T. Kuo

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...

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.

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.

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.

Efficiency and transient time studies of an electron cyclotron resonance ion source for radioactive ion beam production at ISAC/TRIUMF

A 2.45 GHz electron cyclotron resonance (ECR) ion source with a single mode resonator is being developed to produce high efficient single charged ion beams from exiguous gaseous elements. The source is intended to produce short and long half-life radioactive ion beams as well as stable ion beams for low and high energy experiments at ISAC [J. M. Poutissou, Proceedings of the ISAC Workshop (1994)]. It is obvious that for the radioactive ion beam production, the gas and ion transient time and the overall ionization efficiency are the most important parameters. The transient time is measured using ultrafast peizoelectric gas valve which could operate up to a frequency of 2 kHz. A unique feature of the source is that the plasma chamber is considerably smaller (∼170 times) than its resonance cavity in order to minimize the transient time. Quartz tubes with various diameters (5–20 mm) and 80 mm long are tested as the plasma chamber and the results are discussed. The effect of the transfer tube length, which lin...

An electron cyclotron resonance source for radioactive beryllium ion beam production

An ECR ion source is converted to produce a beryllium fluoride beam, which will be stripped to 7Be+2 beam and used in 7Be(p,γ)8B experiments at ISAC. The source consists of an injection chemical chamber and a plasma chamber. Chemically purified (99.9%) BeO is placed in the chemical chamber which can be heated up to 1000 °C. A CF4 leak connected to that chamber serves as the source of CF4 for the reaction to produce BeF2. The BeF2 is then injected into the hot electron layer region of the plasma chamber to enhance the ionization efficiency. A detailed source description, beam parameters and ionization efficiency measurements are presented in this paper.

An emittance–mass scanner for small‐mass, low‐energy beams

An on‐line emittance–mass scanner (EMS), with a size of 10 cm×10 cm×8 cm, has been developed for use with low energy and light ion beams (A<40) at TRIUMF. Computerized data acquisition and procession give the rms emittances, intensities, and contour plots of each beam component. The angular resolution of the scanner is ±1.0 mrad, the maximum divergence of each component that the scanner can take is 140 mrad. Some experimental results of the measurement are given. The comparison between the contour shapes and the values of the emittance measured by both the emittance scanner and EMS is in good agreement.

Design of a parallel-plate energy spread analyzer

A 45° parallel-plate energy spread analyzer has been designed and built for the ISAC project at TRIUMF. It features an energy resolution of ⩽0.04% and a spectrometer constant of k=1.29. Nineteen 0.1 mm by 10 mm metal guard frames with 1 MΩ resistors are used to equalize the electric field in the analyzer to an order of ⩽0.5%. Electric field simulation is done by a code POISSON. This article describes the design of the analyzer. Preliminary experimental results are also presented.

A comparison of two injection line matching sections for compact cyclotrons

Two versions of injection line matching sections between the external ion source and the spiral inflector are used for the compact cyclotrons developed at TRIUMF in cooperation with Ebco Technologies. The 30 MeV model adopts a solenoid-doublet (SQQ) version while the 19 MeV unit takes a four quadrupole/two quadrupole (4Q/2Q) option. Both cyclotrons use a same type of H cusp source and an identical inflector-central region combination. A comparison has been made between these two systems, in terms of DC transmission and RF acceptance as a function of sources H current intensity and emittance. The design and optics characteristics for both systems are described and the results obtained are reported.