Bechtold, V.

Brueckmann, H.

Finken, D.

Friedrich, L.

Hamdi, K.

KITopen

November 1972Institut für Experimentelle KernphysikKFK 1709A Method for Production of Transverse Polarized Deuteron Beams ina Lambshift Source Using Static Magnetic Field~v. Bechtold, H. Brückmann, D. Finken, L. Friedrich, K. HamdiAls Manuskript vervielfältigtFür diesen Bericht behalten wir uns alle Rechte vorGESELLSCHAFT FüR KE RN FORSCHUNG M. B. H.KARLSRUHEKERNFORSCHUNGSZENTRUM KARLSRUHEKFK 1709Institut für Experimentelle KernphysikA Method for Production of Transverse Polarized DeuteronBeams in a Lambshift Source Using Static Magnetic FieldsV. Bechtold, H. Brückmann~, D. Finken,L. Friedrich, K. HamdiGesellschaft für Kernforschung m.b.H. Karlsruhe* Now at 1. Institut für Experimentalphysik, Hamburg- 1 -AbstractA special arrangement consisting of two iron shielded solenoidswas minimized in order to achieve intense metastable hydrogenatom beams with longitudinal polarization. A trans verse polari-zation of the metastables is obtained by superposing thelongitudinal magnetic field with a properly designed field intransverse direction. This whole set-up rnakes it feasible toionize the metastables in the transverse magnetic field. The lossof the metastables by quenching in the transverse magnetic fieldcan be almost avoided by electrical compensation. The measuredtransverse tensorpolarization was P33=-0.73.ZusammenfassungUm einen intensiven Strahl metastabiler Wasserstoffatome mitlongitudinaler Polarisation zu erzeugen, wurde eine Anordnungminimaler Länge von zwei Solenoiden mit Eisenabschirmung ent-wickelt. Wird dem longitudinalen Magnetfeld des zweiten Quenching-magnets ein geeignetes Transversalfeld überlagert, so erhält maneinen Strahl polarisierter metastabiler Atome mit transversalerPolarisation und kann diesen ohne Polarisationsverm~nderungineinem homogenen transversalen Magnetfeld ionisieren. Durch elek-trische Kompensation kann eine Intensitätsabnahme der metastabilenAtome durch Quenchen im transversalen Magnetfeld nahezu vermiedenwerden. Die gemessene transversale Tensorpolarisation betrugP33= - 0,73.- 2 -For injection in the Karlsruhe Isochronous Cyclotron cltransverse polarized ion beam is necessary. This transversepolarization can be achieved in a Lambshift source withoutthe additional spin rotating devices usually following thesource.The Lambshift source takes advantage of the differentlifetimes of the metastable a- and ß-2S~ states of hydrogenin a combined magnetic and electrical field 111. A beamof metastable atoms is polarized by quenching the differentHfs-states selectively while the beam is running throughtwo special longitudinal magnetic fields with oppositedirections 121.In figure 1 the two quenching magnets and the shape of theQUENCHINGMAGNET5 CHARGE EXCHANGE CELLLONGITUDINAL FIELo--20e~- 2 Oe===-0'qIU-30 -20 -10 0 10[fZJ0125)------ --.[t;]o: [:: <>--e- • •-e- • •n [;-e-fi')=-1/3 f?, :::-1fig. 1Eingereicht am 6. Oktober 1972- 3 -longitudinal magnetic field are shown. In addition the change ofoccupation numbers is given while the beam is passing the longitu-dinal field.The polarized metastable atoms are ionized by charge exchange withiodine in a homogeneous longitudinal magnetic field of 2 Oe 13, 41.giving a positively charged ion beam with longitudinal polarization.For getting transverse polarized ions the metastable atoms have tobe ionized in a transverse magnetic field.The charge exchange process can also take place in a transversemagnetic field. But in this case a beam broadening results fromthe transverse magnetic field because the charged particlesoriginate from different parts of the cell. Therefore the magneticfield has to be compensated by an electrical field to avoid lossof intensity and deformation of beam emittance. Before enteringthe charge exchange cell it is necessary to rotate the polarizationof the metastable atoms from the longitudinal to transversedirection. This is feasible by using a specially-formed magneticfield turning from longitudinal to transverse direction alongthe beam. The experimental arrangement and the field shape areshown in figure 2.In between the second quenching magnet and the charge exchangecell is placed the transverse field magnet. The magnet producesa narrow field with a maximum of 30 Oe shown in the lower curve.The position of the transverse field magnet is in the regionwhere the longitudinal field of the second quenching magnet hasnearly the same value as the transverse field. The resultingfield changes its direction along the beam in such a way thatthe Larmor precession frequency of the atoms in this field is- 4 -always higher than the rotation frequency of the magnetic fleldseen by the metastable atoms 12,51. This adiabatic conditionallows the beam energy to vary over a wide range and requirestherefore no special care in designing the magnet.TRANS. FIELDQUENCHINGMAGNETS MAGNET 10DINE CELL~DI2S) .tBLONGITUDINAL FIELD,rig. 2I-40560O.I I ' I-30 -20I I10/<OJ3 Oe20.-----' ._',TRANSVER~E FIE~D I15of----i--r~:.--:::::r-"'----30o.A difficulty however arises if metastable atoms run through atransverse magnetic field. For a moving atom in a transversefield there are opposite Lorentz forces effecting the electronshell and the nucleus. This causes a Stark-effect, reducingthe metastable intensity by quenching. This difficulty can beovercome by electrical compensation of the transverse magneticfield. The electrical field is produced by properly designedelectrodes inside the transverse field magnet. The totalarrangement is shown schematically in figure 3.- ~5 -At left is sketched the second quenching magnet. Between thepole shoes of the transverse field magnet are inserted the twoelectrodes of the electrical compensation field. They must becurved to get optimum compensation.The charge exchange cell is sliced into 12 segments held atdifferent potentials. The sliced cell produces inside a nearlyhomogeneous electrical field. This is necessary to compensate thetransverse magnetic field Hf' The dimensions of the cell are1,8 cm inner diameter and 25 cm length.LONGlTUDINAl flELD2nd QUENCHINGMAGNETCHARGE EXCHANGE CELL84compensatedj uncornpensatedH (Oe)400200ot----+---t--+---+------if-----joTRANSVERSE FIELD MAGNETfig. 3 fig. 4The transparency of the compensated transverse magnetic fieldfor metastable atoms has been investigated as a function ofmagnetic field strength. For this purpose the ion intensityproduced by charge exchange of the a-metastables was measured.In figure 4 the experimental results of this arrangement areplotted.In both cases the intensity decreases with rising magnetic field.However by electrical compensation of the transverse magneticfieId, loss of intensity is reduced. This loss may be explainedby the difficulty to compensate completely the magnetic field atany point of the beam region. Remaining field components(magnetic and electrical) quench the metastable atoms. The- 6 -quenching effect by these remaining field components becomeshigher with increasing transverse magnetic field. In lowerfields the loss of metastable intensity is negligible.fig. 5-Fh Itrcnsv II0,8 i -- -~----I/I- I~I~... i"'o!...... i0,6 ,,-- I!I 1'I'-i'I..........i0,4 ,-- ------ -- "-"'--I0,2 f-- - -_.- .'----- -----1 -- -00 50 H (Oe)In figure 5 the transverse polarization P33 measured by theT(d,n)4 He reaction is given as a function of the transverse field.This transverse field is always optimally compensated. For gettingmaximum polarization a field strength of 30 Oe has to be applied.Lower fields are not able to rotate the polarization completely.With increasing fields there is a loss of metastables by quenching.Because of an unpolarized background the loss of metastablesreduces the polarization of the ion beam delivered by the source.Another effect which also may cause the loss of polarization, isconnected with the special arrangement of the source used for these- 7 -investigations. The beam of thepolarized metastable atomsis admixed with charged particles. This particles aredeflected and separated in this arrangement by rotatingelectrical fields. If the transverse magnetic field is notcompletely compensated some of these charged particles arereflected again into the beam of the metastable atoms. Thiscauses a higher unpolarized background. In present state thereported set-up of the Karlsruhe Lambshift source deliversa positively charged deuteron beam with tensor polarizationof P33= - 0.73 in the transverse direction. The polarizationwas measured by the neutron asymmetry of the T(d,n)4 Hereaction at 140 keV.- 8 -References:111 W. E. Lamb, R. C. Retherford, Phys. Rev. 79 (1950) 549121 P. G. Sona, Energia Nucleare li (1967) 295131 L. D. Knutson, Phys. Rev. A2 (1970) 1878141 H. Brückmann, D. Finken, L. Friedrich,Nucl. Instr. Meth. 87 (1970) 155151 V. Bechtold, H. Brückmann, D. Finken, L. Friedrich,Z. Physik 231 (1970) 98

A Method for Production of Transverse Polarized Deuteron Beams in a Lambshift Source Using Magnetic Fields

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A Method for Production of Transverse Polarized Deuteron Beams in a Lambshift Source Using Magnetic Fields

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