22Research Report of Laboratory of Nuclear Science, Tohoku University Vol. 38 (2005)

Test Operation of Spin-Filter Polarimeter for Deuteron
I. Nishikawa, M. Watabe, and T. Tamae
Laboratory of Nuclear Science, Tohoku University, Sendai 982-0826§1. Spin-Filter Polarimeter at LNS
We have developed a Lamb-shift type polarimeter for probing the polarization of an opticalpumping polarized deuteron gas target. The Lamb-shift polarimeter [1,2] is based on the 3-levelinteraction between D(2S1/2, ↑electron), D(2S1/2, ↓electron) and D(2P1/2, ↑electron) states in the spin-ﬁlter cavity.
The mechanism of the 3-level interaction in the spin-ﬁlter cavity is found elsewhere [3,4]. In this report
the equipment and the test operation result are described brieﬂy. A view of the spin-ﬁlter polarimeteris shown in Fig.1.

III

III
PM-tubespin-filter cavity
quenchingelectrodeCs cellbeam
monitorsolenoidal coils
Fig.1

A view of the spin-ﬁlter polarimeter.

1-1 Charge Exchange Section
Some of the deuteron ions extracted from a deuterium gas target are converted to D(2S) atoms by
the charge exchange reaction d+ + Cs → D(2S) + Cs + [5] in the Cs vapor cell. The cross-shaped Cs vapor
cell is composed of inner copper sleeves and outer ceramic sleeves which are heated by a nickel-chrome
ribbon heater. The cell is placed in the solenoidal coil to suppress the expected depolarization effect.
1-2 Spin-Filter Section
The spin ﬁlter cavity is placed in a solenoidal coil set which generates homogeneous magnetic ﬂux
in the central region of the cavity. The spin-ﬁlter coil set is composed of three main solenoidal coils ofhollow conductor, two correction solenoidal coils and iron yokes. The D(2S) atoms are injected into theaxial area of the cavity, and the longitudinal rf electric ﬁeld and transverse static electric ﬁeld quenchthe D(2S) atoms which are non-selected or off-resonance. The cavity is made of brass, 26cm in fulllength, divided into 4-quadrant parts. It is operated at 1610 MHz in the TM010 mode with an rf powerof about 0.1 W.
1-3 Photon Counting Section
In this section the number of the D(2S) atoms passed the spin-ﬁlter cavity is counted. The D(2S)23atoms contained in the beam are forcedly Stark-quenched in the electric ﬁeld produced by a cylindricalquenching electrode, accompanied by the emission of Lyman-alpha photons. Some of the decay Lymanalpha photons are detected by a UV PM-tube (Hamamatsu R6835) with MgF2 window, CsI cathode, andAC-coupled output. The output signals from the PM-tube are pulse-height-analysed and counted by
NIM modules and a DAQ-board on PC. The typical counting rate is ~400 photons/sec in the following
polarimetry operation.

§2. Test Operation of the Polarimeter
2-1 RF ion injector and beam line
The test operation of the spin-ﬁlter was done by injecting unpolarized deuteron atoms from an RFion- source. The overview of the RF-ion-source and the ion beam optics is depicted in Fig.2.

feed throughaccelerationelectrodes

stirring
Wien Filter electrodefocusing
electrodecurrent monitor------

to polarimeter++++++

D2 gasCryo Pump

RF ionizer

stirring
electrode(Ei=1.5keV)

Fig.2

Test-ion injector and beam line components.

The RF ionizer is composed of a Pyrex glass tube and an RF-coil. An 13.6MHz rf power of 25W wassupplied to the coil through a matching circuit. The partially-ionized and dissociated deuterium gas wasejected through a 1mm-diameter hole on a copper electrode. Ions were extracted and accelerated up to 1.5
keV by cylindrical electrodes and mass-analysed by a Wien filter. The magnetic flux (~1150 gauss at
the central point) was generated by two square permanent magnets in the Wien filter. The ion beam
was guided into to the Cs cell of the polarimeter by two stirring electrodes and a focusing electrode, andthe beam current was measured by a beam monitor at the end of the polarimeter. A typical current ofthe passed ion beam was 0.3 nA at the monitor.
2-2 Test operation result
We measured the populations of the magnetic sub-states of unpolarized deuterons from the RF-ion
source. The ion beam energy was 1.5 keV and the Cs-cell temperature was 313K. A typical result andﬁtted curves are shown in Fig.3. In the figiue, the averaged count rate of photons detected by the PM

24
tube are plotted as a function of a mean magnetic flux on the beam axis in the cavity. At each data

Count Rate [/sec]

point photon pulses were counted in 10 seconds.

450400

350

300

250
550

560

570

580

590

600

B [gauss]
Fig.3.

Observed peaks of the deuteron magnetic sub-state population:, dashed line (Gaussian +linear), dot-dashed line( a linear part of the ﬁtting. )In the ﬁgure the relative height of the three peaks on the straight line corresponds to the relative
populations of the nuclear magnetic sub-states of the D(2S) at the quenching electric ﬁeld. From theFig.3 we note S/N and stability are not sufﬁcient. Improvement of the homogeneity of the magnetic ﬂux
in the spin-ﬁlter region and suppression of background photons will be required.

References[1]

J.L. McKibben and G.G. Olsen : Phys. Rev. Lett. 20 (1968) 831.

[2]

S.K. Lemieux : Nucl. Instrum. and Meth. A313 (1993) 434.

[3]

G.G. Olsen and J.L. McKibben : “Theory of a Radio Frequency “Spin Filter” for a Metastable Hydrogen,
Deuterium, or Tritium Atomic Beam” LA-3725, Los-Alamos Scientiﬁc Laboratory (1967).

[4]

K. Kubo and K. Katori : “Spin and Polarization” Shin-Butsurigaku-Series no.27, Baifuukan-Press.
(1994).

[5]

P. Pradel et al. : Rev. Sci. Instrum. 45 (1974) 44.