Rehim N. Rajan

A design approach for systems based on magnetic pulse compression

A design approach giving the optimum number of stages in a magnetic pulse compression circuit and gain per stage is given. The limitation on the maximum gain per stage is discussed. The total system volume minimization is done by considering the energy storage capacitor volume and magnetic core volume at each stage. At the end of this paper, the design of a magnetic pulse compression based linear induction accelerator of 200 kV, 5 kA, and 100 ns with a repetition rate of 100 Hz is discussed with its experimental results.

Detection of electrical discharges in DC accelerator using photomultiplier tubes

Detection of Electrical Discharges using chemical, electrical, acoustic and optical techniques holds key to the protection of any high voltage (HV) system. DC Accelerator, being a HV system is prone to various electrical discharges. In DC Accelerators, optical technique promises better performance than other detection techniques due to its fast response and inherent immunity to electromagnetic noises. Photomultiplier tubes (PMT) are used for collecting the discharge signatures. Experimental prototypes of the accelerator discharges are developed. PMTs are used to detect the signals from these discharges.

Direct power control PWM rectifier using switching table for series resonant converter capacitor charging pulsed power supply

This paper presents the analysis of a direct power control (DPC) technique and model using switching table for Pulsed power system used in linear electron accelerator. High voltage pulse are required in such accelerator are generated using smart modulator based on capacitor charging power supply (CCPS). The CCPS used has a series-resonant topology, which acts as a nonlinear and discontinuous load. Hence power factor is poor in 3-phase mains supply. Active rectifiers are good choice for power factor correction in non-linear loads. The simplest form of active rectification is based on direct power control (DPC) using switching table where. The Control algorithm stored in switching table in DPC provides smooth regulation of instantaneous active and reactive powers. The unity power factor (UPF) operation maintains the reactive power zero in all sectors. Simulation verifies the harmonic distortion content are maintained within standard limits.

AC resistance calculation of litz wire and its modeling with FEMM

This paper includes calculation of the AC resistance of litz wire in a wide frequency range for an optimal strand diameter by two methods and compared. Calculations of AC resistance for these methods are carried out by using mathematical software SCILAB. Analysis of skin effect is carried out with FEMM. Effect of pitch on AC resistance is analyzed. The results for AC resistance, skin effect and analysis of skin effect presented in this paper are compared with FEM simulations. A graphical comparison of the theoretical calculation and FEM simulation of ac resistance with frequency is done and found to be in good agreement.

Optimization of electric stresses in high voltage system of DC accelerator

Optimization of electrical stresses is essential to ensure the reliable operation of high voltage systems and it can be achieved by careful design of high voltage electrodes and electrical insulation systems. Improper design of electrodes and insulation can cause excessive electrical stresses in the high voltage system and it will eventually lead to electrical breakdown. DC accelerators employing parallel coupled voltage multiplier scheme requires sufficient capacitances to be developed between a set of electrodes, while ensuring operating electrical stresses within the safe limits. The electric field intensity in the system will depend on the applied voltage and also on the geometry of electrodes and insulators. Shape, size and location of electrodes and insulators need to be optimized to maintain the maximum electric field. This paper describes the analysis and simulation done for optimization of electrical stresses in the systComputer Simulation Technology - Electromagnetic (CST EM) Studioem by optimizing the Radio Frequency Feeder Electrodes of an industrial electron accelerator being developed at BARC. Computer Simulation Technology - Electromagnetic (CST EM) Studio has been used for this study.

Automated qualification and analysis of protective spark gaps for DC accelerators

Protective spark gaps are used in the high voltage multiplier column of a 3 MeV DC Accelerator to prevent excessive voltage build-ups. Precise gap of 5 mm is maintained between the electrodes in these spark gaps for obtaining 120kV±5kV in 6kg/cm2 SF6 environment which is the dielectric medium. There are 74 such spark gaps used in the multiplier. Each spark gap has to be qualified for electrical performance before fitting in the accelerator to ensure reliable operation. As the breakdown voltage stabilizes after a large number of sparks between the electrodes, the qualification process becomes time consuming and cumbersome. For qualifying large number of spark gaps an automatic breakdown analysis setup has been developed. This setup operates in air, a dielectric medium. The setup consists of a flyback topology based high voltage power supply with maximum rating of 25 k V. This setup works in conjuction with spark detection and automated shutdown circuit. The breakdown voltage is sensed using a peak detector circuit. The voltage breakdown data is recorded and statistical distribution of the breakdown voltage has been analyzed. This paper describes details of the diagnostics and the spark gap qualification process based on the experimental data.

Optical signatures of discharges in parallel coupled DC accelerator

Parallel coupled voltage multiplier based accelerator topologies offer advantages of better regulation and ripple compared to their series coupled counterparts for Industrial electron beam accelerators. During conditioning and operation these systems undergoes various types of electrical discharges. The discharge can be a direct spark over from the high voltage terminal to ground through SF6 insulation, vacuum breakdown in the accelerating tube maintained in the order of 10-7 mbar pressure, or local discharge between corona guards which are used to couple RF power to the multiplier. There could be discharges in between dynodes of the accelerating tube. As the inter electrode discharges do not reflect in load current, detection of these conditions becomes very difficult. Optical discharge detection methods can be used effectively in this situation. Photo multiplier based optical discharge detection has been deployed in a 3 MeV DC accelerator. Characteristics of the optical signal received during conditioning phase have been presented in this paper.

Compact lumped circuit model of discharges in DC accelerator using partial element equivalent circuit

DC Accelerators undergoes different types of discharges during its operation. A model depicting the discharges has been simulated to study the different transient conditions. The paper presents a Physics based approach of developing a compact circuit model of the DC Accelerator using Partial Element Equivalent Circuit (PEEC) technique. The equivalent RLC model aids in analyzing the transient behavior of the system and predicting anomalies in the system. The electrical discharges and its properties prevailing in the accelerator can be evaluated by this equivalent model. A parallel coupled voltage multiplier structure is simulated in small scale using few stages of corona guards and the theoretical and practical results are compared. The PEEC technique leads to a simple model for studying the fault conditions in accelerator systems. Compared to the Finite Element Techniques, this technique gives the circuital representation. The lumped components of the PEEC are used to obtain the input impedance and the result is also compared to that of the FEM technique for a frequency range of (0-200) MHz.

H.V. support structure of 3MVDC generator and its protection from HV discharges in vacuum and SF6 gas for DC electron Accelerator

Accelerator and Pulse Power Division of BARC has developed a DC electron accelerator for cross linking of polymers, medical starilisation, preservation of food. The demonstration of stack-gas cleanup for green power generation has been demonstrated successfully. The support structure of the 3MVDC voltage generator is made of Perspex for high dielectric strength, easy availability of raw material, excellent radiation resistance and long term dimensional stability. This paper describes the salient design features of the High voltage support structure in brief.

Development of 50kV air-core transformer for electron gun static power source of 3MeV DC accelerator

A 3MeV, 10mA DC Electron Beam Accelerator based on the capacitively coupled parallel-fed voltage multiplier in 6kg/cm2 SF6 gas environment is under commissioning at Electron Beam Centre, Kharghar, Navi Mumbai. Electron Gun is situated at -3MV terminal which requires a constant power for its anode and filament. Gun power source has been derived by suitably coupling the ac components present in the HV Multiplier column. An air-core step down transformer rated for 50kV/600V/120kHz floating at 3MV to extract the required power for electron gun from high voltage column has been developed. The transformer has been operated for 7kW, 1MeV of electron beam in 6kg/cm2 Nitrogen gas environment. The paper describes briefly about the design aspects and test results.