15) Applications of ion sources and examples

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1 15) Applications of ion sources and examples Ion sources are applied in basic science and in industry. In basic science ion sources are used as injectors for heavy ion accelerators. One of the main applications there is the accelerator mass spectrometry (AMS): Typical structure of an injection line: The beam from the ion source must be matched to the acceptance oft he accelerator. In case of heavy ions a mass separation is also required. Examples are the GSI injectors. WS2014/

2 RFQ requirements Specific energy: 2.2 kev/u 131 kv acc. Max mass to charge (A/ ): U 4+ Space charge limit RFQ: 0.25 A/ [ma] 15 ma U 4+ Acceptance RFQ: x,y =138 mm mrad WS2014/

3 The GSI ion source types: Multi Cusp Ion Source Metal Vapor Vacuum Arc WS2014/

4 Mass analyser These are the devices used to separate the ions produced in the ion source into their individual A/q-ratios and focus them on the detector. A number of different mass analysers exist in modern mass spectrometry one of those is the sector magnet. 2 mv qvb B mv q p q Add a second electric sector to provide energy focussing of ions independent of their mass. Can be in a geometry with electric sector before magnetic sector (Nier-Johnson geometry) or reverse geometry with magnetic sector before electric sector. Resolution in mass spectrometry is defined as the ability to separate an ion of mass M from another with mass M+ M. The resolution is defined as: R M M WS2014/

5 Accelerator mass spectrometry (AMS): Determination of the age of organic materials via a non-destructive measurement: C14 Method C14 is only accumulated in living organisms CO 2 from the atmosphere After the death of the organism the ratio 12 C/ 14 C changes due to decay of 14 C. A calibration is done with annual rings of trees and historical data. Half-life of 14 C is = 6730y, 12 C/ 14 C 10-12, accuracy of 1% 83 y AMS: Counting the 14 C-atoms (material of g/h) using an ion accelerator AMS combines several selective processes, which can deliver a high suppression of isobaric contamination. The different process steps are composed by conventional techniques and methods: WS2014/

6 1. Selective ionization for the chosen species by choice of negative ionization in a Sputter source. 2. First conventional mass separation within a magnetic sector field (low energy side). 3. Acceleration in a Tandem-accelerator to energies from some hundred kv up to a few 10 MV. 4. Charge reversing of negative ions within the accelerator terminal by electron stripping within a gas or foil target to a charge state of +1 or higher, depending on the energy. 5. Energy filtering and second conventional mass filtering within magnetic sector field (high energy side). 6. Where required, TOF measurement for further mass selection and background reduction. 7. Where required, use of a gas-filled sector field magnet for charge state compression to increase selectivity. 8. Element and mass selective particle detection via nuclear physics E/E-Detector. WS2014/

7 Example: VERA in Vienna: 12 C 13 C C 14 C + 12 CH CH + 7 Li No 14 N! 13 C C C 3+ WS2014/

8 A Cesium-Beam Sputter Source for Negative Ions is used: Acceleration Region Carbon Target Cs + 50 μa 12 C C /s Cesium Vapor hot surface ~ 1000 C WS2014/

9 Plasma-Oberflächen Konversion Plasma wird vor dem Target generiert und das Target auf negatives Potential gelegt. Ionen aus dem Plasma sputtern negative Ionen aus dem Material Die Produktion negativer Ionen ist besonders effizient, wenn das Atom die Metalloberfläche mit v verlässt, das etwas größer ist als die thermische Geschwindigkeit. Das Elektron wird während des Ejektionsprozesses übertragen. (siehe Graphik) Ein Beispiel für die Produktion negativer Ionen an einem Mg-Target zeigt die nachfolgende Graphik. WS2014/

10 Furthermore, ion sources are used for the production of radioactive ions, in fusion and plasma science as well as atomic and molecular physics. Target ion sources for radioactive isotopes: For the production of radioactive isotopes one uses the coupling of an ion source with a target, which is hit by high energetic beam. After the ionization the ions are Accelerated and afterwards separated by mass. Proton beam (1 or 1.4 GeV) The isotopes can be produced by high energetic p or ions. Also thermal neutrons form reactors in combination with 235 U can lead to fission fragments. WS2014/

11 ISOLDE ion sources: requirements for modern target ion sources are: High ionization efficiency (10-80% according to the element) big intensity range ( particles/s) Short confinement time to reduce losses from radioactive decay. Preferably, element selective (especially the RILIS) Oberflächenionisation Plasmaquelle mit heißer Transferlinie Plasmaquelle mit kalter Transferlinie Targets are heated up to high temperatures (diffusion of isotopes) WS2014/

12 Industrial applications are: Ion- or plasma etching (RIBE, reactive ion beam etching, ion beam milling) The surface is modified by the ion impact. To prevent space charge effects, electrons are sprayed into the beam. WS2014/

13 Evaporation and sputtering of surfaces (e.g. for the production of DVDs, Cds ect.) So called "Metalize" Magnetron ion sources for the sputtering of the metal. Magnetron sputtering The magnetron sputtering uses Argon gas within between the target and the substrate plate. The target plate is on a negative potential. Argon atoms are ionized and accelerate towards the target plate. The argon ions release metal atoms from the target plate which are deposited at the substrate and form a coating. WS2014/

14 Radiography, neutron imaging (X-ray- and neutron-sources) e.g. production of neutrons via a (p,n) reaction at 7 Li or 3 H. Surface modification (Lithography, micro mechanics, nano-structuring) Ion implantation for the doping of semiconductors. WS2014/

15 Ion implantation The typical setup includes an ion source, acceleration section, mass separation, and a target. To regulate the penetration depth the beam energy has to be modified. Volume ion sources like the "multi-cusp source are used. For the semiconductor production, one distinguish three different types of implanters: Medium current implanter with currents of 10 µa up to 5 ma at beam energies of 5 to 900 kev High current implanter with currents of 100 µa to 30 ma at energies of 0.5 to 220 kev High energy implanter with currents of 10 µa to 1 ma and energies of 200 to 3000 kev WS2014/

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17 Advantages of ion implantation are: Precise control of the dose and the depth-distribution Low temperature process (resist can be used as a mask) Low sensitivity against cleaning procedures Very good lateral dose homogeneity (<1% for 8 wafer) Another method is the plasma immersion which brings the target into the plasma chamber of a big volume source. The homogenous treatment of complex surfaces can be a problem with normal implanters. With the plasma immersion,the component is completely covered by the plasma. By applying a negative voltage to the component, the ions from the plasma are accelerated towards the component and implanted. Given that the whole surface is implanted at the same time, this method is very efficient for high dose applications. WS2014/

18 Systems for solid state analysis: Electron and ion beams are used to analyse the composition of solid state systems. The main structure of such a set-up for ion beam analysis (IBA) is shown as follows: Source Detector Accelerator Sample Analyser Particles or photons are scattered by the sample or channelled, so the methods are used are called Rutherford backscattering and ion beam channelling. Usually beams of a few MeV/u are required. Kinematic factor: elastic energy transfer from a projectile to a target atom can be calculated from collision kinematics mass determination WS2014/

19 Scattering cross-section: the probability of the elastic collision between the projectile and target atoms can be calculated quantitative analysis of atomic composition Energy Loss: inelastic energy loss of the projectile ions through the target perception of depth These allow RBS analysis to give quantitative depth distribution of targets with different masses WS2014/

20 Ion sources for fusion science: Currently neutral-particle injectors are worldwide under development. The ITER project has a big interest on the technique of high-frequency ion sources. They have to meet the following parameters: D current densities of 20 ma/cm 2 Electron-Ion ratio I e / I - 1 Gas pressure 0,3 Pascal Pulse length: 1 hour Typical parameters of high-performance sources, In fusion science: High frequency power > 100 Kilowatt, Frequency ~1 Megahertz This sources are huge, partially they have extraction areas of the size of a door. WS2014/

21 Neutral particle heating: HF ion sources are used with big dimensions. The extraction consists out of grids multiaperture extraction with up to 1300 holes. Within the injector the ions are produced inside the ion source, then accelerated and neutralized, to prevent any deflection by the magnetic fields. The fast and neutralized particles penetrate the plasma and lose there energy through collisions with the plasma particles. The remaining ions are deflected by a magnetic field and guided into a beam dump. WS2014/

22 Ion Thruster: An ion thruster is a form of electric propulsion used for spacecraft propulsion that creates thrust by accelerated ions. The term is strictly used to refer to gridded electrostatic ion thrusters, but may often more loosely be applied to all electric propulsion systems that accelerate plasma, since plasma consists of ions. Ion thrusters are categorized by how they accelerate the ions, using either electrostatic or electromagnetic force. Electrostatic ion thrusters use the Coulomb force and accelerate the ions in the direction of the electric field. Electromagnetic ion thrusters use the Lorentz force to accelerate the ions. In either case, when an ion passes through an electrostatic grid engine, the potential difference of the electric field converts to the ion's kinetic energy. According to Edgar Choueiri ion thrusters have an input power spanning 1 7 kilowatts, exhaust velocity km/s thrust millinewtons and efficiency 60 80%. The Deep Space 1 spacecraft, powered by an ion thruster, changed velocity by 4.3 km/s while consuming less than 74 kilograms of xenon. The Dawn spacecraft has surpassed the record with 10 km/s. The applications of ion thrusters include control of the orientation and position of orbiting satellites (some satellites have dozens of low-power ion thrusters) and use as a main propulsion engine for low-mass robotic space vehicles (for example Deep Space 1 and Dawnmass a higher repulsion. In addition, noble gases are safe in operation. WS2014/

23 The operation principle is shown in the following graphic: WS2014/