Erhic – electron-proton collider with polarized beams
The layout and main parameters of the e-ring for eRHIC project are presented. The optics properties to fulfill the so-called spin-transparency condition to obtain sufficient polarization degree at IP are given. The possibility of using super-bends for the polarization time in a wide energy range b...
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Національний науковий центр «Харківський фізико-технічний інститут» НАН України
2004
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| Цитувати: | Erhic – electron-proton collider with polarized beams / D.E. Berkaev, I.A. Koop, A.V. Otboev, Yu.M. Shatunov, V. Ptitsyn // Вопросы атомной науки и техники. — 2004. — № 1. — С. 54-56. — Бібліогр.: 2 назв. — англ. |
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nasplib_isofts_kiev_ua-123456789-785682025-02-23T17:14:26Z Erhic – electron-proton collider with polarized beams Erhic – електронно-протонний коллайдер з поляризованими пучками Erhic – электронно-протонный коллайдер с поляризованными пучками Berkaev, D.E. Koop, I.A. Otboev, A.V. hatunov, Yu.M Ptitsyn, V. Новые и нестандартные ускорительные технологии The layout and main parameters of the e-ring for eRHIC project are presented. The optics properties to fulfill the so-called spin-transparency condition to obtain sufficient polarization degree at IP are given. The possibility of using super-bends for the polarization time in a wide energy range be decreased is also discussed. Представлені основні параметри і розташування e-кільця в проекті eRHIC. Дані оптичні властивості для виконання так званої умови спінової прозорості для одержання достатнього ступеня поляризації в IP. Також обговорюється можливість використання надвигинів для зменшення часу поляризації в широкому енергетичному діапазоні. Представлены основные параметры и расположение e-кольца в проекте eRHIC. Даны оптические свойства для выполнения так называемого условия спиновой прозрачности для получения достаточной степени поляризации в IP. Также обсуждается возможность использования сверхизгибов для уменьшения времени поляризации в широком энергетическом диапазоне. 2004 Article Erhic – electron-proton collider with polarized beams / D.E. Berkaev, I.A. Koop, A.V. Otboev, Yu.M. Shatunov, V. Ptitsyn // Вопросы атомной науки и техники. — 2004. — № 1. — С. 54-56. — Бібліогр.: 2 назв. — англ. 1562-6016 PACS: 29.27.Bd https://nasplib.isofts.kiev.ua/handle/123456789/78568 en Вопросы атомной науки и техники application/pdf Національний науковий центр «Харківський фізико-технічний інститут» НАН України |
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Digital Library of Periodicals of National Academy of Sciences of Ukraine |
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English |
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Новые и нестандартные ускорительные технологии Новые и нестандартные ускорительные технологии |
| spellingShingle |
Новые и нестандартные ускорительные технологии Новые и нестандартные ускорительные технологии Berkaev, D.E. Koop, I.A. Otboev, A.V. hatunov, Yu.M Ptitsyn, V. Erhic – electron-proton collider with polarized beams Вопросы атомной науки и техники |
| description |
The layout and main parameters of the e-ring for eRHIC project are presented. The optics properties to fulfill the
so-called spin-transparency condition to obtain sufficient polarization degree at IP are given. The possibility of using
super-bends for the polarization time in a wide energy range be decreased is also discussed. |
| format |
Article |
| author |
Berkaev, D.E. Koop, I.A. Otboev, A.V. hatunov, Yu.M Ptitsyn, V. |
| author_facet |
Berkaev, D.E. Koop, I.A. Otboev, A.V. hatunov, Yu.M Ptitsyn, V. |
| author_sort |
Berkaev, D.E. |
| title |
Erhic – electron-proton collider with polarized beams |
| title_short |
Erhic – electron-proton collider with polarized beams |
| title_full |
Erhic – electron-proton collider with polarized beams |
| title_fullStr |
Erhic – electron-proton collider with polarized beams |
| title_full_unstemmed |
Erhic – electron-proton collider with polarized beams |
| title_sort |
erhic – electron-proton collider with polarized beams |
| publisher |
Національний науковий центр «Харківський фізико-технічний інститут» НАН України |
| publishDate |
2004 |
| topic_facet |
Новые и нестандартные ускорительные технологии |
| url |
https://nasplib.isofts.kiev.ua/handle/123456789/78568 |
| citation_txt |
Erhic – electron-proton collider with polarized beams / D.E. Berkaev, I.A. Koop, A.V. Otboev, Yu.M. Shatunov, V. Ptitsyn // Вопросы атомной науки и техники. — 2004. — № 1. — С. 54-56. — Бібліогр.: 2 назв. — англ. |
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Вопросы атомной науки и техники |
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ERHIC – ELECTRON-PROTON COLLIDER WITH POLARIZED BEAMS
D.E. Berkaev, I.A. Koop, A.V. Otboev, Yu.M. Shatunov¤,
V. Ptitsyn†
¤Budker Institute of Nuclear Physics, Novosibirsk, 630090, Russia;
†BNL, Upton, NY 19793, USA
The layout and main parameters of the e-ring for eRHIC project are presented. The optics properties to fulfill the
so-called spin-transparency condition to obtain sufficient polarization degree at IP are given. The possibility of using
super-bends for the polarization time in a wide energy range be decreased is also discussed.
PACS: 29.27.Bd
INTRODUCTION
In the Brookhaven National Laboratory (BNL) ex-
periments at the new collider RHIC have successfully
started with both ion-ion and polarized proton-proton
beams. To enhance the experimental capability of the
RHIC complex, different schemes of e - p collisions ar-
rangement are under discussion for the last few years.
High-luminosity polarized e - p scattering will open a
unique opportunity for physics beyond limits of today
experiments in polarized DIS.
This paper presents a study of the ring-ring option of
eRHIC. A project of the electron ring with the energy
5…10 GeV and luminosity up to 5…10 × 32 cm-2s-1 was
developed in collaboration with BINP (Novosibirsk)
and BNL. We suggest (see Fig.1) to construct mainly
outside the RHIC tunnel the electron storage ring which
will have the circumference 4/15 of the RHIC orbit and
an intersection with ions in the one of the existing RHIC
experimental area (on 12 o’clock).
Fig.1. The general layout of the e-ring installed into the
RHIC complex
The radiative polarization of the electron beam and a
combination of solenoids and bending magnets will pro-
vide a high degree of the longitudinal polarization of the
electron beam in the IP. To minimize the reconstruction
of the RHIC rings while adding the new electron ring
two possible schemes of the interaction region arrange-
ment are proposed: so-called horizontal "dog-leg"
scheme and vertical one. Spin-transparency conditions
which are needed for obtaining sufficient polarization
degree in the electron beam have been found for both
options of the IP layout.
THE LUMINOSITY CONSIDERATION
Achieving the high luminosity value of 5×1032 cm-
2s.1 is a main challenge and needs a special consideration
that have to take into account a world wide experience
of many machines, electron and proton ones, as well as
results of beam-beam interaction simulations. In partic-
ular, the simulations predict a number of advantages for
the round beam geometry by the collision due to a con-
servation of the angular momentum [1]. To keep the
round beams we should meet 3 conditions: equal emit-
tances of the both beams (εe = εi = ε); equal tunes of be-
tatron oscillations; equal β-functions in the IP (β*
e = β*
i
= β*). In favour of the round beams the HERA and SPS
experiences witness a bad life time and high background
for unmatched beam sizes even with moderate beam
currents.
The round beam luminosity is given by the equation:
∗⋅=
β
εξξγπγ
ie
ie
ie
coll rr
FL 4
,
where Fcoll is the collision repetition frequency, γ and r
are the relativistic factors and classical radii for elec-
trons and ions respectively. Space charge parameters ξe
and ξi for electrons and ions are determined by the ex-
pressions:
επ γ
ξ
ieie
ieei
ie V
rN
,,
,,
, 4
= ,
where Ne and Ni are electron and ion bunch populations;
Vi is the ion velocity (Ve= c =1). The world wide experi-
ence shows that achievable values of the space charge
parameters due to the beam-beam effects do not exceed
0.5 for electrons and 0.05 for protons. Collision fre-
quency Fcoll is determined in our case practically by the
ion bunch spacing in the RHIC. Single bunch popula-
tions Ne and Ni are limited except the beam-beam inter-
action by different kinds of instabilities. For electrons
the most severe intensity threshold is set by the head-tail
transverse mode-coupling instability that limits the one-
bunch population. The modern accelerator experience
(for instance, in the both B-factories or in the LEP col-
lider), tells us, that Ne =5·1010 is, more or less, a safe
number. The proton bunch population is admitted to
Np=1·1011, which is based on BNL and FNAL experi-
mental results. To achieve the specified luminosity of
L=5·1032 cm-2s-1 the beam size at the IP should be σ
*=80 µm together with the other fixed above parameters
and with the assumption β* = 10 cm.
___________________________________________________________
PROBLEMS OF ATOMIC SIENCE AND TECHNOLOGY. 2004. № 1.
Series: Nuclear Physics Investigations (42), p.54-56.54
RADIATIVE POLARIZATION
AND E-RING DESIGN
The radiative polarization has been observed at the
many electron storage rings. According to this experi-
ence the energy range 5…10 GeV is quite comfortable
for obtaining the polarization degree of about 80 per-
cents. If the equilibrium polarization direction (vector n)
is vertical in the arcs we can expect a relatively low po-
larization losses caused by spin manipulations around
the IP.
A radiative polarization time strongly depends on
the bending field (τp ~ B -3). On the other hand the high
magnetic field increases the energy losses for the syn-
chrotron radiation (∆Eturn ~ B 2). A possible compromise
here may be a special design of the bending magnets.
We propose to use so-called super-bend magnets with a
relatively high field in a short central part of each mag-
net. It allows us strongly decrease the polarization time
at low energies and suppress spin resonances by the rel-
atively minimal energy losses.
The possible optimum is to use high field in the su-
per-bends at low energy (so to keep the polarization
time at the level of 15 minutes at 5 GeV) and the uni-
form field at 10 GeV. But the final strategy of using the
super-bends can be found during practical work with the
beam polarization.
We considered the e-ring which consists of two arcs
with regular FODO structure and two straight sections:
one for the beam collisions and other for technical us-
age. To deliver spin longitudinal into the IP we need to
install two spin rotators on both sides of the interaction
area. At first, the spin is rotated by a solenoidal field rel-
atively to the horizontal plane and then by low-field
dipoles (including final focus of quadrupole magnets)
exactly to the longitudinal direction at the medium ener-
gy 7.5 GeV. On the opposite side of the interaction
straight, the spin is restored to vertical direction by the
mirror symmetrical spin rotator. As a result, due to this
anti-symmetry and the spin transparency of the
solenoidal rotators, the spin phase advance along the
whole interaction region is zero, spin is always restored
to the vertical direction in the next arc at an arbitrary en-
ergy and the polarization behavior is mainly the same as
without the spin rotators. The main parameters of the e-
ring are listed in Table.
Parameter e-ring p-ring
Circumference, m 1022 3833
Energy, GeV 5…10 250
Number of bunches 96 360
Bunch population 5⋅1010 1⋅1011
RMS emittance, mm·µrad 45…63 9…13
Beta function at IP, cm 10 50
Beam-beam parameter 0.05 0.005
Luminosity, cm-2 s-1 5·1032
THE DETECTOR AREA LAYOUT
Besides the spin manipulations there are other issues
for the IR design: beam separation to avoid the parasitic
beam-beam interactions; focusing to the low beta; de-
tector background; protection from the synchrotron radi-
ation, etc. In this consideration we did not touch the ion
ring final focus system except the assumption β*=10 cm.
Both suggested schemes have transverse fields around
the IP that additionally to the spin rotation will separate
the beams due to their big energy difference. The same
fields could be used for a detector momentum analysis.
In the case of a longitudinal field in the detector com-
pensating solenoids are needed to keep the zero spin ro-
tation along the IR. The first option supposes the lift up
(about 1 m) one of the RHIC ion ring for the zero angle
intersection with the flat electron ring. Fig.2 (left) shows
schematically the interaction region (IR) and the spin
vector behavior. Since the spin is lying in the horizontal
plane between the two solenoidal spin rotators, some
depolarization comes from the bending magnets in this
area. A choice of moderate field magnitudes (few
KGauss) helps to avoid considerable polarization losses.
Calculations with the ASPIRRIN code [2] give the equi-
librium polarization degree about 90% and the polariza-
tion time about 500 s at 10 GeV.
Fig.2. The layout of the e-ring interaction region
One can see that this scheme looks well for the electron
polarization, but it might require serious rebuilding in
the RHIC machine. That’s why we considered other
scheme with flat ion ring and a vertical orbit bump
(about 0.5 m) in the electron ring, see the Fig.2 (right).
In this variant the proton ring of the RHIC is almost un-
changed except a new final focusing to get the low beta.
As the polarization calculations by ASPIRRIN
show, despite of the spin transparency, the vertical bend
initiates some spin resonances even in the ring without
any imperfections. The situation is drastically changed
due to random vertical fluctuations of the arc
quadrupoles positioning. The polarization does not ex-
ceed 50 percents with the RMS shift of 0.5 mm.
CONCLUSION
The present study show that the ring-ring option of
the electron-proton collider is able to provide the lumi-
nosity up to 5⋅1032 cm-2s-1 in the SCM energy range
15…100 GeV. The project of the electron ring with the
super bend magnets and the solenoidal spin rotators per-
forms to obtain not less than 70 percents of the longitu-
___________________________________________________________
PROBLEMS OF ATOMIC SIENCE AND TECHNOLOGY. 2004. № 1.
Series: Nuclear Physics Investigations (42), p.54-56.55
dinal polarization in the IP. Two possible layouts of the
interaction region are considered. The scheme with the
flat electron ring (horizontal "dog leg") looks preferable
for the electron polarization. A serious consideration of
a new RHIC final focus design for the low beta is need-
ed together with a number of other topics which have
not be mentioned in this paper.
REFERENCES
1. A.N.Filippov et al. // Proc. 15th Int. Conf. High
Energy Accelerators, Hamburg (Germany), 1992,
p.1145.
2. E.A.Perevedentsev, V.I.Ptitsyn and Yu.M.Shatunov
// Proc. of 5th Int. Workshop on High Energy Spin
Physics, Protvino. 1994, p.281.
ERHIC – ЭЛЕКТРОННО-ПРОТОННЫЙ КОЛЛАЙДЕР С ПОЛЯРИЗОВАННЫМИ ПУЧКАМИ
Д.Е. Беркаев, И.А. Куп, А.В. Отбоев, Ю.М. Шатунов, В. Птицын
Представлены основные параметры и расположение e-кольца в проекте eRHIC. Даны оптические свой-
ства для выполнения так называемого условия спиновой прозрачности для получения достаточной степени
поляризации в IP. Также обсуждается возможность использования сверхизгибов для уменьшения времени
поляризации в широком энергетическом диапазоне.
ERHIC – ЕЛЕКТРОННО-ПРОТОННИЙ КОЛЛАЙДЕР З ПОЛЯРИЗОВАНИМИ ПУЧКАМИ
Д.Є. Беркаєв, І.А. Куп, А.В. Отбоїв, Ю.М. Шатунов, В. Птицин
Представлені основні параметри і розташування e-кільця в проекті eRHIC. Дані оптичні властивості для
виконання так званої умови спінової прозорості для одержання достатнього ступеня поляризації в IP. Також
обговорюється можливість використання надвигинів для зменшення часу поляризації в широкому
енергетичному діапазоні.
56
INTRODUCTION
THE LUMINOSITY CONSIDERATION
RADIATIVE POLARIZATION
AND E-RING DESIGN
THE DETECTOR AREA LAYOUT
CONCLUSION
REFERENCES
Д.Е. Беркаев, И.А. Куп, А.В. Отбоев, Ю.М. Шатунов, В. Птицын
Д.Є. Беркаєв, І.А. Куп, А.В. Отбоїв, Ю.М. Шатунов, В. Птицин
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