Development of high-current ionic liquid ion source toward surface modification

Development of ionic liquid ion source with porous emitter for surface modification

Recent studies on the use of Taylor cones of ionic liquids as ion sources have demonstrated a considerable effect of source geometry on the characteristics of the resulting ion beam. Of particular interest is the recent discovery by Lozano and Martinez-Sanchez of the excellent performance of externally wetted and electrochemically etched and sharpened tungsten tips. These sources are termed ionic liquid ion sources (ILIS), in analogy to conventional liquid metal ion sources (LMIS). Even more noteworthy is the fact that certain ionic liquids that had in a variety of prior reports always operated in the mixed ion-drop regime from capillary tips, do run exclusively in the purely ionic regime (PIR) on ILIS type sources. The present study uses time of flight mass spectrometry to compare full ion beams emitted from the two types of sources for a diversity of ionic liquids. We confirm earlier reports that internally fed capillary sources achieve purely ionic emissions more readily for liquids having high surface tension (γ > 40 dyn/cm) and high electrical conductivity (K ~ 1 S/m), and produce ion beam currents of several hundred nA with non-negligible energy spread. In contrast, externally wetted ILIS sources produce purely ionic emissions at tens of nA with liquids with substantially smaller γ and K, and much narrower energy distributions.

Ionic liquid ion sources: characterization of externally wetted emitters

The first cavity of a standalone superconducting (sc) continuous wave (cw) heavy ion Linac as a demonstration of the capability of 217 MHz multi gap Crossbar H-mode structures (CH) has been already commissioned at high acceleration gain. The worldwide first beam test with a superconducting multi gap CH-cavity was a milestone of the R&D work of HIM and GSI in collaboration with Goethe University Frankfurt (GUF) in preparation of the sc cw heavy ion Linac project, substituting GSI-UNILAC as a heavy ion high duty factor Linac. Recently the first two of four fully equipped cw-Linac cryomodules are in procurement. To meet the future FAIR science requirements higher beam intensity has to be achieved in the present GSI-accelerator complex. In the last years ion source developments, in particular for the high current Vacuum Arc Ion Sources (VARIS), were concentrated on heavy elements, as Bi and Pb, aiming for stable routine ion source operation at a sufficient rep. rate and high production efficiency. Stripping is a key technology for all heavy ion accelerators. After upgrade of the supersonic N2-gas jet implementation of high current foil stripping, recently a new H2gas cell, using a pulsed gas regime synchronized with arrival of the beam pulse has been developed. An enhanced stripper gas density as well as a simultaneously reduced gas load results in an increased stripping efficiency, while the beam emittance remains the same. A new record beam intensity (11.1 emA) for238U28+beams at 1.4 MeV/u has been achieved, applying the pulsed high density H2-stripper target to a high intensity238U4+beam from the VARIS ion source. Further ion source developments have been accomplished recently providing for sufficient heavy ion beam intensities at the High Current Injector Linac. A machine investigation program has been performed in 2020. The focus was to optimize the entire FAIR injector chain for high intensity heavy ion beam after the successful implementation of different upgrade measures. Besides a dedicated operation mode applying UNILAC, as a heavy ion Linac, at a synchronous phase significantly lower than 30 degrees for high intensity proton beam, could be established. Thus, UNILAC is able to deliver a sufficient proton beam intensity for the FAIR commissioning phase, when the FAIR-proton Linac is not yet available.

The author reports on an extensive study of energy deficit measurements of the energy distribution of the ion beam emitted by a gallium liquid metal ion source in an attempt to resolve the controversy arising from the unusually wide divergence of findings by different workers. The controversy can be conceivably resolved in terms of misalignment of the liquid cone, whereby different parts of the beam enter the energy analyser at different times. Coupled to this is an alteration of the work function of the retarding electrode of the energy analyser by contaminants, such as the liquid metal itself, or its oxides, altering in turn the value of the critical energy deficit for surface field ionisation. A detailed investigation is also made for the region of emission current below 1 mu A-a region rarely investigated by the vast majority of researchers, but a most important one from the point of view of the emission mechanism, as well as from an applications' standpoint. Finally, the reasons for the scatter observed in energy spread measurements are considered, and only a tentative explanation can be given, related to ion source misalignment; this misalignment arises from the fact that the liquid cone does not always form at the centre of the apex region of the supporting needle.

Development and conditioning of the high current ion source for the EAST neutral beam injector

Field evaporation of impurity ions from a liquid gallium ion source

The emission and deposition of molten gold droplets from needle-tip liquid metal ion sources was investigated. The Taylor cone was identified as the source of droplet emission. An upper limit of 8 μm for the virtual source size was measured. Gold films were deposited on silicon substrates. The deposited gold spots showed a peaked, axially symmetric, distribution with a half angle for droplet emission of ∼2° which was considerably smaller than the ion emission angle of ∼45°. Typical deposition fluxes were ∼5×105 μm3/s/sr with total deposition rates of ∼3×103 μm3/s and on an average droplet diameter of ∼1 μm at an emission current of 150 μA. Smaller diameter droplets are produced with decreasing emission current and angle. Gold films with a fine textured morphology suitable for submicron patterning were obtained at emission currents less than ∼135 μA.

A high-current, proton linear accelerator, named as Korean multipurposed accelerator (KOMAC), is being proposed mainly for accelerator-driven transmutation technology (ADTT) by Korea Atomic Energy Research Institute (KAERI). High-current, low emittance continuous power (cw) linear accelerators favor electron cyclotron resonance (ECR) microwave ion sources as an injector (Ref. Reference 1). Recently, these microwave sources are developed and constructed by several institutes especially for high-current cw linear accelerators. A high-density microwave ion source has been designed and constructed as a prototype ion source for the proposed KOMAC linear accelerator. The design of microwave power injection system is similar to that of the 75 keV proton injector at Los Alamos National Laboratory (Ref. Reference 2). A 2.45 GHz, 1.5 kW magnetron source is introduced into the stainless steel plasma chamber with 10 cm diam and 20 cm length through a tapered, double-ridged waveguide and a quartz window. The microwave power supply is separated from the plasma chamber by a high-voltage waveguide break. Axial magnetic fields up to 1 kG can be provided by two sets of water-cooled solenoid coils. A single-hole extraction system is designed for extraction current up to 50 mA at 50 kV extraction voltage. The design and initial operations of the ion source in ECR regimes will be presented.

Several ion source related research and development projects are in progress at the Department of Physics, University of Jyväskylä (JYFL). The work can be divided into investigation of the ion source plasma and development of ion sources, ion beams, and diagnostics. The investigation covers the Electron Cyclotron Resonance Ion Source (ECRIS) plasma instabilities, vacuum ultraviolet (VUV) and visible light emission, photon induced electron emission, and the development of plasma diagnostics. The ion source development covers the work performed for radiofrequency-driven negative ion source, RADIS, beam line upgrade of the JYFL 14 GHz ECRIS, and the development of a new room-temperature-magnet 18 GHz ECRIS, HIISI.

We have investigated the emission characteristics of a liquid alloy ion source for focused ion beam implantation of praseodymium (Pr) ions in high-Tc superconductors. The element Pr was used in a ternary Au–Si–Pr alloy with a low melting point and a low vapour pressure. The melting properties of the alloy were determined by differential thermal analysis. We have measured the emission current stability, the current–voltage characteristics and the mass spectra using a single magnetic mass spectrometer. The ion source exhibits a good performance even after storage for several months in air. The mass spectra show a high intensity of double charged Pr ions.

A high-current, high-energy, and long-pulse positive ion source for the KSTAR neutral beam system is being developed on the basis of proven technology. The original prototype ion source was the TFTR developed by LBNL, but the accelerator slit grid brazed with shaped molybdenum tubes was a barrier for success of the copied work. In order to cover the technical and economical problems caused by the molybdenum tubes, a new OFH copper grid with circular apertures has been designed and manufactured. Cooling circuits aligned along every line of the aperture arrays are made with the help of gun drills. The test and the first experimental results of the upgraded ion source, such as high-voltage characteristics, cooling characteristics, discharge characteristics, and first beam extraction characteristics are described.

The application of liquid metal ion sources to ion-microprobe secondary ion mass spectroscopy

A high current hot cathode bucket ion source, which based on the US long pulse ion source is developed in Institute of Plasma Physics, Chinese Academy of Sciences. The ion source consists of a bucket plasma generator with multi-pole cusp fields and a set of tetrode accelerator with slit apertures. So far, four ion sources are developed and conditioned on the ion source test bed. 4 MW hydrogen beam with beam energy of 80 keV is extracted. In Aug. 2013, EAST NBI 1 with two ion source installed on the EAST, and achieved H-mode plasma with NBI injection for the first time. In order to achieve stable long pulse operation of high current ion source and negative ion source research, the RF ion source with 200 mm diameter and 120 mm depth driver is designed and developed. The first RF plasma generated with 2 kW power of 1 MHz frequency. More of the RF plasma tests and negative source relative research need to do in the future.

Production, acceleration and diagnostics of high intensity beams