R. Baartman

On the development of a 15 mA direct current H− multicusp source

A 15 mA dc H− multicusp source has been developed for injection into a TR30 cyclotron. This source is also used with a 900 kV tandem accelerator to obtain 10 mA protons at 1.8 MeV. The program is an extension of the 5–7 mA dc H− cusp source developed at TRIUMF during 1989–1990. Major efforts include the search for the optimal filament materials, shape, and location; comparison of cusp line confinement and magnetic filtering of electrons at the extraction region; optimization of extraction lense configuration; and upgrading of vacuum and power systems capability. The source is noncesiated and the maximum arc power available is only 5 kW. After the H− beams pass through an electron suppression grid and a 20 mm collimator, we obtained 15 mA with 0.66 π mm mrad 4 rms normalized emittance. At this output the e/H ratio was about 4. The best normalized emittance occurs around 5–7 mA, having a value of 0.37 π mm mrad. Further development in the near future is planned using cesium and multiple apertures in the hop...

Low-energy spin-polarized radioactive beams as a nano-scale probe of matter

Abstract We have commissioned a polarized low-energy 8 Li ion beam line, which together with a high-field β-NMR spectrometer, can act as sensitive new probe of thin films and interfaces. The implantation energy can be continuously adjusted from 1 to 90 keV and the maximum polarization achieved thus far is 80%. This instrument opens up new applications for β-NMR which parallel and complement efforts with low-energy muons. For example, it is possible to probe the magnetic field distribution near the surface of a material by stopping a polarized 8 Li beam in a thin overlayer of Ag. Since the 8 Li adopts a site with cubic symmetry in Ag there is no quadrupolar splitting of the resonance, and the 8 Li acts as a purely magnetic sensor.

Betatron resonances with space charge

The point is made that betatron resonances do not occur at the incoherent value of the tune, but rather at the frequencies of the appropriate collective modes. This has important implications not only for the design of high intensity, low energy proton synchrotrons, but also for the interpretation of machine studies at existing synchrotrons of this type.

Polarized radioactive beam at ISAC

Abstract The polarized beam line at ISAC relies on the well known technique of collinear optical pumping to polarize the nuclear spins of a low energy (10–60 keV) radioactive beam. Alkali-metal beams are longitudinally polarized by optical pumping of a fast atomic beam, which is created by charge exchange of the incident ion beam in a Na vapour cell. At ISAC, the beam is then reionized in a He gas target and directed to the experiments. To date, 30 keV beams of 8Li and 9Li have been polarized, and 11Li and 20Na beams are scheduled immediately following this conference. The polarization of the 8Li beam, using a dual frequency, standing wave Ti:sapphire laser, is up to ∼80%. High polarization is achieved by matching the laser bandwidth to the energy spread in the beam. The status of the facility is reported.

Charge state breeding of radioactive ions with an electron cyclotron resonance ion source at TRIUMF

Efficient primary ion sources at ISOL facilities normally produce singly charged ions. This limits the usable mass range for postacceleration due to the A∕Q acceptance of the accelerator. At the ISAC facility at TRIUMF an A∕Q below 7 is desired to avoid further stripping. Thus, charge state breeding is necessary if higher masses are to be accelerated. A 14 GHz ECRIS “PHOENIX” booster has been chosen as a breeder. In order to investigate and optimize its performance under ISAC conditions it has been set up at a test bench equipped with a standard ISAC target-ion-source to produce singly charged ions. A series of measurements has been performed with the noble gases Ar, Kr, and Xe. Efficiencies of more than 6% in the maximum of the charge state distribution after mass separation have been obtained and the emittance of the extracted beam and breeding times have been measured. This article gives a status report on the ongoing measurements.

Evaluation of a prototype Isotope Separator Accelerator surface ionization source

A prototype surface ionization source coupled with a fixed-geometry extraction electrode system was commissioned on the Isotope Separator Accelerator (ISAC) ion source test stand at TRIUMF. The suitability of the ion source and extraction system for use in the ISAC facility was determined by a series of emittance measurements of the extracted beams. The test stand optics were successfully commissioned using the prototype ion source; emittance measurements of the mass-separated beams demonstrated that second- and third-order beam aberrations (introduced by the magnetic dipole mass separation) could be corrected by the use of multipole electrostatic optics elements. An upper limit of the root-mean-square-energy spread (2 eV) was deduced from the emittance measurements. Emittance measurements were performed at beam energies of 10–50 keV, as well as for ion masses ranging from Li+ to Rb+, to demonstrate the feasibility of the prototype for a variety of beam energies and masses.

FURTHER DEVELOPMENT FOR THE TRIUMF H-/D- MULTICUSP SOURCE

We have reported a 15 mA dc H− multicusp source at the sixth International Ion Source Conference in 1995 at Whistler. Since then, the H− beam has been further upgraded to 20 mA for 25 kV dc extraction. The D− beam output of the new cusp source has also been measured at 25 and 12.5 kV energies. An 8 mA D− peak current at 25 kV with 0.5 π mm mrad normalized 4 rms emittance has been obtained. Special attention was given to the effects of gas flow, pumping speed, and neutralization on the 12.5 kV operation which is used for the D− injection into a 15 MeV D− cyclotron. At present, we are making an effort to test the effect of injecting Cs in the vicinity of the plasma aperture. On the other hand, a hybrid of filament plus LaB6 cathode mechanism has been tested for filament lifetime issue. The results from these tests are reported. In particular, the experience in operating this new source for the Triumf/Nordion TR30 cyclotron is summarized.

Charge state breeding for the acceleration of radioactive ions at TRIUMF.

A 14.5 GHz electron cyclotron resonance ion source (PHOENIX from Pantechnik) has been set up at the Isotope Separation and ACceleration (ISAC) facility at TRIUMF for the charge state breeding of radioactive ions. After extensive testing and optimization on a test bench it has been moved on-line and put into operation. During a first test in 2008 a beam of (80)Rb(14+) was successfully created from (80)Rb(1+) and accelerated by the ISAC postaccelerator. Further tests with different stable and radioactive isotopes from the ISAC on-line sources and from a test source with stable Cs have been carried out. Until now an efficiency of 1.4% for (124)Cs(20+) has been obtained.

A high intensity dc H− source for low energy injection

While a 20 mA dc H− source system at 25–30 keV beam energy has been developed at TRIUMF several years ago, another recent demand on the system is to provide a 4 to 5 mA H− at the 4–6 keV energy range. We found that at this low energy range, the existing source/extraction system can only give ∼1 mA with poor emittance due to strong space-charge effect. Fortunately, a very special source/extraction mechanism together with the use of neutralization was discovered and developed to overcome this difficulty. Up to 4 mA with a normalized rms emittance of 0.15 π mm mr has been achieved at 6 keV. This performance finds its usefulness for injection systems where lower beam energy and higher beam intensity are required. A copy of the TRIUMF system was constructed and successfully tested in the summer of 2000 for the “H− Acceleration Project” for the K130 cyclotron at Jyvaskyla University, Finland.While a 20 mA dc H− source system at 25–30 keV beam energy has been developed at TRIUMF several years ago, another recent demand on the system is to provide a 4 to 5 mA H− at the 4–6 keV energy range. We found that at this low energy range, the existing source/extraction system can only give ∼1 mA with poor emittance due to strong space-charge effect. Fortunately, a very special source/extraction mechanism together with the use of neutralization was discovered and developed to overcome this difficulty. Up to 4 mA with a normalized rms emittance of 0.15 π mm mr has been achieved at 6 keV. This performance finds its usefulness for injection systems where lower beam energy and higher beam intensity are required. A copy of the TRIUMF system was constructed and successfully tested in the summer of 2000 for the “H− Acceleration Project” for the K130 cyclotron at Jyvaskyla University, Finland.

AN ION SOURCE TEST STAND FOR THE ISAC FACILITY AT TRIUMF

Abstract The properties of ion sources and the beams extracted from them are critical to the successful design of the ISAC facility at TRIUMF. To better understand these properties, an off line 60 kV test stand has been constructed to test and evaluate targets and ion sources intended for use at the future ISAC facility. The test stand also presents the opportunity to evaluate diagnostics, beam monitoring and system control techniques required for ISAC. The test stand vacuum chamber mimics the ISAC target module. Ion beams are produced using a fixed geometry multielectrode extraction column and transported through 5m of beamline using electrostatic elements. Mass analysis is achieved using a 45° magnetic dipole midway along the flight path. Diagnostic elements positioned throughout the beamline are used to determine beam properties.