VEPP-4M collider: Scurrent activity and future plans
Results of the activity at VEPP-4M collider of the Budker Institute of Nuclear Physics over the period of 2000-2001 and the near future plans are presented.
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Національний науковий центр «Харківський фізико-технічний інститут» НАН України
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| citation_txt | VEPP-4M collider: Scurrent activity and future plans / V.А. Кiselev // Вопросы атомной науки и техники. — 2001. — № 5. — С. 3-5. — Бібліогр.: 10 назв. — англ. |
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| container_title | Вопросы атомной науки и техники |
| description | Results of the activity at VEPP-4M collider of the Budker Institute of Nuclear Physics over the period of 2000-2001 and the near future plans are presented.
|
| first_indexed | 2025-12-07T18:27:23Z |
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VEPP-4M COLLIDER: CURRENT ACTIVITY AND FUTURE PLANS
V.A. Kiselev1
(for the VEPP-4M team)
Budker Institute of Nuclear Physics, Novosibirsk 630090, Russia
Results of the activity at VEPP-4M collider of the Budker Institute of Nuclear Physics over the period of 2000-2001
and the near future plans are presented.
PACS number: 29.20.Dh
1 INTRODUCTION
VEPP-4M is a single-ring e+e- collider intended for
high-energy physics experiments, photo-nuclear study at
the ROKK-1M facility and synchrotron radiation re-
search [1, 2]. Maximum designed energy of VEPP-4M
is around 6 GeV. An electron (or positron) beam con-
sists of two bunches which are spaced at one-half of the
ring circumference (183 m). The beams collide at zero
crossing angle in the interaction point (IP) where the
KEDR detector is located.
Basically, VEPP-4M is intended to study physics of
ϒ-meson and two-photon processes. However, because
of the interest growing to the range of J/ψ and ψ′
physics, it was proposed to concentrate efforts in the
low energy range E = 1.5 –1.8 GeV [3]. This energy
range is unusual for our storage ring and additional in-
vestigation has to be done to obtain optimal perfor-
mance.
Two possible ways to reach reasonable luminosity in
J/ψ region under consideration: (i) redistribution of
damping partition numbers with the help of the gradient
wigglers (GWs) installed in the technical straight at
places of non zero dispersion and (ii) introducing of a
strong radiation damping by two 3-pole dipole wigglers
(DWs) located on the opposite sides of the VEPP-4M
experimental straight section.
In the near future we plan to perform an experiment
on measurement of the τ lepton mass in the vicinity of
its production threshold (1.777 GeV) with a relative ac-
curacy better than 10-4 using the method of the reso-
nance depolarization for beam energy calibration [4].
Earlier, such a method was successfully used in mea-
surements of the J/ψ and ψ′ mass at VEPP-4 [5].
2 LUMINOSITY
For VEPP-4 the peak luminosity at 5 GeV was about
5×1030 cm-2s-1. Now for VEPP-4M at the same energy
we hope to reach 2×1031 cm-2s-1 with the existing optics.
At low energy the luminosity reduces significantly
(∝ E4) and different problems arise due to the low
damping rates (1/τ ~ 10 s-1).
VEPP-4M has relatively large horizontal dispersion
at the IP, so the horizontal beam size here is mainly de-
fined by the energy spread. The ratio between syn-
chrotron and betatron horizontal beam size
(monochromatization factor) is equal to λ = 1.8 in the
nominal operation mode. However, at a low energy we
can vary this parameter by the GWs, which can redis-
tribute damping decrements between horizontal and lon-
gitudinal planes. By changing the GWs strength and
VEPP-4M lattice, we can vary λ within the rather wide
range (from ~ 1 to 4). Analytical studies [6] shows that
the beam-beam effects are most dangerous for λ ≈ 1. In
this case all three degrees of freedom are coupled and
synchro-betatron resonances become strong. On the
contrary, when λ >> 1, the particle horizontal co-ordi-
nate at the IP practically does not depend on the beta-
tron motion and the beam behaviour becomes almost
two-dimensional. The width of horizontal and coupled
synchro-betatron resonances falls down with increasing
λ (for the mere vertical and synchrotron resonances it is
not the case).
Additionally redistribution of the damping decre-
ments by the GWs provides:
• suppression of high-order non-linear resonances
with increasing the horizontal betatron damping,
• reduction of the horizontal betatron emittance (a
dynamic aperture become larger in units of rms
beam size).
• reduction of the horizontal beam-beam parameter ξ
x, since the total horizontal beam size at the IP in-
creases.
The latter allows increasing a bunch intensity keep-
ing ξx constant. Experimental results show that for λ ≈ 3
the maximum bunch current obtained is around 2 mA
that corresponds to ξx ≈ 0.02. For the nominal operation
mode (λ ≈ 1.8) such current can not be reached because
in this case ξx = 0.032 is well above the beam-beam lim-
it.
To study the method of the resonance depolarization
and to check the KEDR detector acquisition system, a J/
ψ test run was performed in summer 2001. Fig. 1 shows
luminosity obtained during this run while Fig. 2 shows
the beam-beam parameter as a function of the bunch
current. The maximum peak luminosity that was
achieved L = 4.7×1029 cm-2s-1 corresponds to ξy = 0.037
(1×1 bunch mode with 2.2 mA per bunch).
1 vkiselev@inp.nsk.su
ВОПРОСЫ АТОМНОЙ НАУКИ И ТЕХНИКИ. 2001. №5.
Серия: Ядерно-физические исследования (39), с.3-5.
3
Fig. 1. Single bunch luminosity versus of beam cur-
rent (DWs off).
Fig. 2. Test run vertical beam-beam parameter cal-
culated from luminosity data.
Another way to improve the luminosity performance
is using of the dipole wigglers (DWs) with the peak
field H = 1.8 T, which allows one to increase the hori-
zontal emittance by a factor of 4 at 1.5 GeV. Numerical
simulations of the beam-beam interaction with the
LIFETRACK code [7] shows that with the help of the
DWs we can reach the single bunch luminosity
L ≈ 1030 cm-2s-1 for 1.5 GeV (with beam-beam parame-
ters ξx = 0.015 and ξy =0.03). The experimental data
with the switching-on DWs correspond to L ≈ 0.7×
1030 cm-2s-1 (Ib = 3.2mA, ξy = 0.046) and the beam life-
time τ = 1.3 hour. Experiments show that the maximum
emittance increasing with DWs (4 times) is not optimal
for the luminosity increasing. The reason as it is consid-
ered now is the dynamic aperture limitation.
3 DYNAMIC APERTURE
Study of the non-linear beam dynamics was already
performed at VEPP-4M several years ago [8]. Since that
time, the new final focus quadrupoles with improved
gradient quality replaced two old ones. Besides, the
working betatron tune point was moved from (8.62;
7.57) to (8.55; 7.60). These two factors yielded to sig-
nificant increase of the horizontal border of stable mo-
tion (twice). However, when two dipole wigglers are
used to enlarge the beam phase volume, the horizontal
aperture shrinks.
At an energy of 1.5 GeV, two 1.8 T dipole wigglers
provide strong distortion to the beam motion (especially
vertical). At their maximum field the linear tune shift is
∆Qy ≈ 0.13 and ∆Qx ≈ 0.02 [9].
Linear wiggler effects, including the tune matching
and the beta-function recovering (inside a 15% accura-
cy), are completed by three pairs of quadrupoles in the
experimental straight section. However, non-linear com-
ponents of the wiggler field (mainly, strong chromatic
sextupoles) together with the fringe field yield a signifi-
cant reduction of the dynamic aperture (by approximate-
ly 30%) as it is illustrated in Fig. 3 [10]. The vertical
border of the aperture is limited by mechanical factors
well below the dynamic aperture limitation and is not
changed due to the wiggler switching-on.
Fig. 3. VEPP-4M dynamic aperture.
As the next step, study of non-linear components of
the wiggler field is planning to be performed. The final
goal is suppression of the DWs non-linearity by the use
of octupoles and sextupoles magnets.
4 POLARIZATION AT VEPP-4
A measurement of the τ+τ‾ production cross section
will be done by the detector KEDR in the energy region
just above the threshold (1.78 GeV). To calibrate the
beam energy, the polarized electron beams are injected
in the storage ring VEPP-4M from a booster storage
ring VEPP-3 (see Fig. 4). Radiation polarization of par-
ticles in VEPP-3 occurs with the characteristic time τ
p ≈ 40 minutes near to the τ threshold (for VEPP-4M τp ≈
85 hours).
Quantum fluctuation of radiation together with im-
perfection of the magnetic field destroys the beam po-
larization with the characteristic spin relaxation time τr.
We assume the horizontal magnetic field produced by
the vertically misaligned quadrupole magnets as a main
factor of depolarization. Estimation shows that for the τ
threshold energy region of 1.777 GeV and vertical COD
of ~ 100 μm (rms), the spin decay time for VEPP-4M is
equal to τr = 30 min [4]. A depolarization rate depends
strongly on the spin resonance tune: τp/τr ∝ (νs-k)-4 (at
E = 1.777 GeV we have νs = 4.032). This fact can limit
the energy calibration time.
4
Fig. 4. A set up for the polarization experiments at
VEPP-4M.
Experimental set up for the depolarisation study at
VEPP-4M includes 4 movable scintillation counters in-
serted into the vacuum tube and two stripline electrodes
and electronics (a frequency synthesiser, wide band am-
plifier, etc.) to produce resonant spin depolarization.
The counters detect the Touschek scattering electrons
whose scattering rate depends on the particle spin. Two
bunches with depolarised/polarized particles are used to
measure the ratio 1-N2/N1 depending on the stripline
electrodes signal frequency where N2 and N1 are count
rates for the fist and second bunch.
Time, sec
1000 1500 2000 2500 3000 3500
D
el
ta
, %
-4
-2
0
2
4
6
Chi2 / ndf = 6.841 / 9
0.4299 ±p0 = 2.337
1-N2/N1, %
Chi2 / ndf = 6.841 / 9
0.4299 ±p0 = 2.337
0.4 %±-1.9 %
Chi2/ ndf = 1.2/4
O
N
: 4
2
2.
12
0
- 4
2
2.
50
K
H
z
depolarization
0.02 KHz± = 422.19 df
O
FF
Fig. 5. Test run on the spin energy calibration.
During a J/ψ test run (summer 2001), a method of
the resonance depolarization was used to calibrate beam
energy. Fig.5 shows typical “jump” in 1-N2/N1 due to
the beam depolarization. The error of the beam energy
definition obtained during the test run is ≈ 30 keV (∆
E/E ≈ 2×10-5).
5 FUTURE PLANS
• Commissioning of the new polarimeter system at
the VEPP-4M.
• Measurement of the beam energy by the method of
resonance depolarization with reasonable accuracy
(∆E/E ≈ 1×10-5) in to the energy range between J/ψ
and τ.
• The KEDR run at J/ψ peak and in the vicinity of
the threshold of τ - lepton production.
REFERENCES
1. V.Anashin et al. // Proc.EPAC'98, Stockholm,
1998, v. 1, p. 400.
2. S.A.Nikitin // Proc. of Intern. Workshop e+e- Fac-
tories’99, KEK, Japan, 1999, p. 37.
3. E.Levichev // Proc. HEACC-2000, Tsukuba, Japan,
2000.
4. V.E.Blinov et al. // Proc. PAC2001, Chicago, Illi-
nois, USA, RPPH041.
5. A.A.Zolents, et al. // Phys. Lett. 1981, v. 96B, # 2,
p. 214-216.
6. A.I.Gerasimov, et al. // Nucl. Inst. Meth. 1991,
v. A305, p. 25.
7. D.Shatilov // Part. Acc. 1996, v. 52, p. 65.
8. V.Kiselev, E.Levichev, V.Sajaev, V.Smaluk // Nu-
cl. Inst. Meth. 1998, v. A406, p. 356-370.
9. V.A.Kiselev, S.A.Nikitin, I.Ya.Protopopov // Proc.
HEACC-98, Dubna, 1998, p. 103.
10. V.Kiselev, E.Levichev, A.Naumenkov // Proc.
PAC2001, Chicago, Illinois, USA, TPPH004.
ВОПРОСЫ АТОМНОЙ НАУКИ И ТЕХНИКИ. 2001. №5.
Серия: Ядерно-физические исследования (39), с.3-5.
5
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| id | nasplib_isofts_kiev_ua-123456789-78367 |
| institution | Digital Library of Periodicals of National Academy of Sciences of Ukraine |
| issn | 1562-6016 |
| language | English |
| last_indexed | 2025-12-07T18:27:23Z |
| publishDate | 2001 |
| publisher | Національний науковий центр «Харківський фізико-технічний інститут» НАН України |
| record_format | dspace |
| spelling | Kiselev, V.A. 2015-03-15T19:27:06Z 2015-03-15T19:27:06Z 2001 VEPP-4M collider: Scurrent activity and future plans / V.А. Кiselev // Вопросы атомной науки и техники. — 2001. — № 5. — С. 3-5. — Бібліогр.: 10 назв. — англ. 1562-6016 PACS: 29.20.Dh https://nasplib.isofts.kiev.ua/handle/123456789/78367 Results of the activity at VEPP-4M collider of the Budker Institute of Nuclear Physics over the period of 2000-2001 and the near future plans are presented. en Національний науковий центр «Харківський фізико-технічний інститут» НАН України Вопросы атомной науки и техники VEPP-4M collider: Scurrent activity and future plans Коллайдер VEPP-4M: состояние и планы на будущее Article published earlier |
| spellingShingle | VEPP-4M collider: Scurrent activity and future plans Kiselev, V.A. |
| title | VEPP-4M collider: Scurrent activity and future plans |
| title_alt | Коллайдер VEPP-4M: состояние и планы на будущее |
| title_full | VEPP-4M collider: Scurrent activity and future plans |
| title_fullStr | VEPP-4M collider: Scurrent activity and future plans |
| title_full_unstemmed | VEPP-4M collider: Scurrent activity and future plans |
| title_short | VEPP-4M collider: Scurrent activity and future plans |
| title_sort | vepp-4m collider: scurrent activity and future plans |
| url | https://nasplib.isofts.kiev.ua/handle/123456789/78367 |
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