Desing of high-current pulse electron accelerator
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Національний науковий центр «Харківський фізико-технічний інститут» НАН України
1999
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Gordeev, V.S. Laptev, D.V. Mikhailov, E.S. Myskov, G.A. 2015-05-14T19:51:46Z 2015-05-14T19:51:46Z 1999 Desing of high-current pulse electron accelerator / V.S. Gordeev, D.V. Laptev, E.S. Mikhailov, G.A. Myskov // Вопросы атомной науки и техники. — 1999. — № 3. — С. 68-70. — Бібліогр.: 9 назв. — англ. 1562-6016 https://nasplib.isofts.kiev.ua/handle/123456789/81347 en Національний науковий центр «Харківський фізико-технічний інститут» НАН України Вопросы атомной науки и техники Desing of high-current pulse electron accelerator Проект сильноточного импульсного ускорителя электронов Article published earlier |
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Desing of high-current pulse electron accelerator |
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Desing of high-current pulse electron accelerator Gordeev, V.S. Laptev, D.V. Mikhailov, E.S. Myskov, G.A. |
| title_short |
Desing of high-current pulse electron accelerator |
| title_full |
Desing of high-current pulse electron accelerator |
| title_fullStr |
Desing of high-current pulse electron accelerator |
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Desing of high-current pulse electron accelerator |
| title_sort |
desing of high-current pulse electron accelerator |
| author |
Gordeev, V.S. Laptev, D.V. Mikhailov, E.S. Myskov, G.A. |
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Gordeev, V.S. Laptev, D.V. Mikhailov, E.S. Myskov, G.A. |
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1999 |
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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 |
Проект сильноточного импульсного ускорителя электронов |
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1562-6016 |
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https://nasplib.isofts.kiev.ua/handle/123456789/81347 |
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Desing of high-current pulse electron accelerator / V.S. Gordeev, D.V. Laptev, E.S. Mikhailov, G.A. Myskov // Вопросы атомной науки и техники. — 1999. — № 3. — С. 68-70. — Бібліогр.: 9 назв. — англ. |
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DESIGN OF HIGH-CURRENT PULSE ELECTRON ACCELERATOR
V.S. Gordeev, D.V. Laptev, E.S. Mikhailov, G.A. Myskov
VNIIEF, Sarov, Russia
INTRODUCTION
For some applications (see, for example, [1])
there are required powerful high-current accelerators
with electron beam power of several TW and higher,
maximum energy of accelerated electrons of ~2 MeV
and bremsstrahlung pulse duration of ≤ 40 ns. For such
facilities it is expedient to use a system aimed at
forming high-voltage pulses of accelerating voltage
with high efficiency. In the accelerators with capacitive
method of energy storage most frequently used are
single (SFL) or double (DFL) forming lines providing
at 0V charging voltage the formation on a matched load
(mode of maximum efficiency) of the voltage pulses (of
rectangular shape ideally) with the amplitude 2/0V and
0V , respectively. For a specified above energy of
electrons the charging voltage of SFL and DFL should
be at a level of 4 and 2 MV, respectively. Besides, to
increase reliability of accelerator operation it is
desirable to decrease at the unchanged efficiency the
charging voltage of the line under whose effect a set of
components and units are under charging process within
a comparatively long (~1 µs) time period. From the
point of view of creating high-power multi-module
facilities the insurance of a high time accuracy of
accelerator turn-on is an important problem.
In the course of creating high-current linear
induction accelerators there has been developed in
VNIIEF a new type of multi-cascade high-voltage pulse
generators formed of homogeneous transmission lines
of a similar electric length [2, 3]. As in such facilities
during transfer from one cascade to another the
impedance changes stepwise, they are called generators
on step lines (SL). The energy stored initially in many
cascades concentrates after a switch turn- on and
resulting from wave processes at the generator output.
For a specific relation of impedances the entire energy
transmission to the load is possible with the formation
on it of a rectangular-shape pulse. The pulse duration
does not depend on the full generator size but is
characterized by a double electric length of a separate
cascade. At the expense of wave processes there is
realized in a set of schemes a significant increase of
voltage what gives the opportunity for the application
considered to reduce the charge voltage to ~1 MV.
Below presented is the description of a project of
accelerator with a 2 MeV electron energy and 1 MA
current at ~60 ns duration of current pulse (FWHM).
PRINCIPAL CIRCUIT DIAGRAM FOR A PULSE
FORMING SYSTEM
Basing on a comparative analysis of different
SL-based generators with a capacitive method of energy
storage there is chosen for the accelerator a circuit
presented in Fig. 1a. It combines two devices: a
generator based on a five-cascade double step forming
line (DSFL, Fig. 1b) and a two cascade pulse duration
converter (Fig. 1c). Let us consider each of the above-
mentioned devices separately.
Z
Z
V0
1
2
S1
Z 4
Z3
Z/25
t=0
S2 t=4.5T0
ZL
Z/25
a
Z
Z
V0
1
2
S1
Z 4
Z3
Z5
t=0
S2 t=4T0
ZL
b
Z/2
Z
t=Tо
Z L
S
VG Z/2
c
Z
Z
V0
1
2
S1
Z 4
Z 3
Z/25
t=0
S2 S3t=4T0 t=5T0
Z 5
Z/25
Z L
d
Fig.1. Principal circuit diagrams.
DSFL (Fig. 1b) is formed by 5 homogeneous
lines of a similar electric length 0T and possesses
ideally a 100-% efficiency for the following relation of
impedances: 12 3ZZ = , 4/15 13 ZZ = , 4/5 14 ZZ = ,
15 15ZZ = . At 0=t time moment, when maximum
charging voltage 0V of lines 1÷4 is achieved, 1S switch
is turned on. LZ load is connected to DSFL output with
5Z impedance through a pre-pulse switch 2S at 04Tt =
time moment. On a matched load 15 15ZZZL == there
is formed a voltage pulse of 02T duration and 03V
amplitude, within which the energy is entirely
transmitted to the load. In the idle mode the output
voltage exceeds the charging one by a factor of 6. This
circuit underwent experimental testing during the
creation of electron pulse accelerator STRAUS, two
STRAUS-2 accelerators and LIA-10M accelerator
injector [4].
A two-cascade converter that is a particular case
of a device with arbitrary number of cascades [5] is
formed by the connected in series at the input similar
lines with 2/0T electric length and 2/Z impedance. The
output of one of the lines is shorted and to the output of
the other one the load is connected through the S
ВОПРОСЫ АТОМНОЙ НАУКИ И ТЕХНИКИ. 1999. №3.
Серия: Ядерно-физические исследования. (34), с. 68-70.
68
switch. A rectangular voltage pulse of GV amplitude
and 02T duration is transmitted from the external
generator along the transmission line with Z
impedance. With the matched load 2/ZZL = ,
connected through S switch with 0T delay time as
related to the time of the first electromagnetic wave
coming from the generator there is formed a rectangular
voltage pulse of GV amplitude and 0T duration. Ideally,
the energy coming from the external generator is
entirely transmitted to the load. The experimental
testing has shown that the converter provides the
increase of power and current by a factor of two (as
compared to the generator) due to the double reduction
of pulse duration.
Such a converter can be connected to any
generator of rectangular pulse including DSFL as it is
shown in Fig. 1d. Furthermore, the converter can be
connected instead of the DSFL output cascade (Fig. 1a),
that makes it possible to decrease the full size of the
forming system and to reduce the number of switches.
On a matched load there should be formed a rectangular
voltage pulse of 03V amplitude and 0T duration. The
scheme of DSFL offers the possibility of varying within
specific limits the relation of impedances at a high
efficiency unchanged. For a forming system with 1 MV
charging voltage there are selected the following
impedances: == 32 ZZ 18.2 Z , 14 ZZ = , 15 10ZZ = . The
output impedance of the generator with a converter
constitutes 2/5Z . Ideally, on a matched load there
should be obtained the voltage of 2.58 MV at the
current of 0.89 MA and power of 2.3 TW. The
calculated efficiency constitutes 98%. When limiting
the maximum voltage on the diode to 2 MV ( 12.3 ZZL =
) the current increases up to 1.1 MA with reduction of
the power to 2.2 TW and the efficiency of 93%.
SCHEME OF HIGH-VOLTAGE
ACCELERATOR PART
The scheme of the high-voltage accelerator part
is presented in Fig. 2. It incorporates the system of
high-voltage pulse formation, pre-pulse switch (PS),
water transmission line (WTL), unit of sectioned in-
sulator, magnetically insulated transmission line
(MITL) and diode with a target unit. The system of
high-voltage pulse formation is designed on the basis of
DSFL having a ~50 ns electric length of coaxial lines
with water insulation. For the purpose of decreasing the
accelerator length the lines with 4Z (0.58 Ohm), 1Z
(0.58 Ohm), 2Z (1.62 Ohm) and 3Z (1.62 Ohm)
impedances are arranged in series on a radius within the
limits of one axial dimension (~ 1.8 m). The electric
capacity of DSFL is ~235 nF. To the output of DSFL
there is connected a converter consisting of two
homogeneous coaxial lines with equal impedance of 2.9
Ohm and similar electric length of ~25 ns. At the
converter output there is installed a PS with the help of
which the pulse formed is delivered to WTL connecting
the output of the forming system and the unit of the
sectioned insulator. The total length of the forming
system is 2.8 m, its diameter is 2.5 m. The charging of
DSFL to the working voltage of 1 MV is supposed to be
realized from two connected in parallel Marx generators
with the total maximum energy store of 190 kJ (at 100
kV). According to preliminary estimations each gene-
rator should include 12 cascades of voltage
multiplication using 4 connected in parallel capacitors
of 400 nF (for example, of IKM-100-0.4 type) in each
cascade. Moreover, the output capacity of two
generators is ~270 nF, their operation charging voltage
is 90 kV (160 kJ) while the time of DSFL charging is ≤
800 ns. In the course of charging the maximum electric
field strength on the cylindrical surface of high-voltage
DSFL electrode does not exceed 110 kV/cm.
The DSFL switching is supposed to be
implemented with the aid of 40 gas-filled controlled
spark switches of trigatron type arranged symmetrically
on azimuth in the DSFL case. The PS should be turned
on ~260 ns after the DSFL multi-channel switch
operation. To decrease the intrinsic inductance of PS it
is supposed to use 6 gas-filled spark trigatron switches
similar by design to the pre-pulse switch of STRAUS-2
accelerator, but of the increased size. The control
signals will be sent through cable lines positioned in the
grounded internal near-axis cavity of DSFL. The unit of
PS is separated from the DSFL and WTL volumes by
dielectric diaphragms and is filled with transformer oil
for the purpose of decreasing the pre-pulse amplitude
and increasing the quality of the pulse formed.
The coaxial WTL serves to deliver the pulse
from the forming system output to the sectioned
insulator unit. Its impedance is matched with the output
impedance of the forming system and constitutes
2.9 Ohm at the external diameter line equal to 1.62 m.
The length of the line depends on a choice of the
scheme of arranging a multi-module facility as a whole,
but for the time isolation of PS inductance and
accelerating tube it should be not less than 1.5 m.
The sectioned insulator external diameter
constitutes ~1.2 m, its length ~ 0.5 m. The insulator
dimensions were selected following the condition of the
required electric strength provision as well as the
condition of minimum permissible distortion of the
pulse shape. The average strength of the electric field
on the vacuum insulator surface constitutes ~50 kV/cm
at the maximum value near 70 kV/cm. The total
inductance of the sectioned insulator unit is ~35 nH.
The external volume of the sectioned insulator is
separated from the transmission line volume by a
dielectric diaphragm and is filled with transformer oil.
MITL serves to transmit voltage pulse from the
sectioned insulator to the diode with a target unit that is
aimed at accelerating the electron flow formed in MITL
and at its transforming into a bremsstrahlung pulse. The
vacuum impedance of MITL will constitute ~4.3 Ohm.
By design it is proposed to make MITL of two sections:
conical and cylindrical ones. The diameters of internal
and external electrodes of MITL section are
approximately equal to 18 cm and 16.8 cm.
The overall dimensions of the accelerator are as
follows: length ~8 m, width – 3 m, height – 4 m.
ВОПРОСЫ АТОМНОЙ НАУКИ И ТЕХНИКИ. 1999. №3.
Серия: Ядерно-физические исследования. (34), с. 68-70.
68
2.8 m
MULTICHANNEL
SWITCH DSFL OUTPUT
CASCADE
PRE-PULSE
SWITCH WATER
TRANSMISSION
LINE SECTIONED
INSULATOR
MITL
WATER
OIL
VACUUM
DIODE
~ 5 m
OIL
∅
2.
5
m
∅
1.
3
m
∅
1.
05
m
∅
1.
62
m
WATER
Fig. 2. Scheme of high-voltage accelerator part.
NUMERIC SIMULATION RESULTS
There was performed a lot of calculations to
study the process of high-voltage pulse formation, to
optimize geometry and parameters of accelerator
components as well as to find time-amplitude
characteristics of pulses delivered to MITL input. To
increase authenticity of the results obtained the
calculations were performed using two independent
algorithms realized and developed in VNIIEF WEC and
ATLAS codes. The electromagnetic code WEC [6] is
based on the numerical solution of Maxwell’s equations
realized using a method of integral equations in two-
dimensional geometry. It allows to calculate forming
systems of complex configuration with the arbitrary
number and geometry of electrodes, with the
availability of material media of different conductivity,
dielectric and magnetic permeability; it makes it
possible to use inhomogeneous space grid for both
coordinates. The calculation technique of ATLAS code
is based on a one-dimensional model using a method of
equivalent circuits. The given method is less exact, but
it allows to perform calculations at considerably higher
rate (~1000 times). The electromagnetic processes in
the lines with distributed parameters were calculated by
solving telegraph equations using a method of modified
characteristics [7]. Inhomogeneities in the places of
DSFL lines junction were described by the shorted
transmission line segments with short electric length
and reactive elements in accord with the technique
presented in [8, 9]. It should be mentioned that ATLAS
code was successfully used at the development of
powerful LIA-10M and STRAUS-2 facilities,
moreover, the experimental results obtained on them
coincided - with good accuracy (~10%) - with the
calculated data.
The pulses of voltage and power on the MITL
input obtained as a result of calculations are presented
in Fig. 3a, b. The amplitudes of voltage and power
constitute 2.4 MV and 2.0 TW at the duration of pulses
(FWHM) being equal to 62 and 47 ns, respectively.
Referring to the above figures it will be observed a
good coincidence, with the accuracy of ~10%, of
calculation data for both codes. Let us mention that the
voltage pulse amplitude (~2.4 MV) is by approximately
7% lower than the theoretical value of 2.58 MV
corresponding to the idealized model. Nevertheless, the
efficiency of energy transmission from the forming
system to MITL turns out to be high enough – at a level
of ~85%. Moreover, the module efficiency
characterized by the relation between the energy of the
pulse formed and the energy stored in Marx generators
can be as high as ~60%. The pre-pulse voltage at the
output of the forming system occurring before the basic
pulse arrival, is revealed in the form of a group of short
pulses with the duration of less than 20 ns (FWHM) and
the amplitude that is not higher than 85 kV.
0
1
2
3
0 40 80 120 160
t, ns
V,
MV
ATLAS WEC
0
1
2
0 40 80 120 160
t, ns
P,
TW
ATLAS WEC
a b
Fig. 3. Calculation pulses of voltage (a) and power (b)
at the MITL input.
The advantages of the considered accelerator are
as follows: small size (dimensions of the forming
system - ∅ 2.5 × 2.8 m2), sufficiently high efficiency
(~60%), comparatively small number of the switches
used (46 units with the exception of Marx generators
switches) and low values of pre-pulse amplitude and
duration at the forming system output.
REFERENCES
1. P. Sincerny, S. Ashby, K. Childers et al.//9th IEEE Pulsed Power
Conf., Albuquerque, 1993. P. 880-883.
2. Bossamykin V.S., Gordeev V.S., Pavlovskii A.I.// 9-th Intern.
Conf. on High-Power Particle Beams, BEAMS-92, Washington,
1992. V. 1. PP. 511-516.
3. Bossamykin V.S A.I,Gerasimov, V.S.Gordeev,. Transactions of
VNIIEF “High energy densities”, Sarov, RFAC- VNIIEF Publ., 1997,
p. 107-133 (in Russian).
4. Bossamykin V.S., Gordeev V.S., Pavlovskii A.I. et. al. // 9-th
Intern. Conf. on High-Power Particle Beams, BEAMS-92, Washing-
ton, 1992. V. 1. PP. 505-510.
5. Bossamykin V.S., Gordeev V.S.// IX IEEE Intern. Pulsed Power
Conf., Albuquerque, 1993. V.2. P. 918
6. Gordeev V.S., Mikhailov E.S. // Problems of Atomic Science and
Techn. 1999. v. 3. Issue: Nuclear Physics Researches. (35), P. 75.
7. V. Dvorak. // Proc. IEEE, Vol. 58, No. 6, 1970, PP. 844-845.
8. J.R. Whinnery, H.W. Jamieson.// Proc. IRE. 1944. PP. 98-114.
9. J.R. Whinnery, H.W. Jamieson, T.E. Robbins.// Proc.
IRE. 1944. PP. 98-114.
ВОПРОСЫ АТОМНОЙ НАУКИ И ТЕХНИКИ. 1999. №3.
Серия: Ядерно-физические исследования. (34), с. 68-70.
68
INTRODUCTION
NUMERIC SIMULATION RESULTS
REFERENCES
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