To understand the plasma evolution mechanism of microwave ion source (MIS), a hybrid discharge heating (HDH) mode is proposed. That mode contains two parts: ignition discharge by surface wave plasma (SWP) and ionization by electron cyclotron resonance. Compared with the traditional electron cyclotron heating (ECH) mode, the HDH mode has a wider scope of application for MIS with a chamber diameter smaller than the cutoff size. The spatio-temporal evolution of electric field, power deposition, electron temperature, and electron density of a miniaturized microwave ion source (MMIS) at Peking University is investigated based on the HDH mode. In addition, the MMIS is optimized based on the theoretical results of the HDH mechanism. Preliminary experiments show that a mixed hydrogen continuous wave beam of up to 25 mA at 30 keV can be extracted with a power efficiency of 25 mA/100 W.

A multi-sample Cs sputter negative-ion source, equipped with a conical-geometry, W-surfaceionizer has been designed and fabricated that permits sample changes without disruption of on-line accelerator operation.Sample changing is effected by actuating an electro-pneumatic control system located at ground potential that drives an air-motor-driven sample-indexing-system mounted at high voltage; this arrangement avoids complications associated with indexing mechanisms that rely on electronic power-supplies located at high potential. In-beam targets are identified by LED indicator lights derived from a fiber-optic, Gray-code target-position sensor. Aspects of the overai 1 source design and details of the indexing mechanism along with operational parameters, ion optics.intensities, and typical emittances for a variety of negative-ion species will be presented in this Negative-ion sources based on the sputter principle have been used for many years for injection into tandem electrostatic accelerators for fimdamental nuclear and astrophysics research applications, and for applied research such as Accelerator Mass Spectrometry (AMS), high-energy ion implantation and modification of materials. In addition, these sources are being used in a variety of low-energy, atomic and molecular physics research applications. As a consequence of these and other demands for sources with improved intensities and beam qualities, this technology has reached a relatively high degree of maturity. Several sources, designed to accommodate single samples, have been developed over the years, including those described in Refs. 1 and 2. For applications that require short-duration beam-on-target, including AMS, it is desirable to be able to quickly and remotely change samples without vacuum disruption to save time and to preserve similar surface conditions between samples. A few sources have been reported that have been designed with this capability, including sources described in Refs, 3-5. In this report, we describe a multi-sample Cs sputter negative-ion source, equipped with a conical-geometry, surface ionizer that permits sample changes without disrupt ion of online accelerator operation. Aspects of the overall source design and details of the indexing mechanism along with operational parameters, ion optics, intensities and emittances for a wide variety of negative ion species are provided in this report.

Miniaturized electron cyclotron resonance (ECR) ion sources are widely used in compact ion implanters, miniature neutron tubes, and miniaturized ion thrusters. To understand the mechanism of miniaturized ECR ion sources, a miniaturized deuterium ion source developed by Peking University is taken as the research object. In this work, a global model based on particle balance equations is developed for hydrogen and deuterium plasma research inside the miniaturized ECR source. The research results show that both the hydrogen discharge process and the deuterium discharge process of the ion source have strong dependences on the gas pressure and microwave power. The calculated results show that high power is beneficial to increase the ratio of H⁺ (D⁺) ions, low pressure is helpful to increase the ratio of H₂⁺ (D₂⁺) ions, high pressure and low power are beneficial to increase the ratio of H₃⁺ (D₃⁺) ions. In addition, there are large differences between the ion ratios of hydrogen discharge and deuterium discharge. Under the same operating parameters, the ratios of D⁺ ions are 10%~25% higher than the ratios of H⁺ ions since the plasma density of deuterium discharge is higher than that of hydrogen plasma. Therefore, during the operation of miniaturized source, H₂ gas can be used instead of D₂ gas to carry out experiments, and a quantitative estimate of the ratio of D⁺ ions under the corresponding operating parameters can be given based on the ratio of H⁺ ions. At last, the calculated results show that high microwave power is a prerequisite for high ratio of H⁺ (D⁺) ions. However, due to the limitation of microwave coupling efficiency, the miniaturized ECR ion source cannot work in the region where the microwave power is greater than 150 W, so that the H⁺ (D⁺) ratio cannot be further increased, which limits its further applications in neutron sources, implanters and etc. Therefore, how to improve the microwave coupling efficiency should be one of the key research contents of the miniaturized ECR ion source. The global model proposed in this paper is helpful to understand the physical process of the miniaturized ECR ion source, but there are also some shortcomings. Firstly, the influence of the secondary electron emission coefficient is not considered in the model, so it is impossible to study the influence of wall materials on ion ratio in detail. Secondly, since the dissociation degree depends on the results of plasma diagnosis, and the error of plasma diagnosis will have a certain impact on the accuracy of the model. In addition, only the models of hydrogen and deuterium plasma are established in this paper, thus it is impossible to study the process of more gas discharge plasma. In the future, the above factors will be considered and the model will be further improved to establish a complete and self-consistent global model of the miniature ECR ion source.

Lithium ions are widely used in many scientific fields; in order to get these ions, it is necessary to study lithium plasma process thoroughly. Recently, a hybrid 7Li3+ ion source has been designed and tested at Peking University (PKU). To understand the lithium plasma behaviour inside the plasma chamber and to provide some guidelines for ion source optimization to generate 7Li3+, a numerical model based on the plasma equilibrium equations is developed in this work, which is helpful not only for our ion source, but also for understanding the physical process of lithium plasma from ECR ion sources with different frequencies. This model can describe the density and fraction of lithium ions in various system parameters. The dependences of the Li+, Li2+, and Li3+ ion density and fraction on electron temperature, gas pressure, microwave power, surface ionizer, and the magnetic field are investigated systematically.

At Peking University (PKU), a compact 2.45 GHz microwave ion source was developed to obtain high-intensity Li+ beam. To improve the generation efficiency of Li+ ions, we developed a built-in lithium oven named surface ionization oven (SIO), which consists of a heating oven for lithium vapor production and a surface ionizer for the ionization of lithium neutrals. Consequently, the surface ionization and electron cyclotron resonance heating (ECRH) principles are combined within the compact microwave ion source. In this work, the structure and materials of the SIO are investigated systemically to lower thermal risk and increase ionization efficiency. The oven is heated by resistance heating. To minimize the heat loss, polished stainless steel shields are used to surround the oven. The surface ionizer is installed at the exit of the nozzle of the heating oven. It consists of six rhenium wires with the diameter of 0.25 mm inside the ionizer tube. Limited space near the microwave window, the dimension of SIO is ⊘ 13.5 mm × 40 mm. This source has been tested with only heating oven and SIO. With only heating oven, which means the absence of surface ionization, and a 200 eμA pulsed Li+ ion beam was stably extracted from this ion source. When the surface ionizer and the heating oven work together, a pulsed Li+ ion beam of 800 eμA is obtained, which increased by about 300%. The experiment proved that surface ionization could dramatically increase the discharge efficiency of lithium plasma in ECRIS.