Functioning of LIA-30 accelerator in the mode of generating bremsstrahlung pulses shortened to several nanoseconds
Deceleration of electrons and further transformation of the beam current lead to the ~2-times increase of the pulse amplitude, self-excited acceleration ofelectrons at the cutoffand shortening of15…20 Gy bremsstrahlung pulse.
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| Дата: | 2004 |
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Національний науковий центр «Харківський фізико-технічний інститут» НАН України
2004
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| Цитувати: | Functioning of LIA-30 accelerator in the mode of generating bremsstrahlung pulses shortened to several nanoseconds / V.P.Veresov, S.A.Gornostaj-Pol’ski, V.P.Gritsina, A.V.Grishin, N.N.Zalomina, V.V.Kul’gavchuk, S.A.Lazarev, B.I.Model’, S.Ya.Slusarenko, A.D.Tarasov // Вопросы атомной науки и техники. — 2004. — № 2. — С. 12-14. — Бібліогр.: 3 назв. — англ. |
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irk-123456789-792952015-03-31T03:02:19Z Functioning of LIA-30 accelerator in the mode of generating bremsstrahlung pulses shortened to several nanoseconds Veresov, V.P. Gornostaj-Pol’ski, S.A. Gritsina, V.P. Grishin, A.V. Zalomina, N.N. Kul’gavchuk, V.V. Lazarev, S.A. Model’, B.I. Slusarenko, S.Ya. Tarasov, A.D. Состояние действующих и проекты новых ускорителей Deceleration of electrons and further transformation of the beam current lead to the ~2-times increase of the pulse amplitude, self-excited acceleration ofelectrons at the cutoffand shortening of15…20 Gy bremsstrahlung pulse. Гальмування електронів на фронті і наступна трансформація струму пучка приводять до збільшення амплітуди імпульсу у ~ 2 рази, до автоприскорення електронів на зрізі й укороченню імпульсу гальмового випромінювання з дозою 15…20 Гр. Торможение электронов на фронте и последующая трансформация тока пучка приводят к увеличению амплитуды импульса в ~ 2 раза, к автоускорению электронов на срезе и укорочению импульса тормозного излучения с дозой 15…20 Гр. 2004 Article Functioning of LIA-30 accelerator in the mode of generating bremsstrahlung pulses shortened to several nanoseconds / V.P.Veresov, S.A.Gornostaj-Pol’ski, V.P.Gritsina, A.V.Grishin, N.N.Zalomina, V.V.Kul’gavchuk, S.A.Lazarev, B.I.Model’, S.Ya.Slusarenko, A.D.Tarasov // Вопросы атомной науки и техники. — 2004. — № 2. — С. 12-14. — Бібліогр.: 3 назв. — англ. 1562-6016 PACS: 29.17.+w http://dspace.nbuv.gov.ua/handle/123456789/79295 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 |
| collection |
DSpace DC |
| language |
English |
| topic |
Состояние действующих и проекты новых ускорителей Состояние действующих и проекты новых ускорителей |
| spellingShingle |
Состояние действующих и проекты новых ускорителей Состояние действующих и проекты новых ускорителей Veresov, V.P. Gornostaj-Pol’ski, S.A. Gritsina, V.P. Grishin, A.V. Zalomina, N.N. Kul’gavchuk, V.V. Lazarev, S.A. Model’, B.I. Slusarenko, S.Ya. Tarasov, A.D. Functioning of LIA-30 accelerator in the mode of generating bremsstrahlung pulses shortened to several nanoseconds Вопросы атомной науки и техники |
| description |
Deceleration of electrons and further transformation of the beam current lead to the ~2-times increase of the pulse
amplitude, self-excited acceleration ofelectrons at the cutoffand shortening of15…20 Gy bremsstrahlung pulse. |
| format |
Article |
| author |
Veresov, V.P. Gornostaj-Pol’ski, S.A. Gritsina, V.P. Grishin, A.V. Zalomina, N.N. Kul’gavchuk, V.V. Lazarev, S.A. Model’, B.I. Slusarenko, S.Ya. Tarasov, A.D. |
| author_facet |
Veresov, V.P. Gornostaj-Pol’ski, S.A. Gritsina, V.P. Grishin, A.V. Zalomina, N.N. Kul’gavchuk, V.V. Lazarev, S.A. Model’, B.I. Slusarenko, S.Ya. Tarasov, A.D. |
| author_sort |
Veresov, V.P. |
| title |
Functioning of LIA-30 accelerator in the mode of generating bremsstrahlung pulses shortened to several nanoseconds |
| title_short |
Functioning of LIA-30 accelerator in the mode of generating bremsstrahlung pulses shortened to several nanoseconds |
| title_full |
Functioning of LIA-30 accelerator in the mode of generating bremsstrahlung pulses shortened to several nanoseconds |
| title_fullStr |
Functioning of LIA-30 accelerator in the mode of generating bremsstrahlung pulses shortened to several nanoseconds |
| title_full_unstemmed |
Functioning of LIA-30 accelerator in the mode of generating bremsstrahlung pulses shortened to several nanoseconds |
| title_sort |
functioning of lia-30 accelerator in the mode of generating bremsstrahlung pulses shortened to several nanoseconds |
| publisher |
Національний науковий центр «Харківський фізико-технічний інститут» НАН України |
| publishDate |
2004 |
| topic_facet |
Состояние действующих и проекты новых ускорителей |
| url |
http://dspace.nbuv.gov.ua/handle/123456789/79295 |
| citation_txt |
Functioning of LIA-30 accelerator in the mode of generating bremsstrahlung pulses shortened to several nanoseconds / V.P.Veresov, S.A.Gornostaj-Pol’ski, V.P.Gritsina, A.V.Grishin, N.N.Zalomina, V.V.Kul’gavchuk, S.A.Lazarev, B.I.Model’, S.Ya.Slusarenko, A.D.Tarasov // Вопросы атомной науки и техники. — 2004. — № 2. — С. 12-14. — Бібліогр.: 3 назв. — англ. |
| series |
Вопросы атомной науки и техники |
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FUNCTIONING OF LIA-30 ACCELERATOR
IN THE MODE OF GENERATING BREMSSTRAHLUNG PULSES
SHORTENED TO SEVERAL NANOSECONDS
V.P.Veresov, S.A.Gornostaj-Pol’ski, V.P.Gritsina, A.V.Grishin, N.N.Zalomina,
V.V.Kul’gavchuk, S.A.Lazarev, B.I.Model’, S.Ya.Slusarenko, A.D.Tarasov
Russian Federal Nuclear Center – All-Russia Scientific Research Institute of
Experimental Physics (RFNC – VNIIEF)
607188, Sarov, Nizhni Novgorod region, Mira Ave., Russia
E-mail: otd4@expd.vniief.ru
Deceleration of electrons and further transformation of the beam current lead to the ~2-times increase of the pulse
amplitude, self-excited acceleration of electrons at the cutoff and shortening of 15…20 Gy bremsstrahlung pulse.
PACS: 29.17.+w
INTRODUCTION
LIA-30 linear induction accelerator of electrons is a
basic irradiating facility of RFNC – VNIIEF [1]. In the
list of its potentialities there is available a mode of gen-
erating bremsstrahlung pulses of short duration τγ ~5ns
with a peak bremsstrahlung dose power Pγ ~ 5⋅109Gy/s
and integral dose up to Dγ ~15 Gy. The mode by itself is
interesting both from the point of view of its physical
realization and for simulating some aspects of nuclear
burst injurious effects.
As differentiated from high-current (~100kA) direct-
action accelerators a 36-module structure of LIA-30 is a
convenient instrument for realization of different func-
tioning modes. This can be fulfilled through the possibili-
ty of changing the number of enabled modules by means
of some moderate variations in configurations of high-
voltage electrodes contained in a vacuum track and
through varying delays of voltage appearance in the ac-
celerating gaps of one or another group of modules [2].
In the experiments aimed at forming high currents of
relativistic electron beams (REB) Iп ~ 100 кА much at-
tention was paid to the shape transformation of REB
current pulses when the beam was accelerated in LIA-
30 modules. Fig.1a, b gives for different time dependen-
cies of current at the accelerating system input iinp(t) fur-
ther changes of its shape in the cross-sections of mod-
ules No 10, 20, 36. To make the picture more demon-
strative the oscillograms of currents were synchronized
in terms of time delays of currents appearance in the
blocks specified. In correlation with the observed
“peaks” of current amplitude i36(t) there were registered
at the accelerator output the pulses modulated with high-
frequency oscillations and shortened as a whole by dura-
tion Рγ (t). It was clear that at a definite time dependence
of current iinp(t) there can be realized the conditions of
REB acceleration in subsequent modules to get a short
pulse of bremsstrahlung. However, this was a difficult
task as a whole because of the lack of a calculation model
of REB space-time location needed to measure its current
pulse in the accelerating structure of LIA-30.
Under these circumstances there was selected an ex-
perimental method of finding conditions for the realiza-
tion of the accelerator operation mode with
bremsstrahlung shortened pulses generation. For this
purpose it seemed expedient to use the accelerator of the
system of pulse currents and voltages registration avail-
able almost in each accelerator module.
iin i10 i20 i36
t
IjkA
а) rise time ~ 23 ns
i10 i20 i36
t
Ij
iin
kA
б) rise time ~ 15 ns
Fig.1. Time dependence of REB currents pulses in LIA-
30 modules No 10, 20, 36 at gently sloping and drasti-
cally growing front pulse of the injection current iinp
SOME PHYSICAL ASPECTS
Simple calculations of transition processes in induc-
tor blocks demonstrate that owing to the availability of
inductively resistant output impedance of accelerating
gaps (~6 Ω as stated in terms of one module on the main
operation frequency f ~ 10 MHz), when passing the cur-
rent pulse of ~100 kA amplitude and standard duration
of ~50 ns, there takes place the induction decrease and
increase of accelerating voltage values at the front and
trail of its pulse, respectively. The total change of volt-
age in the gaps of 10 modules may constitute a suffi-
ciently high for acceleration – deceleration value ∆
U~ 6 MV. More precise calculations in terms of LIA-30
accelerating track electric parameters per unit length [3]
lead to variations of the total induced voltage in N-ac-
celerator modules in the following form:
___________________________________________________________
PROBLEMS OF ATOMIC SIENCE AND TECHNOLOGY. 2004. № 2.
Series: Nuclear Physics Investigations (43), p.12-14. 12
mailto:otd4@expd.vniief.ru
∆U = N⋅ (IREB ⋅W + L ⋅ d IREB /dt),
where W~2,8 Ω is the total wave resistance of the con-
nected module; L ~ 110 nH is the inductance of torus
shaped cavity between the block inductors and REB
boundary (∅ ~ 250 mm). They point to even higher pos-
sible values of ∆U > 14 MV at N=10 and considerable
abruptness of current rise dIREB /dt > 10 kA/ns.
The use of this physical peculiarity forecasted effec-
tive deceleration – acceleration of electrons at REB
front (trail) and, finally, shortening of current pulses and
bremsstrahlung. Fig.2 presents for different current
pulse shapes the examples of voltage (in relative units)
changes in 8 and 30 modules at an additional delay of
their switching for the following cases, respectively:
а) t8 =11 ns and б) t30→∞ (passive condition of mod-
ule).
i8 U8
t
U,I,kA r.u.
а) t8 = 11 ns
i30
t
U30
U, .r.uI,kA
б) t30 → ∞
Fig.2. Voltage changes in the accelerating tracks of the
8th and 30th module depending on the passing current of
the beam during delayed modules switching
As is well seen from the oscillograms in the acceler-
ating gaps of modules there actually induce additional
negative and positive potentials depending on the delay
of module switching and abruptness of current pulses
time dependence. For the current pulses of >100 kA
these potentials were registered to be even more in-
creased.
Deeper understanding of the processes follows from
space-time apprehension of REB. An appreciable cur-
rent pulse transformation occurs if a considerable share
of electrons notably fall behind high-energy electrons
moving at a rate υ≈ с. In the course of deceleration low-
energy electrons with с υ<<с generally pass from inner
to outer trajectories. At a constant azimuth density of
currents a large electron charge can be dislocated just in
the outer annular layers of the tubular REB. Moreover,
electrons leaving the process of acceleration collide
with the track walls causing intrinsic leakage currents of
modules what was observed in reality. Later it leads to
an abrupt reduction of acceleration tempo for all elec-
trons. This is and important limiting point for the real-
ization of current pulse transformation with no loss of
bremsstrahlung dose and power.
To prevent shunting of accelerator gaps there was
proposed in one of operation versions to discharge the
remaining electrons by means of local decrease of the
leading longitudinal magnetic field. On the other hand it
followed from the experiments that transformation of
current pulses can be easier realized for the beams of
large diameters (>150 mm). In this case there appeared
a proposal to use for space separation of electrons a sep-
arate outer beam injected simultaneously with the chief
one with the aid of additional coaxial emitter especially
because the amplitude of the total current could be con-
siderable due to additional outer layer of electrons.
INVESTIGATION RESULTS
The first experiments were performed for the accel-
erating track configuration presented in Fig.3, i.e. step-
by-step coaxial cathode possessing 100 and 150 mm-di-
ameter annular emitters to form two simultaneous
beams. The emitters provided REB injection with rela-
tively low for LIA-30 current iinp=50…70 kA (through
disconnecting of a share of inductors of 1-4 modules).
To decelerate the beams there was installed a program
of advance injection according to which modules
No 5,6,7,8 were connected with the following delays,
correspondingly: t5=4 ns, t6 =4 ns, t7=3 ns, t8=3 ns. The
total delay of the 8th model switching as related to the 4th
module constituted 14 ns.
The establishment to cathode-anode gap of three di-
aphragms with the aperture of ∅ 210…240 mm and at a
distance of 0,1…1,0 m from the cathode trail (Fig.3,
dotted) made it possible to increase through the decrease
of anode-cathode gap the input current up to 100 kA,
cause effective pulse transformation and essential short-
ening of τγ. However, the operation mode was not stable
enough because of the fact that the beams were too
close to each other. Constant shift of beams by ~60 mm
from the axis caused by some engineering peculiarities
of magnetic field realization on the accelerator track
hampered the mode realization as well.
15
0III III IV
10
0
21
0
22
0
24
0
39
0
5 6 7 8 15 16 17 18 19 36
37 42
1
40
0
4
30
HVSSU(t )1 U(t )2 U(t )3 U(t )4
TT
26 м
OD
Fig.3. Scheme of LIA-30 accelerating track with a step-
by-step two-emitter cathode:
1, 2, 3…36 – serial number of modules; U(t1), U(t2),
U(t3), U(t4) – starting voltages;
ТТ – transportation track ; OD – output device; HVSS –
high-voltage system of modules synchronization.
I, II – cathode-anode electrodes; III – drift tube with
solenoid; IV – target
Finally the mode was elaborated in the configuration
presented in Fig.3, where the emitters 135 and 245 mm
in diameter were used instead of the available ones. The
___________________________________________________________
PROBLEMS OF ATOMIC SIENCE AND TECHNOLOGY. 2004. № 2.
Series: Nuclear Physics Investigations (43), p.12-14.13
axial distance between the ends of emitters constituted
~1 m. To keep sufficiently high current of injection
Iinp =90 kA the blocks from 7…15 and from 16…36
were connected 4 and 8 ns earlier, respectively. For the
purpose of local dump of decelerated particles to the
walls of the accelerating track the magnetic field in the
12th module was decreased from 0.5T to 0.4 T. As a result
there was achieved a required transformation of REB cur-
rent pulses and decrease of τγ to the value of <4 ns at the
bremsstrahlung integral dose Dγ = 19 Gy and peak dose
rate of bremsstrahlung Рγ ~ 5 ⋅109 Gy/s. However, after
some pulses had passed there took place a breakdown of
a solenoid of the leading magnetic field in module 15 be-
cause of failure of its coils insulation resulting from their
irradiation with locally dumped electrons.
To somehow disperse the dumped electrons the
magnetic field was reduced by a lower value (from 0.50
to 0.45 T) simultaneously in three modules: No
10,11,12. Finally the shortening of current pulses was
not so efficient and the value of τγ was higher- ~6 ns.
Fig.3 presents transformation of the REB current
pulse in the accelerating operation mode at which the
injection current was additionally increased to the am-
plitude iinp = 100 kA. The magnetic field was kept at a
level of 0.5T by the entire accelerator length. A more
regular dump of scattered electrons was implemented
through their deceleration in some disconnected mod-
ules (No 12,14,17,21,36). In this case there took place
the reduction of bremsstrahlung parameters to the level
Dγ = 15 Gy, Рγ ~ 3 ⋅ 109 Gy/s the shortening of pulses
remaining equal to τγ = 5 ns.
i1
t
Ij,
Pγi36
Pγ
i5 i11 i26
kA
Fig. 4. Time dependence of current beam pulses in ac-
celerator modules 1, 5, 11, 26, 36 and bremsstrahlung
dose rate at the LIA-30 output
The characteristic peculiarity of bremsstrahlung was
reduction of its spot diameter (as compared to the avail-
able in the standard mode of operation) by >20% be-
cause in the generation of bremsstrahlung at electron de-
celeration in the target there basically participates an in-
ternal beam ~135 mm in diameter.
CONCLUSIONS
The performed experimental investigations of the
process of REB current pulse transformation made it
possible to realize generation of shortened - by duration
- bremsstrahlung pulses with the following parameters:
τγ = 5...10 ns, Dγ = 15...20 Gy, Рγ up to 5⋅109 Gy/s. Of
course, to increase the levels of Dγ and Рγ with keeping
τγ ~ 5 ns unchanged one must perform more optimiza-
tion of selecting amplitude, shape of current beam pulse
iinp(t) and program of accelerator modules connection.
The maximum dose and dose rate could be realized in
case of total joining of all the accelerator modules due
to the lack of modules shunted by intrinsic leakage cur-
rents initiated by transformation electrons spreader by
the current pulse, with axial REB shift elimination.
Most probably at that time we managed to implement
the distributed dump of electrons from υ << c in the
available prolonged (≈ 4 m) transportation magnetic
track connecting the last accelerator module (No 36)
with its output assembly and target.
REFERENCES
1. A.I.Pavlovskii, V.S.Bossamykin, A.I.Gerasimov et
al. // IX Intern. Conf. on High. Power Particle
Beams "Beams '92". Washington, DC, May 25-29,
1992. Springfield, V.A. NTIS. 1992, v.1, p.273.
2. A.I.Gerasimov, A.S.Fedotkin, A.D.Tarasov, V.S.-
Gordeev, A.V.Grishin et al. Powerful linear pulse
accelerator of an electron beam LIA-30 // Pribory i
tekhnika ehksperiment. 1998, №2, p.13-25.
3. V.S. Bossamykin, A.I. Gerasimov, V.S. Gordeev et.
al. // X Intern. Conf. on High. Power Particle
Beams "Beams ‘94". San Diego, CA, June 20-24,
1994. Springfield, V.A. NTIS. 1994, v.1, p.128.
РАБОТА УСКОРИТЕЛЯ ЛИУ-30 В РЕЖИМЕ ГЕНЕРАЦИИ ИМПУЛЬСОВ ТОРМОЗНОГО
ИЗЛУЧЕНИЯ, УКОРОЧЕННЫХ ДО НЕСКОЛЬКИХ НАНОСЕКУНД
В.П. Вересов, С.А. Горностай-Польски, В.П. Грицина, А.В. Гришин, Н.Н. Заломина, В.В. Кильгавчук,
С.А. Лазарев, Б.И. Модель, С.Ю. Слюсаренко, А.Д. Тарасов
Торможение электронов на фронте и последующая трансформация тока пучка приводят к увеличе-
нию амплитуды импульса в ~ 2 раза, к автоускорению электронов на срезе и укорочению импульса тормоз-
ного излучения с дозой 15…20 Гр.
РОБОТА ПРИСКОРЮВАЧА ЛІП-30 У РЕЖИМІ ГЕНЕРАЦІЇ ІМПУЛЬСІВ ГАЛЬМОВОГО
ВИПРОМІНЮВАННЯ, УКОРОЧЕНИХ ДО ДЕКІЛЬКОХ НАНОСЕКУНД
В.П. Вересов, С.А. Горностай-Польскі, В.П. Грицина, А.В. Гришин, Н.Н. Заломіна, В.В. Кільгавчук,
С.А. Лазарєв, Б.І. Модель, С.Ю. Слюсаренко, А.Д. Тарасов
Гальмування електронів на фронті і наступна трансформація струму пучка приводять до
збільшення амплітуди імпульсу у ~ 2 рази, до автоприскорення електронів на зрізі й укороченню імпульсу
гальмового випромінювання з дозою 15…20 Гр.
14
Introduction
излучения, укороченных до нескольких наносекунд
|