Beam forming system modernization at the MMF linac proton injector
The isolation improvements of the beam forming system (BFS) of the ММF linac proton injector ion source are reported. The mean beam current and, accordingly, BFS electrode heating were increased when the ММF linac has began to operate regularly in long beam sessions with 50 Hz pulse repetition rate....
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| Zitieren: | Beam forming system modernization at the MMF linac proton injector / V.I. Derbilov, S.K. Esin, E.S. Nikulin, O.T. Frolov, V.P. Yakushev // Вопросы атомной науки и техники. — 2001. — № 5. — С. 131-133. — Бібліогр.: 6 назв. — англ. |
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irk-123456789-790202015-03-25T03:02:28Z Beam forming system modernization at the MMF linac proton injector Derbilov, V.I. Esin, S.K. Nikulin, E.S. Frolov, O.T. Yakushev, V.P. The isolation improvements of the beam forming system (BFS) of the ММF linac proton injector ion source are reported. The mean beam current and, accordingly, BFS electrode heating were increased when the ММF linac has began to operate regularly in long beam sessions with 50 Hz pulse repetition rate. That is why the BFS electrode high-voltage isolation that was made previously as two consequently and rigidly glued solid cylinder insulators has lost mechanical and electric durability. The substitution of large (160 mm) diameter cylinder insulator for four small diameter (20 mm) tubular rods has improved vacuum conditions in the space of beam forming and has allowed to operate without failures when beam currents being up to 250 mA and extraction and focusing voltage being up to 25 and 40 kV respectively. Moreover, the construction provides the opportunity of electrode axial move. The insulators are free from electrode thermal expansion mechanical efforts in a transverse direction. 2001 Article Beam forming system modernization at the MMF linac proton injector / V.I. Derbilov, S.K. Esin, E.S. Nikulin, O.T. Frolov, V.P. Yakushev // Вопросы атомной науки и техники. — 2001. — № 5. — С. 131-133. — Бібліогр.: 6 назв. — англ. 1562-6016 PACS number: 29.17.+w http://dspace.nbuv.gov.ua/handle/123456789/79020 en Вопросы атомной науки и техники Національний науковий центр «Харківський фізико-технічний інститут» НАН України |
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The isolation improvements of the beam forming system (BFS) of the ММF linac proton injector ion source are reported. The mean beam current and, accordingly, BFS electrode heating were increased when the ММF linac has began to operate regularly in long beam sessions with 50 Hz pulse repetition rate. That is why the BFS electrode high-voltage isolation that was made previously as two consequently and rigidly glued solid cylinder insulators has lost mechanical and electric durability. The substitution of large (160 mm) diameter cylinder insulator for four small diameter (20 mm) tubular rods has improved vacuum conditions in the space of beam forming and has allowed to operate without failures when beam currents being up to 250 mA and extraction and focusing voltage being up to 25 and 40 kV respectively. Moreover, the construction provides the opportunity of electrode axial move. The insulators are free from electrode thermal expansion mechanical efforts in a transverse direction. |
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Article |
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Derbilov, V.I. Esin, S.K. Nikulin, E.S. Frolov, O.T. Yakushev, V.P. |
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Derbilov, V.I. Esin, S.K. Nikulin, E.S. Frolov, O.T. Yakushev, V.P. Beam forming system modernization at the MMF linac proton injector Вопросы атомной науки и техники |
| author_facet |
Derbilov, V.I. Esin, S.K. Nikulin, E.S. Frolov, O.T. Yakushev, V.P. |
| author_sort |
Derbilov, V.I. |
| title |
Beam forming system modernization at the MMF linac proton injector |
| title_short |
Beam forming system modernization at the MMF linac proton injector |
| title_full |
Beam forming system modernization at the MMF linac proton injector |
| title_fullStr |
Beam forming system modernization at the MMF linac proton injector |
| title_full_unstemmed |
Beam forming system modernization at the MMF linac proton injector |
| title_sort |
beam forming system modernization at the mmf linac proton injector |
| publisher |
Національний науковий центр «Харківський фізико-технічний інститут» НАН України |
| publishDate |
2001 |
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http://dspace.nbuv.gov.ua/handle/123456789/79020 |
| citation_txt |
Beam forming system modernization at the MMF linac proton injector / V.I. Derbilov, S.K. Esin, E.S. Nikulin, O.T. Frolov, V.P. Yakushev // Вопросы атомной науки и техники. — 2001. — № 5. — С. 131-133. — Бібліогр.: 6 назв. — англ. |
| series |
Вопросы атомной науки и техники |
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2025-07-06T03:08:31Z |
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| fulltext |
BEAM FORMING SYSTEM MODERNIZATION AT THE
MMF LINAC PROTON INJECTOR
V.I. Derbilov, S.K. Esin, E.S. Nikulin, O.T. Frolov, V.P. Yakushev
Institute for Nuclear Research, RAS
117312, 60thOct.Anniversary Pr. 7a, Moscow, Russia
nikulin@al20.inr.troitsk.ru
The isolation improvements of the beam forming system (BFS) of the ММF linac proton injector ion source are re-
ported. The mean beam current and, accordingly, BFS electrode heating were increased when the ММF linac has
began to operate regularly in long beam sessions with 50 Hz pulse repetition rate. That is why the BFS electrode
high-voltage isolation that was made previously as two consequently and rigidly glued solid cylinder insulators has
lost mechanical and electric durability. The substitution of large (160 mm) diameter cylinder insulator for four small
diameter (20 mm) tubular rods has improved vacuum conditions in the space of beam forming and has allowed to
operate without failures when beam currents being up to 250 mA and extraction and focusing voltage being up to 25
and 40 kV respectively. Moreover, the construction provides the opportunity of electrode axial move. The insulators
are free from electrode thermal expansion mechanical efforts in a transverse direction.
PACS number: 29.17.+w
1 INTRODUCTION
The results of operation of the Moscow meson facto-
ry linac injector were previously reported at various
meetings and conferences on charged particle accelera-
tors [1-3]. Since 1992 the MMF linac regularly operates
about 2000-4000 hours per year in long-lived beam ses-
sions. The efficient linac performance substantially de-
pends on reliable, trouble-free injector operation. In the
course of routine functioning many feeble places had
come to light. Among others - high-voltage isolation of
the beam forming system (BFS), that was revealed
when the injector mean beam current has increased. At
50 Hz pulse repetition rate (PRR) of the beam current
with energy 750 keV and pulse duration 80 µs the mean
current was 600 µA. Since 1998 the injector runs at
50 Hz PRR with energy 400 keV at pulse duration up to
200 µs. The mean current has increased accordingly. In
the future it is supposed to increase PRR up to 100 Hz.
2 DISCUSSION AND CONSTRUCTIVE SO-
LUTIONS
The problem came up because of destruction of BFS
isolation. As a source of protons the duoplasmatron is
used. The beam is formed from wide expander ∅
60/70mm by an extraction electrode in the form of a flat
grid and by focusing electrode ∅200mm (Fig. 1). The
extraction and focusing electrodes are installed at the
source housing, cooled by water, initially with the help
of two consequently connected cylindrical insulators of
large diameter 140 mm (Fig. 1, above the axis). The in-
sulators were stuck with the stainless steel fixture by
hot-curing PVA glue. There was a backlog of insulators
from the fixture in process of operation. It is supposed
that because of the electrodes heating: at strong joint of
steel electrodes with porcelain (coefficients of a linear
thermal expansion accordingly αst=12·10-6 1/degree and
αp=3·10-61/degree) porcelain when heating prevents
from strain of electrodes and can be influenced upon
marked stresses. Critical temperature, at which stresses
reach the threshold of fracture for porcelain, is deter-
mined by a relation: ∆tcr = σd / Ecr.∆α [4, V.2]. At ulti-
mate strength σd=200-300 kg/sm2, Young modulus
Ep=0.5·106 kg/sm2 and ∆α=αst-αp it is approximately
100-120oC. As the strength of a glue joint of insulators
with the fixture was broken while fracture of insulators
had not taken place, it is possible to assume, that tem-
perature is less than critical one for porcelain (strength
of a glue joint is lower than strength of porcelain).
Fig. 1.
In regular injector operation mode (at rated energy)
the heating of BFS electrodes is determined basically by
secondary electrons flying from the accelerating tube
output diaphragm (ATOD) in a direction of the ion
source. The secondary electrons are caused by H+ beam
current sifting on the ATOD and walls of the beam
transport channel. The gas pressure in the channel is
about 10-4-10-5 Pa, so influence of residual gas on gener-
ation of secondary electrons is negligible. A current of
secondary electrons in the direction of the ion source
which was evaluated following the results of measure-
ВОПРОСЫ АТОМНОЙ НАУКИ И ТЕХНИКИ. 2001. №5.
Серия: Ядерно-физические исследования (39), с. 131-133.
131
ments of beam sifting on ATOD and of gamma radia-
tion is ~ 6 µA [5] or ~ 4.5 W of power at 750 keV.
Drain of heat from BFS electrodes depends on tem-
perature [4] and can to occur by a thermal conduction
through the insulators and by means of infrared radia-
tion from surface of electrodes. Drain of heat by a ther-
mal conduction through insulator (in kcal per hour):
Qt = λ.∆T.F/L, where the thermal conduction λ is ex-
pressed in kcal/m.h.oC, area F and length L accordingly
in m2 and m. Heat exchange by means of infrared radia-
tion between gray bodies (in kcal per hour): QL = 4.9·ϕ
*1,2·F1·[(T1/100) 4- (T2/100)4], where the area F1 - in m2,
temperature - in degrees of Kelvin, and ϕ*1,2 = 1 / [1 / ϕ
1,2 + (1 / ε1-1) + (F1/F2) (1 / ε2-1)] - coefficient of mutu-
al irradiation for gray bodies. In our case, for two coaxi-
al cylinders with the areas F1 and F2, located at close
distance, 1 / ϕ1,2 ≈1, ε1 ≈0,2, ε2≈ 0.8 and F1/F2 ≈0.5 and
ϕ*1,2 ≈ε1. The results of calculation are shown in Fig. 2.
The horizontal dashed line (Qe) corresponds to heat
brought by secondary electrons in a regular mode (max-
imum value). The heat balance temperature corresponds
to a cross point of dotted direct line Qe with a curve QΣ
=QT+QL and does not exceed ~ 50oC.
0
5
10
15
20
25
0 20 40 60 80 100 120 140
0C
Ккал/час
QL
QS = QL+ QT
QЕ QT
Fig. 2.
In some modes the heat flow on electrodes can be
much higher, for example when accelerating voltage
(AV) is increasing and the discharge of ion source is
switched on, or under aging of the tube with a warming-
up by a scattered beam, since at decreased AV both the
sifting of the beam on ATOD and secondary electrons
flow are increasing [6]. In this case the current of sec-
ondary electrons from ATOD in the direction of the ion
source exceeds values for a rated mode by an order of
magnitude and its power may be about tens of watts.
The speed of electrodes heating is higher too. When in-
side the tube all things are in working order, the AV in-
creasing occurs promptly and the dangerous mode “is
slipped” imperceptibly. However transition of the injec-
tor H+ to regular operation at a 50 Hz PRR was difficult
one and was accompanied by permanent tube aging for
increasing its electrical strength.
The basic problem of improvement of BFS isolation
- to exclude a mechanical loading on isolation when
heating the electrodes, nevertheless having maintained
their position on the tube axis in tolerance limits. It was
supposed that the cross travels of the extracting elec-
trode with a grid in relation to the ion source expander
and of the large diameter focusing electrode in relation
to the tube electrode with a grid will appear not so criti-
cal concerning fields and beam position.
The general view of improved BFS is shown on a
Fig. 1 (below the axis), fastening of electrodes - on a
Fig. 3.
Fig. 3.
The isolation is assembled from 4 tubular rods (1) ∅
20/5/170 mm (from radioporcelain GB-7), which past
through extraction (2) and focusing (3) electrodes. The
rods are rigidly anchored by the cantilever at basic
flange (4). The fastening of basic flange (4) to a housing
of the ion source (5) is made on the fit flange by 4
screws after assembly of construction on an assembly
table.
The rods pass through extraction (2) and focusing
(3) electrodes with a clearance 0.5-0.6 mm. The position
of electrodes along the tube axis is determined by
clamps (6), which are rigidly fixed on the rods. The
electrodes fasten to each clamp by two profile washers
(7) from the external part of the rod in relation to the
axis of the system. The axial symmetry is sustained with
accuracy to within 0.1 mm. At heating such assembly is
expanded outside from the insulating rod with slide
along fastening washers, forming a radial clearance
about 0.1 mm/100oC. On a ∅20 mm clamp a clearance
approximately 0.015 mm will appear too. At a horizon-
tal working position of BFS electrodes such values are
permissible.
3 CONCLUSION
Improved BFS has designed in a supposition, that
the thermal factor plays the basic role in fractures of iso-
lation. The suppositions were expressed too, that the
fractures of insulators can be associated with possible
large electrodynamic loadings on insulators at disrup-
tions, because the fractures were always accompanied
by disruptions but there is no precise model. After re-
placement of BFS insulators breakdowns took place, but
fractures were not fixed any more. No influence on the
beam position, in connection with possible thermal trav-
el of BFS electrodes across an axis, was marked. Any
weakening of mechanical fastening of electrodes to in-
sulator were not observed.
One of improved BFS advantages is an appeared op-
portunity of electrodes travel along the axis. Length of
rods can be increased if necessary. The ends of the rods
ВОПРОСЫ АТОМНОЙ НАУКИ И ТЕХНИКИ. 2001. №5.
Серия: Ядерно-физические исследования (39), с. 132-133
132
in the region of the electrodes should be closed with
metal caps with galvanic connection with the electrode
in order to prevent accumulation of charges and field
distortion. In process of designing it was supposed to
use an opportunity of BFS electrodes travel along the
axis for correction of optics in the case of 400 kV injec-
tion voltage.
The work is performed under the auspices of Rus-
sian Foundation for Fundamental Research,
Agr. N 01-02-16148.
REFERENCES
1. V.I.Derbilov et al. // Voprosy Atomnoj nauki i
tekhiniki (1997),4,5 (31,32), p. 57.
2. A.S.Belov et al. Voprosy Atomnoj nauki i tekhiniki
(1999), 3 (34), p. 28.
3. V.I.Derbilov et al. // Proceedings of 16 Internation-
al Conference on Charged Particle Accelerators,
Protvino, 1999, p. 128 – 131 (in Russian).
4. Short physical-technical reference book (Kratkij
physico-tech. Spravochnik). volums 1, 2, 3.
Moscow: Fizmatgiz, 1960. (In Russian).
5. B.P.Golubev. Dozymetry and Protection from ion-
izing radiation. Energoatomizdat, M., 1986. (In
Russian).
6. A.I.Akischin. Ion Bombardment in Vacuum. M-L:
GEI, 1963. (In Russian)
ВОПРОСЫ АТОМНОЙ НАУКИ И ТЕХНИКИ. 2001. №5.
Серия: Ядерно-физические исследования (39), с. 133-133.
133
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