D. Wutte

Ion energy spread and current measurements of the rf-driven multicusp ion source

Axial energy spread and useful beam current of positive ion beams have been carried out using a radio frequency (rf)-driven multicusp ion source. Operating the source with a 13.56 MHz induction discharge, the axial energy spread is found to be approximately 3.2 eV. The extractable beam current of the rf-driven source is found to be comparable to that of filament-discharge sources. With a 0.6 mm diameter extraction aperture, a positive hydrogen ion beam current density of 80  mA/cm2 can be obtained at a rf input power of 2.5 kW. The expected source lifetime is much longer than that of filament discharges.

High intensity metal ion beam production with ECR ion sources at the Lawrence Berkeley National Laboratory

The large number of different experiments performed at the 88 Inch Cyclotron requires great variety and flexibility in the production of ion beams. This flexibility is provided by the two high performance electron cyclotron resonance (ECR) ion sources, the LBL ECR and the AECR-U, which can produce beams of ions as light as hydrogen and as heavy as uranium. With these two sources, up to six different metals can be preloaded using two types of ovens. The ovens are mounted radially on the ion sources and inject the metal vapor though the open sextupole structure into the plasma chamber. For the superconducting ECR ion source VENUS, which is under construction at Lawrence Berkely National Laboratory, the use of radial ovens is no longer possible, because the magnetic structure is closed radially. Therefore, we are developing two new axial oven types for low and high temperature applications. Metal ion beam production in ECR ion sources using the oven technique is discussed. The design of the axial oven is pre...

Development of an rf driven multicusp ion source for nuclear science experiments

Abstract A compact 13.56 MHz radio-frequency (rf) driven multicusp ion source is under development at Lawrence Berkeley National Laboratory (LBNL) for radioactive ion beam applications. In this paper we describe the ion source design and the general ion source performance using H 2 , Ar, Xe gas and a 90% Ar/10% CO gas mixture for generating the discharge plasma. The following ion source characteristics have been analyzed: extractable ion current, ion species distributions, ionization efficiency for nobel gases, axial energy spread and ion beam emittance measurements. This ion source can generate ion current densities of approximately 60 mA/cm 2 .

Multicusp sources for ion beam projection lithography

Multicusp ion sources are capable of producing positive and negative ions with good beam quality and low energy spread. The ion energy spread of multicusp sources has been measured by three different techniques. The axial ion energy spread has been reduced by introducing a magnetic filter inside the multicusp source chamber which adjusts the plasma potential distribution. The axial energy spread is further reduced by optimizing the source configuration. Values as low as 0.8 eV have been achieved.

A compact filament-driven multicusp ion source☆

Abstract A compact filament-driven multicusp ion source has been studied using both hydrogen and helium. Three aspects of the source have been investigated: hydrogen ion species, axial energy spread and extractable current. An atomic ion fraction (H+) of approximately 30% could be obtained with a discharge power of 80 V and 3 A. A magnetic analyzer was used to determine the axial energy spread of the extracted (i.e. accelerated) ion beam species, and an electrostatic energy analyzer was used to determine the energy spread of the ions at the source exit. The energy spread of the extracted beam for the individual species of positive hydrogen ions (H+, H2+, H3+) and that for the negative hydrogen ions (H−) was measured as well. Energy spreads as low as 2.3 eV were obtained for H+, 2 eV for H2+, 1.7 eV for H3+, and 1 eV for H−. The axial energy spread in the source exit without extraction for hydrogen and helium was measured to be approximately 1 eV for both cases. The source can generate a hydrogen beam current density of approximately 12 mA/cm2.

High intensity ion beam injection into the 88-inch cyclotron

Low cross section experiments to produce super-heavy elements have increased the demand for high intensity heavy ion beams at energies of about 5 MeV/nucleon at the 88-Inch Cyclotron at the Lawrence Berkeley National Laboratory. Therefore, efforts are underway to increase the overall ion beam transmission through the axial injection line and the cyclotron. The ion beam emittance has been measured for various ion masses and charge states. Beam transport simulations including space charge effects were performed for both the injection line and the ion source extraction. The relatively low nominal injection voltage of 10 kV was found to be the main factor for ion beam losses, because of beam blow up due to space charge forces at higher intensities. Consequently, experiments and simulations have been performed at higher injection energies, and it was demonstrated that the ion beams could still be centered in the cyclotron at these energies. Therefore, the new injector ion source VENUS and its ion beam transpor...

Lifetime enhancement of a multicusp ion source for lithography

The acceleration system designed by Ion Microfabrication System (IMS) for ion projection lithography (IPL) generates a divergent beam of which only a small portion is employed in the process. Computer simulation shows that by optimizing the accelerator design, the source can be operated with lower discharge power, resulting in longer lifetime and lower energy spread. RF induction discharge operation provides long ion source lifetime with energy spread comparable to that of the filament discharge multicusp source when RF modulation in the extraction voltage is eliminated through proper shielding. New antenna designs have been developed which can further extend the lifetime of the RF-driven ion source.

Ionization efficiencies for highly charged stable and radioactive ions in the AECR-U ion source

Abstract Ionization efficiencies for high charge state ions have been measured with the LBNL AECR-U ion source for ion beams produced from stable and radioactive gases. Various calibrated gas leaks from stable CO, CO2, O2, Ne, Ar, CHF3, Kr and Xe were used in the measurements. Ionization efficiencies as high as 25% or higher were measured for 16O6+ and 12C4+ ion beams and more than 10% for high charge state stable ion beams of Ar, Kr and Xe. In addition, ionization efficiency measurements for radioactive species of 11C and 14O were carried out in which an efficiency of more than 10% for 11C4+ was achieved.

A 2.45 GHz ECR ion source for production of medium charge states ions

At Lawrence Berkeley National Laboratory we are constructing an ECR ion source test facility for nuclear science experiments. For this purpose a single-stage 2.45 GHz electron cyclotron resonance ion source has been designed and fabricated. It features an axial magnetic field with a mirror ratio of up to 5.5 and a hexapole field produced by a novel Nd-Fe-B permanent magnet assembly. In order to enhance the ion confinement time the source plasma volume has been enlarged as much as possible while still maintaining a high mirror ratio. This paper describes the design of the source. Ion optics simulation of the extraction system currently under design will also be presented.

Development of a compact, rf-driven, pulsed ion source for neutron generation

Lawrence Berkeley National Laboratory is currently developing a compact, sealed-accelerator-tube neutron generator capable of producing a neutron flux in the range of 109 to 1010 D-T neutrons per second. The ion source, a miniaturized variation of earlier radio-frequency (rf)-driven multicusp ion sources, is designed to fit within a ∼5 cm diameter borehole. Typical operating parameters include repetition rates up to 100 pps, with pulse widths between 10 and 80 μs (limited only by the available rf power supply) and source pressures as low as ∼5 mTorr. In this configuration, peak extractable hydrogen current densities exceeding 1180 mA/cm2 with H1+ yields over 94% having been achieved.