M. McDonald

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...

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.

Measurements on a dc volume H− multicusp ion source for TRIUMF

We describe a dc volume H− source, employing multicusp plasma confinement, which has been constructed for use with the TRIUMF cyclotron. An extracted H− current density of 12 mA/cm2 has been obtained. Beam emittance and brightness have been measured as a function of current density and beam fraction. Beam brightness values for normalized beam emittances of the order of 0.2 πmm mrad at 81% beam fraction are typically 10 mA/(mm mrad)2 [equivalent rms B=223 mA/(mm mrad)2].

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.

A design of an ECR ion source for radioactive ion beams for ISAC on-line facility at TRIUMF

A 2.45 GHz ECR ion source for the ISAC on-line operation is being tested at the TRIUMF ion source test stand prior to its installation in the radioactive ion beam production target module. Steps were taken at the design stage to ensure short transient time and high ionization efficiency for single charged ions. Further considerations were given to radiation hardness, reliability, and remote handling capabilities. Transient time was measured using an ultrafast piezoelectric valve. Efficiencies were measured using calibrated gas leaks of stable and radioactive isotopes such as 127Xe. This article describes the overall characteristics of the source.

Optimization studies of proton polarization in the TRIUMF optically pumped polarized H− ion source

Abstract The TRIUMF optically pumped polarized ion source presently produces a 15 μA dc beam of up to 80% polarized H − ions within a calculated normalized emittance of ≲ 0.16 π cm mrad. Extracted beam parameters, after acceleration by the TRIUMF cyclotron to 230 MeV, are ∼ 4 μA with a proton polarization of 75%. The source is based on optical pumping of Rb vapor by Ti:sapphire lasers, resulting in improved polarization compared to previous results using Na as the polarized medium. The instrumentation and results of a detailed study of parameter dependences are reported.

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.

Microwave‐driven multipurpose ion source

A microwave‐driven ion source being developed at TRIUMF is designed to produce stable, reliable, and gas‐efficient negative and positive ion beams for cyclotrons and other accelerators. The source has been tested for H− and achieved 2.1 mA at 0.25 π mm mrad normalized emittance for 500 W of input power at a frequency of 2.45 GHz. The source was operated over one month without interruption for a H− beam stability test and demonstrated 2.5% stability over the period. For positive beam extraction H+, He+, N+, and Ar+ species have been studied. A 2 mA N+ beam was obtained at 0.3 π mm mrad normalized emittance for 1 kW of input power. A beam density as high as 7 mA/cm2 with 45% gas efficiency has been achieved for the Ar+ beam. In this paper the source parameters and characteristics are discussed.

The ECRIS charge state breeding project at TRIUMF.

The performance of charge state breeding with an electron cyclotron resonance (ECR) ion source intended to increase the charge state of online produced radioactive ions at the ISAC facility at TRIUMF has been investigated. A 14 GHz PHOENIX from PANTECHNIK has been setup on a test bench. Singly charged ions have been produced with several ion sources typical for the on-line operation and were injected into the charge breeder. The main purpose of the tests has been the optimization of the efficiency for the charge breeding into the desired charge state. Maximum efficiencies reached so far with the standard one step deceleration of the ions in front of the plasma are up to about 6% for noble gas ions and about 3.5% for alkalines. As ion optics simulations show, the acceptance can be increased by a two step deceleration. In order to meet the velocity acceptance of the accelerator at different A/q values a similar two gap acceleration system for the highly charged ions has been installed to allow the source to run at different voltages. For the further beam transport to the accelerator, cross sections for charge exchange of the highly charged ions with the residual gas have been determined.