The Polarized Internal Gas Target
of ANKE at COSY
1
F. Rathmann , R. Brüggemann† , R. Engels , S. Geisler , A. Gussen , P.
Jansen , H. Kleines‡ , F. Klehr , P. Kravtsov§ , S. Lemaître† , B. Lorentz ,
S. Lorenz¶ , M. Mikirtytchiants § , M. Nekipelov § , V. Nelyubin§ , H.
Paetz gen. Schieck†, U. Rindfleisch , J. Sarkadi , H. Seyfarth , E.
Steffens¶, H. Ströher , V. Trofimov§ , A. Vassiliev§ and K. Zwoll‡
Institut für Kernphysik, Forschungszentrum Jülich, Germany
†
Institut für Kernphysik, Universität zu Köln, Germany
Zentralabteilung Technologie, Forschungszentrum Jülich, Germany
‡
Zentrallabor für Elektronik, Forschungszentrum Jülich, Germany
§
Petersburg Nuclear Physics Institute, Gatchina, Russia
¶
Physikalisches Institut II, Universität Erlangen-Nürnberg, Germany
Abstract. For future few–nucleon interaction studies with polarized beams and targets at COSY–
Jülich, a polarized internal–storage cell gas target is currently being developed and will be implemented in the near future at ANKE. The polarized atomic beam source, which will feed the target,
provides beam intensities of 74 10 16 atoms/s in two hyperfine states of hydrogen. The implementation of the target at the internal spectrometer ANKE constitutes a major technological enterprise.
The differential pumping system at ANKE has already been installed, as well as a new large target
chamber to accomodate storage cells in the future, a new set of small–aperture horizontal and vertical beam position monitors, and a system of target–near detectors. In order to determine the nuclear
polarization of the target, a Lamb–Shift polarimeter is currently set up. Tests with prototype storage
cells aiming at the identification of cell dimensions suitable for the ANKE target are underway.
1. INTRODUCTION
At present two new polarized internal gas targets (PIT’s) are being developed. One,
intended for the physics programme at the BLAST facility at Bates [1], will utilize a
refurbished source, formerly used at the PIT of the AmPS of NIKHEF [2]. With the
closing of the Cooler operation at IUCF in 2002, COSY at Jülich remains the only ring
capable to store polarized protons and deuterons on a worldwide scale. The polarized
atomic beam source (ABS) described in this paper is intended to feed a PIT at COSY.
One of the first experiments that will be carried out with the target deals with the proton–
induced deuteron breakup2 at the ANKE spectrometer. A presently developed Lamb–
shift polarimeter [5] will be employed to measure the polarization of atoms extracted
1
This work has been supported by the BMBF (contracts RUS 649-96, RUS 99/686, 06 ER 831, 06 ER
930, 06 OK 862, and WTZ 99/686), by DFG (contract 436 RUS 113/430), by the Forschungszentrum
Jülich (FFE contracts 41149451, 41445283 (COSY–59)), and by the Russian Ministry of Sciences.
2 Described in a separate contribution to these proceedings [4].
CP675, Spin 2002: 15th Int'l. Spin Physics Symposium and Workshop on Polarized Electron
Sources and Polarimeters, edited by Y. I. Makdisi, A. U. Luccio, and W. W. MacKay
© 2003 American Institute of Physics 0-7354-0136-5/03/$20.00
924
from the storage cell. The storage cell target at ANKE will be operated initially in a
vertical guide field, provided by the stray field of the spectrometer magnet, which varies
in magnitude along the axis of the storage cell. At a later stage also orientations other
than vertical will be made available.
2. THE POLARIZED ATOMIC BEAM SOURCE
Details about the source developement have been reported elsewhere, e.g. ref. [3],
therefore the description of the setup given here is only brief.
The spatial conditions at the magnetic spectrometer ANKE [6] require vertical mounting of the source. The atomic beam source has to move together with the target chamber,
when the central spectrometer dipole magnet is set to a different beam deflection angle.
For that reason, the atomic beam source is designed around a central plate (label 6 in
Fig. 1), which serves as the main support for mounting and reference for alignment of
internal elements, as well as with respect to the external environment. Other external
support is not required, i.e. no optical bench like in conventional sources oriented horizontally. The layout of the vacuum vessel of the atomic beam source is shown in Fig. 1.
Two cylindrical chambers are attached above and below a massive, 400 500 mm 2 steel
plate of 50 mm thickness. The inner diameter of the upper chamber is 390 mm, it houses
the first three stages of the differential pumping system, separated from each other by
two baffles. Mounted on rods attached to the central plate are the first three magnets
of the sextupole system [7], and the medium–field rf transition unit (MFT). The lower
chamber has an inner diameter of 200 mm. It makes up stage IV of the differential
pumping system, houses the second set of magnets and in a separate appendix chamber, provides space for the two transition units behind the magnet system. In front of
the last two magnets, a beam chopper is installed (label 9 in Fig. 1), which consists of
a cylindrical Al body with rectangular cutouts on opposite sides that rotates about an
axis perpendicular to the beam. The lateral extension of the source, mostly defined by
the large turbomolecular pumps, was minimized. Therefore, shutters on the cryopumps,
commonly used in other sources, were omitted in the design. The horizontally oriented
turbomolecular pumps and the cryopumps near the beam pipe have to be operated in the
stray field of the central spectrometer magnet of a few hundred Gauss.
3. SOURCE PERFORMANCE
The source performance has been optimized by means of a calibrated compression tube
device [8]. The pressure–to–flow dependence has been calibrated prior to the measurements and afterwards. The entrance tube of the compression tube (inner diameter of
10mm, length of 100 mm) correponds to that of the future cells at ANKE. The distance between the exit of the last magnet to the entrance of the compression tube
amounts to 300 mm. The dependence of the beam intensity on the primary hydrogen
flow into the dissociator is depicted in Fig. 2. The highest hydrogen beam intensity of
74 03 1016 atoms/s in two hyperfine states is found at a flow of 1.2 mbar/s, a
nozzle temperature of T 62 K, and an admixture of O2 of 110 3mbar /s.
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FIGURE 1. Cut through the mid plane of the atomic beam source. 1: dissociator, 2: adjustment screws
to move the nozzle transversely and longitudinally, 3: coldhead with heat–bridge for cooling of the nozzle,
4: first set of sextupole magnets, 5: medium–field rf transition unit (MFT), 6: central 50 mm thick stainless
steel support plate, 7: rotational feedthroughs for adjustment of lower baffle, 8: second set of sextupole
magnets, 9: rotating beam chopper, 10: weak– and strong–field rf transition units (WFT and SFT), and
11: storage cell located on the COSY beam axis. Roman numbers, I–IV, denote the four stages of the
differential pumping system.
The system of hyperfine transition units to provide polarized beams of hydrogen
and deuterium atoms in the states listed in Table 1 has been completely assembled
and successfully tested. The tests could be carried out efficiently with the Lamb–shift
polarimeter. Results of these tests are described in more detail in ref. [5].
4. THE INTERNAL TARGET FOR COSY
The implementation of a PIT at a storage ring requires a powerful differential pumping
system, in particular for a storage–cell target. In case of a polarized jet, a beam dump can
be used. At the ANKE spectrometer space is severely limited, thus the design of such
a system turns out to be quite complicated. With the implementation of the new target
chamber at the end of the year 2002 at ANKE, a major fraction of the preparations
for the installation of the polarized source have been completed (Fig. 3). The design
of the support structure for the ABS between magnets D1 and D2 is underway. The
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16
Intensity [atoms/s]
7.8x10
Tnozzle=62 K
W disso=350 W
q(02)=1x10-3 m barl/s
16
7.6x10
16
7.4x10
16
7.2x10
16
7.0x10
16
6.8x10
16
6.6x10
0.8
0.9
1.0
1.1
1.2
1.3
1.4
1.5
1.6
1.7
H2 primary gas flow [mbar l/s]
FIGURE 2. Atomic beam intensity as function of the primary hydrogen flow into the discharge tube.
The parameters listed in the insert correspond to those for which the maximum intensity was achieved.
TABLE 1. System of hyperfine transitions employed to provide nuclear vector polarization
for hydrogen (H) and nuclear vector and tensor polarization for deuterium atoms (D). The
sextupole magnets are located before and behind the MFT.
Pol
H
1
Pz
Pzz
Hyperfine Transition 1
Hyperfine Transition 2
MFT
3
—
D
1
—
1
1
—
2
H
MFT
3
2
MFT
4
3
WFT
3
—
1
Hyperfine Transition 3
—
—
into cell
H1
H3
D
D
1
1
0
1
MFT
4
3
D
MFT
4
1
WFT
0
2
MFT
4
1
—
—
1 4
2 3
SFT
6
2
D
1
6
—
D
3
4
SFT
6
2
D
3 6
SFT
5
3
D
2 5
new target chamber also accomodates movable horizontal and vertical beam position
monitors (BPM). Together with a set of similar BPM’s in the section between the two
magnets D2 and D3 (Fig. 3), these monitors will facilitate a determination of the beam
position during acceleration of the beam. In addition, it should be possible to determine
the beam angle at the target location from the measured positions in front and behind
the target.
Among other aspects, the new chamber provides sufficient space to install the storage
cells of the PIT. As a next step we will carry out tests at ANKE to identify dimensions
suitable for those cells. The setup for these tests inside the new target chamber is depicted
in Fig. 4. Details regarding these tests can be found in ref. [9].
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FIGURE 3. 3D view of the setup at ANKE with the PIT. The ABS is located between the dipole magnet
D1 and the central spectrometer magnet D2. The COSY beam enters from the left.
FIGURE 4. Target chamber with two xy manipulators to move a frame carrying the cells perpendicular
to the COSY beam. The beam enters from the lower right. The movable BPM system is not shown. The
dimensions of the chamber are 800 mm, w 600 mm, and h 400 mm.
REFERENCES
1.
2.
3.
4.
5.
6.
7.
8.
9.
H. Kolster et al., Proc. 9 th Int. Workshop on Polarized Sources and Targets (PST01), Nashville,
Indiana, USA, 2001. V. P. Derenchuk and B. von Przewoski (Eds.), World Scientific, p. 37 (2002).
L.D. van Buuren et al., Nucl. Instr. Meth. A 474, 209 (2001).
M. Mikirtytchiants et al., p. 47 of ref [1].
F. Rathmann et al., The Polarized Deuteron Break-up Experiment at COSY, contribution to these
proceedings.
R. Engels et al., A precision Lamb–shift polarimeter for the polarized gas target at ANKE, contribution to these proceedings.
S. Barsov et al., Nucl. Instr. Meth. A 462, 364 (2001).
A. Vassiliev et al., Rev. Sci. Instrum. 71, 3331 (2000).
M. Nekipelov, Device for absolute beam intensity measurements at the ANKE atomic beam source,
Diploma thesis Saint–Petersburg State Technical University, 1999. (Available upon request.)
F. Rathmann, Storage Cell Tests, Proceedings of the 4 th ANKE workshop on Study of protondeuteron Interactions, Dubna, Russia 2002. A. Kacharava, V. Komarov, and F. Rathmann (Eds.), to
be published as JÜL–Bericht 4012 (2003).
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