液体介质快脉冲电压下击穿特性研究

设计了液体介质快脉冲击穿试验装置和电压电流测量系统，研究了重复频率、电极形状及电极间距与介质击穿场强、击穿电压和击穿时延等击穿特性参数的关系，比较了变压器油、十二烷基苯、蓖麻油三种典型液体绝缘介质在直流及快脉冲电压作用下的绝缘性能。结果表明:短脉冲持续时间下液体绝缘材料有异常高的击穿场强；重复脉冲串作用下的击穿场强比单个脉冲下明显减小，重复频率2 kHz时击穿场强减小了约30％；电极头半径大小对击穿也有影响，半径R＝5 mm时，击穿电压最高；击穿时延随击穿场强减小而变长，在其他条件相同的情况下，测得击穿时延随机波动；蓖麻油的快脉冲电压绝缘性能最好，变压器油次之。

Comparison of laser characteristics of neodymium doped glass, YAG and GGG operating in heat capacity mode

Considering some necessary factors in the design of SSHCL,material properties of Nd doped glass,YAG and GGG were compared.Transient temperature fields and thermal stress in these slab mediums during one working cycle were simulated.Numerical analysis results showed that the internal-external temperature difference in a neodymium doped glass slab was 75 K and the peak temperature value was 400 K when pumping time arrived 5 s.The maximum stress came to 50% of glass fracture limit.During subsequent water cooling period,the initial state was recovered after 120 s.On the same boundary conditions,Nd: YAG and Nd: GGG slabs could maintain relatively smooth temperature profile while the temperature rising and equivalent thermal stress were lower compared to glass.In later cooling phase,both of them could reach their operating commencement within 30 s.As cooling,the maximum stress of Nd: YAG overran 50% of the stress limit,thus increasing its tendency to fracture.Taken cooling time, fracture limit and obtainable size of the crystal into account,Nd: GGG should be the suitable active medium for high average power,repetitive frequency heat capacity laser.