The analysis and choice of the system for attaining vacuum in a 300 MeV electron storage ring
Conditions are considered for attaining a pressure of ~10⁻⁹ Torr in a vacuum chamber of the redesigned storage ring N100M with the use of both concentrated and distributed pumps. Estimates are made for admissible outgassing due to thermal desorption and synchrotron radiation-induced desorption; a va...
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irk-123456789-1108392017-01-07T03:04:40Z The analysis and choice of the system for attaining vacuum in a 300 MeV electron storage ring Grevtsev, V.G. Zelinsky, A.Yu. Karnaukhov, I.I. Mocheshnikov, N.I. Theory and technics of particle acceleration Conditions are considered for attaining a pressure of ~10⁻⁹ Torr in a vacuum chamber of the redesigned storage ring N100M with the use of both concentrated and distributed pumps. Estimates are made for admissible outgassing due to thermal desorption and synchrotron radiation-induced desorption; a variant of arranging the pumps along the perimeter of the N100M storage ring is proposed. Розглянуто умови для отримання тиску ~10⁻⁹ Тор електронопроводі нагромаджувача Н100М, що модернізується, з використанням як зосереджених так і розподілених насосів. Визначено дозволені значення для обумовленого термодесорбцією газовиділення, та десорбції за рахунок синхротронного випромінювання. Запропоновано варіант розташування насосів по периметру нагромаджувача Н100М. Рассмотрены условия получения давления ~ 10⁻⁹ Торр в электронопроводе реконструируемого накопителя Н100М при использовании как сосредоточенных, так и распределенных средств откачки. Определены допустимые значения газовыделения за счет термодесорбции и десорбции за счет синхротронного излучения. Предложен вариант расстановки средств откачки по периметру накопителя Н100М. 2003 Article The analysis and choice of the system for attaining vacuum in a 300 MeV electron storage ring / V.G. Grevtsev, A.Yu. Zelinsky, I.I. Karnaukhov, N.I. Mocheshnikov // Вопросы атомной науки и техники. — 2003. — № 2. — С. 126-130. — Бібліогр.: 9 назв. — англ. 1562-6016 PACS: 29.20.Dh, 29.27.Bd http://dspace.nbuv.gov.ua/handle/123456789/110839 en Вопросы атомной науки и техники Національний науковий центр «Харківський фізико-технічний інститут» НАН України |
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Theory and technics of particle acceleration Theory and technics of particle acceleration |
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Theory and technics of particle acceleration Theory and technics of particle acceleration Grevtsev, V.G. Zelinsky, A.Yu. Karnaukhov, I.I. Mocheshnikov, N.I. The analysis and choice of the system for attaining vacuum in a 300 MeV electron storage ring Вопросы атомной науки и техники |
| description |
Conditions are considered for attaining a pressure of ~10⁻⁹ Torr in a vacuum chamber of the redesigned storage ring N100M with the use of both concentrated and distributed pumps. Estimates are made for admissible outgassing due to thermal desorption and synchrotron radiation-induced desorption; a variant of arranging the pumps along the perimeter of the N100M storage ring is proposed. |
| format |
Article |
| author |
Grevtsev, V.G. Zelinsky, A.Yu. Karnaukhov, I.I. Mocheshnikov, N.I. |
| author_facet |
Grevtsev, V.G. Zelinsky, A.Yu. Karnaukhov, I.I. Mocheshnikov, N.I. |
| author_sort |
Grevtsev, V.G. |
| title |
The analysis and choice of the system for attaining vacuum in a 300 MeV electron storage ring |
| title_short |
The analysis and choice of the system for attaining vacuum in a 300 MeV electron storage ring |
| title_full |
The analysis and choice of the system for attaining vacuum in a 300 MeV electron storage ring |
| title_fullStr |
The analysis and choice of the system for attaining vacuum in a 300 MeV electron storage ring |
| title_full_unstemmed |
The analysis and choice of the system for attaining vacuum in a 300 MeV electron storage ring |
| title_sort |
analysis and choice of the system for attaining vacuum in a 300 mev electron storage ring |
| publisher |
Національний науковий центр «Харківський фізико-технічний інститут» НАН України |
| publishDate |
2003 |
| topic_facet |
Theory and technics of particle acceleration |
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http://dspace.nbuv.gov.ua/handle/123456789/110839 |
| citation_txt |
The analysis and choice of the system for attaining vacuum in a 300 MeV electron storage ring / V.G. Grevtsev, A.Yu. Zelinsky, I.I. Karnaukhov, N.I. Mocheshnikov // Вопросы атомной науки и техники. — 2003. — № 2. — С. 126-130. — Бібліогр.: 9 назв. — англ. |
| series |
Вопросы атомной науки и техники |
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2025-07-08T01:13:49Z |
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2025-07-08T01:13:49Z |
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| fulltext |
THE ANALYSIS AND CHOICE OF THE SYSTEM FOR ATTAINING
VACUUM IN A 300 MeV ELECTRON STORAGE RING
V.G. Grevtsev, A.Yu. Zelinsky, I.I. Karnaukhov, N.I. Mocheshnikov
National Science Center “Kharkov Institute of Physics and Technology”, Kharkov, Ukraine
e-mail: karnaukhov@kipt.kharkov.ua
Conditions are considered for attaining a pressure of ~10-9 Torr in a vacuum chamber of the redesigned storage
ring N100M with the use of both concentrated and distributed pumps. Estimates are made for admissible outgassing
due to thermal desorption and synchrotron radiation-induced desorption; a variant of arranging the pumps along the
perimeter of the N100M storage ring is proposed.
PACS: 29.20.Dh, 29.27.Bd
1. INTRODUCTION
The currently available 160 MeV electron storage
ring H100 can be used as a base to create a powerful
source of -quanta, where the effect of Compton
backscattering of a laser beam by relativistic electrons is
used [1]. The existing infrastructure and equipment will
provide a rise in the circulating beam energy of N100M
(after redesign) up to 250…300 MeV. The common
practice of attaining the required vacuum (~10-10 Torr) in
high-energy (2...6 GeV) and lower-energy (up to 1
GeV) storage rings calls for the use of both concentrated
and distributed pumps in view of intense gas flows
stimulated mainly by synchrotron radiation (SR).
Though the action of SR is less critical in low-energy
facilities, the incorrect estimate of its effect can
nevertheless impede the attainment of design parameters
significantly [2].
2. THE CHOICE OF PUMPING SCHEME
AND REQUIREMENTS ON GAS
EVOLUTION VALUE
The storage ring N100M is to be operated with a
circulating current of about 1 A in the energy range
between 60 and 300 MeV.
To provide the electron beam lifetime of no less than
2 and 0.5 hours in the storage ring at injection energies
of 250 and 60 MeV, respectively, the pressure P has to
be about 5⋅10-9 Torr. Irrespective of the nature of gas
molecule desorption from the walls of the vacuum
chamber, the pressure P in the chamber will be
determined by the effective pumping speed Seff and the
total outgassing Q0, the main constituents of the latter
being the thermal desorption Qt and the stimulated
desorption Qγ:
limlim P
S
QQ
P
S
Q
P
э
t
э
o +
+
=+= γ
, (1)
where Plim is the limiting pressure of pumps in the
absence of outgassing.
To calculate the required Seff at a given Q0, we
assume the vacuum chamber to be homogeneous along
the whole perimeter of the storage ring, i.e., there are no
elements of RF systems, diagnostics; there is no
interaction between the electron beam and the laser
beam, etc. The inner surface of the chamber has
elliptical cross-section with semi-axes axb = 5x1.5 cm2
at a length L0 ~15 m, and has the area Ss
≈ 3.3 m2. The
surface at bending sections makes only 21% of the total
area, this being of importance in deciding on the
pumping equipment with regard to desorption
stimulated by synchrotron radiation. With storage rings
as SR sources, it is common practice that more than
80% of the chamber length (e.g., for the LEP this is
83%) is subject to “cleaning” with the SR beam [3].
Let us consider the pumping system (Fig. 1) that
comprises N pumps equally spaced over the length of
the chamber, i.e., L=L0/N, each pump having the
pumping speed S0.
-4 -2 0 2 4 6 8 10 12 14
-6
-4
-2
0
2
4
L
S
0S
0
X0
Fig. 1. Scheme of pumping
126 PROBLEMS OF ATOMIC SCIENCE AND TECHNOLOGY. 2003, № 2.
Series: Nuclear Physics Investigations (41), p. 126-130.
At molecular pumping conditions, the gas flow
along the chamber is
,,)( Aq
dx
dQ
dx
dPxQ =ω−= (2)
where
22
22171
ba
ba
+
=ω is the specific molecular
conductivity of the N100M chamber, being equal to
14.74 l⋅m/s for air; A is the specific area of the inner
surface of the chamber, cm2/m; q is the specific
outgassing, Torr⋅l/(cm2⋅s), whence we have
.2
2
Aq
dx
Pd −=ω (3)
Using the boundary conditions dP/dx=0 at x=L/2
and P=AqL/S at x=0, we obtain from eq. (3) the
following relations:
;)(
2
+−=
oS
LxLxAqxP
ω (4)
+=
oS
LLAqP
ω4
2
max ; (5)
effeffo
av nS
Aq
S
ALq
S
LLAqP ==
+
ω
=
6
2
; (6)
ω+
ω
=
6
6
LS
SS
o
o
eff , (7)
where for the N100M we have A≅2.202⋅103 cm2/m; Seff
is the efficient pumping speed of one pump, l/s;
effeffn LSS = , (8)
where nSeff is the pumping efficiency per unit length, l/(s
⋅m); C = ω/L is the chamber conductivity, l/s.
From expressions (4)-(8) it is seen that at L → 0
(distributed pumping) Seff = S0 and δ = Seff/So → 1, and
at L → ∞ we have Seff → 0 and δ → 0.
So, the choice of S0 will mainly depend on various q,
L values. The decisive factor here will be the choice of
the parameter:
+
ω
==
oeff
av
S
LAL
S
AL
q
P 1
6 (9)
so that Pav ≤ P0, i.e.,
+≥
o
o
S
LAL
q
P 1
6ω
(10)
or
AL
SP
q effo ⋅
≤ (11)
for the concentrated pumping, and
A
SP
q effno ⋅
≤ (12)
for the distributed pumping. The value of specific
outgassing due to all desorption processes will be
deciding in the choice of S0, L at given P0.
Table 1 lists the values of q0, Seff and ΣnSeff = nSeff L0
for the distributed pumping.
At present, it appears most judicious to use
nonevaporable getters (NEG) for the distributed
pumping [4]. For getter St707, the specific pumping
speed is about 3 l/(s⋅cm2). Table 1 gives the required
NEG area values for the mentioned pumping speeds Σ
nSeff. If the NEG strip width is chosen to be 2 cm, then at
a two-sided deposition of getter on the strip, ~15 m in
length, a pressure of 5⋅10-9 Torr will be provided at a
specific outgassing less than ~3⋅10-9 Torr⋅l/(cm2⋅s).
Table 1. Parameters of distributed pumping for the
required NEG with SNEG=3 l/(cm2⋅s), and two-side strip
of width 2 cm
q0, Torr/(cm2⋅s) 10-8 10-9 10-10 10-11 10-12
nSeff, l/(s⋅m) 4040 440 44 4.4 0.44
nSeff, l/s 66000 6600 661 66.1 6.6
Area, cm2 22020 2202 220 22 2.2
Length, m 55.1 5.5 0.55 0.06 0.006
Let us now consider the requirement on qadd in the
case of concentrated pumping.
Fig. 2 shows the functions qadd=f(N) for different S0
values at P0=Pav=5⋅10-9 Torr. It is seen that with increase
in the number of pumps and their pumping speed, the
requirements for qadd tend to decrease, but even at S0 =
∞ and N=15 (with interspace L = 1m, and this being
impracticable) qadd must be no more than 2⋅10-10 Torr⋅
l/(cm2⋅s). Besides, an increase in S0 over 150 l/s exerts
no essential effect on the permissible qadd value. Fig. 3
and 4 show the functions Seff=f(S0) and δ=Seff/S0=f(S0)
for different number of pumps. From the analysis of
data in Fig. 2 to 4 it appears most reasonable for N100M
to choose 8 sites of pumping with pumps having S0 =
150 l/s. Their arrangement is shown in Fig. 6. The
pressure distribution over the superperiod length is
presented in Fig. 5.
0 2 4 6 8 10 12 14 16
0
20
40
60
80
100
120
140
160
180
200
220
So=∞
So=400
So=300
So=200
So=150
So=100
So=50
So=20
So=10
N
⋅qadd·1012 [Torr·l/cm2s]
Fig. 2. qadd = f(N) for different S0 values
127
0 100 200 300 400
10
20
30
40
50
60
70 N=15
N=12
N=10
N=8
N=6
N=4
S o , l/s
S
eff
Fig. 3. Seff = f(S0) for different number of pumps
0 100 200 300 400 0
10
20
30
40
50
60
70
80
90 S
eff / S o
S
o , l/s
N =15
N =12
N =10
N =6 N =8
N =4
Fig. 4. δ=Seff/S0=f(S0) for different number of pumps
0,0 0,4 0,8 1,2 1,6 2,0 2,4 1 2 3
4 5 6
7 8 9
P · 10 9 Torr
L, m
Fig. 5. Pressure distribution over the length of
superperiod
The above-given requirements can be met with the
pump Trion-150-HMTO-01-1 [5], which provides a
limiting residual pressure of ~ 10-11 Torr with an
increase in the start-up pressure up to ~5⋅10-2 Torr,
evacuates noble gases and hydrocarbons. In the start of
the pump a water cooling is used, while at ultimate
vacuum conditions liquid nitrogen is used. Besides, at
bending magnet sections, along with pumps 1, 4, 5 and
8, nonevaporable getters are provided for pumping. In
this case, the process of manufacturing the chamber
becomes more complicated in order to keep its
electrodynamics smoothness. For N = 8, S0 = 150 l/s,
P0= 5⋅10-9 Torr we have qadd = 4.35⋅10-11 Torr⋅l/(cm2⋅s).
A further increase of demands for P0 leads to a
proportional decrease in qadd.
1
2
3
56
47
8
Fig. 6. Layout of the facility H100M; the arrangement of pumps is shown by arrows.
128
3. THE PROCESS OF VACUUM CHAMBER
SURFACE TREATMENT
As mentioned above, of all the outgassing sources,
thermal desorption and the desorption due to the SR
effect (in the absence of leaks) are the main ones.
Of fundamental importance in the formation of
desorption flows are the chemical composition and the
structure of vacuum chamber material, the initial gas
content in the chamber, the technological prehistory and
the state of the surface. To reduce the flows, various
technological techniques, methods and their
combinations, realized during both the process of
chamber manufacture and the periods of start-
adjustment operations, long-term service, are used.
For N100M, stainless steel (SS) Kh18N10T appears
the most suitable material.
For all storage-ring facilities, much attention is
given to different methods of vacuum surface cleaning
in order to reduce gas evolution. The description of
these methods can be found in numerous publications; a
short survey of the methods has been given in ref. [6].
Eventually, it has become possible to make chambers
with qT ~10-13 l⋅Torr/(cm2⋅s). However, in this case,
expensive methods of chemical, physical and special
cleaning (including the SR-beam or glow-discharge
cleaning) are used.
For our purposes, the most low-cost methods of
attaining vacuum-clean surfaces must be chosen. In any
case, to initiate start-adjustment operations, qT must not
exceed 10-10 l⋅Torr/(cm2⋅s). So, for our conditions and
possibilities, the NIIEFA experience [7] appears the
most acceptable. According to this experience, the
untreated stainless steel has qT ≅ 3 ... 8⋅10-7 l⋅Torr/(cm2⋅
s), and after turning followed by washing in gasohol qT
= 10-9 ... 5⋅10-10 l⋅Torr/(cm2⋅s). A subsequent continuous
pumping (no less than 100 hours), a moderate warming-
up (no higher than 150°C), the use of glow discharge
provides a more than two-order improvement in the q
value. And the following cleaning with the SR makes q
still better. Though here there are some questions
arising from the comparison with other storage rings,
including the SR sources. First, since the SR flow
3, EEIN c ≈≈ εγ
, and the injection energy in the
N100M is assumed to be 60 MeV, then the SR
“cleaning” without a rise in the stacked beam energy
would be little efficient. At E = 60 MeV, there will be
very little photons having an energy higher than 5 …
10 eV, starting with which the process of gas molecule
desorption is most probable. Therefore, as early as at the
injection stage we must have vacuum no worse than 5⋅
10-9 Torr before the necessary lifetime (~0.5 h) can be
provided. Therefore, it is desirable that the chamber
should be moderately warmed-up (up to 150°C) and
could be cleaned with a glow discharge. Secondly, as
mentioned above, the SR cleaning in the N100M is
possible only for ~20% of the chamber surface (at
bending sections), therefore 80% of the chamber should
be cleaned with a glow discharge, this being most
efficient with simultaneous warming-up of the chamber.
Besides, considering that the binding energy of water is
higher than that of gases (H2, CO, CO2, CH4, etc.), the
removal of water also calls for warming-up. The
vacuum surface can efficiently be cleaned with a glow
discharge in a gas mixture. Ar + O2 (10%) is the mixture
most widely used for glow-discharge cleaning.
However, the presence of Ar after the cleaning is
completed may have a significant effect on the beam
life (inversely proportional to z2). The removal of Ar is
favored by the chamber warm-up and by the use of
trions. So, it appears more preferable to use the helium-
oxygen (10%) mixture for the glow discharge [6].
In the general case, the gas flow from the vacuum
chamber walls is determined by the desorption from the
surface, by diffusion from the bulk of the material and
by the wall permeability. The kinetics of heat evolution
of gas physically adsorbed by the surface in vacuum is
described by the function close to t-1 for unbaked metal
materials. The process of attaining the required vacuum,
during which the desorption of physically adsorbed
gases (vapors of water, nitrogen; carbon and
hydrocarbon oxides; oxygen) is dominant, lasts for 105
to 106 s (28 to 277 hours). At the next stage of pumping,
it is the diffusion flow from the bulk of materials
(mainly, hydrogen) that becomes dominant, it is
described by the kinetic dependence of type t-0.5. The
duration of this stage is estimated to be 106 < t < 107 s
(277-2770 hours). Later on, the gas flow due to wall
permeability, having a constant value, becomes
dominant. It is obvious that at these conditions the role
of chemical and thermal methods of cleaning reduces to:
(i) a decrease in the quantity of physically adsorbed gas,
(ii) acceleration of desorption processes, and (iii) the
formation of an oxide layer on the surface; this layer has
a very low permeability and thus “blocks” hydrogen
dissolved in the metal. All the mentioned cleaning
methods (chemical, thermal, radiation-stimulated)
provide a significant decrease in gas flows for a shorter
time and to lower values. For example, a one-hour
warming-up in vacuum at 1000°C is equivalent (in q) to
a 2500-hour warming-up at 300°C [8]. Therefore, in our
case, the use of only a part of the methods developed for
mechanical, chemical and thermal cleaning of surfaces
cannot provide the required degree of vacuum chamber
surface quality.
4. SYNCHROTRON RADIATION AND ITS
EFFECT ON GAS DESORPTION
Below, we give the main relations that describe the
SR characteristics.
The general losses by the SR are given by
;6.88
4
ργ
IEP = [GeV], [mA], [wt], [m] (13)
The critical energy of the photon is
;1022.2
3
3
ρ
ε E
c ⋅= [eV], [GeV], [m] (14)
The total flux of photons of all energies is
estimated as:
;1008.8 17 IE⋅=Γ ) [l/s], [GeV], [mA] (15)
129
The linear photon flux is calculated as
;1028.1 17
ρ
IE
dS
d ⋅=Γ
[l/(s⋅m)] (16)
The gas flow due to the photon-induced desorption
is given by Q = η Γ , where η is the desorption
coefficient [molecule/photon].
For the N100M, at I = 1 A we have Pγ=1.772⋅105 E4,
Γ = 8.08⋅1020 E, εc = 4.4⋅103 E3. Table 2 lists the
values of these parameters.
The process of gas desorption by SR photons
consists of two stages: under the action of photons
secondary electrons are knocked out from the surface,
these electrons then desorb the gases. It is assumed that
the threshold photon energy is 10 eV, though some
authors give it to be about 5 eV.
Table 2. SR characteristics for the N100M at different energies
One liter of gas at a pressure of 1 Torr comprises
3.54⋅1019 molecules/(l⋅Torr). Correspondingly, the flow
of gas evolution under the SR action will be given by
s
ТоrrlQSR
⋅
⋅
Γ= 191054.3
ηχ
, (17)
where χ is the factor taking into account the number of
photons having an energy higher than 5 to 10 eV.
This gas flow will mainly be concentrated at
bending sections, where the chamber surface area equals
6918 cm2, therefore the specific outgassing due to the
SR will be
.10 2
3
сms
lТоrrqSR ⋅
⋅≈ − η χ (18)
Considering that this parameter should not be higher
than 10-10 Torr⋅l/(cm2⋅s), the η value should not be
higher than 10-7.
Numerous experimental data give
η = ηо⋅ D --α , (19)
where η0 is the initial coefficient of desorption, η is the
final desorption coefficient, D is the SR dose (in units
mA h), α is the index equal to 0.6 … 1, depending on
the information source.
Let us estimate the required time, for which η→10-7.
From expression (19) it follows that
η
η
α
αηη o
o DD lg1lg;lglglg =−= . (20)
For E=300 MeV and a stainless steel as a chamber
material, we have η0 ~10-3 [9].
Then at α = 0.6 we have D0.6 = 106 mA⋅h; at α = 1.0
D1.0 = 104 mA⋅h. Or at I = 1000 mA, we have tα=0.6 = 816
hours, tα=1.0 = 12 hours.
In practice, the time of attaining the necessary
vacuum conditions will be within the mentioned ranges.
5. CONCLUSION
At this stage of work on a preliminary choice of
vacuum system design for the storage ring N100M it is
evident that the attainment of necessary pressure (5⋅10-9
Torr) will mainly be determined by both the quality of
the chamber material and the thoroughness of chemical,
thermal and radiation-stimulated treatments of the
chamber surface so that the initial specific gas evolution
should be as minimum as possible at our conditions
(~10-10 Torr⋅l/(cm2⋅s)), and the pumping equipment
should meet the above-mentioned requirements. At
design stages to follow, it will be necessary to consider
the arrangement of elements of different N100M
systems in vacuum volumes, the principles of injection
line structure.
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1. E. Bulyak, P. Gladkikh et.al. A compact X-
ray source based on Compton scattering // Nucl.
Instr. and Meth. In Phys. Res. A. № 467-468, 2001,
p. 88-90.
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130
E, GeV 0.05 0.06 0.07 0.1 0.15 0.2 0.25 0.3
с , eV 5.5⋅10-4 0.95 1.51 4.4 14.85 35.2 68.75 118.8
Р , Wt 1.1075 2.3 4.25 17.72 89.71 283.52 692.19 1435.32
Γ , 1/s 4.04⋅1019 4.85⋅1019 5.66⋅1019 8.08⋅1019 1.21⋅1020 1.62⋅1020 2.02⋅1020 2.42⋅1020
National Science Center “Kharkov Institute of Physics and Technology”, Kharkov, Ukraine
References
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