Acceleration of Polarized Protons and Deuterons
at COSY
A. Lehrach, U. Bechstedt, J. Dietrich, R. Gebel, B. Lorentz, R. Maier,
D. Prasuhn, A. Schnase, H. Schneider, R. Stassen, H. Stockhorst, R. Tolle
Forschungszentrum Julich GmbH, Postfach 1913,52425 Julich, Germany
Abstract. At the cooler synchrotron COSY, protons and deuterons are accelerated up to
3.65GeV/c. Vertically polarized proton beams with more than 70% polarization have been delivered in recent years to internal as well as to external experiment areas at different momenta up
to the maximum momentum of COSY. In a strong-focusing synchrotron like COSY, imperfection
and intrinsic resonances cause polarization losses during acceleration. The existing magnet system
of COSY allows to overcome all imperfection resonances by exciting adiabatic spin flips without
polarization losses. A tune-jump system consisting of two fast quadrupoles has been developed to
handle intrinsic resonances in COSY. This magnet system is being successfully utilized at all intrinsic resonances in the momentum range of COSY. For the acceleration of vertically polarized
deuterons, additional correction provisions are not necessary to preserve polarization during acceleration because depolarizing resonances are not crossed in the momentum range of COSY at
ordinary transversal betatron tunes.
In future upgrades we are planning to install spin rotators to provide longitudinally polarized
beam to internal as well as to external experiments. Such devices can also be used as Siberian snake
to overcome depolarizing resonances. Since strong first order depolarizing resonances are crossed
in COSY, it will be possible to study snake resonances in detail. In particular the behavior of the
spin field and the mechanism of polarization loss during snake resonance crossing are of major
interest for high energy polarized beam acceleration. In this paper the status of the polarized beam
acceleration at COSY is presented and the upgrade plans are discussed.
INTRODUCTION
The COoler SYnchrotron and storage ring COSY at the Forschungszentrum Julich accelerates protons and deuterons to momenta between 600 MeV/c and 3.65 GeV/c [1,2].
At present four internal and four external experiments are in operation. In addition, polarized beams are produced and accelerated at COSY. A polarized ion source originally
developed by a collaboration of the universities of Bonn, Erlangen, and Cologne [3]
provides vector polarized proton beam and all possible combinations of vector and tensor polarized deuteron beams [4]. The polarized H~ or D~ ion beam delivered by this
source is pre-accelerated in the cyclotron JULIC and injected by charge exchange into
the COSY ring. To increase the intensity of polarized beams in COSY, a superconducting
linear accelerator (COSY-SCL) is being designed and developed to replace the existing
cyclotron [5]. The new COSY injector linac is planned to deliver polarized H~ and polarized D~ ions for injection into COSY with an energy of at least 50 MeV. The number
of particles accepted in COSY is to be risen up to its space charge limit, which is a
significant improvement especially for polarized ions. The improved capabilities will
CP675, Spin 2002:15th Int'l. Spin Physics Symposium and Workshop on Polarized Electron
Sources and Polarimeters, edited by Y. L Makdisi, A. U. Luccio, and W. W. MacKay
© 2003 American Institute of Physics 0-7354-0136-5/03/$20.00
153
enable us to fully exploit the unique experimental opportunities of the COSY facility.
The main diagnostic tool to develop polarized beams in COSY is the EDDA detector [6], primarily designed to measure the pp-scattering excitation function during synchrotron acceleration. The polarization is determined by measuring the asymmetry of
scattering between the circulating COSY beam and carbon or C7/2-fiber targets. Additional polarimeters are installed in the injection beamline to COSY, in the COSY ring
and in the extraction beamline of COSY. The intensity of the polarized beam in COSY
can be increased by stacking injection with an electron-cooler and the beam quality can
be further improved with an stochastic cooling systems [7, 8]. The layout of the accelerator complex COSY is shown in Fig. 1.
POLARIZED PROTON AND DEUTERON BEAM
ACCELERATION
For an ideal planar circular accelerator with a vertical guide field, the particle spin vector
precesses around the vertical axis. Thus the vertical beam polarization is preserved. The
spin motion in an external electro-magnetic field is governed by the so called ThomasBMT equation [9], leading to a spin tune of vsp = yG, which describes the number of
spin precessions of the central beam per revolution in the ring. G is the anomalous magnetic moment of the particle (e.g. G = 1.7928 for protons, -0.1423 for deuterons), and
y=E/m the Lorentz factor. During acceleration of a polarized beam, depolarizing resonances are crossed if the precession frequency of the spin yG is equal to the frequency of
the encountered spin-perturbing magnetic fields. In a strong-focusing synchrotron like
COSY two different types of strong depolarizing resonances are excited, namely imperfection resonances caused by magnetic field errors and misalignments of the magnets,
and intrinsic resonances excited by horizontal fields due to the vertical focusing. For
deuterons the spin tune is about 25 times lower than for protons at the same energy.
Depolarizing resonances for deuterons are therefore 25 times further apart compared to
those for protons. Depolarizing resonances for deuterons are also about 13 times weaker
at low energies and 25 times weaker for high energies. Another important difference is,
that deuterons are spin-1 particles. Hence they appear in three spin states (1,0,-1) relative
to an arbitrary quantization axis, compared to two spin states (1,-1) of a spin-* particle
like protons. Three vector components and five components of a second-rank tensor are
required to describe spin-1 polarization. The spin dynamics in circular accelerators of
spin-1 particles have been discussed in [10].
Polarized protons have been accelerated in many accelerators like the ZGS, KEK,
SATURNEII, AGS and RHIC. Polarized deuterons have first been accelerated to energies in the GeV range at KEK and very recently at IUCF [11, 12].
ACCELERATION OF POLARIZED PROTONS AT COSY
In the momentum range of COSY, five imperfection resonances have to be crossed.
The existing correction dipoles of COSY are utilized to overcome all imperfection
154
FIGURE 1. The layout of the existing accelerator complex COSY in Jiilich, which includes polarized
and unpolarized sources, the Cyclotron JULIC and the Cooler Synchrotron COSY. The position of the
three different polarimeters (Low Energy Polarimeter, High Energy Polarimeter, Ring Polarimeter) and
the four internal experiments (ANKE, COSY 11, EDDA, PISA) are indicated. The beam is also delivered
to four external experiment areas (Big Karl, JESSICA, NESSI, TOE).
resonances by exciting adiabatic spin flips without polarization losses. The number
of intrinsic resonances depends on the superperiodicity of the lattice. In principle the
magnetic structure in the arcs of COSY allows to adjust a superperiodicity of P=2 or 6.
A tune-jump system consisting of two fast quadrupoles has especially been developed
to handle intrinsic resonances at COSY.
155
Imperfection Resonances
The imperfection resonances in the momentum range of COSY are listed in Table 1.
They are crossed during acceleration, if the number of spin precessions per revolution of
the particles in the ring is an integer (yG = &, k: integer). The resonance strength depends
on the vertical closed orbit deviation.
TABLE 1. Resonance strength er and the ratio of preserved polarization PyY/^ at imperfection
resonances for a typical vertical orbit deviation
yr™s, without considering synchrotron oscillation.
yG
2
3
4
5
6
Ekin
P y™
er
MeV
MeV/c
mm
KT3
108.4
631.8
1155.1
1678.5
2201.8
463.8
1258.7
1871.2
2442.6
2996.4
2.3
1.8
1.6
1.6
1.4
0.95
0.61
0.96
0.90
0.46
-1.00
-0.88
-1.00
-1.00
-0.58
A spin flip occurs at all resonances without considering synchrotron oscillation. However, the influence of synchrotron oscillation during resonance crossing cannot be neglected (Fig. 2). At the first imperfection resonance, the calculated polarization with a
momentum spread of Ap/p = 1 • 10~3 and a synchrotron frequency of fsyn = 450//Z is
about Pf/P* ~ -0.85. The resonance strength of the first imperfection resonance has to
be enhanced to er = 1.6 • 10~3 for a beam with momentum spread of Ap/p = 1 • 10~3 to
excite spin flips with polarization losses of less than 1%. At the other imperfection resonances the effect of the synchrotron oscillation is smaller, due to the lower momentum
spread at higher energies. Vertical correction dipoles or a partial snake can be used to
preserve polarization at imperfection resonances by exciting adiabatic spin flips. Simulations indicate that an excitation of the vertical orbit with existing correction dipoles
by 1 mrad is sufficient to adiabatically flip the spin at all imperfection resonances. In
addition, the solenoids of the electron-cooler system inside COSY are available for use
as a partial snake. They are able to rotate the spin around the longitudinal axis by about
8° at the maximum momentum of COSY. A rotation angle of less than 1 ° of the spin
around the longitudinal axis already leads to a spin flip without polarization losses at all
five imperfection resonances [13].
Intrinsic Resonances
The number of intrinsic resonances depends on the superperiodicity P of the lattice, which is given by the number of identical periods in the accelerator. COSY is a
synchrotron with a racetrack design consisting of two 180° arc sections connected by
Ratio of beam polarization before (i) and after (f) crossing a depolarizing resonance.
156
0.0005
0.001
resonance strength
0.0015
0.001
resonance strength
0.0015
FIGURE 2. Effect of synchrotron oscillation during crossing imperfection resonances in COSY. Ratio
of preserved beam polarization Pf/Pt after crossing the first imperfection resonance for two different
momentum spreads of Ap/p = 1 • 10~3 and Ap/p = 2 • 10~3 with a synchrotron frequency offsyn = 450//Z
(left), and ratio of preserved beam polarization (cutaway in the spin flipping region) after crossing different
imperfection resonances for a momentum spread of Ap/p = 1 • 10 ~3 taking the synchrotron frequencies at
the various resonance energies into account (right). The corresponding synchrotron tunes are in the range
between vsyn = 6 -10~4 and 8 -10~5.
straight sections. The straight sections can be tuned as telescopes with 1:1 imaging,
giving a 2n betatron phase advance. In this case the straight sections are optically transparent and only the arcs contribute to the strength of intrinsic resonances. One then
obtains for the resonance condition yG = k-P± (Qy — 2), where k is an integer and Qy
is the vertical betatron tune. The magnetic structure in the arcs allows adjustment of the
superperiodicity to P= 2 or 6. The corresponding intrinsic resonances in the momentum
range of COSY are listed in Table 2.
TABLE 2. Resonance strength er of intrinsic resonances for a normalized emittance of
iTrmmmrad and a vertical betatron tune of
Qy= 3.61 for different superperiodicities P.
p
jG
Ekin
MeV
P
MeV/c
io-3
2
6-2,
0 + 2?
8-2,
2 + 2,
312.4
826.9
0.26
0.21
2
2,6
2
10-2,
£r
950.7
1639.3
1358.8
2096.5
1.57
1997.1
2781.2
0.53
2405.2
3208.9
0.25
157
Tune-Jump System
A tune-jump system was developed to preserve polarization at intrinsic resonances by
increasing the crossing speed significantly. This is accomplished by abruptly changing
the vertical betatron tune during resonance crossing in the range of microseconds. The
magnet system consists of two pulsed air core quadrupoles and is designed to achieve
polarization losses of less than 5% at the strongest intrinsic resonance, and of less than
1 % at all other intrinsic resonances in COSY [ 14]. To meet this goal, a vertical tune jump
of more than AQy= 0.06 in lOjUs is needed. The existing stainless steel vacuum chamber
at the location of the tune-jumping quadrupoles had to be replaced by a ceramic vacuum
chamber. A layer of lOjUw titanium was sputtered on the inside surface of the ceramic
chamber. To avoid double crossing of resonances, the fall time of the tune jump can
be adjusted for different jump widths and acceleration rates. The maximum fall time is
40 ms. Fig. 3 shows the polarization of the COSY beam measured during acceleration
around the strongest intrinsic resonance yG = 8 — Qy. This resonance excites a natural
, , , , . , , , . ,
1 H—
• —t-—--fr——*-
s^" 0.75
CL
0.5 I
:
EDDA
for COSY MD 7/98
—-*~ .
-
——£_ —
0.25 r
-
0
-0.25 '--
-
-0.5 '-
-
-0.75
-1
—— :
'- o no tune jump
\ • tune jump
1900
1950
2000
2050
2100
2150
2200
FIGURE 3. Ratio of preserved beam polarization Pf/Pt after crossing the strongest intrinsic resonance
at 2090 MeV/c with and without tune jump measured during acceleration with the EDDA detector.
spin flip. The polarization loss depends on the vertical emittance of the beam. With a tune
jump, the polarization was almost preserved. Particle losses during tune jumping due to
emittance increase can be kept low by adjusting to beam orbit carefully at the position of
the tune-jump quadrupoles. The tune jump method can be extended to all other intrinsic
resonances because they are at least a factor three weaker than the strongest resonance.
Optimized Optics
To optimize the optics for a polarized beam, phase advances and betatron amplitudes
have been determined along the ring. The measurements were done by exciting continuous betatron oscillations and observing the beam response with a network analyzer between a pair of beam position monitors. With the phase advance of the straight sections
matched to 2n, the superperiodicity of the COSY lattice is determined by the arcs. Both
arcs are composed of three unit cells that are each mirror-symmetrical. A half-cell has a
158
QD-bend-QF-bend structure (Fig. 1). The superperiodicity equals six if all unit cells operate with the same quadrupole settings. In this case only one intrinsic resonance occurs
(jG = 8 — Qy) but the transition crossing takes place at about 1600 MeV/c. To accelerate
the beam to maximum momentum, the strength of the horizontally focusing quadrupoles
of the inner unit cells in the arcs is enhanced by about 40% to shift the transition energy
above the maximum momentum. At the same time, the strength of the horizontally focusing quadrupoles in the outer unit cells is decreased by 20% to keep the betatron tunes
constant. The superperiodicity of the beam optics is then P = 2. Consequently, four additional intrinsic resonances are introduced (Table 2), which can be suppressed if the
harmonics of the corresponding spin-perturbing fields are corrected. Theoretical studies of the COSY lattice revealed the possibility of suppressing the strength of intrinsic
resonances using the vertically focusing quadrupoles of the inner unit cells in the arcs,
leading to a modified P=2-optics [15]. This new method avoids the drawbacks associ-
0.5—
0—
-0.5—.
i =3
0
20
40
60
80
1000
100
;0 + v
4
8-v
5:
1500 2000
2500
3000
momentum [MeV/c]
enhancement of focusing strength (%)
FIGURE 4. The graph on the left side shows the resonance strength of depolarizing resonances in
case of a modified P=2-optics versus the enhancement of focusing strength of the vertically focusing
quadrupoles in the inner unit cells. The betatron tune is fixed by reducing the strength of the vertically
focusing quadrupoles in the outer unit cells. In this calculation the focusing strength of the horizontally
focusing quadrupoles in the inner unit cells is enhanced by about 40%. The graph on the right side shows
the polarization during acceleration measured with the EDDA detector in the momentum range between
1.1 GeV/c and 2.7 GeV/c. The spin was flipped at the imperfection resonances jG = 3, 4 and 5. At the
second intrinsic resonance jG = 0 + Qy the polarization was almost preserved by adjusting a modified
JP=2-optics. The third intrinsic resonance jG = 8 — Qy excites a natural spin flip with some polarization
losses.
ated with the non-adiabatic nature of tune jumps, which otherwise would be necessary
to preserve polarization at all intrinsic resonances of COSY. The method is called suppression of intrinsic spin harmonics, and can also be used at other accelerators like the
Brookhaven AGS [16].
During a running period in the year 1998, the new method to overcome intrinsic
resonances has been confirmed by measurements with polarized beam (Fig. 4). The
polarization was preserved at the two intrinsic resonances, jG = 6 — Qy and jG =
0 + Qy, by modifying the optics during acceleration. To avoid polarization losses at
the first intrinsic resonance, jG = 6 — Qy at 827 MeV/c, the acceleration of the beam
started with P=6 optics. The ratio of preserved polarization was P/Pj = 0.97 ± 0.05. At
159
about 900 MeV/c, the COSY beam optics was then switched to superperiodicity P=2
to shift the transition energy. As expected, crossing jG = Q + Qy at 1640MeV/c led
to polarization losses (Pf/Pi = 0.13±0.05) in this mode. After suppressing the strength
of intrinsic resonances using the vertically focusing quadrupoles in the inner unit cells,
the ratio of the preserved polarization at this intrinsic resonance could be significantly
increased to Pf/Pt = 0.88± 0.05 [15].
However, due to symmetry-breaking installations in the COSY ring (e.g. ANKE
spectrometer and electron-cooler magnets) the superperiod of the accelerator lattice
in COSY is reduced to P = 1, leading to five additional intrinsic resonances in the
energy range of COSY: (yG = -1 + Qy, 1 - Qy, 1 + Qy, 9 - Qy, 3 + Qy\ To preserve
polarization up to maximum momentum of COSY tune jumps are utilized at all ten
intrinsic resonances.
Beam Set-up for Polarized Beams
The beam is usually set-up with unpolarized beam, due to better accuracy of COSY
diagnostics with about a factor of ten higher beam intensity [17]. Polarization optimization becomes much more efficient and particle losses due to emittance growth can be
kept low if the beam position is aligned carefully during the acceleration ramp, especially at the location of the tune-jump quadrupoles. Dynamic tune measurements are
carried out to adjust the transversal betatron tunes during acceleration [18]. The vertical betatron tune is fixed close to 3.62 during acceleration in order to optimize the
distance between intrinsic resonances for consecutive tune jumps. The horizontal tune
is set at around 3.60 during acceleration. After closed orbit and betatron tune correction,
the beam manipulations for polarized beam are applied. The magnet currents and trigger times for the tune-jump quadrupoles and vertical correction dipoles are set to values
used at previous polarized beam times, as can be seen in Fig. 5. The tuning of magnet
FIGURE 5. Trace 1 shows the beam current, trace 2 the current of vertical correction dipoles, and trace
3 the current of the tune-jump system versus time, applied at various depolarizing resonances.
160
currents and trigger times is done after switching to polarized beam by utilizing polarization measurements. For any applied correction to preserve polarization, the number of
particle are observed. Particle losses due to correction dipole and tune-jump quadrupole
fields during depolarizing resonance crossing are kept below 10% in total. For extracted
polarized beams the momentum has to be chosen carefully to avoid polarization losses.
The beam is extracted via a third-order betatron resonance. Corresponding intrinsic resonances lead to significant polarization losses. Momenta near imperfection resonances
can also not be provided. Since the beam is stored for relatively long times at extraction energy and because the momentum spread increase during the extraction process,
higher order depolarizing resonances can also lead to polarization losses. After excluding these momenta, one still has to carefully adjust the tunes to prepare the stored beam
for extraction.
Polarized Beam Acceleration at COSY
During a running period in the year 2000, the polarized beam was accelerated to
3300MeV/c [17]. The spin was flipped at the imperfection resonances jG = 2, 3, 4,
5 and 6 using correction dipoles. To avoid polarization losses at all intrinsic resonance
tune jumps were applied. The measured polarization after the optimization for polarized
beam is shown in Fig. 6.
-i——|——i——i——i——i—
—I——I—1—1——1—
11""'
"TV"-
OJ --
••-9-Q--h"
-0.5
! yG=
j
i •
1500
4
i
i
i a - q 1 +Q
10-Q
lU..'
•i... :
i
1
2000
5
•
i
•
i
1
2500
p [MeV/c]
i
•
i
•
6
1
i
i
•
3000
FIGURE 6. Vertical beam polarization during acceleration measured with the EDDA detector in the
momentum range between 1 lOOMeV/c and 3300MeV/c.
The polarization losses up to final momentum were rather small, only in the order
of a few percent. Between 2-109 to 5-109 polarized protons have been stored at final
momentum. Below the strongest intrinsic resonances the beam has been extracted with
a polarization of about 80%. Above this resonance we recently reached about 60%
polarization of the extracted beam.
161
ACCELERATION OF POLARIZED DEUTERONS AT COSY
In January 2002, 2-1011 unpolarized deuterons have been accelerated to maximum momentum of COSY. The first injection and acceleration of polarized deuterons is scheduled for February 2003. The polarized source is capable to produce any kind of possible
vector and tensor polarization [4]. In Fig. 7 the depolarizing resonance momentum is
plotted versus fractional betatron tune.
\\
£ 3500 ? 3000 ? 2500 | 2000 |j 1500 | 1000 1 500 -
\
\\
\
\
\
n 0.5
0.6
0.7
0.8
0.9
1
Fractional Tune
FIGURE 7. Depolarizing first order resonances for deuterons in the momentum range of COSY. The
resonance momentum is plotted versus fractional tune. The rectangular box indicates the ordinary operation range of COS Y.
No first order depolarizing resonance is crossed in the momentum range of COSY
at an ordinary transversal betatron tune. However, one intrinsic resonance is crossed
(jG = — 4 + Qy) if the vertical betraron tune in COSY is pushed up to unusually high
values in the range between 3.7 and 3.85. This could be an interesting option to study
depolarizing resonance crossing of polarized deuterons.
SIBERIAN SNAKE
Siberian snakes are used to eliminate depolarizing resonances in circular accelerators.
The spin is rotated by 180° in the snake, forcing the spin tune to be a half integer,
independent of the beam energy. This concept has been proposed by Ya.S. Derbenev
and A.M. Kondratenko [19]. If only one Siberian snake is used, the invariant spin axis2
is in the horizontal plane. This is an interesting feature to deliver longitudinally polarized
beam to internal and external experiments at COSY.
To preserve the polarization using a Siberian snake with a solenoid field, the direction
of the spin vector has to be longitudinal at the symmetry point of the snake, which
is point in the ring opposite to the position of the snake. This can be achieved if the
spin is prepared in the injection beamline by one or two additional solenoid magnets.
Another possibility is to inject the beam vertically polarized with the snake turned off,
and switch on the snake after injection. During ramping the snake, the spin direction
changes from vertical to longitudinal at the symmetry point, and the spin tune of the
2
Invariant of spin motion for the central beam, called invariant spin field for a particle in the six
dimensional phase space [20, 21].
162
central beam from vsp = jG (without snake) to the nearest half -integer tune (180° spin
rotation in the snake). To avoid crossing depolarizing resonances during this process,
the snake can be turned on at half -integer spin tune. Then the spin tune for the central
beam stays half integer for any snake strength. This condition is satisfied whenever the
kinetic energy Ekin is given by: Ekin = 31QMeV + k • 523MeV, where k is an integer.
One can also use tune jumps to avoid crossing depolarizing resonances during turning
on the snake, if the snake is ramped fast enough, because the maximum fall time of
the tune-jump system in COSY is limited to 40 ms. To realize a Siberian snake in the
momentum range of COSY, only solenoid magnets are suitable. A solenoid field not
only rotates to spin, but also the transversal phase space. For a spin rotation of 180° the
transversal phase space is rotated by 32.2°. This can be compensated with two skewed
quadrupole doublets. Different snake schemes for COSY have been investigated [13].
One possible magnet arrangement consists of four skewed quadrupoles, with maximum
field gradients of 34.2 T/m and -32.2 T/m rotated by 21.5 and 15.2° in each doublet, and
one solenoid located in between (Fig. 8). The required integral field of the solenoid is
SQ SQ
Lange(cm)
45
45
25
Feld(T/m)
Feld (T)
Winkel(°)
SOL
SQ SQ
260
35
45
35
34.2-32.2
45
25
-32.2 34.2
4.9
-21.5-15.2
15.2 21.5
FIGURE 8. Magnet arrangement for a Siberian snake consisting of four skewed quadrupoles (SQ) and
one solenoid magnet (SOL).
12.4 Tm at 3.3 GeV/c. Superconducting magnet technology has to be used to achieve an
acceptable length of the snake. The total length of such a magnet system is 5.6 m, and it
would fit into one of the straight sections of COSY. The required gradient of the skewed
quadrupoles to compensate coupling is more then a factor of three higher compared to
the maximum gradient of the focusing quadrupoles in COSY. Calculation of the beam
optics indicated that the betatron amplitude in the snake is rather small, leading to large
betatron amplitudes at other places in the ring. Another option would be to run COSY
fully coupled without skew quadrupoles. Further investigations of the beam optics with
Siberian snake magnets in the COSY lattice are needed.
If such a magnet system is utilized as Siberian snake, the magnets have to be ramped
during acceleration in a few seconds to final field, which is a real challenge for superconducting magnets. Another option is to use this system as a spin rotator. The spin of the
vertically polarized beam is rotated after acceleration. Suitable ramp times in the range
of a few minutes can be applied. This method provides longitudinally polarized beam
at all stored energies at the symmetry point of the snake in the ring. At five different
energies in intervals of 523 MeV, longitudinally polarized beam can also be provided to
external experiments. These energies depend on the bending angles of the beam in the
different extraction beamlines.
For a polarized deuteron beam the rotation angel of the spin in a longitudinal field is
163
about a factor three lower the one for protons. Hence longitudinally polarized deuteron
beams with the proposed magnet system can be delivered up to about 1 GeV/c.
CONCLUSION
The solenoids of the electron-cooler acting as a partial snake and vertical correction
dipoles were successfully used in COSY to preserve the polarization by exciting adiabatic spin flips. Both methods are available for all five imperfection resonances in the
momentum range of COSY. Since solenoids introduce transversal coupling, which excites depolarizing coupling resonances, the vertical correction dipoles are preferred to
overcome imperfection resonances in COSY. With the standard optics of COSY, five intrinsic resonances are excited. Measurements confirm, that three of these resonances can
be suppressed by changing the optics during acceleration. Due to symmetry-breaking
installations, the superperiodicity of the COSY lattice is reduced to one, leading to ten
intrinsic resonances. It has been shown that the tune-jump system can handle all ten intrinsic resonances in the momentum range of COSY. Polarization measurements during
acceleration confirm that the developed concept allows the acceleration of a vertically
polarized proton beam with polarization losses of only a few percent up to the maximum
momentum of COSY. The polarization losses at individual depolarizing resonances are
within the accuracy of the polarization measurement. Highly polarized proton beams are
routinely delivered to internal and external experiments at different momenta. The installation of a Siberian snake in COSY could also provide a longitudinally polarized beam
to internal as well as to external experiments at certain momenta. The first acceleration
of polarized deuterons is scheduled for next year. Since depolarizing resonances are not
crossed with a deuteron beam at ordinary transversal betatron tunes in the momentum
range of COSY, no additional corrections have to be applied. To increase the intensity of
the polarized beams in COSY by typically one order of magnitude, a superconducting
injector linac is presently being developed and built.
ACKNOWLEDGMENTS
We are indebted to all members of the COSY team and the collaboration of the polarized
source for their support. We are especially grateful to the EDDA collaboration for their
sophisticated measurement of the beam polarization during acceleration.
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