JAERI-Conf 95-021

2p1-2
PRODUCTION OF POLAREIZED NEGATIVE DEUTERIUM ION BEAM
WITH DUAL OPTICAL PUMPING
M. Kinsho*, K. Ikegami, A. Takagi, andY. Mori***Research Fellow of the Japan Society for the Promotion of Science
1-1 Oho, Tsukuba-shi, Ibaraki-ken, 305 JAPAN
National Laboratory for High Energy Physics ( KEK)
1-1 Oho, Tsukuba-shi, lbaraki-ken, 305 JAPAN**Institute for Nuclear Study, University of Tokyo
3-2-1 Midori-cho, Tanashi-shi, Tokyo, 188 JAPAN
Abstract
To obtain highly vector-spin polarized negative deuteriumion beam, a dual optically pumped polarized negative deuterium
ion source has been developed at KEK. It is possible to select apure nuclear-spin state with this scheme, and negative deuterium

radiation trapping. However, we have re-examined the dual optically pumped scheme in detail and found that radiation trapping was not a serious problem and highly nuclear-spin polarized negative deuterium ion beam could be obtained with thedual optically pumped scheme.[8]In this paper, we report the experimental results which

ion beam with 100 % nuclear-spin vector polarization can be produced in principle. We have obtained about 70% of nuclear-spin

showed that the highly nuclear-spin vector polarized negative

vector polarized negative deuterium ion beam so far. This result

deuterium ion beam could be produced by OPPIS with dual

may open up a new possibilities for the optically pumped polar-optical pumping.

ized ion source.

2. DUAL-OPPIS FOR DEUTERON

1. INTRODUCTION

The principle of a dual optically pumped polarized

An ordinary deuteron beam was successfully accelerated

negative deuterium ion source is shown in Fig.1 schematically.

to an energy of 11.2GeV (5.6GeV/u) in the KEK 12 GeV proton
synchrotron (KEK-PS), the limiting energy of the ring, in 1992.

The idea of this scheme is as follows: After picking up the polarized electrons from optically pumped alkali atoms, for ex-[ 1] The beam intensity of the accelerated deuterons reached more

ample, deuterium atoms are electron-spin polarized in the statethan 2 x 10 12 ppp which was almost the same as that for protons.

of mj =+ 1/2 as shown in Fig.l. These electron-spin polarized
deuterium atoms equally populate three hyperftne sub-levels
lz=+ 1, 0, and -1 in a high magnetic field, which are labeled theFollowing this success, it has been strongly requested to accelerate polarized deuteron beam, and it will be started from this autumn. For this purpose, a polarized deuteron beam with highnuclear-spin vector polarization and large beam intensity is demanded. So we started development of polarized negative deuterium ion source with dual optical pumping.
As for polarized ion source, an optically pumped polarized
ion source(OPPIS) has been used for generating nuclear-spin polarized negative hydrogen ion beam so far. The idea of this type ofstates 1, 2, and 3, respectively in Fig.l. Using the Sona transition, the state 1 (mj =+ l/2, Iz=+ 1) goes to the state 1' (mj =-1/2,Iz=-1 ), the state 2 (mj =+ 1/2, lz=O) goes to the state 2' (mj =+ 1/2,Iz=-1), and the state 3 goes to the state 3' (mj =+1/2, Iz=O),
respectively as shown in Fig.l. Therefore, the deuterium atoms
with only the hyperftne sub-level oflz=-1 (state 1' in Fig.l) has
an opposite electron-spin state, mj =-l/2, of the other two sub-[3] Afterwards, various institutes have developed an opticallylevels (2' and 3') after Sona transition. When the alkali atoms in
the ionizer are also optically pumped and their electrons are to
be spin polarized in the mj =+ l/2 state, only deuterium atoms

pumped polarized ion source (OPPIS) for their accelerators.

with the electron-spin state of mj =-112 ( state 1' ) can form

[4][5][6]It has been believed that this type of polarized ion source isnegative ions because of the Pauli exclusion principle. Thenuclear-spin state of the negative deuterium ions in this case is

not useful to produce a highly nuclear-spin polarized(vector andIz=-1, the nuclear-spin vector polarization becomes -1. The

polarized ion source was proposed by Anderson[2] and the ftrst
operational ion source has been successfully developed at KEK.

tensor) deuterium ion beam. In 1987, Schneider and Clegg[?] pro-nuclear-spin tensor polarization is, in this case, -1. Using a

posed a new nuclear-spin state selection scheme. In spite of thisproper rf transition simultaneously, a pure nuclear-spin tensor

possibility of making a highly polarized deuteron beam by opticalpolarization of -2 may become possible.

pumping, they concluded eventually in their paper that this dual
optical pumping scheme might not be practical because efficient
optical pumping of the thick target in the ionizer is difficult due to-221-

3. EXPERIMENTAL APPARATUS

JAERI-Conf 95-021

izer are measured by Faraday rotation with linearly polarizedlaser light tuned to the rubidium D2 transition at 780 nm. Thisprobe laser fed into neutralizer and ionizer from upstream ofthis ion source.
ECR Deuteron Source
D0 (etJFigure 3 shows a schematic diagram of ECR deuteronD0source and extraction electrode system. The ECR cavity is a'Optical Pumping'stainless steel cylinder of 29 em length and 6 em inner diameter.
It is mounted to an insulating Teflon holder to allow the applica-'Optical Pumping'

Fig.l The principle of a dual optically pumped polarized negative
deuterium ion source
Schematic of dual-OPPIS
Figure 2 shows a schematic diagram of a dual-optically
pumped polarized negative deuterium ion source which has beendeveloped at KEK. There are ECR ion source and neutralizer inthe super conducting magnet which makes a high magnetic fieldof about 2.7 Tesla. A microwave is fed into ECR source fromupstream of it. The solenoid has three independent coils whichallows control of the magnetic field shape. A deuteron beam isextracted from ECR ion source by an electrode system which accelerates the beam to energy of approximately 6 keV. The deu-tion of the 6 kV potential for deuteron extraction. The Teflon
holder also supports the extraction ,electrode system. The
plasma chamber is made of stainless steel and the inside of it aquartz glass tube contains to evacuate the plasma. Externalgrooves in the stainless steel cylinder hold a Sm-Co hexapole
structure to make a good plasma confinement. Microwave is fed
into a plasma chamber through a thin vacuum sealed microwave
window. Microwave power is generated by a 18 GHz klystron
which operates with a long pulse duration ( upto 1 msec ) andhigh repetition rate ( 20Hz ). A maximum power of microwave
generated by this klystron is 1 kW.
18 GHzConducting

teron beam enters a electron-spin polarized rubidium vapor cell ,where a fraction of the deuterons picks up a polarized electron bycharge transfer from rubidium and are thus neutralized. we callthis cell neutralizer. The electron-spin polarization is induced by
optical pumping with circularly polarized laser tuned to the rubidium D 1 transition at 795 nm. Rubidium is chosen because_ of its
relatively high charge exchange cross section with fast deuteron[9], and the availability of high laser power at the wavelength.
FaradyCup

Most of neutralized deuterium is created in the excitedn=2 state. For that reason it is necessary that charge exchange
occurs within a high magnetic field which preserves the electronspin polarization of deuterium atom as the atom decays to theground state [10]. The ECR cavity extraction electrodes and neu-~Ocm

Fig.2 Schematic diagram of a dual optically pumped polarized
negative deuterium ion source at KEK
Extraction Electrode System

tralizer are both contained within the same high magnetic field so
as to reduce the effective emittance increase of the deuteron beam

lybdenum disks with an hexagonal array of 91 holes 0.9 mm inas it enters the magnetic field region of the neutralizer. The mag-diameter. The first electrode is integral to ECR cavity. The

netic field reverses direction in the region between neutralizer andouter two electrodes are supported by stainless steel holders

negative ionizer cell, and as the neutral deuterium beam passes

which are attached to the Teflon insulator. The first electrodethrough this region, the nuclear-spin polarization is enhanced byand second one are consisted in 1 mm apart, and the distancemeans of a Sona transition [11]. This deuterium atom picks up abetween second electrode and third one is, 1.5 mm. The elec-

A three-electrode system consists of 0.5 mm thick mo-polarized electron by charge transfer from rubidium in ionizer.

trodes are operated in an accel-accel mode with the second elec-

The electron-spin polarization is induced by optical pumping.

trode set about 1 kV below the cavity potential. The third elec-

Nuclear-spin vector polarized negative deuterium ion beam is cre-trode is kept at ground potential.

ated with this scheme. In the downstream of the ionizer, there areeinzellens, wien filter and Faraday cup for which n- beam current

4. EXPERIMENTAL RESULTS

is measured. In order to pump the rubidium atoms in neutralizer

In a dual optical pumping scheme, the deuteron polar-and ionizer, two broad band Ti-sapphire lasers are fed into neutral-ization can be estimated with an unique method, which is calledizer and ionizer from downstream of it respectively. The thickness
and electron-spin polarization of rubidium in neutralizer and ion-as "intensity modulation method". One of three hyperfine
sublevels is selected to be n- ions by Pauli exclusion principle.

-222-JAERI-Conf 95-021

RFWindow,

Electrode I

Electrode2

up polarized electrons from the optically pumped rubidium atoms in the neutralizer, reduces the electron-spin polarization at
the large magnetic field strength.

5. CONCLUSION
We have been developing at a dual optically pumped
polarized negative deuterium ion source for producing deuteronII
100200

D Glass Chamber

M~ti -Aperture Electrodewith high nuclear-spin vector polarization. With this source,
negative deuterium ion beam with about 70% nuclear-spin vector polarization was obtained in the present experiment. In order~Insulator""' (b) Extraction Electrode system(a) ECR Deuteron Source
Fig.3 Schematic diagram ofECR deuteron source
and the extraction electrode syatem
Beam intensity can be modulated by switching an optical pumping
from on to off or changing a electron-spin polarization direction.
Deuterium atoms in only one hyperfine sub-level can become

to obtain a large beam intensity, we are optimizing thissource.We are now installing this source into the high voltage
station for the KEK 12 GeV proton synchrotron (KEK-PS). We
hope to get the polarized deuteron beam acceleration in theKEK-PS by the end of this year.

negative deuterium ions by picking up polarized electrons fromthe optically pumped alkali atoms in the ionizer. Thus, the beam
intensity of negative deuterium ions depends upon the population-0.2-0.4

of deuterium atoms in each hyperfine sub-level after the Sonatransition. This means that the deuteron vector polarization ( Pz )and the electron-spin polarization of optically pumped alkali at--0.6- O.EIoms in the ionizer ( Pei ) affect the beam intensity of negative
deuterium ions. These values are related each other as expressed

-I

0.05

0.1

£

in the following equation.

0.15

0.2

0.2:5

0.35

( ( 1 crr- 1 ~~) I 1orl)

Fig.4 The relation berween e and nuclear-spin vector polar-

Pz = -2 £I Pei ( 1 - £ ).
Here,£= (10 ff- Ion) I loff• where Ioffand Ion are the beam intensitiesof negative deuterium ions when the optical pumping of the alkali
atoms in the ionizer is turned off and on, respectively. The resultof the experiment is shown in Fig.4. The vertical axis in the figure
presents the nuclear-spin vector polarization of negative deuterium ions. The horizontal axis shows the relative change of thebeam intensity of the negative deuterium ions by switching theoptical pumping of the alkali atoms in the ionizer on and off. The
solid line in the figure presents the relation between£ and nuclearspin vector polarization for Pei = 0.95. In our experiment, theelectron polarization of the alkali atoms in ionizer was 95 %. The
electron-spin polarization of alkali atoms in the ionizer ( Pei) wasmeasured by using a Faraday rotation method. The nuclear-spin
vector polarization ofD- ions can be estimated from that equation.
The triangle plot in the figure shows the experimental result whenthe magnetic field strength of the neutralizer is 1.2 Tesla, and thecircle plot shows the experimental result when the magnetic fieldis 2. 7 Tesla. The errors shown in the figure present the fluctuationsof the data taken at different times. In 1.2 Tesla £ value obtain in
our experiment was about 0.21. It correspond to nuclear-spin vector polarization ofD- ions of 55%. In 2.7 Tesla £was about 0.25
and nuclear-spin vector polarization was 70 %. The magnetic
field strength of the neutralizer increased from 1.2 Tesla to 2.7
Tesla, the nuclear-spin vector polarization of D- ions also increased from 55 % to 70 %. This is because of the spin-orbit cou-ization for Pei=0.95. The plots in the figure show the experimental results when the magnetic field strength of neutralizer is
1.2 T and 2.7 T.

REFERENCES[l]Y.Mori et. al.: Proc. of the 1993 Particle Accelerator
Conference. (1993) Vol. 5 page 3754
[2] W.L.Anderson: Nucl. Instr. and Meth. 167,363(1979).
[3] Y.Mori, K.Ikegami, Z.Igarashi, A.Takagi,and S.Fukumoto:
AlP Proc. 117 New York(1983)123.
[4] R.L.York, O.B. VanDyck, D.R.Swenson and D.Tupa:
Proc. of the Int. Workshop on Polarized Ion Sources andPolarized Gas Jets, KEK Report 90-15(1990),page 142.
[5] L.Buchmann,C.D.P.Levy, M.McDonald, R.Ruegg, andP.W.Schmor: ibid page 161.
[6] A. Zelenskii, S.A.Kokhanovskii, V.G.Polushkin and K.N.
Vishnevskii:ibid page 154.
[7] M.B.Schneider and T.B.Clegg: Nucl. Instr. andMeth.,A254,630( 1987).
[8] M.Kinsho, and Y.Mori: Rev.Sci.Instrum. 65(4), April
1994, page 1388.
[9] H.Tawara : Atomic Data and Nuclear Data Tables, 22,491(1978)[10] E.A.Hinds, W.D.Conerius and R.L.York: Nucl. Instrumand Meth., 189, 599(1981)[11] P.G.Sona: Energia Nucl., 14, 295(1967)

pling in the neutral deuterium atoms, which are created by picking-223-