calculation have been accepted
from the following beam parameters: pulse current is
4.5 A, normalized emittance is 200 mm⋅mrad and parti-
cle energy is 500 keV.
The collimating plate P is made of tantalum of
0.2 mm thickness. The plate material and its thickness
are defined by the length of the total beam absorption in
material. The length is approximated by the relation [6]:
( )
( ) ( )2 1 31.5s
W MeVWL dW MeV cm g g cmdx ρ− − −
= ≈
⋅ ⋅ ⋅ ⋅ , (3)
where W is the beam particle energy, ρ is the material
density. Twenty-five apertures of 0.5 mm diameter are
disposed in crossing of horizontal and vertical lines and
grouped in five per line. The lines are distributed from
the origin axial lines uniformly across the plate P with
the step of 2 mm. The distance between the plate P and
the plane M is 50 mm. For the calculated parameters of
the measuring system, the ratio K in a single beamlet is
5⋅10-4 that fits the condition K<<1 of the space charge
forces neglecting in a beam.
The particle density distribution in each beamlet is
defined from the total beam current distribution that has
been measured within the detecting plane using the ac-
tuator-driven slit and Faraday cup. Distribution of the
total beam current measured in transverse direction X
includes four beamlet current distributions (Fig.2). The
point X=0 mm corresponds to an axial symmetry of the
beam pipe.
Fig.2. Intensity distribution of the total beam passed
through the collimated plate
The fifth distribution that should be in the left-hand
side was not detected. It is most evidently that the
amount of particles is too small to be detected or the
particle divergence is too large to be resolved. Each dis-
tribution can be approximated by a Gaussian function
[11] that permits derivation of the angular divergence in
each beamlet. Beam trace space constructed from the
beamlet intensity profile is illustrated in Fig.3.
Fig.3. Beam trace space
Each point represents the position of the beamlet in
the trace space and the error bars indicate the most prob-
able thermal spread of the beamlets. RMS emittance is
derived from the second moments of the trace space dis-
tributions as following:
22 2
x x x xxε ў ў= − .
It is easy to derive Twiss parameters of the total beam
from this equation that permits definition the matrix co-
efficients for each beamlet. The matrix coefficients con-
version into rectangular frame coordinates resolves el-
lipse envelope for each beamlet and the total beam. A
____________________________________________________________
PROBLEMS OF ATOMIC SCIENCE AND TECHNOLOGY. 2006. № 3.
Series: Nuclear Physics Investigations (47), p.104-106.105
contour plot (Fig.4) is the representation of the resolved
ellipse envelopes. According to the resolved phase
space of the total beam (Fig.4, the largest ellipse) the
measured normalized beam emittance is 40 mm⋅mrad
for 50% of particles passed through the collimating
plate.
Fig.4. Phase space approximated ellipses for the mea-
sured beam intensity distributions
CONCLUSION
Because of too large errors (up to 300%), the pro-
file-scan technique cannot be used for the emittance
measurements of the beam generated by the RF gun
with the plasma ferroelectric cathode. The emittance
measurement has an essentially lower error in case of
using the ‘pepper-pot’ technique. Corresponding mea-
suring system has been designed and applied to the
emittance measurements of beam with current in a
bunch 60 A and electron energy 500 keV. The measured
normalized beam emittance is 40 mm⋅mrad.
ACKNOWLEDGEMENT
The authors are exceedingly grateful to the staff of
R&D "Accelerator" of the NSC KIPT for their help
throughout the experimental period. Special thanks are
to Dr. V.V. Mitrochenko for the useful discussions of
the emittance evaluation procedure.
REFERENCES
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3. N.V. Demidov, V.S. Demin, A.N. Dovbnya et.al.
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4. I.V. Khodak, V.A. Kushnir. Performances of the
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Switzerland. 2004, p.767-769.
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fects in high brightness electron beam emittance
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8. L.M. Young. PARMELA. Los Alamos LA-UR-96-
1835, Ver.3.21 for PC, 2002.
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tation. Los Alamos LA-UR-97-886, Third edition,
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nance accelerators. М.: “Атомizdat”, 1966, p.310
(in Russian).
11. M.E. Dolinska, N.L. Doroshko. Pepper-pot diag-
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ИЗМЕРЕНИЕ ЭМИТТАНСА ЭЛЕКТРОННОГО ПУЧКА В ВЧ-ПУШКЕ С ПЛАЗМЕННЫМ ФЕРРО-
ЭЛЕКТРИЧЕСКИМ КАТОДОМ
И.В. Ходак, В.А. Кушнир
ВЧ-пушка с плазменным ферроэлектрическим катодом может генерировать интенсивные электронные
пучки с током в сгустке до 102 A. Силы пространственного заряда такого пучка увеличивают погрешности
измерения эмиттанса с использованием квадруполей. В работе рассмотрены погрешности измерений и реа-
лизован ‘pepper-pot’-метод измерения эмиттанса. Был исследован эмиттанс пучка, генерируемого однорезо-
наторной ВЧ-пушкой S-диапазона с плазменным ферроэлектрическим катодом. Импульсный ток пучка со-
ставляет 6 A (ток в сгустке до 60 А) при длительности импульса 40…90 нс и энергии электронов ≅ 500 кэВ.
106
ВИМІР ЕМІТАНСУ ЕЛЕКТРОННОГО ПУЧКА У ВЧ-ГАРМАТІ З ПЛАЗМОВИМ
ФЕРОЕЛЕКТРИЧНИМ КАТОДОМ
І.В. Ходак, В.А. Кушнір
ВЧ-гармата з плазмовим фероелектричним катодом може генерувати інтенсивні електронні пучки зі
струмом у згустку до 102 A. Сили просторового заряду такого пучка завищують погрішності вимірювання
емітансу з використанням квадруполів. В роботі розглянуті погрішності вимірювань та реалізований
‘pepper-pot’-метод вимірювання емітансу. Було досліджено емітанс пучка, що генерується
однорезонаторною ВЧ-гарматою S-діапазону з плазмовим фероелектричним катодом. Імпульсний струм
пучка дорівнює 6 A (струм в згустку до 60 А) при тривалості імпульсу 40…90 нс та енергії електронів
≅ 500 кеВ.
____________________________________________________________
PROBLEMS OF ATOMIC SCIENCE AND TECHNOLOGY. 2006. № 3.
Series: Nuclear Physics Investigations (47), p.104-106.107
ИЗМЕРЕНИЕ ЭМИТТАНСА ЭЛЕКТРОННОГО ПУЧКА В ВЧ-ПУШКЕ С ПЛАЗМЕННЫМ ФЕРРОЭЛЕКТРИЧЕСКИМ КАТОДОМ
ВИМІР ЕМІТАНСУ ЕЛЕКТРОНнОГО ПУЧКА У ВЧ-гарматі з ПЛАЗМовим ФЕРОЕЛЕКТРИЧнИМ КАТОДОМ
|
| id | nasplib_isofts_kiev_ua-123456789-79732 |
| institution | Digital Library of Periodicals of National Academy of Sciences of Ukraine |
| issn | 1562-6016 |
| language | English |
| last_indexed | 2025-12-07T16:28:17Z |
| publishDate | 2006 |
| publisher | Національний науковий центр «Харківський фізико-технічний інститут» НАН України |
| record_format | dspace |
| spelling | Khodak, I.V. Kushnir, V.A. 2015-04-04T12:30:12Z 2015-04-04T12:30:12Z 2006 Emittance measurement of electron beam of RF gun with plasma ferroelectric cathode / I.V. Khodak, V.A. Kushnir // Вопросы атомной науки и техники. — 2006. — № 3. — С. 104-106. — Бібліогр.: 11 назв. — англ. 1562-6016 PACS: 29.25.Bx, 41.75.-i, 52.59.Sa, 06.90.+v https://nasplib.isofts.kiev.ua/handle/123456789/79732 An RF gun with a plasma ferroelectric cathode can generate intense electron beams with peak current in a bunch up to 10² A. The space charge forces of the beam increase errors of the beam emittance measurement using a ‘quadrupole’ technique. The errors of the measurements and the implementation of the ‘pepper-pot’ technique are referred in the paper. Studied is the beam emittance generated by a single-cell S-band RF gun with the plasma ferroelectric cathode. The beam pulse current is 6 A (current in a bunch is 60 A) with pulse duration 40…90 ns and particle energy ≅ 500 keV. ВЧ-пушка с плазменным ферроэлектрическим катодом может генерировать интенсивные электронные пучки с током в сгустке до 10² A. Силы пространственного заряда такого пучка увеличивают погрешности измерения эмиттанса с использованием квадруполей. В работе рассмотрены погрешности измерений и реализован ‘pepper-pot’-метод измерения эмиттанса. Был исследован эмиттанс пучка, генерируемого однорезонаторной ВЧ-пушкой S-диапазона с плазменным ферроэлектрическим катодом. Импульсный ток пучка составляет 6 A (ток в сгустке до 60 А) при длительности импульса 40…90 нс и энергии электронов ≅ 500 кэВ. ВЧ-гармата з плазмовим фероелектричним катодом може генерувати інтенсивні електронні пучки зі струмом у згустку до 10² A. Сили просторового заряду такого пучка завищують погрішності вимірювання емітансу з використанням квадруполів. В роботі розглянуті погрішності вимірювань та реалізований ‘pepper-pot’-метод вимірювання емітансу. Було досліджено емітанс пучка, що генерується однорезонаторною ВЧ-гарматою S-діапазону з плазмовим фероелектричним катодом. Імпульсний струм пучка дорівнює 6 A (струм в згустку до 60 А) при тривалості імпульсу 40…90 нс та енергії електронів ≅ 500 кеВ. The authors are exceedingly grateful to the staff of R&D "Accelerator" of the NSC KIPT for their help throughout the experimental period. Special thanks are to Dr. V.V. Mitrochenko for the useful discussions of the emittance evaluation procedure en Національний науковий центр «Харківський фізико-технічний інститут» НАН України Вопросы атомной науки и техники Ускорители заряженных частиц Emittance measurement of electron beam of RF gun with plasma ferroelectric cathode Измерение эмиттанса электронного пучка в ВЧ-пушке с плазменным ферроэлектрическим катодом Вимір емітансу електронного пучка у ВЧ-гарматі з плазмовим фероелектричним катодом Article published earlier |
| spellingShingle | Emittance measurement of electron beam of RF gun with plasma ferroelectric cathode Khodak, I.V. Kushnir, V.A. Ускорители заряженных частиц |
| title | Emittance measurement of electron beam of RF gun with plasma ferroelectric cathode |
| title_alt | Измерение эмиттанса электронного пучка в ВЧ-пушке с плазменным ферроэлектрическим катодом Вимір емітансу електронного пучка у ВЧ-гарматі з плазмовим фероелектричним катодом |
| title_full | Emittance measurement of electron beam of RF gun with plasma ferroelectric cathode |
| title_fullStr | Emittance measurement of electron beam of RF gun with plasma ferroelectric cathode |
| title_full_unstemmed | Emittance measurement of electron beam of RF gun with plasma ferroelectric cathode |
| title_short | Emittance measurement of electron beam of RF gun with plasma ferroelectric cathode |
| title_sort | emittance measurement of electron beam of rf gun with plasma ferroelectric cathode |
| topic | Ускорители заряженных частиц |
| topic_facet | Ускорители заряженных частиц |
| url | https://nasplib.isofts.kiev.ua/handle/123456789/79732 |
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