H. Klein

Four-rod-λ/2-RFQ for light ion acceleration☆

Abstract A simple type of RFQ structure with circular rods as electrodes has been developed in Frankfurt. The improved design uses a linear arrangement of supporting stems on a massive common bar. This linear rf structure consists of a chain of λ/2-line pairs and leads to an advantageously simple but nonetheless effective RFQ structure. With this stable cheap type of RFQ resonator preaccelerator prototypes have been built for light ions. New results of electrode and structure optimization and beam measurements are presented.

Matching of a cylindrical ion beam to a periodic quadrupole channel

Abstract A procedure to match a cylindrically symmetric ion beam to a periodic electrostatic quadrupole channel is described. He + beams are extracted from a plasma source with a voltage of 40 kV. Behind the ion source the beam current and emittance are measured. The extracted beam current is variable from 1 to 20 mA, while the measured emittance is 10–20 π mm mrad. For a chosen zero-current phase advance per cell μ 0 in the focusing channel the so-called periodic solution is calculated for the measured current and emittance. μ 0 is varied between 43° and 114°. The model, which is used for the calculations, is based on the Kapchinsky-Vladimir-sky equations. The quadrupole lens forces are calculated separately by solving the Laplace equation in 2 dimensions. Furthermore, the voltages on the first five quadrupole singlet lenses, which adapt the extracted beam to the periodic solution, are determined. The beam current and emittance are again measured after the sixth quadrupole singlet lens, which is the first lens of the periodic channel. These measured values are compared with the calculated beam parameters. A reasonable agreement is found.

Multichannel acceleration of intense, low-energy ion beams

We present measurements on multichannel acceleration of intense, low‐energy ion beams with a multiple electrostatic quadrupole array linear accelerator. The beam properties are investigated for different transverse and longitudinal focusing strengths, which can be adjusted independently in the accelerator. A maximum He+ ion current of four times 2 mA has been accelerated from 40 to 115 keV with an acceleration efficiency of 50%. Measurements and computer simulations suggest that the current is limited by transverse fields and by mismatch and misalignment of the beams, whereas longitudinal fields are of minor importance. The energy spread in the bunches is roughly three times the gap voltage.

High current ion implantation by plasma immersion technique

Abstract Plasma immersion ion implantation (PIII) is a novel technique which is under investigation at several laboratories. In this paper we present a short review on existing experiments and work which is done at the Frankfurt PIII experiment.

Influence of plasma density and plasma sheath dynamics on the ion implantation by plasma immersion technique

Abstract Plasma immersion ion implantation (PIII) is a new technique for surface modifications of materials. In contrast to conventional ion implantation techniques the target is surrounded by the plasma and then pulse biased to high negative voltages. The implantation dose and homogeneity are essentially dependent on plasma density and plasma sheath dynamics. In this paper we present measurements on plasma density and sheath expansion. The plasma is generated in a rf ion source with inductive coupling (13.56 MHz) and diffuses into the target processing chamber. Carbon targets are implanted with Ar ions and analysed by RBS analysis.

Sputter and diffusion processes in a plasma immersion device

Abstract Plasma immersion ion implantation (PIII) is a technique for surface modification. In contrast to conventional ion implantation techniques the target is surrounded by plasma and then pulse biased to high negative voltages. In our experiment the plasma is generated in a radio frequency ion source with inductive coupling (13.56 MHz) and diffuses into the target processing chamber. In this paper we report on the measurements of surface sputtering occurring during oxygen and argon implantation into silicon targets. Surface sputtering accounts for the dose limitation of the implanted ions. By combining vapor-deposition of neutral atoms with implantation and diffusion we obtained layers of stoichiometric silicon and oxygen ratio with thicknesses of > 300 nm.

Design study of high energy, high current rf accelerators for ion implantation

Abstract Ion implantation is of great importance in semiconductor device fabrication. Due to the increasing interest of the microelectronic industry in the implantation of ions in the MeV energy range, high energy beams are required. Furthermore, for several applications the implanted dose is as high as some 1018 ions/cm2, which implies that high currents are needed also. For both requirements the rf linac is well suited. The presented design studies are based on new linac structures (RFQ, MEQALAC, Spiral Loaded Cavity), which fulfill the specific demands of various applications. The discussed systems cover a current range from 1 to 150 mA and an energy range from 0.3 to 6 MeV for ion masses between 10 and 133.

Simultaneous transport of N+ and N2+ ions through a periodic focusing quadrupole channel

Abstract The transport of a mixed beam containing N+ and N2+ ions through a periodic focusing electrostatic quadrupole structure is investigated for 20 and 40 keV beam energy and for a wide range of the zero-current phase advance per cell. The current limit for a mixed beam has been derived by means of the Kapchinski-Vladimirski equations and the matrix formalism. Both the theory and experimental results show that ion beams which contain various ion species are transported in essentially the same way as ion beams which contain only one ion species. The dependence of the current limit on the ion mass and energy, as predicted by the theory, is encountered experimentally. For high injected currents the maximum transmission, which is 85%, is reached for a phase advance per cell of 60°–84°, independent of the particle mass and energy.

Beam diagnostics using an emittance measurement device

Abstract For beam diagnostics aside from Faraday cups for current measurements and analysing magnets for the determination of beam composition and energy the most important tool is an emittance measurement device. With such a system the distribution of the beam particles in phase-space can be determined. This yields information not only on the position of the particles but also on their angle with respect to the beam axis. There are different kinds of emittance measurement devices using either circular holes or slits for separation of part of the beam. The second method (slit-slit measurement), though important for the determination of the rms-emittance, has the disadvantage of integrating over the y - and y ′-coordinate (measurement in xx ′-plane assumed). This leads to different emittance diagrams than point-point measurements, since in xx ′-plane for each two corresponding points of rr ′-plane there exists a connecting line. With regard to beam aberrations this makes xx ′-emittances harder to interpret. In this paper the two kinds of emittance diagrams are discussed. Additionally the influence of the slit height on the xx ′-emittance is considered. The analytical results are compared to experimental measurements in rr ′-, rx ′- and xx ′-phase-space.

Comparison of two types of low-ß RF linacs: MEQALAC and RFQ

Abstract The current limit and the power consumption of a Multiple Electrostatic Quadrupole Array Linear Accelerator (MEQALAC) and a Radio Frequency Quadrupole (RFQ) accelerator are compared theoretically. Design studies are presented for 1 MeV, 24 mA N + accelerators for ion-implantation purposes and for 1.5 MeV, 100 mA D − accelerators. The latter are specified to be used for fusion plasma diagnostics.