Hard Tube Pulser Research Articles

High voltage pulser with a fast fall-time for plasma immersion ion implantation

A novel high voltage (HV) modulator that offers a short fall time to minimize sputtering effects and allow more precise control of the incident ion fluence in plasma immersion ion implantation is described. The use of 36 insulated-gate bipolar transistors in the 30 kV hard-tube pulser reduces the HV fall time to 3.5 μs, compared to a fall time of 80 μs if a pull-down resister is used. The voltage balance is achieved by a voltage-balancing resistor, clamped capacitance, and the synchronization of drive signals. Compared to the traditional method employing a pull-down resister or an additional hard tube, our design consumes less power and is more economical and reliable.

Pulsed power modulators for surface treatment by plasma immersion ion implantation

The treatment of surfaces by plasma immersion ion implantation requires pulsed power modulators to provide negative high voltage pulses. To achieve this requirement, we have developed three basic circuit configurations in our laboratory: pulse forming network (PFN), hard-tube pulser (HT) and Blumlein line. In this paper we discuss these three types of circuit topologies.As experimental results, first we present the voltage/current characteristic waveforms of PFN and HT pulsers in the PIII treatment of different materials (aluminum, silicon and stainless steel) as well we describe the surface characterization of the materials thereof treated.And finally,we show recent high voltage tests of a high voltage Blumlein pulser (150kV/300A/1mus) to be used in surface treatments of polymers and aluminum alloys.

Metal-arc plasma ion implantation in a straight magnetic filter

Ion implantation is a well-known technique used in surface treatment of materials. During the 1980s, ion implantation using a sample immersed in an ionized gaseous medium (known as plasma immersion ion implantation) revealed to be an alternative to the conventional ion beam implantation. Development of this nonconventional surface processing using metallic ion species increased significantly when metal vacuum arcs began to be used as ion sources. In this paper, we present the experimental results obtained on Si wafers used as test targets, using metallic arc ion implantation. High-density plasmas (up to 10/sup 19/ m/sup -3/) made of aluminum vacuum arcs were used for the metallic implantation process. Arc currents of 200-700 A and 16 ms duration were pulsed every 30 s, and samples were biased from 2 kV to 10 kV with 50 /spl mu/s pulses at 700 Hz, using a hard tube pulser. A straight magnetic filter was used to clean the plasma from macroparticle contaminants, with complete filtering being achieved in samples oriented so that their surfaces were parallel to the plasma stream. This is an interesting alternative to 90/spl deg/ curved magnetic duct filters usually used for this purpose. High-resolution X-ray diffraction analysis shows that aluminum was successfully implanted.

Plasma immersion ion implantation of nitrogen in Si: formation of SiO 2, Si 3N 4 and stressed layers under thermal and sputtering effects

Plasma immersion ion implantation (PIII) of nitrogen in silicon (Si) wafers was carried out using a dc glow discharge plasma source and a hard tube pulser. Ion irradiation times ranging from 3 to 60 min were used to accumulate different doses. Surface analysis of these samples was carried out by Auger electron spectroscopy (AES), revealing a high atomic concentration of nitrogen (up to 60%) in the as-implanted Si wafer, besides the presence of different impurities as oxygen and carbon in significant quantities. Depth profiles of these elements were obtained as well as of compound species as SiO 2 and Si 3N 4, using this high-energy resolution AES. Comparing the concentration profiles of implanted nitrogen in Si and the corresponding retained doses in these samples, it was possible to understand the thermal and sputtering effects in our present PIII experiment. High-resolution XRD results corroborate the formation of highly stressed layers in the as-implanted substrates. These experimental results are compared to simulations obtained by TRIDYN code.

Plasma immersion ion implantation experiments at the Instituto Nacional de Pesquisas Espaciais (INPE), Brazil

Historical perspective of the development of PIII devices at the Instituto Nacional de Pesquisas Espaciais (INPE) is given, together with the description of the present system under operation and our overall results on this three-dimensional implantation research. Starting with an ignitron switched pulser (1 pulse per 3 min) and an intermittent microwave plasma, we improved our PIII system developing a pulse forming network (PFN) based pulser (20 Hz), 2 years later. We also improved our plasma source towards a DC, highly stable, medium density glow discharge system. A much faster hard tube pulser was recently incorporated to our PIII system (670 Hz) allowing us to achieve good implantation results in different materials. Presently, we are testing a recently purchased RUP-4 commercial pulser to obtain arc prevented, 1.1 kHz, square pulses for new experiments in this active field of PIII research.

Plasma immersion ion implantation using a glow discharge source with controlled plasma potential

A DC glow discharge plasma source was used in a plasma immersion ion implantation (PIII) experiment providing nitrogen plasmas with densities of 1–3 ×10 10 cm −3 and temperatures of 5–10 eV. Nitrogen ions were extracted from these plasmas and implanted in a variety of immersed samples (Al 5040, SS 304, Si) using repetitive high voltage pulses from two types of sources: PFN pulser and a hard tube pulser. Due to the high potential present in our plasma (350 V), a significant sputter etching of the samples surface occurred at long irradiation times. An electron shower source was used to lower this potential allowing its control from 0 to 350 V. Operating the plasma source at potentials below 70 V reduced the sputtering to negligible levels and a retained dose of 1.5×10 17 cm −2 was achieved in a silicon surface, after irradiation of 1500 min. For plasma with potential of 350 V (no electron shower), the retained doses in Al 5040 and SS 304 samples were smaller than 5×10 16 cm −2 , for same plasma and pulser conditions (but 2500 min irradiation), confirming the deleterious effects of sputtering measured in Si samples. Upon using the higher repetition rate pulser, the treatment time was reduced by a factor of 700, thus easing considerably the sputtering problem.

High Power Switches for Ion Induction Linacs

The success of linear induction ion accelerators for accelerator inertial fusion (AIF) applications depends largely on innovations in pulsed power technology. There are tight constraints on the accuracy of accelerating voltage waveforms to maintain a low momentum spread. Furthermore, the non-relativistic ion beams may be subject to a klystronlike interaction with the accelerating cavities, leading to enhanced momentum spread. In this paper, we describe a novel high power switch with a demonstrated ability to interrupt 300 A at 20 kV in less than 60 ns. The switch may allow the replacement of pulse modulators in linear induction accelerators with hard tube pulsers. A power system based on a hard tube pulser could solve the longitudinal instability problem while maintaining high energy transfer efficiency. The problem of longitudinal beam control in ion induction linacs is reviewed in Section 2. Section 3 describes the principles of the plasma flow switch. Experimental results are summarized in Section 4.

Generation of High Intensity Beams of Nanosecond Pulse Duration by Electron Linacs

Acceleration of electron beams with a very short pulse duration and high peak intensity is achieved in electron linacs. As pulse generators for very short pulse duration, a coaxial line-type pulser, a hard-tube pulser and a pulse sharpener are newly developed which can produce pulses of about 5 nanoseconds in pulse duration and about a few thousands volts in amplitude in 50-ohm load. In Tohoku linac, peak intensity of 1.3 amperes is obtained with pulse duration of 7 nanoseconds and energy of 75 MeV, while in Mitsubishi linac, 2.0 amperes, 10 nanoseconds and 6.4 MeV, respectively. Their results agree with Leiss theory. As a parameter of transient beam loading, the ratios of the energy contained in a pulsed beam to the stored energy in the accelerating structure and of the peak beam power to the peak input RF power are presented.