# Updates on Impact Ionisation Triggering of Thyristors
## 1 Introduction  
Particle accelerator facilities often rely on pulse generators capable of delivering high voltage (>20 kV) and current levels (>10 kA) to ensure the efficient transfer of particle beams. At CERN, the sequence of accelerators acts like a relay system, each stage boosting the energy of the particles before handing them off to the next accelerator in the chain. Consequently, pulsed magnets in the transfer lines require fast (in the range of <100 ns for the fastest magnets) and precisely controlled magnetic fields [1]. Achieving such speed and precision necessitates the use of fast pulse generators. Pulse power systems employed at CERN frequently utilize pulse forming lines (PFLs) and pulse forming networks (PFNs) to energize kicker magnets [2]. These configurations typically feature at least one high-voltage closing switch, which may consist of a spark gap, IGBT modules, thyratrons or thyristors [3]. Thyratrons, in particular, provide precise control over switching characteristics, fast switching times, and high reliability. This makes them suitable for high-current and high-voltage applications. However, their inherent drawbacks such as complex triggering and biasing electronics, high cost, rarity, and limited market presence [4], have prompted the exploration of alternative, more reliable, and cost-effective replacement systems based on different technologies. An alternative approach to delivering high-voltage nanosecond pulses is detailed in [5]. This method centers on the utilization of Insulated-Gate Bipolar Transistors (IGBTs) within a solid-state microsecond pulse charger design. These IGBTs switch the primary capacitor bank to a pulse transformer, facilitating the generation of high-voltage microsecond pulses. These pulses charge the pulse-forming line (PFL), which subsequently discharges through a spark gap to produce the final nanosecond pulses. Employing IGBTs in a parallel configuration in the pulse charger enhances their capacity to handle the high power required for rapid and repeated pulse generation. However, the implementation of such a solution would result in excessive bulkiness, rendering it impractical for applications requiring tens of kilovolts and tens of kiloamperes. Additionally, the requirement for a microsecond charging phase poses another limitation. A different approach is the inductive adder as presented in [6]. An inductive adder is a solid-state modulator that generates high-voltage pulses through a series of transformers, each equipped with a 1:1 turn ratio. Key components include semiconductor switches (like IGBTs or MOSFETs) to control pulse timing, capacitors to store energy, diode clamps for voltage spike protection, and gate drive circuits for switch management. Its modular design allows for scalable configurations, facilitating maintenance and adaptation to varying needs. However, like the previous approach, inductive adders tend to be bulky, limiting their use in space-constrained environments. Moreover, the transformers within these adders are prone to magnetic saturation if exceeded in capacity, complicating their design. Additionally, while inductive adders are scalable, each added module increases the overall impedance, complicating impedance matching and requiring further adjustments, especially as system specifications expand. A Marx generator can also be implemented as presented in [7]. This Marx Generator, based on SiC MOSFETs, is engineered to provide fast switching capabilities, targeting specifications for rapid rise and fall times with high voltage and current outputs. The key advantage of this system lies in its use of off-the-shelf components to achieve lower inductance and faster switching times. The use of such a system introduces significant component stress, which can reduce its reliability and lifespan.