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In this paper, the power electronics for a sulfur plasma lamp is presented. The plasma is obtained by heating the sulfur using microwaves generated by a magnetron. A custom high voltage (5 kV) power supply has been developed to supply the magnetron. To protect the bulb from melting, a suitable modulation technique has been implemented.
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Citations
... The plasma sulfur tube is a plasma light bulb that is produced by microwave [1]. A magnetron tube is a microwave generator used to supply the energy needed to produce plasma from sulfur gas. ...
This paper presents a new method for driving the magnetron for a sulfur plasma tube using the two‐switch forward converter structure with a phase‐shifting active clamp (1000±40 W, 285 mA, 4 kV). Depending on the output voltage level required, the magnetron driver circuit is boosted and insulated and also has high gain. The use of the two‐switch forward converter reduces the transistor voltage stress. In addition, applying the clamp structure balances the magnetization current. Besides, by controlling the phase shift of the clamp transistor, while maintaining the magnetic current balance of the power transformer, the duty cycle of the main transistors can be increased. This allows more voltage level transfer to the secondary winding of the transformer. Therefore, with a fixed transformer core, more voltage transmission is possible in comparison with a conventional forward converter.
Moreover, using the PFC converter improves the power factor and stabilizes the DC‐link voltage. The magnetron driver circuit provides a maximum power of 1 kW with an average power of 125–250 W by adjusting the converter's active time under minimum loss conditions. The magnetron driver circuit provided is validated by the simulation and experimental results.
... We have modified an off-the-shelf plasma lamp to allow pulsing of the microwave power supply 13,14 at frequencies between 5 and 75 kHz. The periodic heating excites sound waves inside the bulb 15,16 that modulate the light emission. ...
Acoustics is used to probe the temperature profile within a sulfur plasma lamp. A spherically symmetric temperature profile is assumed that drops with the square of the radius, consistent with a constant volumetric heating model. Acoustic resonance frequencies are calculated exactly in the case of an ideal gas. Experimental measurement of a few resonant frequencies allows determination of the temperature profile curvature. This technique can be viewed as an extension of ultrasonic resonant spectroscopy to systems that are highly non-uniform due to off-equilibrium energy flow.
... from a conventional magnetron heat the sulfur to a final molecular density of ∼2×10 19 cm −3 and ∼10 −5 ionization fraction [15,16]. To drive acoustic resonances within the bulb, our magnetron power supply has been modified to be able to pulse at frequencies between 5 and 100 kHz, and 5-95% duty cycle, according to a design by Gavin et al. [17,18]. We have described our waveguide circuit elsewhere [19]. ...
Sound can hold partially ionized sulfur at the center of a spherical bulb. We use the sulfur plasma itself to drive a 180 dB re 20 μPa sound wave by periodically heating it with microwave pulses at a frequency that matches the lowest order, spherically symmetric, acoustic resonance of the bulb. To clarify the trapping mechanism, we generalize acoustic radiation pressure theory to include gaseous inhomogeneities and find an interaction of high-amplitude sound with density gradients in the gas through which it propagates. This is the pycnoclinic acoustic force (PAF). Though generated by rapidly oscillating sound waves, it has a finite time average and manipulates the plasma through density gradients at its boundary. The PAF is essential for the description of the trap holding a plasma against its own buoyancy as well as understanding convection in the region outside the plasma. It has implications for pulse tubes, thermoacoustic engines, thermal vibrational convection in microgravity, combustion in the presence of sound, and the modeling of Cepheid variable stars.
... It consists of a magnetron, an isolator, a directional coupler, a three-stub tuner, an aperture-coupled mesh cavity containing the sulfur bulb, and a sliding short. The magnetron high-voltage supply was purchased from the Institut d'Energie et Systemes Electriques and is described by Gavin et al. [14]. It provides pulsed power at a variable frequency of 1-100 kHz and a duty cycle between 10% and 90% for the purpose studying the plasma acoustic response. ...
Sulfur plasma lamps are a convenient, table-top system for the study of acoustics in dense, weakly ionized plasmas. Herein, we describe the construction and tuning of a passive waveguide circuit capable of igniting and sustaining the sulfur plasma and exciting acoustic modes within it.
... In some scientific applications such as tube power supplies (Magnetrons, gyrotrons, klystrons, etc,) high voltage and high dynamic power supplies may be required [1]- [3]. In [2], for instance, short pulses are needed to modulate the RF heating power for plasma stabilization. ...
In this paper, a high voltage power supply based on an asymmetric multilevel cascaded bridge converter is presented. The required power supply shall be able to reach output voltages up to 30kV with rising and falling times shorter than 10 microseconds. Each module of the converter is supplied by an insulated dual bridge DC/DC converter allowing an independent DC-link voltage control with bidirectional capability. In order to validate the principle, a small scale prototype has been successfully built and tested.
This paper presents a new driving method for a sulfur plasma lamp in low-power applications. The newly developed magnetron power supply (MPS) is a series-resonance type with a full-bridge topology controlled by the phase shift to track the beam current of the magnetron. To drive the sulfur plasma lamp optimally, the MPS should: 1) provide peak power above a discharge condition to excite the sulfur plasma lamp, and 2) allow average power control of the light dimmer while satisfying condition 1. The newly developed driving method uses the burst mode, which enables both peak and average power controls to satisfy these conditions. Furthermore, a magnetizing current offset balancer is developed; it guarantees zero-voltage switching of all field-effect transistors, although the MPS operates in the burst mode. Thus, the proposed method provides easy lighting and relighting under optimized conditions with high efficiency. The power of the MPS delivered by the proposed method reached 1.6 kW with variable average power of 200 ∼ 400 W by adjusting burst-on time proportionally. Experimental results proved the feasibility of the proposed driving method.
In this paper, the power electronic for an innovating pasteurization technology is presented. A specific high AC voltage, 120kV at a frequency as high as 800kHz, has to be generated in order to apply an alternating electrical field of 3kV/cm through the liquid.
The high voltage generator is based on a modular approach. The module’s inputs are paralleled on a DC voltage, while outputs are connected in series to generate the high AC voltage. The modules are made with an H-bridge and a transformer providing the required insulation. The system has been designed to obtain the simplest and most reliable connections.
By controlling in real time the number of operating modules, the output voltage of the entire system can be quickly changed. With an accurate model of the system, the output voltage measurement is not necessary and permits to avoid complex and expensive sensors.
The electronics have been build and tested. However, due to some air breakdown in high voltage inductances, a reduced voltage of 64kV @ 820kHz has been reached. The system optimization is foreseen for further research activities.
