Polarized D Operation and Development of the
IUCF Ion Source CIPIOS1^
V.P.Derenchuk1, A.S. Belov2
Indiana University Cyclotron Facility, Bloomington, Indiana
Institute for Nuclear Research of the Russian Academy of Sciences, Troitsk, Russia
2
Abstract. The Cooler Injector Polarized lOn Source (CIPIOS)[1] has most recently been used to
provide polarized and unpolarized beams of negative deuterium ions for filling the injector
synchrotron. More than 1.8 mA of up to 90% polarized D" was available for injection into the
RFQ pre-accelerator and several milliamperes of unpolarized beam was available. The addition
of an electron blocker in a charge exchange ionizer with a two-stage converter[2] improved the
source operation by reducing the total electron current extracted for the maximum 300 A arc
discharge current available. A doubling of this discharge current is now possible and should
result in a corresponding increase in polarized current. [3]
INTRODUCTION
At Indiana University (IUCF) an atomic beam source (ABS) with a resonant
charge-exchange ionizer is used to provide D" (or H") ions [1,7] for acceleration
through an RFQ/DTL to an energy of 4 MeV (7 MeV for H'). This D~ beam fills the
Cooler Injector Synchrotron (CIS)[4] using the strip injection technique and after
acceleration to 90 MeV is extracted. Between January and July of 2002, the source
was used to provide polarized and unpolarized beams of D" for injection into the
Cooler synchrotron[5]. The IUCF experiment CE-82, a search for the isospinforbidden d+d^a+7$ [6] and CE-64, a measurement of three body spin observables
by the Pintex group were two of several that utilized this beam. At the completion of
the CE-82 experiment on July 28th, 2002, the nuclear physics program with the Cooler
synchrotron ended. The source is now used to provide unpolarized beam for
acceleration by the RFQ/DTL and for CIS. A purchase agreement is being negotiated
by the Forschungszentrum Jiilich where the source will be used as the polarized ion
source of a new Linac based injector for the COSY ring. The source is expected to be
shipped in the late spring of 2003.
SOURCE DEVELOPMENT AND OPERATION
A new two stage converter assembly built and tested at INR [2] is installed in
CIPIOS and together with a four electrode extraction system results in an increase of
f
Work supported by grants from Indiana University and National Science Foundation PHY-9724216 and PHY-9314783.
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
887
the polarized D" beam intensity to 2 mA with up to 90% polarization. Source
operation with the pulse length increased from 200 (is to 0.5 ms FWHM is also
improved with an average polarized beam current during the pulse of about 1.5 mA.
An electron blocker added to the ionizer converter assembly reduces the extracted
electron current. The electron current is reduced from several hundred milliamperes to
less than 100 mA during high intensity operation.
Ionizer Development
The design and development of a new lengthened plasma source and two stage
converter with a redesigned extraction system is reported by Belov[2]. Similar
modifications are installed on the CIPIOS ionizer. An electron blocker is added to the
converter assembly as shown in Figure 1 and results in significantly reduced electron
current extracted from the ionizer. The magnetic field generated by the plasma
injector solenoid is opposite to the ionizer solenoid which results in a transition
between negative to positive axial field in the vicinity of the neutralizer. Electrons and
ions from the plasma source follow the magnetic field and collide with the inside
surface of the neutralizer. Electrons streaming from the inside of the neutralizer
surface follow the ionizer field lines into the blocker. The ions have a higher rigidity
and are not focused as strongly into the blocker.
Plasma Source
Neutralizer
Permanent magnet
dipole to clear
electrons
FIGURE 1. A schematic of the two stage converter at INR, Moscow and photograph of the
implementation with electron blocker at IUCF. The photograph is taken from the vantage point of the
plasma source solenoid. The electron blocker was added later at IUCF.
Without the blocker, the electron current exceeds 500 mA resulting in a reduction
of polarized beam intensity, possibly due to the destruction of the polarized negative
ions by plasma electrons inside the ionizer[8]. High electron currents also cause the
extraction voltage to sag and damage the extraction grids on the high voltage
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electrodes. As a result, the beam brightness and pulse shape are degraded at the RFQ
entrance.
The reduced electron current will allow a significant increase in the plasma injector
arc current. The unpolarized H" current extracted is 40 mA for an arc current of
300 A. With 450 A of arc current Belov reports[2] 90 mA of extracted unpolarized D"
ion current and 150 mA of unpolarized H- ion current with a corresponding
improvement in plasma density. A comparable improvement in the polarized beam
current is expected[8]. Higher arc currents have not yet been tested on CIPIOS.
The new four electrode extraction system built at INR for CIPIOS is designed to
increase the space-charge neutralization in the vicinity of the source exit. The
unpolarized negative ion current extracted from the ionizer together with the polarized
ions total several tens of milliamperes before they are separated in the mass analysis
magnet. In this region, positive ions will act to compensate the space-charge with the
negative ion beam. The third electrode of the extraction system is biased slightly
positive in order to block the positive ions from accelerating back into the ionizer.
Source Operation and Future
The nuclear physics research program based on the IUCF accelerators ended on the
final day of the CE-82 experiment, July 28th, 2002. Since it was installed in 1999,
CIPIOS was used exclusively to provide polarized and unpolarized beams to dozens of
Cooler based nuclear physics and accelerator physics experiments. The total hours of
operation, are tabulated in Table 1. The operation is very reliable, maintenance on the
ABS cold nozzle and ciyo-pumps is required once every two weeks and the plasma
injector cathode replacement occurs on an interval of 4 to 6 weeks.
TABLE 1. CIPIOS Hours of Operation
Year
Total Hours of
Operation
1999
2000
2001
2002 (to July 28th)
Unpolarized
Operation
672
840
1,200
1,775
3,100
4,500
4,620
3,700
During the final months of operation in 2002, the polarized D" peak beam intensity
reached 2.2 mA, measured after mass analysis. The polarization for most states is
between 85% to 90% (Table 2). The lower polarization of the -Vector state is due to
TABLE 2. D Polarization Results
State Name
Nominal Pz
Measured
Nominal Pzz
Measured
+ Vector
+1
0.909(31)
+1
0.891 (13)
- Vector
-1
-0.684 (30)
+1
0.695 (14)
+ Tensor
0
0.003 (32)
+1
0.875 (13)
- Tensor
0
0.020 (33)
-2
-1.591(13)
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an inefficient weak field transition which was not repaired due to scheduling
constraints.
CIPIOS will be disassembled and shipped to the Forschungszentrum Jiilich in 2003
where it will be prepared for operation with a new Linac injector for the COSY ring.
For this new purpose, it is required that the intensity of the polarized beam be
optimized for a 0.5 ms pulse length with a low duty factor. The lengthened plasma
injector and two stage converter resulted in an improvement of the polarized and
unpolarized beam pulse shapes. With the source tuned for maximum average intensity
during a 0.5 ms width pulse, an average beam current during the pulse of 1.5 mA is
measured after mass analysis. The unpolarized beam current is 35 mA and the arc
current is 350 A.
FIGURE 2. Polarized H" beam tuned for wide pulse operation is measured after a
mass analysis bending magnet. The horizontal scale is 0.1 ms/div and the vertical
scale is 0.5 mA/div with zero current at the third division.
ACKNOWLEDGMENTS
The results reported would have been impossible without the help of Ron Kupper,
Bill Lozowski and many other technical and professional staff at IUCF. The
assistance and many important suggestions by Ralf Gebel during his visit to IUCF in
November, 2001 is greatly appreciated.
This work is funded by NSF grants PHY-97-24216 and PHY-93-14783 and by the
Indiana University.
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REFERENCES
1. V.P.Derenchuk, et al, 2001 Particle Ace. Conf., eds. P. Lucas, S. Webber, IEEE 01CH37268, 2001,
pp. 2093-2905.
2. A.S. Belov, et al, Proc. of Polarized Sources and Targets 2001, eds. V. P. Derenchuk and B. v.
Przewoski, World Scientific, 2002, pp. 205-209.
3. A.S. Belov, et al, Nucl. Instr. Methods A333, 1993, pp. 256-259.
4. D.L. Friesel et al, Proc. 1997 Particle Ace. Conf., IEEE 97CH36167, 1997, p. 2811.
5. D.L. Friesel et al, Proc. 7th European Particle Ace. Conf., Vienna, Austria, eds. J.-.Laclare,
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6. Browse to http://www.iucf.indiana.edu/Experiments/COOLCSB/.
7. V.P. Derenchuk, A.S. Belov, Proc. of Polarized Sources and Targets 2001, eds. V. P. Derenchuk
and B. v. Przewoski, World Scientific, 2002, pp. 210-214.
8. A.S.Belov, et al, Proc. of 14th International Spin Physics Symposium, eds. K. Hatanaka et al,
Osaka, Japan, 2000, AIP Conf. Proc., 570 , 2001, pp. 835-840.
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