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Mar 2001

Volume 72, Issue 3, pp. 1613-1923

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back to top ELECTRONICS; ELECTROMAGNETIC TECHNOLOGY; MICROWAVES

On 30 MHz TE11 mode piston attenuator

R. Swarup, J. R. Anand, and P. S. Negi

Rev. Sci. Instrum. 72, 1858 (2001); http://dx.doi.org/10.1063/1.1344173 (4 pages)

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A precision 30 MHz TE11 mode waveguide below cut-off piston attenuator has been designed for 0–100 dB attenuation range to serve as transfer standard of attenuation. The attenuator has been fabricated using a precision cylindrical copper waveguide and resonant inductive antennas with type-N connector at its input and output ports. The 30 MHz matched antennas have been incorporated in the cylindrical waveguide in such a manner that one serves as fixed transmitter and the other as moveable receiver for changing the attenuation. A Faraday screen type mode filter has also been fabricated to attenuate the amplitude of unwanted TM01 mode to an attenuation level of 60 dB. The piston attenuator has approximately 20 dB insertion loss and has been calibrated in steps of 10 dB over the 0–60 dB range. The results were found to lie within ±0.01 dB/10 dB. © 2001 American Institute of Physics.
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84.40.Az Waveguides, transmission lines, striplines
06.20.F- Units and standards
84.37.+q Measurements in electric variables (including voltage, current, resistance, capacitance, inductance, impedance, and admittance, etc.)
84.40.Ba Antennas: theory, components and accessories

Development of a Blumlein based on helical line storage elements

V. P. Singal, B. S. Narayan, K. Nanu, and P. H. Ron

Rev. Sci. Instrum. 72, 1862 (2001); http://dx.doi.org/10.1063/1.1344597 (7 pages) | Cited 3 times

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A Blumlein based on helical line storage elements was conceived and developed for generation of a rectangular pulse of 150 kV, 5 μs duration and which can drive a load of about 1 kΩ impedance. The helical line consisting of an aluminum tube of 750 mm length and 100 mm diam, wound with mylar film insulation to withstand 200 kV and then wound with copper wire was built and tested in our laboratory. It has a capacitance of 1.2 nF and has a characteristic impedance of 2 kΩ. The pulse generator built here, uses ten such coils in Blumlein configuration with five elements in parallel in each section giving total capacitance of about 10 nF. It has the advantages of compactness, simplicity, low cost, reliability, and high performance towards good flat top, low rise time, and small jitter. It can be designed to match load impedances in the range of a few ohms to several kilo ohms. This pulse power system was built and successfully tested for accelerating electrons in the gun chamber of an electron beam controlled CO2 laser operating in the single shot mode. This article describes the design, fabrication, and performance of the pulse power system. © 2001 American Institute of Physics.
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84.70.+p High-current and high-voltage technology: power systems; power transmission lines and cables
42.55.Lt Gas lasers including excimer and metal-vapor lasers
42.60.By Design of specific laser systems
84.30.Ng Oscillators, pulse generators, and function generators

High power continuous wave microwave system at 3.7 GHz

D. Bora, S. Dani, S. Gangopadhyay, B. Jadav, M. Jha, B. R. Kadia, P. L. Khilar, S. V. Kulkarni, M. Kushwah, A. P. Patel, K. G. Parmar, K. M. Parmar, P. Parmar, K. Rajnish, S. Raghuraj, et al.

Rev. Sci. Instrum. 72, 1869 (2001); http://dx.doi.org/10.1063/1.1347373 (7 pages) | Cited 2 times

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The lower hybrid current drive (LHCD) system is an important system in superconducting steady state tokamak (SST-1). It is used to drive and maintain the plasma current for 1000 s with a duty cycle of 17%. The LHCD system is being designed to launch 1 MW of radio frequency (rf) power at 3.7 GHz. The rf source is comprised of two high power klystron amplifiers, each capable of delivering 500 kW rf power. In this article, the results obtained during installation and commissioning of these klystrons are presented. Two klystrons (model TH2103D) have been successfully installed and commissioned on dummy loads, delivering ∼200 kW power for more than 1000 s. The maximum output power that could be obtained is limited due to the available direct current (dc) power supply. The test system is comprised of a TH2103D klystron, a low power rf (3.7 GHz/25 W) source, two high power four port circulators, two high power dual directional couplers, two arc detector systems, and two dummy water loads. To avoid rf breakdown in the rf components of the transmission line, the system has been pressurized with dry air to 3 bar. To energize and operate the klystron, a high voltage dc power supply, a magnet power supply, an ion pump power supply, a −65 kV floating anode modulator power supply, and a filament power supply are used. An arc detector unit has been installed to detect and initiate action within a few microseconds to protect the klystron, waveguides, and other rf passive components during arcing. To protect the klystron in the event of an arc, a fast responding (<10 μs), rail gap based pressurized crowbar unit has been used. The entire system is water cooled to avoid excess temperature rise during high power continuous wave operation of the klystron and other rf components. The tube requires initial conditioning. Thereafter, the output rf power is studied as a function of beam parameters such as cathode voltage and beam current. © 2001 American Institute of Physics.
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52.55.Fa Tokamaks, spherical tokamaks
52.55.Wq Current drive; helicity injection
84.70.+p High-current and high-voltage technology: power systems; power transmission lines and cables
28.52.Av Theory, design, and computerized simulation
84.40.Fe Microwave tubes (e.g., klystrons, magnetrons, traveling-wave, backward-wave tubes, etc.)

An ac method for the precise measurement of Q-factor and resonance frequency of a microwave cavity

B. Nebendahl, D.-N. Peligrad, M. Požek, A. Dulčić, and M. Mehring

Rev. Sci. Instrum. 72, 1876 (2001); http://dx.doi.org/10.1063/1.1336823 (6 pages) | Cited 16 times

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We have developed a new and fast method for the determination of the complex frequency shift of a microwave resonant cavity. The method is based on frequency modulation of the microwave source around the cavity resonance and detection of the 2nd and 4th harmonic of the modulation frequency. With this procedure the static measurement of the response amplitude is not necessary and all the data are obtained through a single ac channel. The optimal frequency deviation is shown to be comparable to the cavity resonance width. © 2001 American Institute of Physics.
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84.37.+q Measurements in electric variables (including voltage, current, resistance, capacitance, inductance, impedance, and admittance, etc.)
84.40.Az Waveguides, transmission lines, striplines
07.57.-c Infrared, submillimeter wave, microwave and radiowave instruments and equipment

Radio-frequency based monitoring of small supercurrents

E. Il’ichev, V. Zakosarenko, L. Fritzsch, R. Stolz, H. E. Hoenig, H.-G. Meyer, M. Götz, A. B. Zorin, V. V. Khanin, A. B. Pavolotsky, and J. Niemeyer

Rev. Sci. Instrum. 72, 1882 (2001); http://dx.doi.org/10.1063/1.1347374 (6 pages) | Cited 25 times

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We consider the applicability of the established rf readout technique, which allows to obtain the supercurrent-phase relation of a Josephson element from impedance measurements in the phase-biased regime. In experiments on Nb-based single and double tunnel junctions, we demonstrate that this method holds even if the Josephson coupling energy is smaller than the thermal energy. Compared with conventional current–voltage measurements, we evaluate the rf technique to be favorable in particular for investigations of small supercurrents in low-capacitance Josephson elements. © 2001 American Institute of Physics.
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85.25.Cp Josephson devices
85.25.Dq Superconducting quantum interference devices (SQUIDs)
84.37.+q Measurements in electric variables (including voltage, current, resistance, capacitance, inductance, impedance, and admittance, etc.)

A phase-locked loop

S. M. Shahruz

Rev. Sci. Instrum. 72, 1888 (2001); http://dx.doi.org/10.1063/1.1347381 (5 pages) | Cited 2 times

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In this article, a phase-locked loop (PLL) is introduced. The proposed PLL, denoted by NPLL, is similar to the standard PLL except that it incorporates a nonlinear element and a low pass filter in its loop. The NPLL outperforms the standard PLL: (i) it has a large acquisition range, i.e., it can achieve locking in situations where the standard PLL cannot; and (ii) it achieves locking much faster than the PLL. The superior performance of the NPLL is due to the nonlinear element and the low pass filter added to the loop. Results of many tests, only three of which are reported in this article, show the superior performance of the NPLL. © 2001 American Institute of Physics.
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84.30.Ng Oscillators, pulse generators, and function generators
84.30.Qi Modulators and demodulators; discriminators, comparators, mixers, limiters, and compressors
84.30.Vn Filters
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