Configurations and Applications of Saturable Pulse Transformers in High Power Pulse Modulation

In this paper, saturable pulse transformers (SPTs) based on multiple batches of windings in parallel combination and coaxial cylindrical conductors are presented. The proposed SPT can be employed as the transformer and magnetic switch simultaneously for pulse capacitor or high-voltage pulse modulator of several hundred kV range. The SPT which has important features such as auto-resetting of core, high step-up ratio and low saturation inductance, achieves a compact integration of common transformer and magnetic switch. The proposed SPTs were applied in a high power pulse modulator based on a helical Blumlein pulse forming line (HBPFL). When the SPT played as a pulse transformer, the HBPFL can be charged to 200 kV. When the SPT played as a main magnetic switch of the HBPFL, it helped to form a quasisquare voltage pulse with amplitude of 180 kV,pulse duration of 130 ns, rise time of 60 ns. Furthermore, important applications of SPT in 100kV-range compact Marx generator and ns-range synchronization of multiple high-voltage pulses are proposed and demonstrated. Compact high power pulse modulator with high repetition rate and long life time has hot applications in defense, industrial, agriculture, environmental protection, medical care, bio-electronics, and so on. Voltage transformation and switch are crucial in pulse modulator. Saturable pulse transformer (SPT) is a compact integration device which combines the functions of the independent pulse transformer and magnetic switch [1,2]. Through the transition from the unsaturated state to the saturated state of core, the secondary windings of SPT can operate at transformer mode and magnetic switch mode in order. As the volume and cost of the magnetic core are decreased, the SPT shows promising applications in high-power pulse modulator. However, when the working voltage is higher than dozens of kV, the common SPT can not obtain high step-up ratio and low saturation inductance (<1 μH) simultaneously, due to the large size of the magnetic core and windings [2,3]. This difficulty hinders further applications of a common SPT. In order to provide possible solutions to the difficulty aforementioned, SPTs based on multiple batches of windings in parallel combination and coaxial cylindrical winding configuration are both introduced. In the SPT, The physical suppression effect caused by reversed magnetic coupling mechanism among primary and secondary windings [4] can reduce the saturation inductance of the SPT windings to a level lower than their structure inductances, which helps to achieve a magnetic switch with low saturation inductance. Traditional spark gap can be substituted by the proposed SPT. This paper explores and demonstrates a pulse modulator in which the proposed SPT plays as the charging transformer and discharging magnetic switch of a helical Blumlein pulse forming line (HBPFL). In addition, important applications of the SPT in compact integrated Marx generator and high-voltage ns-range synchronization of multiple pulses are also introduced. CONFIGURATION CONSIDERATIONS OF SPT AND APPLICATION IN PULSE MODULATOR SYSTEM SPT Configuration Based on Multiple Batches of Windings in Parallel Combination The introduced new SPT consists of the magnetic core, primary windings and secondary windings. As Fig. 1 shows, the magnetic core consists of m piles (m=6) of magnetic toroids stacked along the axial direction. The primary windings of SPT are formed by 6 batches of primary sub-windings in a parallel combination, and each sub-winding is formed by a curled copper tape which has only one turn. As shown in Fig. 1, the first primary subwinding goes across the top of the first magnetic toroid, goes down to the bottom, and finally goes out across the bottom of the first magnetic toroid. The 6 batches of primary sub-windings almost have the same characteristic parameters. The equivalent turn number of the entire primary windings of the SPT is as Np=1/m=1/6. The secondary windings contain s batches (s=12) of sub-windings along the azimuthal direction of the magnetic core can be separate or in a parallel combination. Every secondary sub-winding with the same turn number as Ns (4.75) has a uniform coil distribution along the azimuthal direction. As all the s batches of the secondary sub-windings in parallel combination share the same primary windings as shown in Fig. 1, the proposed SPT with new configuration has a step-up ratio as (1/m): Ns=1:28.5. After the magnetic core saturates, the strong magnetic coupling effects between the primary and secondary windings disappear. The secondary subwindings of the SPT play as a magnetic switch which controls the discharge course of the secondary circuit of the SPT. The parallel combination structures of the multiple SPT windings ensure the properties such as high step-up ratio and low saturation inductance of the SPT [5]. ____________________________________________ *Work supported by the National Science Foundation of China No.51177167 and China Academy of Engineering Physics No.