| dc.description.abstract | The archetypal chemical propellant-based launchers (e.g., guns, missiles, spacecraft launchers, etc.) with their hot trailing plume (hence, known as the “hot-launching system”) has been widely deployed over the decades by various agencies. However, because of certain disadvantages of these systems and the physical limitations associated with their designs, electromagnetic launchers (EMLs) seem to offer an alternative way forward as the next-generation hypervelocity (>3 km/s) launchers. They are being researched in select countries around the globe due to their promising capability to successfully replace the archetypal chemical launchers in hypervelocity launching applications. The multistage induction coilgun is one such futuristic class of EMLs that works on the principle of electromagnetic induction between an array of coils (or drive coils), which are wound on a long insulating barrel of appropriate length, and an electrically conducting projectile (or armature) placed inside the barrel. Previously charged high-voltage capacitor banks are sequentially discharged into the coils through high-voltage solid-state switches leading to the generation and flow of high-magnitude impulse currents through the coils. Time-varying electromagnetic flux thus produced by the pulsed currents through the coils interact with the projectile inside and induce a resultant current on it. The propulsive electromagnetic force exerted on the projectile is a product of the excitation current through the coil, the induced current on the projectile, and the mutual inductance gradient (i.e., the change in mutual inductance between the coil and the projectile as the projectile travels through the barrel). The “turn on” and “turn off” of the coils in the various stages must be precisely and appropriately synchronized during the multistage operation to achieve a higher projectile velocity ─this makes its successful design and operation a challenge. The absence of flame and high-pressure gas makes the induction coilgun a “cold-launching system.”
Several applications of the induction coilgun include:
1. Civilian and Atomic Energy Application ─ To produce hypervelocity particles for impact studies.
2. Missile Launching ─ To launch to an altitude where the main rocket motor can be ignited. Thus, the launch pad can stay hidden from the enemies’ infrared (IR) sensors due to the absence of initial flame and high-pressure gas during launching.
3. Artillery Guns ─ Heavy class guns, viz., cannon, howitzer, mortar.
4. Naval Guns ─ Low fire risk in the absence of storage requirements of explosive-laden cartridges in the ship.
5. Anti-tank Guns ─ They can penetrate the thick armor due to high velocity.
6. Space Application ─ To place small satellites (a few hundred kilograms or less) into low-earth orbit (LEO: 180-2,000 km from earth’s surface).
The USA, USSR, China, and South Korea are a few countries to name, who are working on developing coilgun technology to implement it in their defense and space sectors. Owing to its high confidentiality in defense and space applications, not much details can be known from their published works. Under these circumstances, a project to design and develop a multistage induction coilgun was taken up at the author’s laboratory. The author of this thesis has successfully achieved his research objective, which is to design and develop a four-stage induction coilgun. The research work presented in this thesis aims to understand the factors contributing to achieving a higher muzzle velocity for a projectile of a given mass while launching a payload with the coilgun, which can be used for the applications mentioned earlier. This thesis focuses on the author’s step-by-step design and developmental work on the induction coilgun-based EML starting from a single-stage coilgun to a four-stage coilgun. Also, this thesis reports the computer simulation and experimental studies performed with the laboratory prototype of coilgun at the Pulsed Power Laboratory of the Department of Electrical Engineering in the Indian Institute of Science, Bangalore, India.
The author has designed and developed a laboratory-scale prototype of a four-stage induction coilgun. The computer simulation analysis has been performed using MATLAB and finite element method (FEM)-based Ansys software. The author also presents experimental verification of the simulation results. The projectile of a coilgun can be either sleeve-type (ring-shaped projectile) or solenoid-type (multi-turn projectile). The sleeve projectile is of the metallic hollow cylinder type, whereas the solenoid projectile is of the wire wound type. Solenoid and sleeve-type projectiles of different shapes and dimensions have been fabricated to perform the analysis. A maximum of 40 m/s muzzle velocity with a 40 g projectile has been achieved using the developed four-stage induction coilgun.
The author also designed and fabricated a high-speed infrared transmitter-receiver-based sensor (with 25 ns rise and fall time) to quickly sense the moving projectile (or armature) inside the barrel. The triggering instant of the subsequent stage coils of a multistage coilgun critically depends on the projectile’s position inside the barrel. The projectile will fail to achieve the highest muzzle velocity if the subsequent stage coils are not optimally triggered in a sequence. The fast-moving projectile through the barrel necessitates the fast sensing of its position inside the barrel.
In addition, the author has also designed, developed, and fabricated a high-speed gate driver circuit with a peak 25 kV DC isolation for the signal circuit from the high voltage power circuit within a compact space of the printed circuit board (PCB) to trigger the high-voltage SCRs used for triggering the pulsed power source of each stage of the coilgun. Solid-state SCRs are necessary for a reliable and spontaneous triggering of the stage coils in a multistage coilgun. The high-speed triggering of the SCRs is simultaneously important with the high-speed sensor development for a successful operation of a multistage coilgun. An appropriate gate current with proper pulse shape and width is crucial for the fast triggering of an SCR. Also, transient overvoltage protection, overcurrent protection, dv/dt protection, di/dt protection, and gate protection of the SCR are essential since the coilgun operates with a high magnitude impulse current and voltage. The gate driver circuit developed to trigger the SCR considers all these aspects.
The large current flowing through each stage coil can create electromagnetic interference (EMI) problems in the coilgun. The EMI issues corrupt the sensor data, which prevents successful sensing of the projectile’s position. Also, EMI causes the SCRs to trigger the coils spuriously, being indifferent to the projectile’s optimal triggering position inside the coil. Synchronizing the triggering of stages by preventing the EMI issues is the most significant challenge and importance in successfully operating a multistage induction coilgun. The author used optical fiber links in the signal circuit to prevent EMI in the data transmission due to the large drive coil current. The author could successfully synchronize the stages of the coilgun by preventing the spurious triggering of SCRs using the EMI-shielded gate-cathode leads.
A 32-bit ARM core microcontroller board with an 84 MHz clock has been used to fast control the flow sequence of the sensor and gate driver circuits.
The dependency of the projectile velocity on the number of winding layers and the number of winding turns per layer of the drive coil has been studied. Study has been performed to optimize the shape and dimensions of the projectile, viz., length, thickness, and aspect ratio of the projectile, to achieve the highest muzzle velocity. The subject of the study presented in this thesis also focuses on analyzing the parameters on which the efficiency of an induction coilgun depends and how it can be optimized.
An empirical relationship between the projectile velocity and the charging voltage of the capacitor bank has been formulated for the first time in this thesis.
A novel SCR-based pulsed power source (PPS) scheme to commutate the drive coil current and successfully arrest the “armature capture effect” in an induction coilgun operating at high voltage and high current has been proposed. The “armature capture effect” is the phenomenon for which the velocity of a projectile decreases from its peak value. First, the instant of occurrence of the armature capture effect has been computationally investigated and then the suitable instant for commutating the drive coil current has been determined.
The dependency of the projectile motion on the flow of induced current in the subsequent stages has been analyzed. It has been shown that the influence of the induced current on the projectile motion depends on the distance between the stages and the projectile length. The study also focuses on establishing an approach to choosing a proper distance between the stages in a multistage induction coilgun.
The influence of the capacitance of the capacitor bank used in the PPS on the optimum triggering position of the projectile inside a drive coil of a four-stage induction coilgun has also been analyzed.
A comprehensive and explicit analysis has been performed to study and explain the reasons behind the differences in the optimum triggering positions of the projectile inside each stage coil and the achieved muzzle velocities for different arrangements of the drive coil current directions in a multistage induction coilgun.
The simulation and experimental results obtained from the electromagnetic launching studies performed on the sleeve projectiles of different materials and dimensions have also been discussed in this thesis. Four materials of different electromagnetic properties, viz., copper (Cu: diamagnetic), aluminum (Al: paramagnetic), stainless steel (SS: paramagnetic), and mild steel (MS: ferromagnetic), have been chosen as the materials of the sleeve projectiles studied.
Finally, the difference between the launching performance of the sleeve and solenoid projectiles has been analyzed and presented in the thesis.
The work reported in the thesis has resulted in seven IEEE journal publications and eight international conference publications. | en_US |
