On a possibility of using a superconducting cavity in the RF system of the storage ring LESR-N100
In the Kharkov Institute of Physics and Technology the design project of the 200 MeV electron storage ring LESR-N100 is under development. The essential feature of this facility is the large beam energy spread (of about 1%). To ensure a reasonable beam lifetime the RF-system should provide the accel...
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| Zitieren: | On a possibility of using a superconducting cavity in the RF system of the storage ring LESR-N100 / V.P. Androsov, I.M. Karnaukhov, Yu.N. Telegin // Вопросы атомной науки и техники. — 2002. — № 2. — С. 75-77. — Бібліогр.: 5 назв. — англ. |
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Androsov, V.P. Karnaukhov, I.M. Telegin, Yu.N. 2015-04-12T06:36:02Z 2015-04-12T06:36:02Z 2002 On a possibility of using a superconducting cavity in the RF system of the storage ring LESR-N100 / V.P. Androsov, I.M. Karnaukhov, Yu.N. Telegin // Вопросы атомной науки и техники. — 2002. — № 2. — С. 75-77. — Бібліогр.: 5 назв. — англ. 1562-6016 PACS: 29.20.Dh, 29.27.Bd https://nasplib.isofts.kiev.ua/handle/123456789/80121 In the Kharkov Institute of Physics and Technology the design project of the 200 MeV electron storage ring LESR-N100 is under development. The essential feature of this facility is the large beam energy spread (of about 1%). To ensure a reasonable beam lifetime the RF-system should provide the accelerating voltage of about 0.5 MV, while the total energy losses do not exceed ~700 eV/turn. The power dissipated in two 700 MHz normal-conducting (NC) cavities much exceeds the power transmitted to the beam. We considered a possibility to use in LESR-N100 a high-Q superconducting RF-cavity (SRF-cavity) in which the dissipated power is the same order of magnitude as the beam-transmitted power. The studies show that the system with SRF-cavity cannot operate in the standard mode when the cavity is matched to the power transmission line at some nominal beam current. The optimal operation mode with high overcoupling is proposed that requires the RF-power one order of magnitude less than in the case of NC-cavities. en Національний науковий центр «Харківський фізико-технічний інститут» НАН України Вопросы атомной науки и техники Theory and technics of particle acceleration On a possibility of using a superconducting cavity in the RF system of the storage ring LESR-N100 О возможности использования сверхпроводящего резонатора в высокочастотной системе накопителя LESR-N100 Article published earlier |
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| title |
On a possibility of using a superconducting cavity in the RF system of the storage ring LESR-N100 |
| spellingShingle |
On a possibility of using a superconducting cavity in the RF system of the storage ring LESR-N100 Androsov, V.P. Karnaukhov, I.M. Telegin, Yu.N. Theory and technics of particle acceleration |
| title_short |
On a possibility of using a superconducting cavity in the RF system of the storage ring LESR-N100 |
| title_full |
On a possibility of using a superconducting cavity in the RF system of the storage ring LESR-N100 |
| title_fullStr |
On a possibility of using a superconducting cavity in the RF system of the storage ring LESR-N100 |
| title_full_unstemmed |
On a possibility of using a superconducting cavity in the RF system of the storage ring LESR-N100 |
| title_sort |
on a possibility of using a superconducting cavity in the rf system of the storage ring lesr-n100 |
| author |
Androsov, V.P. Karnaukhov, I.M. Telegin, Yu.N. |
| author_facet |
Androsov, V.P. Karnaukhov, I.M. Telegin, Yu.N. |
| topic |
Theory and technics of particle acceleration |
| topic_facet |
Theory and technics of particle acceleration |
| publishDate |
2002 |
| language |
English |
| container_title |
Вопросы атомной науки и техники |
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Національний науковий центр «Харківський фізико-технічний інститут» НАН України |
| format |
Article |
| title_alt |
О возможности использования сверхпроводящего резонатора в высокочастотной системе накопителя LESR-N100 |
| description |
In the Kharkov Institute of Physics and Technology the design project of the 200 MeV electron storage ring LESR-N100 is under development. The essential feature of this facility is the large beam energy spread (of about 1%). To ensure a reasonable beam lifetime the RF-system should provide the accelerating voltage of about 0.5 MV, while the total energy losses do not exceed ~700 eV/turn. The power dissipated in two 700 MHz normal-conducting (NC) cavities much exceeds the power transmitted to the beam. We considered a possibility to use in LESR-N100 a high-Q superconducting RF-cavity (SRF-cavity) in which the dissipated power is the same order of magnitude as the beam-transmitted power. The studies show that the system with SRF-cavity cannot operate in the standard mode when the cavity is matched to the power transmission line at some nominal beam current. The optimal operation mode with high overcoupling is proposed that requires the RF-power one order of magnitude less than in the case of NC-cavities.
|
| issn |
1562-6016 |
| url |
https://nasplib.isofts.kiev.ua/handle/123456789/80121 |
| citation_txt |
On a possibility of using a superconducting cavity in the RF system of the storage ring LESR-N100 / V.P. Androsov, I.M. Karnaukhov, Yu.N. Telegin // Вопросы атомной науки и техники. — 2002. — № 2. — С. 75-77. — Бібліогр.: 5 назв. — англ. |
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2025-11-26T01:26:10Z |
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2025-11-26T01:26:10Z |
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| fulltext |
ON A POSSIBILITY OF USING A SUPERCONDUCTING CAVITY IN
THE RF SYSTEM OF THE STORAGE RING LESR - N100
V.P. Androsov, I.M. Karnaukhov, Yu. N. Telegin
National Science Center “Kharkov Institute of Physics and Technology”, Kharkov, Ukraine
e-mail: telegin@kipt.kharkov.ua
In the Kharkov Institute of Physics and Technology the design project of the 200 MeV electron storage ring
LESR-N100 is under development. The essential feature of this facility is the large beam energy spread (of about
1%). To ensure a reasonable beam lifetime the RF-system should provide the accelerating voltage of about 0.5 MV,
while the total energy losses do not exceed ∼700 eV/turn. The power dissipated in two 700 MHz normal-conducting
(NC) cavities much exceeds the power transmitted to the beam. We considered a possibility to use in LESR-N100 a
high-Q superconducting RF-cavity (SRF-cavity) in which the dissipated power is the same order of magnitude as
the beam-transmitted power. The studies show that the system with SRF-cavity cannot operate in the standard mode
when the cavity is matched to the power transmission line at some nominal beam current. The optimal operation
mode with high overcoupling is proposed that requires the RF-power one order of magnitude less than in the case of
NC-cavities.
PACS: 29.20.Dh, 29.27.Bd
1. INTRODUCTION
The RF system of any electron storage ring is
developed to provide both the compensation of total
energy losses of the beam and the required energy
acceptance.
The storage ring LESR-N100 [1] is intended for
studies of the laser-beam cooling effect and feasibility
of producing intensive X-ray beams through Compton
scattering of a laser light on an electron beam [2]. The
main parameters of the ring are presented in Table 1.
Table 1. Parameters of the LESR-N100
Electron energy, Е0, MeV 200
Beam current, Ib, mA 10
Momentum compaction
factor, α
0.021
Number of bunches 1
RF-frequency, fRF, MHz 699.3
Accelerating voltage, Vc, MV 0.5
RF- bucket width, ∆RF/E0, % 5.3
Radiation loss, Urad, eV/turn 283
Energy spread, ∆Е/Е0, % 0.8
Accelerating cavities: NC SC
Number of cavities 2 1
Parasitic energy loss, eV/turn:
-RF-cavities
- vacuum chamber
-total, Utot
330
140
750
60
140
480
Synchronous phase, Фc, deg 89.913 89.945
Power transmitted to the
beam, Pb, W
7.5 4.8
Dissipated power, Pc, kW/cell 11.5 0.0025
RF-generator power, Pg, kW 23 1.25
The essential feature of this facility is the large beam
energy spread ∆Е/Е0≈1% [3]. To ensure a reasonable
beam lifetime, the accelerating system should provide
the RF voltage Vc=0,5 MV, while the total energy losses
Utot do not exceed ~700 eV/turn. The result of such
disproportion is the necessity to operate practically in a
minimum of a wave of an accelerating voltage
(Фs=arccos(Utot/Vc)≈90
о
). The power dissipated in two
normal conducting (NC) cavities (Pc=11.5 kW/cavity)
much exceeds the power transmitted to the beam (Pb∼
7W). In view of the above mentioned, it seems an
inviting prospect to use in LESR-N100 a high Q
superconducting RF cavity (SRF-cavity), in which the
dissipated power is the same order of magnitude as Pb.
Such a possibility is considered below.
2. OPERATION PARAMETERS
Let's consider a phase vector diagram for the cavity
gap voltages, presented in Fig. 1. The accelerating
voltage Vс is determined by a sum of voltages Vg and Vb
induced by an RF-generator and a beam, accordingly.
For the projections of these vectors onto axes X (X is
selected along the vector -Ib ) and Y the following
relations are valid:
( ) ψψθ coscoscos bgsc VVV −+⋅=Φ⋅ (1a)
( ) ,sinsinsin ψψθ ⋅++⋅=Φ⋅ bgsc VVV (1b)
The cavity tuning angle ψ is defined by the
expression (ω0 -ω << ω0):
2
2
1
2 0
0
0
0
00
Γ
−−=−⋅−=−⋅
+
⋅−= ωω
ω
ωω
ω
ωω
β
ψ LQQtg ,
(2)
where Q0 is an unloaded quality-factor of a cavity; β is
PROBLEMS OF ATOMIC SCIENCE AND TECHNOLOGY. 2002, p.
Series: Nuclear Physics Investigations (40), p. 75-77. 75
a coupling coefficient of a cavity with a transmission
line; QL is a loaded quality factor; ω0 is a fundamental
frequency of a cavity, ω is a generator frequency, Γ is a
width of resonance curve of the loaded cavity at half its
height in maximum. One can see from the relation (2)
that tgψ is equal to the relative cavity detuning in terms
of the resonance width.
Fig. 1. The phase-vector diagram
for steady-state beam loading
The voltages Vb and Vg are given by the relations [4]:
ψ
β
ψ cos
1
cos
0
+
=⋅=
Q
Q
RI
VV
b
brb
(3a)
,cos
1
2
cos
2
1
0
ψ
β
β
ψ
+
=⋅=
Q
Q
RP
VV
g
grg
(3b)
where Vbr and Vgr represent the values Vb and Vg in the
resonance, Pg is the generator power at the cavity input,
and the factor R/Q is a figure of merit sometimes called
“a geometrical shunt resistance” of a cavity.
By excluding θ from the relations (1a, 1b),
substituting in the obtained equation Vg with (3b), and
solving it with respect to Pg, one can get the following
expression for the generator power:
( )
( )
( ) )4(sincos
1
sin
cos
1
cos
cos4
1
2
0
2
2
0
2
0
22
⋅
+
+Φ+
+
+
+Φ
+⋅=
ψψ
β
ψ
β
ψβ
β
c
b
s
c
b
s
c
g
V
Q
Q
RI
V
Q
Q
RI
Q
Q
R
VP
Usually, in the RF-systems of electron storage rings the
fundamental frequency of the loaded cavity is tuned so
that to compensate the reactive beam-loading
component and reduce the power consumed from the
generator. The corresponding expressions for Pg can be
obtained by optimizing the equation (4) for a cavity
tuning angle ψ:
s
c
shb
V
RI
tg Φ⋅
+
−= sin
)1( β
ψ , (5a)
( )
( )
22
cos
14
1
Φ
+
+⋅
⋅
+= s
shb
c
sh
g
RI
V
R
P
ββ
β
. (5b)
The optimization of the equation (5b) for a coupling
coefficient β reduces the expressions (5) to:
c
b
P
P+= 10β , (6a)
stgtg Φ⋅
+
−
−=
1
1
0
0
0 β
β
ψ , (6b)
,0 cbg PPP += (6c)
where Pb = IbVc cosФs is the power transmitted to the
beam, and Pc = Vc
2/[(R/Q)Q0] is the power dissipated in
cavity walls. So, the equations β =β0 and ψ=ψ0 are the
conditions of matching of a beam-loaded cavity to a
transmission line, because no reflection takes place at a
cavity input, and the required generator power is
minimal.
Substituting in expressions (3) and (6) the values
R/Q=100 and Q0=109, typical for superconducting
cavities, one obtains the following results:
Pg0=7.3 W; β0=2.9; ψ0≅Фs≅900; Vb>>Vg;
that is a matched operation demands a complete
detuning of a cavity (∆ω=4.4 kHz, while Г=8.8 Hz),
and the above considerations make no sense.
It should be noted that the control of the accelerating
voltage parameters is carried through changing the
phase and amplitude of Vg, and the practical operation
of the RF-system is possible when the dominant
contribution to the total cavity voltage Vc gives this
vector, i.e. when Vb≤Vg. Then, assuming that the
reactive component of beam loading is compensated by
a cavity detuning one can obtain the following relation:
( ) ( )β+≤Φ−⋅
⋅ 1cos10 csb VQ
Q
RI . (7)
Taking into account that in our case cosФs<<1 we
derive the relation restricting a magnitude of β:
1
0
−
⋅
⋅
≥
c
b
V
Q
Q
RI
β
. (8)
Having substituted in expression (8) R/Q=100 and
Q0=109, we obtain β≥2х103, that is the system should
operate under strongly overcoupled conditions. It
returns us to the traditional operation of
superconducting cavities at modern accelerating
facilities, where overcoupling is stipulated by a high
value of Pb, i.e. all RF-power is transmitted to the beam.
In our case Pb∼Pc, and practically all power will be
76
reflected at the cavity input and should be dissipated in
a circulator load. For the boundary case β=βopt the
generator power Pg is given by the simple expression:
cbg VIP
4
1= . (9)
From this expression one can see, that the power
required from a generator does not depend on the cavity
parameters. Using the above mentioned relations, we
obtain the main parameters for the boundary case β=β
opt=2000:
ψ=-45o; Pc=2.5 W; Pb=4.8 W; Pg=1.25 kW;
One can see that according to (2) ∆ω =Γ/2, i.e. the
optimal coupling corresponds to the cavity detuning
equal to the resonance half-width, and the required RF-
power is one order of magnitude less than in the case of
NC cavities (∼20 kW). However, it should be noted, that
in the first case the required RF-power grows
proportionally to the beam current, while in the second
case it practically does not depend on the beam current.
3. STABILITY OF PHASE OSCILLATIONS
As the result of a beam interaction with a
fundamental mode of an accelerating cavity a growth
rate of the rigid-bunch phase oscillations (Robinson
instability) is possible. For the cavity voltage phase and
amplitude control loops opened, and for the case of
reactive beam loading compensation, the stability
criteria is given by [4]:
,cos sbrc VV Φ⋅> (10)
In our case the synchronous phase Φs is defined by:
,cos
c
lossbrad
c
tot
s V
RIU
V
U ⋅+==Φ (11)
where Rloss is a total loss resistance of the ring.
Substituting the expressions (11) and (3a) in (10), we
obtain the following limitation on the beam current:
mA
QQ
RR
VI
loss
cb 5001
2
1
0
=
⋅
⋅
+⋅< β . (12)
This estimate far exceeds the designed value of the
beam current.
4. THE SUPERCONDUCTING CAVITY
For the LESR-N100 accelerating cavity we consider
a single-cell spherical cavity with wide beam pipes. The
cavity cell geometry is shown in Fig. 2.
Cavity calculations were performed with
SUPERFISH [5]. The cavity spectrum for monopole
modes is presented in Table 2. Boundary conditions E
or M correspond to Dirichlet or Neumann boundaries,
accordingly, at the ends of the half-cell.
The cavity has beam pipes by a diameter of 170mm,
and the cut-off frequencies are 1349 MHz for ТМ01-like
modes and 2150 MHz for ТМ11-like modes. The
calculated field topography for monopole cavity modes
shows that only the fundamental mode is trapped in the
spherical part of the cavity, all other modes propagate
effectively into the beam pipes. It is supposed to reduce
the Q-factors of these modes with a pair of coaxial
antennas-dampers located on the cavity beam pipes.
Fig. 2. The SRF cavity for the LESR – N100
storage ring
Table 2. Cavity modes
Frequency,
MHz
Boundary
conditions
Q⋅1010 R/Q, Ω
699.95 ЕМ 1.57 82.8
1368.50 ЕМ 1.90 23.0
1368.87 МЕ 1.68 236.0
1502.46 МЕ 1.59 78.2
1584.28 ЕМ 1.65 375.8
1965.64 ЕМ 1.60 122.8
2200.46 ЕМ 1.50 112.4
2814.42 ЕМ 1.22 12.4
5. CONCLUSIONS
The consideration presented above shows that the
implementation of a SC-cavity in the RF-system of
LESR-N100 is justifiable for the stored beam currents
up to ∼10mA. In the case of project upgrading for
storing higher currents (multibunch mode), it seems
reasonable to use conventional room-temperature RF-
cavities.
REFERENCES
1. E. Bulyak et al. A compact X-ray source
based on Compton scattering. Proceedings of
PAC-99, N.Y., 1999, p. 3122.
2. Z. Huang and R.D. Ruth. Radiative cooling
of relativistic electron beams. Proceedings of PAC-
99, N.Y., 1999, p. 262.
3. P. Gladkikh et al. Beam dynamics
simulations in the storage ring N100 with electron-
photon interaction. Proceedings of EPAC-2000,
2000, p. 1199.
4. P.B. Wilson. Fundamental mode rf design in
e+e storage ring factories. SLACPUB 6062,
Stanford Univ., Stanford, 1993, 19 p.
5. J.H. Billen and L.M. Young. POISSON/
SUPERFISH on PC Compatibles. Proceedings of
the PAC-03, 1993, p. 790.
77
National Science Center “Kharkov Institute of Physics and Technology”, Kharkov, Ukraine
Table 1. Parameters of the LESR-N100
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