Compact Electron Cyclotron Resonance Ion Research Articles

Design of Compact All-Permanent Magnet Electron Cyclotron Resonance (ECR) Ion Sources for Atomic Physics Experiments

In order to improve the performance of existing ECR ion sources, different magnetic field configurations and their influence on the extracted ion currents have been investigated. Furthermore the source performances were found to be strongly dependent on the microwave frequency. At optimum frequency the microwave power requirements could be significantly reduced allowing the use of a low-power solid-state microwave system.

Development of the compact electron cyclotron resonance ion source for heavy-ion therapy

Carbon–ion cancer treatment is successfully being made at the Heavy Ion Medical Accelerator in Chiba (HIMAC). Design philosophy for the ion sources for medical facilities are as follows: (1) sufficient beam intensity, a few hundred e μA; (2) long lifetime with good stability; (3) easy operation and easy maintenance; and (4) compactness. In order to develop such source for future heavy-ion facilities, we have tested compact electron cyclotron resonance (ECR) ion sources using permanent magnets both for axial and radial confinement of hot electrons. Since the yield of C2+ ion in the first developed source (2.45 GHz ECR) was 15 e μA and far below the medical requirement (∼150 e μA for the HIMAC), a new source has been proposed, having a frequency of 10 GHz. The extracted intensity of C4+ (and C2+) ions is expected to be higher than 200 e μA.

Beam extraction from a compact Ku-band electron cyclotron resonance ion source with double resonance modes

Beam extraction tests were carried out using a new compact Ku-band electron cyclotron resonance (ECR) ion source. In the case of a single rf frequency operation, a B2 zone can contribute for increase of single and low charged state ion beams when the gas flow rate is relatively higher than that for the basic ECR mode. The scheme seems, however, not so effective for the production of multicharged state ion beams. A double frequency heating (12 and 14 GHz) is, on the other hand, effective for increase of extracted ion current when the rf power is injected into the chamber from both the axial and the radial ports, as succeeded at the LBL experiment.

Production of multiply charged metallic ions by compact electron cyclotron resonance ion source with SF6 plasma

A new technique has been developed to introduce very refractory materials into an electron cyclotron resonance ion source by fluorinating them with SF6 plasma, and we succeeded in generating multiply charged ions of B, Mo, Nb, W, and Ta. A metallic sample is set inside the plasma chamber with SF6 plasma, in which the metallic fluoride is generated with sufficiently high vapor pressure by a chemical reaction between fluorine and the metal. The gaseous metallic fluoride is decomposed into fluorine and metal, which are ionized by the SF6 plasma. Generally, ion sources are corroded by gases of fluorine and fluoride, but utilization of SF6 gas reduces the corrosion and allows stable operation for a long time.

Manufacture of a compact Ku-band electron cyclotron resonance ion source with two resonance zones and variable frequency

A compact ECR ion source working at a Ku band has been manufactured for the production of both low and multiple charged ions. This source can be formed for both the ordinal ECR zone and second Bernstein resonance zone with a half Becr field. The B minimum field configuration is realized by the use of permanent magnets and its axial mirror field can be adjusted within ±0.03 T by a small auxiliary solenoid. Microwave power can be injected from both axial and radial ports. Effective power of 200–250 W can be supplied to the source with a continuously variable frequency in the range of 12.0–14.5 GHz and with a variable pulse mode. The outer dimension of the source is φ180×230 and its total weight is just 30 kg. The design, manufacture and results of the preliminary test are reported.

Development of a 2.45 GHz electron cyclotron resonance ion source for ion-implanter application

A compact electron cyclotron resonance (ECR) ion source has been designed at 2.45 GHz microwave frequency for ion implanter and is being tested. The design is based on a straightforward application of the method adopted for conventional ECR ion sources for multiply charged ions: a closed ECR surface completely contained in the plasma chamber. Initial tests have shown a promising indication: a total current of about 7 mA of Ar ions has been extracted at 25 kV extraction voltage. Design features and preliminary performance are reported.

Modeling the electron heating in a compact electron cyclotron resonance ion source

An electromagnetic particle-in-cell (PIC) model and a guiding-center particle model are developed and used to model a compact electron cyclotron resonance (ECR) plasma source. The finite-difference time-domain technique is used to model the microwave fields which excite the plasma at 2.45 GHz. The PIC technique is used to model the dynamics of the electrons in the plasma. The electromagnetic fields and the plasma dynamics are solved in a self-consistent manner. The ECR heated electrons are confined to magnetic field lines and subsequently make multiple passes through ECR regions experiencing both increases and decreases in energy. The distribution function of these energy changes is determined from the electromagnetic PIC model and used in a guiding-center particle model. The longer time scale collisional phenomenon in the plasma is modeled using this guiding-center particle model. A compact ECR plasma source used for the generation of ions for materials processing is simulated. This source has a plasma size of 3.6 cm in diameter and 3 cm in height.

A compact electron cyclotron resonance source for 200-2000 eV ion beams

Ion-beam-sputtered and -assisted deposition technologies need medium energy, 100-2000 eV, ion beams of current density 1-3 mA cm-2, operated in a reactive and corrosive gas environment. We designed, built and characterized a compact electron cyclotron resonance ion beam source generating 2 cm diameter ion beams with currents of 2-8 mA and energy 200-1700 eV. Continuous wave microwave power (2.45 GHz, P1=0-300 W) was introduced into a 5 cm diameter plasma chamber via a 50 omega cable and a half-wavelength antenna. A ceramic cup sealed the plasma chamber and separated the antenna from the plasma. Boron nitride spacers electrically isolated the high-voltage plasma from the earthed chamber walls. Two Sm-Co ring-shaped magnets formed a circular electron cyclotron resonance surface in the plasma generation zone near the microwave introduction point. An external magnetic coil generated in the chamber an axial magnetic field, which helped to ignite the plasma and to control the plasma shape and density. The ignition microwave power was 5-40 W, with operational (argon) pressures in the beam line of 2*10-5 to 2*10-4 Torr. An argon ion beam was extracted using two multi-aperture pyrolitic graphite grids: a positive plasma grid and a negative electron suppression grid. The ion beam current increased linearly with microwave power; the beam half-angle divergence near the target was alpha /2=4-6.

A very compact electron cyclotron resonance ion source

A new electron cyclotron resonance (ECR) ion source has been developed in the laboratory. The ECR condition at 2.45 GHz is obtained in a multicusp arrangement using a set of four parallelepiped-shaped SmCo magnets regularly spaced around a cylindrical ionization chamber 50 mm in diameter and 50 mm in height. The electromagnetic cavity is made of a shielded quarter-wavelength Lecher line resonator coaxially coupled to the microwave generator through an excitation loop antenna and a SMA-type connector. The extracted argon ion beam current density has been measured for different excitation modes fixed by the loop antenna orientation. A current density of 1 mA/cm2 has been reached with an incident microwave power of 110 W and a chamber pressure of 9×10−3 mbar. The small dimensions of this ion source and its performance allow to use it not only in applications such as ion beam processing and cleaning or surface treatments in advanced microelectronics, but also as a neutralizer for ion deposition applications.

Compact electron cyclotron resonance ion source with a permanent magnet

A new compact electron cyclotron resonance ion source that uses a magnetic mirror field and a divergent magnetic field to generate high-density and multicharged ions has been developed. A cylindrical permanent magnet is utilized to produce those magnetic fields. Excited electrons are effectively confined in the mirror field near the exit of the plasma chamber, making it possible to generate high-density and multicharged ions. The generated ions are transported near the center axis and a plasma stream is formed along the divergent magnetic field. A plasma chamber with a diameter 4 cm smaller than the cutoff size (7.2 cm for 2.45 GHz) and a two-layer microwave window are used to fashion the compact structure and to couple microwaves with high-density plasma. The plasma stream is highly directional (plasma stream diameter ∼1.8 cm), and high ion saturation current densities of 18 mA/cm2 (Ar gas) are achieved 12 cm downstream at a low microwave power of 200 W. Moreover, a high Ar2+/(Ar++Ar2+) ratio of above 50% is obtained.

Commissioning of the ECR ion source Alice

The ion source Alice, a component of the ALPI linac phase 3, is now in operation. Alice is a 14.4 GHz, very compact electron cyclotron resonance ion source, and a 24-piece NdFeB hexapole, a removable plasma chamber and a carefully designed extractor are some of its noteworthy features. After switching on the plasma in late December 1991, tests began in February 1992. The new plasma chamber cooling circuit and the regulation of the gas flow inside the plasma chamber are described. First performances of the source with gas mixtures including helium, nitrogen, oxygen, argon and krypton, are reported and discussed.

Compact electron cyclotron resonance ion source with high density plasma

A compact electron cyclotron resonance (ECR) ion source has been developed that has an outer diameter of 11 cm and generates a high-density plasma (1×1013 cm−3, O2 gas) at low microwave power (200 W). The source incorporates a plasma chamber with a 5-cm diam., which is smaller than the cutoff size (7.2 cm) as determined by the microwave frequency (2.45 GHz). To accommodate this chamber size, the waveguide for coupling microwaves into the chamber through a vacuum window was miniaturized by filling it with dielectric material. A plasma density of 4×1011 cm−3 was obtained by using a BN plate as the microwave window. Moreover, the coupling efficiency of the microwaves to high-density plasma was enhanced by choosing alumina with a high dielectric constant as the window. With this window, a much higher plasma density of 1×1013 cm−3 was achieved at a low microwave power of 200 W. A coaxial cable can be utilized at this power for easily adapting this compact ECR source to vacuum systems.

Production of H− in a new type compact electron cyclotron resonance ion source

A new type compact electron cyclotron resonance ion source is constituted by using permanent magnets and a 2.45-GHz microwave. A cylindrical vessel of Pyrex glass is mounted inside a TE11-mode waveguide. A cusp field is formed in the vessel by two water-cooled permanent magnets, the one being a SmCo cylinder and the other being a ferrite doughnut-shaped ring. The cusp field is modified from the conventional one in that the field at the upper part serves commonly as a wave radiator and a plasma confinement space. As a result, an overdense plasma can be realized with typical parameters Ne=2.5×1011 cm−3 and Te=3.5 eV at 5×10−4 Torr. The field at the lower section is opened toward the bottom extraction part to allow a downward drift of the produced plasma. This facilitates the extraction of the H− beam from the bottom electrode system. The beam current density showed a maximum value of 0.5 mA cm−2 at 4×10−4 Torr. The result is compared with the calculation by using rate equations.

Compact ECR ion sources with permanent magnets in a cusp geometry and in a magnetic mirror structure

Two compact Electron Cyclotron Resonance (ECR) ion sources exclusively built with permanent magnets in a cusp geometry and in a magnetic mirror structure are compared. The microwave discharge power is 60–120 W at a frequency of 2.45 GHz. The cusp structure enables to produce an argon-ion current of 1.5 mA at an extraction voltage of 2 kV with an aperture of 4 mm diameter at a gas pressure of 10−3 mbar. The ion source built with a magnetic mirror operates at lower pressure (10−4 mbar) with an ion current density of 5 mA/cm2 (the total current is 0.6 mA). Spectroscopic measurements of photons emitted by an oxygen plasma enable us to detect multicharged ions such as O4+ and O5+ ions. With these two magnetic structures, sharp variations of current density with gas flow rates are observed and the different ranges of operating pressure are presented.