Forming of precision thin-wall hollow electron beams for microwave generators
The electron gun producing the precision hollow relativistic electron beam for coherent microwave generator applications has been developed and tested. It is based on the large non-adiabatic compression of the beam emitted by ring-shaped cathode with an active surface big enough to produce a wa...
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Національний науковий центр «Харківський фізико-технічний інститут» НАН України
1999
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| Zitieren: | Forming of precision thin-wall hollow electron beams for microwave generators / A.V. Agafonov, E.G. Krastelev, A.N. Lebedev, V.S. Voronin, P.N. Lebedev // Вопросы атомной науки и техники. — 1999. — № 4. — С. 77-78. — Бібліогр.: 5 назв. — англ. |
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irk-123456789-814982015-05-18T03:01:58Z Forming of precision thin-wall hollow electron beams for microwave generators Agafonov, A.V. Krastelev, E.G. Lebedev, A.N. Voronin, V.S. Lebedev, P.N. The electron gun producing the precision hollow relativistic electron beam for coherent microwave generator applications has been developed and tested. It is based on the large non-adiabatic compression of the beam emitted by ring-shaped cathode with an active surface big enough to produce a wanted current level. Further improvement of beam quality is possible by decreasing of the width of the annular emitter and increasing its emissive power. 1999 Article Forming of precision thin-wall hollow electron beams for microwave generators / A.V. Agafonov, E.G. Krastelev, A.N. Lebedev, V.S. Voronin, P.N. Lebedev // Вопросы атомной науки и техники. — 1999. — № 4. — С. 77-78. — Бібліогр.: 5 назв. — англ. 1562-6016 http://dspace.nbuv.gov.ua/handle/123456789/81498 en Вопросы атомной науки и техники Національний науковий центр «Харківський фізико-технічний інститут» НАН України |
| institution |
Digital Library of Periodicals of National Academy of Sciences of Ukraine |
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DSpace DC |
| language |
English |
| description |
The electron gun producing the precision hollow
relativistic electron beam for coherent microwave
generator applications has been developed and tested. It
is based on the large non-adiabatic compression of the
beam emitted by ring-shaped cathode with an active
surface big enough to produce a wanted current level.
Further improvement of beam quality is possible by
decreasing of the width of the annular emitter and
increasing its emissive power. |
| format |
Article |
| author |
Agafonov, A.V. Krastelev, E.G. Lebedev, A.N. Voronin, V.S. Lebedev, P.N. |
| spellingShingle |
Agafonov, A.V. Krastelev, E.G. Lebedev, A.N. Voronin, V.S. Lebedev, P.N. Forming of precision thin-wall hollow electron beams for microwave generators Вопросы атомной науки и техники |
| author_facet |
Agafonov, A.V. Krastelev, E.G. Lebedev, A.N. Voronin, V.S. Lebedev, P.N. |
| author_sort |
Agafonov, A.V. |
| title |
Forming of precision thin-wall hollow electron beams for microwave generators |
| title_short |
Forming of precision thin-wall hollow electron beams for microwave generators |
| title_full |
Forming of precision thin-wall hollow electron beams for microwave generators |
| title_fullStr |
Forming of precision thin-wall hollow electron beams for microwave generators |
| title_full_unstemmed |
Forming of precision thin-wall hollow electron beams for microwave generators |
| title_sort |
forming of precision thin-wall hollow electron beams for microwave generators |
| publisher |
Національний науковий центр «Харківський фізико-технічний інститут» НАН України |
| publishDate |
1999 |
| url |
http://dspace.nbuv.gov.ua/handle/123456789/81498 |
| citation_txt |
Forming of precision thin-wall hollow electron beams for microwave generators / A.V. Agafonov, E.G. Krastelev, A.N. Lebedev, V.S. Voronin, P.N. Lebedev // Вопросы атомной науки и техники. — 1999. — № 4. — С. 77-78. — Бібліогр.: 5 назв. — англ. |
| series |
Вопросы атомной науки и техники |
| work_keys_str_mv |
AT agafonovav formingofprecisionthinwallhollowelectronbeamsformicrowavegenerators AT krasteleveg formingofprecisionthinwallhollowelectronbeamsformicrowavegenerators AT lebedevan formingofprecisionthinwallhollowelectronbeamsformicrowavegenerators AT voroninvs formingofprecisionthinwallhollowelectronbeamsformicrowavegenerators AT lebedevpn formingofprecisionthinwallhollowelectronbeamsformicrowavegenerators |
| first_indexed |
2025-07-06T06:28:11Z |
| last_indexed |
2025-07-06T06:28:11Z |
| _version_ |
1836877921256472576 |
| fulltext |
FORMING OF PRECISION THIN-WALL HOLLOW ELECTRON BEAMS
FOR MICROWAVE GENERATORS
A.V. Agafonov, E.G. Krastelev, A.N. Lebedev, V.S.Voronin, P.N. Lebedev
Physical Institute of RAS, Moscow, Russia
INTRODUCTION
Effective operation of a short-wave-length
Cherenkov-type free-electron laser implies employment
of a high-quality intense electron beam with small
spread in longitudinal momentum and beam-wall
separation comparable with the radiation wave-length
times Lorentz-factor of the electrons. A specialized e-
gun to produce a high brightness beam for sub-
millimeter FEL application has been designed and
constructed with parameters indicated in Table 1, [1, 2].
A plane, ring-shaped, thermionic lanthanum
hexaboride cathode, having a 28-mm average radius
and a 6−8 mm width, is used to produce an annular
beam. The cathode surface is screened by two focusing
electrodes to operate in a space charge limited regime.
Uniformity of temperature distribution across the ring-
shaped cathode is provided by a machined-graphite
heater. Its current is fed in bifilar geometry. The
focusing system must form a laminar beam inside the
accelerating gap at rather low magnetic field and
transport the beam to an experimental region of about
50 cm length with large magnetic field of about 15 kG.
Table 1
Voltage, V 300 − 500 kV
Beam current, I > 100 A
Repetition rate, f Up to 10 Hz
Beam mean diameter inside
the interaction region, d
5 mm
Beam mean diameter at the
cathode, D
56 mm
Beam thickness inside the
interaction region, ∆
< 1 mm
Longitudinal momentum
spread, ∆pz /pz
<1%
BUMP-SCHEME OF BEAM FORMATION AND
COMPUTER SIMULATION OF BEAM
DYNAMICS
To preserve the low beam emittance under the
strong non-adiabatic compression and under possible
variations of beam energy, the main dynamics was
calculated using three codes.
A single particle code TRACE providing high-
precision trajectory calculations was used to optimize
the magnetic field profile with respect to the
longitudinal momentum spread of electrons emitted
from different points of the cathode. The main
calculations of the beam self-consistent dynamics were
carried out with electromagnetic PIC-code KARAT [3].
The steady-state code SAM [4] was used to verify
integral characteristics of the beam.
The last two codes gave approximately the same
integral characteristics of the beam but different
structures of the flow especially in the region near the
cathode surface. In particular, in a transient regime
some hysteresis effects were observed [5].
The results of computations listed below are
relevant to the gap region. An additional compression
with a separate matched solenoid will be provided at the
FEL entrance.
Fig 1: A simplified electrode configuration with
magnetic coils and corresponding beam profile. The
calculated microperveance was 0.525 µA/V3/2
A simplified electrode configuration with
magnetic coils and corresponding beam behavior are
presented in Fig.1. The required magnetic field formed
by three coils is also shown in Fig.2.
Fig 2: The required magnetic field formed by three
coils
The third coil produces the main magnetic field.
It is used for investigation of beam dynamics and its
parameters at the output of the gun. It has to be changed
for a long matched solenoid for experimental
investigation of FEL. The second coil and the first one
are correcting and focusing elements simultaneously.
The distance between them and currents in the coils are
parameters, which used to “seat” electrons on the right
magnetic force line. The first coil provides an opposite
magnetic flux to create a correcting bump in the
magnetic field profile. The second coil provides the
sharp rise of the magnetic field at the background of the
field created by third coil.
The longitudinal momentum spread was found
to be rather sensitive with respect to coil position and
currents: ± 1 mm displacement of one of the first two
coils led to a significant increase in the spread and in
the beam wall thickness. About the same effect was
induced by ± 1% current variations in the coils. The
effect of common displacements of the coils or
common variations of the currents was weaker. The
position of the 3-d coil and its current variations are not
so crucial. It should be noted that the crossover formed
ВОПРОСЫ АТОМНОЙ НАУКИ И ТЕХНИКИ. 1999. № 4.
Серия: Ядерно-физические исследования (35), с. 77-78.
77
close to the cathode under action of the focusing
electrodes in single-particle calculations disappears as a
result of beam space charge, which in this case
favorably affects beam quality.
Fig.3a shows the trajectories of three individual
particles emitted, respectively, from the cathode central,
inner and outer radius of the annular cathode, and the
magnetic field line of force passing through the
emitting point at the central radius. Fig.3b shows the
behavior of the longitudinal and transversal momenta of
these three electrons.
Fig 3: The trajectories of three test particles, emitted
from central, inner and outer radius of the annular
cathode (a) and the behavior of longitudinal and
transversal momenta (b).
The trajectory of the electron emitted from
central part of the cathode follows along magnetic field
line in the region of large magnetic field and crosses
field lines inside the gap (Fig. 3a). The jump of the
electron finishes smoothly at the slope of the field line
with transversal momentum close to zero (Fig. 3b).
Varying the bump of the field and the position of the
first coil the same thing can be done with electrons
emitted from inner or outer radius of the cathode.
An interesting feature of the chosen scheme is
the scaling of coil exciting currents when changing
accelerating voltage. For a fixed anode-cathode
separation and variation of voltage from 200 to 500 kV,
the beam structure remains practically unchanged if the
coil currents are varied proportionally to the total
momentum of particles corresponding to the applied
voltage. This feature can turn out to be useful in
creating an overall control system.
THE EXPERIMENTAL GUN
The scheme of the experimental gun is shown in
Fig.4. The insulator of the gun consists of two parts: a
conical ceramic (situll) part and a base Plexiglas
diaphragm. A cathode cap with a water-cooled power
supply junction is located at the top of the cone. The
Plexiglas diaphragm is specially profiled to distribute
the electric field uniformly. The 1:3 voltage ratio on the
two parts of the insulator is produced by a resistive
divider.
The cathode block includes a ring-shaped
thermo emitter, central and peripheral focussing
electrodes, a heater and heat screens. The changeable
thermoemitter was formed by LaB6 deposition on a thin
molybdenum ring-shaped electrode. The inner and outer
diameters of the emitting layer are 48 and 64 mm,
respectively.
Fig. 4: The scheme of the electron gun.
The heater is made from a solid graphite block
with machined non-conducting slots of bifilar geometry
to decrease magnetic field perturbations at the cathode.
The vacuum vessel and the anode block are
additionally cooled by water circulating through special
channels within flanges and chamber walls.
The emission current of over 100 A is reached
for 1.7 kW consumed power (20 V, 90 A).
Gun tests are carried out in a single-pulse regime
on a special test facility based on a 10-stage open-air
generator. For pulse shaping each stage is formed by a
6-cell artificial line. The facility includes a dividing
transformer for the heater power supply, an oil tank for
high voltage and heater current inputs, and a vacuum
system.
The gun is positioned vertically on the oil tank.
The maximum test voltage of 200 kV with a pulse flat
top of 10-µs duration is limited by the dividing
transformer of the cathode heater. The electron beam
parameters measured in the test are close to theoretical
calculations for the experiments. The thickness of the
hollow beam measured at distance of 30 cm is less than
1 mm. This value indicates about the small longitudinal
and transverse momentum spread.
CONCLUSION
The electron gun producing the precision hollow
relativistic electron beam for coherent microwave
generator applications has been developed and tested. It
is based on the large non-adiabatic compression of the
beam emitted by ring-shaped cathode with an active
surface big enough to produce a wanted current level.
Further improvement of beam quality is possible by
decreasing of the width of the annular emitter and
increasing its emissive power.
REFERENCES
[1]. Agafonov A.V., Krastelev E.G., Lebedev A.N et al.
// Proc. of the 10th International Conference on
High-Power Particle Beams, San Diego, USA. 1994,
v. 2, 522 − 525.
[2] Agafonov A.V., Krastelev E.G., Lebedev A.N et al.
// Nucl. Instrum. and Methods in Phys. Research,
1995, A385, 100 − 103.
[3] Kotetashwily P.V., Rybak P.V., Tarakanov P.V.
Institute of General Physics, Moscow, Preprint N
44, 1991.
[4] Tiunov M.A., Fomel B.M., Yakovlev V.P. Preprint
Inst. Nucl. Phys., Novosibirsk, no. 87 − 35, 1987.
ВОПРОСЫ АТОМНОЙ НАУКИ И ТЕХНИКИ. 1999. № 4.
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77
[5] Agafonov A.V., Lebedev A.N., Voronn V.S. // Proc.
of the 5th EPAC, Sitges, Spain, 1996, v. 2, p.
1230 − 1232.
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