Analysis of Projectile Motion in Bore and Transfer Efficiency for Electromagnetic Railgun
Electromagnetic railgun (EMG) use a high-current, high-energy electrical pulse to accelerate projectiles to hypersonic velocities. A pulsed power supply (PPS) that employ capacitors as the energy store are typically used to shape the required electrical pulse. In this paper, the differential equations of projectile moving in the bore has been given and solved. The general pattern of projectile moving in the bore has been studied. Considering the influence of current fluctuation on velocity, the stability of armature has been discussed. In order to improving system performance, the efficiency of main energy transfer process has been calculated. The influence of current shape consists of several electrical pulse on muzzle velocity and efficiency has been studied. And some important conclusions have been reached, which provide theoretical references for guiding railgun design and choosing waveform of discharging current.
Analysis of the Factors Influencing the Dynamic Response of Electromagnetic Rail Launcher
The dynamic response of an electromagnetic rail launcher (EMRL) has a direct influence on launch accuracy. With the Bernoulli–Euler beam located in the elastic support as an object of study, this paper presents an analytical model of the dynamic response of EMRL under the conditions of electromagnetic (EM) repulsive force and armature-and-rail contact force and obtains the analytical solution of the model. The redevelopment of the finite-element software makes it possible to perform a strong coupling transient simulation of the moving EM repulsive force, armature-and-rail contact force, moving thermal power, frictional thermal power, and the structural response in the dynamic launching process. Through the comparison of the results obtained by the analytical method, 2-D finite-element method (2-DFEM), and 3-D FEM (3-DFEM) for the dynamic response of the EMRL, the proposed model proves to be accurate and reliable. It is found that 3-DFEM can more accurately reflect the dynamic response process of the EMRL. On this basis, an analysis is made on the influence of the contact force, structural damping and heat on the dynamic response. The studies show that the contact force and the structural damping have little influence on the dynamic response under the condition of noncritical velocity, but have a great influence under the condition of critical velocity. However, the heat has a great effect on the dynamic response in both the conditions.
A High Reliability, Fail Safe, Thyratron Crowbar System For The Protection Of High Power Microwave Tubes In Television Transmitters
EEV is a world leader in the production of Inductive Output Tubes (IOT's), which are now beginning to replace conventional klystrons in television transmitters. Unlike conventional TV klystrons, the I O T requires a crowbar to protect its carbon control grid and its cathode in the event of a fault. A bought-in IOT test equipment at EEV originally used a spark gap crowbar, but this was replaced by a thyratron crowbar when an IOT under test was destroyed because the spark gap failed to fire. The thyratron choice for this socket, which ages and tests 40kW IOT's at 28kVd.c., was a single gap glass thyratron type CX1722A/3 . This was installed in November 1991 and is still working satisfactorily after 10,000 filament and 4,200 high voltage hours and 2,600 crowbar events. Commercial transmitters require 24 hour a day, seven day a week operation. Transmitter reliability is essential and fault conditions must be dealt with by a fail-safe crowbar system. Accordingly, EEV has developed a two gap ceramic thyratron, CX2708, for use in commercial equipments. This 3" diameter thyratron is rated for 40kV d.c. hold-off, and for a fault level of 6 coulombs. All CX2708 thyratrons are tested for 24 hour hold-off at 40Kv d.c. at the maximum specified heater and reservoir voltages, and are also tested discharging 16pF from 40kV through a resistance of 23R followed by 6.4C of power supply follow-on at the minimum specified heater and reservoir voltage. These exacting tests were essential to meet the severe reliability reqirements, and are being performed on all production CX2708 thyratrons to ensure continued reliability and quality. Measurements have been made of the capabilities of the CX2708 with regard to capacitor discharge and follow-on current level and duration. These measurements show that the requirements of commercial equipments are well within the capabilities of the CX2708. A complete crowbar unit (type MA2447A) has also been developed for use with the CX2708. This unit incorporates automatic fault current triggering of the crowbar when a preset current level is exceeded. Interlocking of the grid 1 current to indicate that the crowbar is ready to fire and external triggering via optic links are additional important features. Two methods of setting the triggering level are discussed in detail with particular reference to noise immunity. Under typical operating conditions the unit will protect a 0.05mm diameter wire (47 SWG). Protection is fast with a firing delay of only 1lOns under fault conditions and 50011s via the external trigger. Under fault conditions at the full 40kV the "let through" to the fault is 2.3mC and only 0.023A2s. Many CX2708 thyratrons are now operating satisfactorily in transmitters throughout the world. The target spurious firing rate from the thyratron is less than one per year to ensure first class reliability. A d.c. hold-off test at 40kV at EEV has reached 3,500 hours without a single spurious firing and is ongoing. A further j~mportant consideration for the user is the thyratron warm-up time. Current production CX2708's have a warm-up time of 10 minutes, but a new design has now matched the IOT warm-up time of 5 minutes.