High-temperature metallic cathode for RF gun
In the paper a metallic thermionic cathode with an electron beam heating to be used in RF gun is proposed. The high-temperature metallic emitter made of high-melting material will allow to decrease significantly the pulse current growth and to increase pulse repetition rate. The electron-optic syste...
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| Cite this: | High-temperature metallic cathode for RF gun / E.Z. Biller, I.V. Khodak, V.A. Kushnir, V.V. Mitrochenko, L.K. M'akushko, D.L. Stepin, V.F. Zhiglo // Вопросы атомной науки и техники. — 2001. — № 5. — С. 103-105. — Бібліогр.: 5 назв. — англ. |
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Biller, E.Z. Khodak, I.V. Kushnir, V.A. Mitrochenko, V.V. M'akushko, L.K. Stepin, D.L. Zhiglo, V.F. 2015-03-24T15:45:04Z 2015-03-24T15:45:04Z 2001 High-temperature metallic cathode for RF gun / E.Z. Biller, I.V. Khodak, V.A. Kushnir, V.V. Mitrochenko, L.K. M'akushko, D.L. Stepin, V.F. Zhiglo // Вопросы атомной науки и техники. — 2001. — № 5. — С. 103-105. — Бібліогр.: 5 назв. — англ. 1562-6016 PACS numbers: 29.25.Bx, 41.85.Ar https://nasplib.isofts.kiev.ua/handle/123456789/78980 In the paper a metallic thermionic cathode with an electron beam heating to be used in RF gun is proposed. The high-temperature metallic emitter made of high-melting material will allow to decrease significantly the pulse current growth and to increase pulse repetition rate. The electron-optic system of the heating gun provides a beam current density at the plane of the heated emitter that is enough for its heating up. Simulation showed that at the heating beam power of 75 W, the emission current from the tantalum emitter surface would be about 150 mA. The cathode assembly prototype has been designed and results of its pilot tests are described. en Національний науковий центр «Харківський фізико-технічний інститут» НАН України Вопросы атомной науки и техники High-temperature metallic cathode for RF gun Высокотемпературный металлический катод для высокочастотной электронной пушки Article published earlier |
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| title |
High-temperature metallic cathode for RF gun |
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High-temperature metallic cathode for RF gun Biller, E.Z. Khodak, I.V. Kushnir, V.A. Mitrochenko, V.V. M'akushko, L.K. Stepin, D.L. Zhiglo, V.F. |
| title_short |
High-temperature metallic cathode for RF gun |
| title_full |
High-temperature metallic cathode for RF gun |
| title_fullStr |
High-temperature metallic cathode for RF gun |
| title_full_unstemmed |
High-temperature metallic cathode for RF gun |
| title_sort |
high-temperature metallic cathode for rf gun |
| author |
Biller, E.Z. Khodak, I.V. Kushnir, V.A. Mitrochenko, V.V. M'akushko, L.K. Stepin, D.L. Zhiglo, V.F. |
| author_facet |
Biller, E.Z. Khodak, I.V. Kushnir, V.A. Mitrochenko, V.V. M'akushko, L.K. Stepin, D.L. Zhiglo, V.F. |
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2001 |
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English |
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Вопросы атомной науки и техники |
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Національний науковий центр «Харківський фізико-технічний інститут» НАН України |
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Article |
| title_alt |
Высокотемпературный металлический катод для высокочастотной электронной пушки |
| description |
In the paper a metallic thermionic cathode with an electron beam heating to be used in RF gun is proposed. The high-temperature metallic emitter made of high-melting material will allow to decrease significantly the pulse current growth and to increase pulse repetition rate. The electron-optic system of the heating gun provides a beam current density at the plane of the heated emitter that is enough for its heating up. Simulation showed that at the heating beam power of 75 W, the emission current from the tantalum emitter surface would be about 150 mA. The cathode assembly prototype has been designed and results of its pilot tests are described.
|
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1562-6016 |
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https://nasplib.isofts.kiev.ua/handle/123456789/78980 |
| citation_txt |
High-temperature metallic cathode for RF gun / E.Z. Biller, I.V. Khodak, V.A. Kushnir, V.V. Mitrochenko, L.K. M'akushko, D.L. Stepin, V.F. Zhiglo // Вопросы атомной науки и техники. — 2001. — № 5. — С. 103-105. — Бібліогр.: 5 назв. — англ. |
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2025-11-24T18:04:31Z |
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2025-11-24T18:04:31Z |
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| fulltext |
HIGH-TEMPERATURE METALLIC CATHODE FOR RF GUN
E.Z. Biller, I.V. Khodak, V.A. Kushnir, V.V. Mitrochenko,
L.K. M'akushko, D.L. Stepin, V.F. Zhiglo
NSC KIPT, Kharkov, Ukraine
e-mail: khiv@kipt.kharkov.ua
In the paper a metallic thermionic cathode with an electron beam heating to be used in RF gun is proposed. The
high-temperature metallic emitter made of high-melting material will allow to decrease significantly the pulse cur-
rent growth and to increase pulse repetition rate. The electron-optic system of the heating gun provides a beam cur-
rent density at the plane of the heated emitter that is enough for its heating up. Simulation showed that at the heating
beam power of 75 W, the emission current from the tantalum emitter surface would be about 150 mA. The cathode
assembly prototype has been designed and results of its pilot tests are described.
PACS numbers: 29.25.Bx, 41.85.Ar
1 INTRODUCTION
Radiofrequency electron sources (RF guns) have
been recently very common used in high-energy re-
search accelerators as well as in various applied acceler-
ators. RF guns permit to obtain intense high-brightness
electron beams. However, RF guns with thermionic
cathodes are featured by the cathode back electron bom-
bardment inducing the cathode heating-up during a RF
power supply pulse that results in a rise of the output
current of the gun. Cathodes with a low operating tem-
perature (800°-1400°С), commonly used in such guns,
limit their application in linear resonance electron accel-
erators due to the cathode overheating when operating
in a high average current mode (pulse repetition rate
usually not exceeds a few tens of pulses per second).
There is some experience to reduce the back electron
bombardment effect [1-3]. A method we propose to re-
duce the influence of bombardment effect on output
beam performances of a RF gun consists in using a
thermionic cathode with high work function. A metallic
emitter heated to high temperature by an electron beam
of an additional heating-up gun can be used as well. It
will permit to decrease the rise of output current as well
as to increase the pulse repetition rate. We aim to reach
pulse repetition rate of 50 pps at least.
The paper represents the design of a cathode assem-
bly for the multipurpose two-cavity RF gun [4]. The
cathode assembly includes a diode heating-up electron
gun of the metallic emitter. The paper describes the cal-
culation of the electron-optic system of this gun and
beam temperature distribution in the metallic emitter.
Design features of the cathode assembly and results of
pilot tests are also considered.
2 CALCULATIONS
High operating temperature of the RF gun cathode
decreases the relative temperature variation under back
electron bombardment and as result decreases the
change of the emission current. For example the temper-
ature variation of cathodes in 100°С causes the emission
current growth in 100 % for a high-temperature emitter
(work function is equal to 4.2 eV) and in 300% for the
low-temperature emitter (work function is equal to
1.8 eV). In the above example the Schottky effect was
taken into account for typical values of the electric field
near a cathode in the thermionic RF guns. The heating
cathode power is increased under application of the
high-temperature cathode that permits its operation un-
der high value of average back bombardment power.
It is assumed the RF gun operation with a pulse cur-
rent of 50-100 mA at its output. Taking into account
electron losses in the gun cavities, the current of the
metallic cathode should be ∼ 100-150 mA. Size of the
emitting surface should not be higher of 3 mm in diame-
ter.
Comparative analysis of emission properties of vari-
ous materials has shown that tantalum is most suitable
for given requirements.
Solving of the heat conduction equation with bound-
ary conditions taking into account radiant heat transfer
we carried out the estimation of a heating beam power,
under which the required emission current can be pro-
duced. The blackness factor of the material was taken
equal to 1 to estimate the maximum heating power to
obtain a required temperature. The temperature distribu-
tion on a surface of the tantalum emitter having 5 mm in
diameter and 0.3 mm in thickness was computed for
various heating power values. Temperature distributions
obtained for the three values are shown in Fig. 1.
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5
600
800
1000
1200
1400
1600
1800
2000
2200
2400
2600
R, mm
T
, °
K
50 W
60 W
70 W
Fig. 1. Temperature distribution versus emitter sur-
face.
Integrating the emission current density over the
emitter surface allows obtaining the emitted current as a
ВОПРОСЫ АТОМНОЙ НАУКИ И ТЕХНИКИ. 2001. №5.
Серия: Ядерно-физические исследования (39), с. 103-105.
103
mailto:khiv@kipt.kharkov.ua
function of the heating power. Computed results are
shown in Fig. 2.
50 55 60 65 70 75 80
2000
2200
2400
2600
2800
3000
P (W)
T (°K)
50 55 60 65 70 75 800
100
200
300
400
Ic (mA)
Fig. 2. Temperature in a center of the emitting sur-
face ( --- ) and emission current ( ) versus heat-
ing power.
Analysis of emitted current distribution over the sur-
face shows that a diameter of an emitting spot actually
is not more than 3 mm.
Calculation shows that the heating beam power is no
higher than 80 W. Nevertheless, this value was accepted
of 90 W for the design of the heating-up electron gun to
have some reserve of power.
The heating-up gun was designed on the basis of the
needed heating power and hardware features of the RF
gun cathode assembly. The flat cathode of 2.8 mm in di-
ameter is used in the heating-up gun. Therefore the
beam compression ration should be 1 or little higher.
Geometry of the electron-optic system of the gun was
calculated using the EGUN code [5]. The final geome-
try of the heating-up gun is shown in Fig. 3 where the
beam envelope is shown too. Herein the position Z=0
corresponds to the cathode position and the position
Z=18 corresponds to the position of the tantalum emit-
ter.
0 2 4 6 8 10 12 14 16 18
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
R
, m
m
Z, mm
Fig. 3. EGUN simulation of heating-up electron
gun.
The gun produces a laminar electron beam with uni-
form current density distribution on the cathode surface.
The ratio of the current density between edge and center
of the cathode is 1.05 and the maximum current density
is 0.48 A/cm2. The geometry obtained permits the gun
to produce the electron beam with a maximum current
of 30 mA, perveance of 0.187⋅10-6 A/V3/2 under the an-
ode voltage of 3 kV. Fig. 4 shows the transverse elec-
tron beam profile at the plane of tantalum emitter re-
computed using the results of EGUN simulation.
-1.5 -1 -0.5 0 0.5 1 1.5
0
0.05
0.1
0.15
0.2
X, mm
J,
A/
cm
2
Fig. 4. Transverse beam profile at the tantalum
emitter plane.
Summarizing calculated results, accepted were pa-
rameters of the heating-up gun and tantalum emitter
which are tabulated in Table 1.
Table 1
Emission current of tantalum emitter,
mA
100-150
Heating-up power, W Up to 90
Maximum current of heating-up gun,
mA
∼30
Perveance, ⋅10-6, A/V3/2 0.187
Maximum anode voltage, kV 3
Beam compression ratio ∼1
3 CATHODE ASSEMBLY DESIGN
The designed hardware combines hardware proper-
ties that are featured for both diode electron guns and
cathode assemblies for RF guns. First ones are as fol-
lowing: electric reliability, accuracy in manufacturing
and mounting the elements of a gun electron-optic sys-
tem. In the second case, the importance is in the possi-
bility of RF gun resonance system tuning by a cathode
moving in the longitudinal direction.
Calculated overall dimensions of the heating-up gun
permitted to place it in the safety tube applied in RF gun
(see Fig. 5) and to use the tube as an anode. Tantalum
emitter is placed at the safety tube face. Seeing that
safety tube can move in the longitudinal direction the
heating-up gun is rigidly fixed with safety tube holders.
When assembling, cathode is rigidly fixed with the fo-
cusing electrode and, further, is rigidly fixed relatively
to the anode. The cathode together with focusing elec-
trode is insulated from the anode by cylindric insulating
ВОПРОСЫ АТОМНОЙ НАУКИ И ТЕХНИКИ. 2001. №5.
Серия: Ядерно-физические исследования (39), с. 104-105.
104
inserts that except temperature distortions besides the
insulation.
Because the heating-up gun is in closed volume the
safety tube has additional holes for a vacuum pumping
down. Cathode based on the impregnated tungsten emit-
ter is applied in the heating-up gun that gives the low
filament power.
The cathode assembly hardware is enough compact.
Overall longitudinal dimension of the assembly is no
higher then 170 mm.
Fig. 5. Cathode Assembly Design:
1 - heating-up gun, 2 - tantalum emitter, 3 - safety
tube (anode), 4 - cathode, 5 - focusing electrode.
4 PILOT TESTS
After being assembled the cathode unit was installed
on the test set-up and was tested under an anode voltage
of 3 kV. Then the current of heating-up gun of 20 mA
was obtained. Temperature was measured using the op-
tic pyrometer. Under an anode voltage of 3 kV the tem-
perature of the tantalum emitter surface localized by the
beam of the heating-up gun was ~2300°K. Size of this
surface was controlled visually by its bright glow and
was no higher then 3 mm in diameter. Vacuum in the
test set-up was no lower then 10-6 torr during tests.
Regardless of the fact that obtained temperature of
the tantalum emitter is some lower that needed one it is
possible to start experiments with cathode assembly in-
stalled into the RF gun. Back electron bombardment
will create additional source of tantalum emitter heat-
ing-up therefore we hope to reach needed output cur-
rent. The experiments will start in near future.
5 CONCLUSION
Application of the electron emitter with a high oper-
ating temperature permits to reduce influence of the
back electron bombardment effect on the RF gun beam
parameters.
The compact cathode assembly based on the tanta-
lum emitter heated by an additional electron beam was
designed and manufactured for the multipurpose RF
gun. Pilot tests of the cathode assembly have shown that
electron heating-up provides the cathode temperature
proximate to the calculated one.
Further investigations of the metallic emitter will be
held after its mounting in the RF gun.
REFERENCES
1. V.A.Kushnir, V.V.Mitrochenko, Wang-Gang. Re-
ducing the back bombarding effect in a thermionic
RF-gun // Proc. of 14 Workshop on Charged Parti-
cles Accelerators, Protvino, 1994, v. 3, p. 97-102.
2. С.B.McKee and John M.J. Madey // Nuclear In-
struments and Methods in Physics Research. 1990,
A296, p. 716-719.
3. V.V.Mitrochenko. Thermionic RF Gun with High
Duty Factor // Proc. of the 17th Particle Accelerator
Conference, Vancouver (Canada), 1997, vol. 3,
p. 2817-2819.
4. N.I.Aizatsky, E.Z.Biller, A.N.Dovbnya et. al. Two-
cell RF gun for a high-brightness linac // Proc. of
the fifth European Particle Accelerator Conference,
Sitges (Barcelona), 1996, v. 2, p. 1553-1555.
5. W.B.Herrmannsfeldt. EGUN: Electron Optics Pro-
gram, Stanford Linear Accelerator Center, SLAC-
PUB-6729, 1994.
ВОПРОСЫ АТОМНОЙ НАУКИ И ТЕХНИКИ. 2001. №5.
Серия: Ядерно-физические исследования (39), с. 105-105.
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