Atomic Beam Polarized Ion Source Research Articles

Installation of an on-line Lamb shift spin-filter polarimeter in the Triangle Universities Nuclear Laboratory atomic beam polarized ion sourcea)

An atomic beam polarized ion source, used heavily since 1989 for producing polarized H± and D± beams for experiments between 25 keV and 20 MeV, has been modified to accept a Lamb shift, spin-filter polarimeter. In this source, polarized ground-state H or D atoms enter an electron cyclotron resonance ionizer where they are stripped to produce an outgoing positive polarized ion beam. When negative ions are desired, cesium vapor is introduced into a downstream charge-exchange canal. The polarimeter, based on an atomic physics concept first developed to produce nuclear-spin-polarized beams at Los Alamos, is designed to monitor the polarization of 2S1/2 metastable H or D atoms emerging from the cesium canal. Metastable 2S1/2 atoms created by electron pickup in a collision with cesium are ‘‘filtered’’ by the polarimeter according to magnetic substate, as the magnetic field imposed on the polarimeter cavity is tuned between 53 and 61 mT. Photons produced by subsequent quenching of these filtered atoms to their ground state are monitored downstream by a phototube to reveal the magnetic substate population of the incident positive beam. To install the polarimeter cavity and phototube assembly, the existing polarized ion source was lengthened by 30 cm. Installation is complete, and comparisons with calibrated nuclear polarimeters have shown agreement to better than 0.023. Principles of operation, a description of the hardware, measurements for cross calibration, and impressions gained from its use are all presented.

Installation of an on-line Lamb–shift spin–filter polarimeter in the Triangle Universities Nuclear Laboratory atomic beam polarized ion source (abstract)a)

An atomic beam polarized ion source, used heavily since 1989 for producing polarized H± and D± beams for experiments between 25 keV and 20 MeV, have been modified to accept a Lamb–shift, spin–filter polarimeter. In this source, polarized ground-state H or D atoms enter an electron cyclotron resonance ionizer where they are stripped to produce an outgoing positive polarized ion beam. When negative ions are desired, cesium vapor is introduced into a downstream charge-exchange canal. The polarimeter, based on an atomic physics concept first developed to produce nuclear–spin-polarized beams at Los Alamos, is designed to monitor the polarization of 2S1/2 metastable H or D atoms emerging from this cesium canal. Metastable 2S1/2 atoms created by electron pickup in a collision with cesium are ‘‘filtered’’ by the polarimeter according to a magnetic substate, as the magnetic field imposed on the polarimeter cavity is tuned between 53 and 61 mT. Photons produced by subsequent quenching of these filtered atoms to their ground state are monitored downstream by a phototube to reveal the magnetic substate population of the incident positive beam. To install the polarimeter cavity and phototube assembly, the existing polarized ion source was lengthened by 30 cm. Installation is complete, its calibration has been checked, and initial impressions gained from its use are presented.

RF transition systems for the Triangle Universities Nuclear Laboratory atomic beam polarized ion source

A system of compact radio-frequency transitions, consisting of two medium-field units and a single strong-field unit, has recently been installed and tested in the atomic-beam polarized ion source at the Triangle Universities Nuclear Laboratory. With care and proper tuning, this new system provides deuteron pure vector beam polarizations of p z = ±0.55 and deuteron pure tensor beam polarizations of p zz = +0.90 and p zz = −1.50 as well as proton beam polarizations of p z = ±0.75. In this report, we describe both an earlier system and this new improved version, with emphasis on the problems we experienced and the solutions devised to solve them.

A new atomic beam polarized ion source for the Triangle Universities Nuclear Laboratory: overview, operating experience, and performance

A newly constructed source of polarized H ± and D ± ions is described. Atomic H or D beams from a dissociator with a cooled nozzle enter a system of two sextupole magnets and several radio-frequency transitions where they are focused and polarized. They enter a downstream electron-cyclotron-resonance-heated plasma ionizer from which positive ions are extracted. When negative ions are desired, they may be produced from the positive beam by charge-exchange in cesium vapor. Emerging beams are intense, have good polarization, low energy spread, and good optical quality. Descriptions are included for all major systems and for diagnostic procedures used to optimize both the intensity and the polarization of the output H ± or D ± beams obtained. Typical operating experience, performance figures, and a description of routine maintenance procedures are given.

Measurement of beam polarization using the D(, p)3H reaction

The D(d, p) reaction was used to measure the vector polarization of the deuteron beam from the atomic beam polarized ion source at King Fahd University of Petroleum and Minerals. The vector polarized deuteron beam was produced using a weak field transition. The polarization pz of the deuteron beam was determined from the measured asymmetry and known analyzing power Ay(θ) of the D(d, p) reaction with 200 keV deuterons. The experimentally determined value of pz was found to be −0.462±0.029 which is 69±6% of the maximum theoretical value. Within the statistical uncertainties, the measured beam polarization agrees with the value given by the manufacturer.

Intensity measurements of polarized beams from an atomic beam polarized ion source

Beam intensity measurements have been carried out for neutral and ionic beams from the atomic beam polarized ion source at King Fahd University of Petroleum and Minerals, Saudi Arabia. The intensity of the polarized hydrogen beam was measured at several points in the source. The intensity of the neutral atomic beam was measured at the end of the atomic beam chamber. The measurement was carries out by measuring the sextupole on-off pressure difference with a vacuum gauge, which was mounted in a compression tube attached to the atomic beam chamber. It was observed that mixing of the source gas hydrogen with nitrogen increased the polarized beam intensity by a factor of 2 at 33 K. The maximum beam intensity was measured to be 1.6 × 10 16 atoms/s at 33K temperature of the nozzle. For the ionic beam, a current of 41 μA has been measured after the ionizer, while a current of 23 μA has been measured for mass selected H ∗ ions after the spin processor. The unpolarized background was low for mass selected H ∗ ions and a beam polarization of 86% was measured for the H ∗ beam using the sextupole on-off current ratio.

Permanent sextupole magnets

Compact but very strong sextupole permanent magnets have been assembled for use in a newly developed cold atomic beam polarized ion source. The sextupole magnetic field characteristics have been found to be satisfactory.

The new high intensity polarized proton and deuteron source for the Bonn isochronous cyclotron

An atomic-beam polarized ion source for the production of polarized protons and deuterons is described. Beam intensities of 160 μA for polarized protons and deuterons are obtained at an emittance of 9π cm· rad· eV . Within the phase space accepted by the Bonn isochronous cyclotron 50 μA of deuterons and 35 μA of protons were measured. The atomic beam emerging from a liquid nitrogen cooled dissociator nozzle is polarized and focussed by two tapered sextupole magnets. Two radiofrequency transitions can be mounted either before or behind the second sextupole, leading to theoretical values for deuterium vector and tensor polarizations of P z =±1 and P zz =−2, respectively. The polarized atoms are ionized by electron impact inside a cold-cathode Penning ionizer working at a magnetic field of 4 T produced by a superconducting solenoid. The efficiency for this ionizer is estimated to be η=6.2×10 −2.

Production of intense beams of polarized negative hydrogen ions by double charge exchange in alkali vapour

The intensity of the polarized negative hydrogen ion beam of the ETHZ atomic beam polarized ion source has been substantially improved by a new double charge exchange device. Increasing the diameter of the charge exchange canal to 1.4 cm results in a beam output of the source of 6 μA of polarized negative hydrogen ions. Further improvements of the charge exchanger are proposed and discussed. With an updated design of the atomic beam apparatus, beams of 0.5 mA polarized negative hydrogen ions may be obtained from such a source.

Analysing power for neutron-proton scattering at 14.1 MeV

The analysing power A γ ( θ) for neutron-proton scattering has been measured at 14.1 MeV for c.m. angles between 50° and 157°. A polarized neutron beam was produced by the reaction 3 H( d, n ) 4 He at 110 keV, using polarized deuterons from an atomic beam polarized ion source. Liquid and plastic scintillators were used for proton targets and the scattered particles were detected in an array of plastic scintillators. Use of the associated alpha technique, multi-parameter recording of events and off-line computer treatment led to very low backgrounds. The results differ significantly from the predictions of the phase-shift analyses of Yale IV, Livermore X and Arndt et al. We find, however, excellent agreement with the predictions of the “Paris potential” of Lacombe et al. Existing n-p analysing power results up to 30 MeV are surveyed and found to be consistent. An attempt was made to look for an isospin splitting of the triplet P-wave phase shifts.

External Ion Sources and Injection Lines at the Bonn Isochronous Cyclotron

The complex of external ion source facilities at the Bonn Isochronous Cyclotron is described. A universal ion source of the Penning type was developed for the production of intense beams of multiply charged ions. Details of this ion source and performance figures are presented. An atomic beam polarized ion source is used for the production of polarized protons and deuterons. A modified atomic-beam polarized ion source using a superconducting solenoid ionizer is under construction. For the combined installation of the universal ion source and the polarized ion source a compact beam transport system has been developed which allows the optimum matching with the cyclotron. A buncher with triangular shaped pulses is used in order to increase the beam intensities. Ionoptical and technical details of the external beam lines and the axial injection are presented.

Ionization of a polarized atomic beam in a high magnetic field by use of charge exchange reactions

An experiment is described to increase the intensity of polarized protons or deuterons in an atomic beam polarized ion source. A beam of polarized hydrogen atoms is ionized by charge exchange with an unpolarized proton beam. Charge exchange takes place in a magnetic field of up to 75 kG. The properties of this field were calculated for best injection of unpolarized ions and best extraction of the ionized particles. In a first test of the experimental arrangement it was possible to extract 1 μA protons from the atomic beam by using the reaction H + H + → H + + H. The efficiency of this process is about 1 × 10 −3 and can be increased.

The polarized proton and deuteron source for the Bonn isochronous cyclotron

An atomic-beam polarized ion source for production of polarized protons and deuterons at the Bonn isochronous cyclotron is described. At the end of the source a proton beam of 1.5 μA or a deuteron beam 2 μA is obtained (typical values). The emittance of the beam corresponds to the acceptance of the cyclotron. A tensor polarization value P zz = 0.8 of the deuteron beam was measured via T(d,n) 4He. For the proton beam a polarization of P ≈ 0.6, for the deuteron beam a vector polarization of P z ≈ 0.5 is to be expected.

Ionisierung eines atomstrahls mit hilfe von ladungsaustauschreaktionen zur erzeugung polarisierter protonen und deuteronen

Charge-exchange reactions were used in an atomic-beam polarized ion source instead of electron impact ionization for production of protons and deuterons. The reactions H + + D→H + D + and D + + H → D + H + were tested. 0.27 μA deuterons and 0.17 μA protons were produced mass-separated from the atomic beam. Behind the charge-exchange volume approximately 0.4 μA deuterons or 0.25 μA protons are available in the test source. The efficiency of ionization by charge exchange is about 4 × 10 −4 and can be increased.