Factors Enhancing Production of Multicharged Ion Sources and Their Applications

In this article, Principle of plas ma generation is discussed and investigated. In all types of ion sources, ions are produced by various types of gas discharge including electron collisions with gas particles. The general parameters are a source of electrons, a small region of relat ively h igh gas pressure, an electric field to accelerate the electrons in order to produce an intense gas discharge (plasma) with a relat ively h igh electron and ions density and some mechanism for extracting a collimated parallel h igh current ion beam. Ou r research work was quickly described, reviewed and gave some results showing the importance in some areas of applications. A short historical review on basics and applications of some mul- ticharged ion sources is presented. The mult icharged ion source is evaluated by; the large ion current ext racted fro m it, the large percentage of ions in the beam, the higher degree of ionization inside the atom, the small gas consumptions, and the degree of divergence of the extracted ions must be small.


Introduction
Ion sources are used in many research fields as mass separation, ion imp lantation, atomic physics, fusion and a variety of accelerators for nuclear and particle physics with different requirements. The develop ment of mu lt icharged ion (MCI) sources received a strong push from heavy ion accelerator centers, due to the fact that the energy range of a heavy ion accelerator is strongly increased by the charge state of the injected ions. Moreover, the mult icharged ion sources are useful for basic investigations in atomic physics, surface physics and related areas.The more demanding the applicat ions, the mo re the ion source has to be carefu lly designed and optimised to get optimu m performance. High performance of ion sources represents in having ionization efficiency, maximu m current, h igh charge state, size and cost with taking into account the limits of power and the radiation environ ment. Ion sources are dev ices fo r p roducing and delivering ion beams that may be directly used fro m the source or after acceleration by a simple or co mplex accelerator structure. Ion sources may be classified according to the ion characteristics in sources of positive ions and sources of negative ions. Posit ive ions are produced in most ion sources by electron-ato m and elect ron-ion collisions in a plasma containing neutral particles, ions and electrons. In the most co mmon positive ion sources, electrons are produced by a hot filament and the plasma is created by an electric arc discharge with low gas pressure. Multicharged ion sources have emerged with the existence of accelerators, when mu lticharged ions of carbon were observed by Alvarez at the 37-inch cyclotron in 1940 [1]. There are many types of multicharged ion sources for use in heavy ion accelerators and atomic physics experiments, e.g., PIG ion sources, Duoplasmatron-and Duopigatron ion sources [2]. PIG ion sources have found widespread application in injectors of large particle accelerators used for nuclear and high-energy physics research [3]. Multicharged ions were also produced by Duoplasmatron-and Duopigatron ion sources [4] for applications in accelerators, ion imp lantation, sputter deposition and ion beam analysis. A new line for production and acceleration of mu lticharged ion beams was in itiated by electron cyclotron resonance ion sources (ECRIS) [5][6][7], electron beam ion sources (EBIS) [8] and laser beam ion sources (LBIS) [9]. Electron cyclotron resonance ion sources are very reliable p roducers of multicharged ions and now used in many fields as atomic, nuclear and high energy physics; they are also useful for studies related to plasma physics [10]. Electron beam ion sources are useful for fundamental and applied areas of research in the physics of mu lticharged ions [11], and for lo w energy collision e xperiments [12]. Laser beam ion sources have been used, e.g., for various applications as surface modification, very large scale integrated circuit fabrication, laser mass spectrometry and in medicine [13]. Nowadays, mu lticharged ions are relevant in studies on mu ltiply excited species (hollow atom spectroscopy), plasma chemistry and technology, semiconductor industry, informat ion technology and thermonuclear fusion reactor development [14], X-ray astronomy, solar physics, microelectronics and nanotechnology, ion implantation, ion lithography and medicine [15].

Criteria for Production of Multicharged Ion Beams
Production of intense beams of mu lticharged ions is difficult since suitable conditions for effective ionization and minimu m losses of highly charged ions have to be realized. The primary mechanis ms for production of mu lticharged ions are photo ionization and electron impact ionization. The electron impact ionization process is most generally used in the laboratory. Electron impact ionization can result in the removal of more than one electron from an atom or ion, provided that the bombarding electrons have sufficient energy. In order to produce multicharged ions, some criteria have to be fulfilled [10]: (1) The energy of the electrons should be higher than the ionization potential for reaching the desired charge state, (2) Ions should be confined for a time sufficient to reach the required charge state, (3) To min imize charge exchange the residual gas pressure should be kept as low as possible.

Ionizati on Processes
Ionizat ion is a process in which an atom loses one or more of its electrons to another atom. The process of ionization occurs in nature as a result of interactions of photons, electrons, or other atoms or ions with matter. Understanding this process and inelastic processes in atomic co llisions in general is important for a wide range of pure and applied research fields such as astrophysics, plasma physics and thermonuclear fusion. Multicharged ions produced by electron impact ionization can be produced by one of the following processes: outer shell ionizat ion (single ionization), and inner shell ionizat ion with subsequent rearrangement processes (successive-single ionization). In multicharged ion sources, the maximu m charge state that can be obtained is limited by the maximu m incident electron energy. The impact of a free electron of high enough kinetic energy on an atom or an ion may result in the transfer of energy to a bound electron with mo re than the b inding energy in the ato m or ion; as a result this electron is transferred to the continuum of unbound states. In a single ionization event, the incident electron must have an energy equal to the sum of all ionization potentials of the removed electrons, whereas for successive-single ionizat ion they require only the energy of each electron removed. In the case of single ionizat ion, there are two main parameters that determine the process namely the electron temperature T e and the electron density n e . For successive-single ionizat ion which is the main process for the production of mu lticharged ions. The probability of producing mu lticharged ions by single impact ionization falls off rapid ly with increasing charge state of ions. Therefore, a more efficient method to obtain a reasonable yield of highly charged ions is by successive-single ionizat ion. The loss of an electron from the atom A or the ion A + is an ionization process that can be described as: In ECR ion sources, a high density of hot electrons serves for the production of highly charged ions because ionization cross sections decrease with increasing charge states. Ions and electrons are kept in a dynamic equilibriu m by amb ipolar diffusion that maintains the neutrality of the ECRIS plasma. The average ion confinement time τ i is linked to the average electron confinement τ e which depends on the whole electron population. The average electron confinement time τ e can be appro ximated as [16]: where n ec and n eh are the cold and hot electron density, τ ec is the average cold electron lifetime. Fro m equ. 2 we see that a high ratio of hot to cold electrons increases the average electron confinement time and consequently also the average ion confinement t ime. Since the average electron confinement time τ e is close to the collision time τ coll which is given by [17]: With q eff = 2 q e n q n ∑ the mean effective ion charge and T e the electron temperature.
The ionization rate for an ion of charge state q is: where n ef is the effective electron density with electrons of energies at least equal to the ionization potential of the ion charge state q-1, σ q-1 and ν are the ionization cross section and the electron velocity, respectively. The ionizat ion cross section σ q-1 is approximately given by [18]: where E e and P q-1 are the electron energy and the ionization potential of the ion charge state q, respectively.
Substitute σ q-1 fro m equ. 5 into equ. 4, then: Equ.6 shows that at given electron density, electrons with energies of a few tens to hundreds of keV are needed to maximize the ionizat ion rate of ion charge state q with ionization potentials of a few ten keV. This means that a higher density of hot electrons will reduce the ionization time of ions of intermed iate and high charge states, and consequently enhance the production of mu lticharged ions.
The maximu m charge state that can be obtained is limited by the maximu m incident electron energy. Multi-step ionization process takes a long time which depends on the plasma density and the ionization cross section and this time must be less than of the ion lifetime in the plas ma. The time τ i (q) needed for stripping to charge state (q) by successive electron impact and mult i-step ionization in p lasma of electron density n e is given by [4]: where σ k, k+1 is the cross section for ionization fro m charge state k to charge state k+1, ν e is the electron velocity and σv is taken over the distribution of electron velocit ies. If the single collision, mu ltiple ionization process contributes negligibly to total ion p roduction, the ionization process can be described following the rate equation. The ionization process in ECR p lasma has been considered as follow [5]: where the right hand side term was the creation term of charge i through ionization of charge (i-1) and through charge exchange of charge (i+1) with neutrals and the loss term through ionization towards charge (i+1) and charge exchange with neutrals of charge i and the losses due to diffusion outside the plasma. The system was solved under different assumptions; constant electron temperature T e , constant electron density n e and constant pressure p.

Performance Parameters of Mul ticharged Ion Sources
The development of ion sources was stimulated in the early times by the requirements of particle accelerators, mass spectrometers, neutron generators, etc. Nowadays the field of ion sources has grown into a wide variety of ion source subfields and has an essential impact on various high technology areas from material modificat ion, isotope separation to nuclear fusion and ion propulsion. Each applicat ion of ion source requires a somewhat different form of source of certain performance characteristics. Different applicat ions of ion sources require somewhat different sets of certain performance characteristics. Mult icharged ion sources are characterized by the fo llo wing parameters [19]: (1) The type of ion species that can be produced by the source (2) The ability of producing mult icharged ions of different elements for their applications in particle accelerators, atomic physics, etc.
(3) The ext racted ion current which can be produced by the ion source, (4) The beam emittance of the ion source should be as low as possible, (5) Brightness; the brightness is inversely proportional to the beam emittance; a high value is desired, (6) The energy spread of the extracted beam fro m the source which depends on the ion source parameters as the magnetic field, gas pressure and RF power (in case of RF ion sources). Ion sources with low ion energy spread is preferred, (8) Ionizat ion efficiency; this is the efficiency of the process by which the plasma is formed. A high efficiency allo ws high ion currents to be produced with relatively low gas flow, (9) There are a nu mber of other parameters that are more or less important, depending on applications as the source lifetime, the source size, the power efficiency and the ease of maintenance.

Penning Ion Sources-(PIG)-MCIS
The typical PIG-arrangement is shown in Fig. 1, for production of MCI, the discharge is typically operated in homogeneous magnetic field of so me kG, at gas pressures between 10 -4 Torr and some 10 -1 Torr. Primary electrons are released fro m the cathodes either by ion impact (cold cathode PIG) or by thermionic emission (heated cathode PIG). The cold cathode Penning ion source is found to be more successful than other sources for many types of accelerators [20]. It is characterised by long time of operation with no filament and operates at low pressure (< 10 -4 Torr). It used for production of multicharged ions from heavy gaseous atoms [21]. The hot cathode Penning ion source has been used in cyclotrons for production of heavy ions and mult icharged ions [22]. The ions can be extracted either through one of the cathodes (axial extraction) or through the anode (radial ext raction). In this ion source, the discharge mechanism depends on the electron oscillation between the two cathodes through a cylindrical anode fixed in between. The magnetic field confines the electrons from moving to the anode wall and due to its helical motion, these electrons collide with gas ato ms. Th is enables the discharge to operate at low p ressure. Anode chamber must be made of high ionization coefficient material such as stainless steel, copper, carbon, etc. The cathode material must have high secondary emission coefficient as alumin iu m, magnesium and berylliu m which y ields an increase for the plasma density and therefore a higher ion current could be produced. Abdelrahman et al [23] in their work has been designed, and constructed a cold cathode Penning ion source for using in a low energy accelerator (150 keV). Th is study includes the experimental arrangement for electron and ion beam extraction fro m hydrogen gas under the influence of discharge parameters. These data are important for in jection and transmission in low energy accelerators (Fig.2). On applying positive potential of 10 kV on the extractor at P r = 1.5 x 10 -4 torr (in the high vacuum region), arc voltage = 200 V, I arc = 1 A and magnetic field = 0 gauss, the electron current on the extractor reaches 70 mA and collector proton current reaches 4 mA . By apply ing negative potential of 14 kV on the extractor the collector current reaches 3 mA at P r = 5.5 x 10 -5 torr, V arc = 200 V, I arc = 1 A, B = 180 G (near the cathode). Figure 3 shows the influence of the magnetic on the collector ion current field which increases it to 4 times its value without magnetic field. The influence is more clear at pressures lower than 10 -4 torr. Figure 4 shows the change of ion current with distance. It reaches 1.8 mA at 20 cm, where the change of ion current with distance is needed in accelerator. Operating characteristics of the low energy accelerator with energy in the range fro m zero to 100 keV has been studied and investigated by Abdelrah man et al [24]. This accelerator includes an ion source of the cold cathode Penning type (with Pierce geo metry for ion beam extract ion), an accelerating tube (with 8 electrodes) and Faraday cup (FC) for measuring ion beam current (Fig.5). A vacuum system that evacuates the system to the order of 6.3 x 10 -6 torr. A palladiu m tube is used to supply the ion source with pure hydrogen atoms. It was possible to operate this accelerator with energy of 50 keV at minimu m hydrogen pressure, 6.3 x 10 -6 torr. The total resistance applied between the accelerating electrodes, R T = 31.5 MΏ. These data include the in-fluence of the pressure in the accelerating tube, the magnetic field of the ion source, the extract ion potential and the accelerating potential on the collector ion current. It was possible to accelerate protons with an energy 50 keV with current 100 μA at pressure 6.3 x 10 -6 torr, the source magnetic field = 110G (I B = 2 A), the arc current = 0.4 A, and the extraction potential = 10 kV.   Figure 6 shows the potential distribution along the acceleration electrodes where the first electrode is at zero potential. This figure shows the value of the acceleration voltage of the high voltage on each electrode when applying the acceleration voltage of the high voltage generator on the eighth electrode. This potential distribution is adjusted by using resistance 4.5 MΏ between the electrodes. The total resistance is equal to 31.5 MΏ. The maximu m voltage reaches 60 kV at pressure 5.25 x 10 -6 torr without breakdown. Figure 7 shows the influence of the extract ion voltage on the collector ion current for different values of the acceleration voltage applied on the acceleration tube at low pressure. It is clear that the change of extraction voltage (V ex ) fro m 0 to 8 kV causes a small change in collector ion current, wh ile at V ex > 9 kV , this change begins to increase rap idly. The application of the accelerating voltage greater than 30 kV is characterized by a large effect on the collector ion current.

Duoplasmatron and Duopigatron-MCIS
The duoplasmatron ion source was developed by V. Ardenne [24] as a powerfu l source for gas ions. The duoplasmatron ion source consists as shown in Fig. 8 of t wo plas ma regions; the lower density plasma between the cathode and the intermed iate electrode (IE) and the high density plasma between the IE and the anode. The plasma is compressed by double layers into the IE region and then more co mpressed by an axial magnetic field. In this way, a very high plas ma density can be produced. Different versions of the douplasmatron ion source were introduced by many investigators came fro m the group around Septier [25] and Gautherin [26]. Douplasmat ron ion source was used for production of multicharged ions in different laboratories [4]. The duopigatron ion source [4] is a modification of the duoplasmatron with an additional reflector electrode following the electrode (Fig.9). Multip ly charged ions especially of heavier elements could be produced by using a duopigatron ion source [4].

Electron Cyclotron Resonance Ion Sources (ECRIS)
The properties of an ECRIS for delivering intense beams of mult icharged ions depend on the microwave frequency that determines the electron density n e and electron temperature T e , and on the product (n e τ i ). The product (n e τ i ) may be increased by improving the plas ma confinement (strong magnetic fields) and by techniques that add cold electrons to the plasma. An additional important condition for obtaining mu lticharged ions is a low background gas pressure (10 -7 -10 -8 Torr) in the plasma chamber. In the ion beam line, charge exchange recomb ination processes should be avoided. In this subsection, a short historical review on basics and applications of ECR mu lticharged ion sources are described.

Basics of Multicharge d ECR Ion Sources
The main parts of an ECR ion source are shown in Fig. 10. There is a vacuu m p lasma chamber (p lasma tube), a gas feeding system, min imu m-B-field configuration (co mbination of solenoid magnets and hexapole permanent magnet), and the microwave system. A set of solenoid magnets either permanent magnets or solenoids produces an axial magnetic mirror field inside the plasma chamber. The necessary radial field gradient is generated by a mu ltipole permanent magnet (usually NdFeB). When electrons move in a magnetic field, they gyrate around the magnetic field lines due to the Lorentz force. The micro wave radiation is launched into the plasma chamber, and the electrons absorb energy fro m the electro magnetic wave if its frequency ω rf is equal to the gyration frequency ω ce of the electrons [27]: where e is the electronic charge, B is the magnetic flu x density and m e is the mass of the electron.

RF Coupling and Ionizati on Efficiency
In the ECRIS, the electrons are delivered by plas ma and not by a cathode; they are accelerated by electro magnetic waves at the frequency of the electron cyclotron resonance. The electro magnetic waves can be introduced into the plasma chamber (plasma tube) through coaxial lines, antennas, loops and vacuum-t ight dielectric windows. The choice depends on the frequency and the desired electromagnetic field pattern. Proper coupling of the RF power into the plasma in the ECR ion source is the most important factor in achieving high performance. Poor coupling of RF power to the plasma can result in undesirable effects as high reflected power, low p lasma density, unstable operation and poor performance. The production of mult icharged ions in an ECR ion source requires high microwave power to increase the plasma density, and low background gas pressure to reduce the charge exchange between ions and neutral particles. Once high microwave power is launched from the waveguide, it propagates into the plasma. An ECR zone is created when the magnetic field and the RF fields are superimposed and the electron cyclotron resonant frequency ω ce equals the resonant frequency ω rf of the RF applied. In this ECR zone, a co mponent of the electrical RF fields is perpendicular to the magnetic field and electrons crossing the zone are accelerated in circular o rbits. Du ring their acceleration, they collide with gas atoms. If these collisions allo w electrons to reach energies above the ionization energy of the gas atoms, then the ECR plas ma is ignited. The most efficient way for heating the plas ma in an ECR ion source is by injecting right-hand circularly polarized waves along the direction of the magnetic field. The electric field vector for a right-hand circularly polarized wave rotates clockwise in time along the direction of magnetic field and has a resonance at the electron cyclotron frequency ω ce which equals the resonant frequency ω r f of the RF applied. The d irection of rotation for the plane of polarizat ion for the right-hand circularly polarized wave is the same as the direction of gyration of the electrons. The electro magnetic wave looses energy by continuous acceleration of electrons and is therefore damped. The left-hand circularly polarized waves do not have a resonance with the electrons because they rotate in the opposite direction of the electron gyration.
The relation between the electro magnetic fields and the input power derived for a cylindrical cav ity is given by [28]: where P is the input power, Q an effective quality factor, and W the electromagnetic energy density. By integrating over the field vo lu me V, we obtain: where E, H are the electric and magnetic amplitudes of the electro magnetic wave, ε 0, µ 0 are the permittiv ity and permeab ility of free space, respectively and ω rf the frequency of the electromagnetic wave.
The electric field amp litude E is roughly given by: where G is a geometrical factor. The electric field amp litude E 0 in the empty cylindrical cavity of an ECRIS is [29]: where r and a are the radius and the length of the cavity, respectively. Microwave power can be coupled into the plasma until the plas ma density reaches the critical value of the electron density n e , where the plasma frequency ω p becomes equal to the excitation frequency ω rf and the electron cyclotron frequency ω ce . The plasma frequency is related to the critical plas ma density as [30]: Therefore, Fro m equ.13, it is possible to see that for a higher frequency at a higher electron density can be achieved, consequently a higher ionization efficiency. The ion plas ma frequency ω pi is given by: where q is the ion charge state, e is the electronic charge, n i is the plasma ion density, m i is the ionic mass.

Mini mum-B-fiel d
An important feature of ECR ion sources is their magnetic field structure. Th is structure is made up by the superposition of an axial field produced by a set of solenoid coils or permanent magnets and a rad ial field produced by a permanent magnetic mu ltipo le. Most ECRIS use min imu m-B-field geometry. In th is magnetic field structure, the ECR condition is fulfilled in the valley between the peaks of the magnetic field formed by the two solenoid coils. This form of magnetic structure does not stably confine the plasma if the magnetic field decreases in the radial direct ion. In o rder to secure a stable confinement, a mult ipole fields (octopoles, hexapoles and quadrupoles), have to be added (Fig.11).
Such mu ltipole fields provide radial confinement since they increase with distance from the axis. This magnetic confinement structure is called min imu m-B-structure, where the magnetic field is the s mallest in the center and increases in every d irection fro m this center. Such magnetic mu ltimirrors not only affect the ionization efficiency and thus the gas consumption, but also the ion lifetime. The better the confinement, the higher are the efficiencies of ionization and of production for highly charged ions. Usually, hexapole magnets are applied in ECRIS, because a higher order multipole has a larger loss surfaces at both ends usable for the ion ext raction. On the other hand, the loss area of the quadrupole is just a line at the end wh ich is not suitable for effective ion extraction. The region of higher magnetic field strength of an octopole is closer to the tube wall than that of a hexapole magnet. The magnetic mirro r structure for minimu m-B-configuration is principally characterized by the loss cone and the plasma pressure. The ratio of the maximu m magnetic field strength at the magnetic throats to the magnetic field strength at the center is called the mirro r rat io ( ). Figure 11(a). Loss surfaces of different multipoles: octoples, hexapoles and quadrupoles and corresponding radial fields Bradi al [29] Figure 11(b). Magnetic mirror structure [29]

Applicati ons of Multicharged ECR Ion Sources
Electron cyclotron resonance ion sources (ECRIS) can produce singly charged and mult icharged ions. Singly charged ECR ion sources have significant commercial applications. The performance of ECRIS has been continuously increased since their introduction by raising the magnetic field and the frequency of the RF generators. Large accelerators need higher charge state and higher ion currents fro m the ion sources. This demand can also be met by using ECR ion sources. Electron cyclotron resonance ion sources are used as injectors into linear accelerators, cyclotrons and Van-de-Graaff generators in nuclear and elementary particle physics. ECR ion sources deliver intense beams of multicharged ions for collision experiments and for investigations in surface physics. Also, ECR ion sources are now used as injectors for linear accelerators to deliver ion beams for treatment of cancerous tumors. Finally, microelectronic processing constitutes a field of application for ECRIS.

Properties of ECRIS for mul ticharged ions
Ion sources based on the electron cyclotron resonance (ECR) princip le have played an essential role in the advancement of ato mic and mo lecular science since their starting of operation because of their capabilit ies for generating mu lticharged ion beams. ECR ion sources have many advantages over more conventional arc ion sources including the following [31]: (1) the source has a long lifetime since there is no filament; (2) the source operates in stable mode over a wide pressure range which allows to use it as a source for production of intense multicharged ions (3) easy to maintain and operate. Electron cyclotron resonance ion sources were g radually imp roved and developed for different applications, starting with conventional (classical) ECR ion sources and nowadays including all-permanent magnet structures.
Classical ECR ion sources [32] utilize electro-magnetic coils for the axial field and permanent magnets for the radial mu ltipole field. The production of the axial field demands high power consumption. They produce highly charged ions and high current intensities especially at mediu m charge states. The next step of develop ment of ECR ion sources consisted in the superconducting ECR ion sources as a solution for reducing the huge power consumption of the classical ECR ion sources [33]. Ion sources of this kind had even better performance than the classical ones. Finally, ECR ion sources have been built exclusively with permanent magnets [34][35][36]. The advantages of an all-permanent magnet ECR ion source are: (1) simple power supply and cooling systems because of no electromagnetic coils (2) high performance for operation, (3) co mpact in total size. However, in co mparison with electro magnetic co ils the magnetic field is mo re difficult to adjust with respect to the plasma chamber.

Details on ECRIS Plasma Operation
In order to enhance the output of highly charged ions from an electron cyclotron resonance ion source (ECRIS), several techniques like wall coating, biased disk, electron gun have been proposed and are meanwhile employed as standard tools at most of the existing installat ions. Although the detailed mechanis ms are not clear, it has become evident that the additional inject ion of electrons into the plasma chamber of an ECRIS considerably imp roves its performances. Depending on the special conditions of the source these additional electrons can either co mpensate for losses of plasma electrons or even may change global plasma parameters (e.g. plasma potential) and hence positively influence the extraction at high rates of highly charged ions. The ext ractable output current of mu lt icharged ECRIS depends on three parameters governing the plasma configuration, which are the confining magnetic field, the neutral pressure and the micro wave power. In order to improve the output of highly charged ions in ECR ion sources, different techniques like wall coating, secondary electron emission, a biased electrode and finally gas mixing are applied.

Ion cooling by gas mixing
The so called gas mixing technique can help fo r enhancing the yields of highly charged ions in ECR ion sources [4,37]. For this technique, addition of some amount of cooling gas (lighter atoms) to the principal gas (heavier ato ms) does increase the beam currents of higher charge states. Moreover, optimization for high charge states requires the smallest possible amount of the injected principal gas. In this case, plasma is mainly co mposed of cooling gas ions with a small component of the principal gas. The cooling gas has always to be lighter than the principal gas.
For this technique, the addit ion of cooling gas to the principal source gas decreases the plasma temperature (ion cooling) and therefore increases the lifetime of the ions in the plasma which results in more successive-single ionization processes, which increases the yields of the mu lticharged ions. The light ions remove some energy fro m heavy ions in a short time and decrease the ion temperature. At the same time the light ions have lower charge and lower life time. They are lost fro m the source taking away the energy of heavy ions. The decreasing of heavy ion temperature causes the raising of heavy ion lifet imes and consequently the mean ion charge state.

Injection of cold electrons into the plasma tube
Supplying cold electrons along the main axis of the magnetic configuration is a necessary condition to obtain an electron density large enough for efficient ionization. Different techniques for supply of cold electrons to the ECRIS discharge are used to imp rove the ionizat ion efficiency and, consequently, the probability for production of mu lticharged ions either from internal or external electron sources. These cold electrons compensate for electron losses in an ECR plasma. Therefore, the equilib riu m values of the electron and ion densities become more equal, and increases the ion lifetime and consequently, the higher charge states. As external sources, low voltage electron guns [38] or p lasma cathodes [39] can be utilized. A lo w voltage electron gun is quite effective to in ject cold electrons directly into the plasma. However, the electron gun has a limited lifet ime due to filament erosion. With the plas ma cathode method, the potential difference produced between first and second stages of the ECR ion source ext racts electrons from the first into the second stage. Internal sources as negatively biased electrodes reduce the plasma electron losses and provide new electrons via secondary electron emission [40][41][42]. Wall coatings with a high y ield for secondary electrons on the ECRIS walls [4,43] have the same effect. Enhanced production of high charge state ions as a result of wall coatings has been experimentally observed for different coatings as silicon, thorium and alu min iu m o xide. All these materials have high secondary emission coefficients and can emit cold electrons into the plasma, by which means the yields of mu lticharged ions will be increased. A negatively biased disk has been successfully used in many cases to increase the beam intensity of mult icharged ions [44][45][46]. The increase of highly charged ion current by insertion of a negatively b iased electrode is explained in terms of increasing electron density in ECR p lasma due to injection of cold secondary electrons fro m this electrode to the d ischarge region. This leads to increase the density of highly charged ions in plasma. Biased electrodes can improve the ion beam intensity when operated at floating potential. In this case, optimizing the properties of the electrodes (position, dimension, shape and material) are important.

Electron Beam Ion Sources (EBIS)
The electron beam ion source (EBIS) [8] is a relatively new type of ion source for production of mu lt iply charged ions including bare nuclei of heavy elements. The main physical process used in the EBIS to produce highly charged ions is ionization by electron impact [47]. The field of applications of EBIS becomes larger and larger as; plasma physics, nuclear physics, surface physics and atomic physics [4]. The princip le is illustrated in Fig. 12. An electron gun launches a small d iameter electron beam down the axis of a magnetic solenoid about 1 m long. The potential along the axis is defined by a number of hollow cylindrical drift tubes. The ions are contained rad ially in the electrostatic potential well o f the electron beam, and axially by positive potential barriers on the end drift tubes as shown in the potential distribution. During a short in jection period, the desired number of ions is accu mulated in the well. Then the potential d istribution is switched to the ionizat ion mode, in which the first barrier is moved downstream to prevent additional lo w charge state ions from entering the potential well. The ions reach progressively higher charge states as the containment continues. The electron beam ion sources can be divided into two types with respect to the mode of an electron beam fo rmation and focusing [4]: (1) Sources with the electron gun fu lly or partially immersed in the magnetic field of the solenoid (IGEBIS); (2) Sources with an external electron gun that is fu lly shielded fro m magnetic field (EGEBIS). At present, the main reg ions of applications for the EBIS used are atomic physics, plasma physics and synchrotron accelerators. These applications are connected with increasing the highly charged ions for this type of ion sources.

Laser Beam Ion Sources (LBIS)
The laser induced plasma fro m a solid target is based on the use of powerful laser (power 10 10 -10 13 W/cm) p roducing a short beam in a nanosecond range (Fig.13). This powerful laser will be focused on a target made fro m (Li, LiF, C, Zi, and Ta). Ions in the plasma have a mixture of charge states and energies and the major problem in the laser ion source is the extraction of the desired ion species as a beam of reasonable characteristics. Principle of operation of the laser ion source is based on plasma generation by a laser beam focused by a mirror system (lens) on a solid movable target. The focused laser light is used to evaporate particles fro m a target which is made out of the material to be ionized. The electrons of the plasma, which is generated during the evaporation process, are heated by the laser radiation to temperatures up to several hundreds of eV. The ions are ionized due to electron-ion collisions. The temperature of the plasma and the final ion charge state distribution are strongly depend on the laser power density on the target. The first operation of a laser ion source based on Nd-glass on a cyclotron machine was reported by Ananin [48]: Laser ion sources for Van-de-Graaf accelerators have been emp loyed at the Technical University of Munich [4] and at ITEP-Moscow[4]:

Conclusions
In the present work, different types of mult icharged ion sources with their applicat ions have discussed and reviewed. In all types of multicharged ion sources, the ions are produced by various types of gas discharge including electron collisions with gas particles. Criteria for production of multicharged ion beams are studied. In further consequence, our research work was quickly described, reviewed and gave some results showing the importance in some areas of applications.