Accelerator Beam Kicker High-Voltage Fast Pulse Power Supply

In particle accelerator complexes, the precise manipulation of beam timing and destination is essential for multi-user operation, injection/extraction cycles, and beam diagnostics. Beam kickers are fast deflection systems that impart a transverse momentum kick to a bunched particle beam over an extremely short distance. They are used for injecting beam into a ring, extracting it, or "kicking" it into a diagnostic line or abort dump. The performance of a kicker is fundamentally defined by the high-voltage fast pulse power supply that drives its deflection plates or stripline electrodes. This supply must generate a high-voltage pulse with a flat-top duration matched to the bunch passage time, an exceptionally fast rise and fall time to avoid affecting adjacent bunches, and remarkable amplitude stability to ensure reproducible deflection angles.

The electrical specifications are extreme. For proton or heavy-ion synchrotrons, the required voltage can range from 5 to 50 kV. For electron machines, it may be lower (1-10 kV) but with even faster timing. The pulse duration (flat-top) is typically between 50 nanoseconds and a few microseconds, depending on the bunch length and machine revolution period. The most critical parameters are the rise and fall times, which must be a small fraction of the flat-top duration, often specified to be less than 10-20 nanoseconds. This fast transition is necessary to cleanly deflect a single bunch without "leaking" field onto the preceding or following bunch in the beam pipe. Furthermore, the flat-top ripple must be minimal (<0.1%) as any variation modulates the deflection strength, causing beam orbit errors or emittance growth.

The standard topology for such a supply is a transmission line-based pulser, often a Blumlein or a pulse-forming network (PFN) charged to a high DC voltage and discharged via a fast closing switch. A Blumlein configuration, using two parallel transmission lines, is favored for its ability to produce a rectangular pulse with a duration equal to twice the electrical length of the lines. The PFN uses discrete inductors and capacitors to approximate a transmission line. The high-voltage DC charging supply that energizes these lines must be very stable but does not need high speed; its role is to bring the network to a precise voltage, which defines the pulse amplitude.

The switch is the technological heart of the system. It must hold off the full DC charging voltage and then close in nanoseconds with minimal jitter. For the highest performance applications, gas-filled thyratrons were historically used. However, modern systems increasingly employ solid-state switches based on stacks of avalanche transistors, silicon avalanche diodes, or, for higher voltages and currents, series-connected stacks of fast, high-voltage Silicon Carbide (SiC) MOSFETs or Gallium Nitride (GaN) HEMTs. These solid-state switches offer superior lifetime, reduced jitter (sub-nanosecond), and do not require the high-maintenance gas handling systems of thyratrons. Driving these switches uniformly and simultaneously in a series stack at these speeds is a major design challenge, requiring carefully balanced gate drive circuits with high common-mode transient immunity.

Pulse shaping and termination are critical. The kicker magnet or plates present an essentially resistive load (often 50 ohms to match standard coaxial transmission lines). To prevent reflections that would distort the pulse shape, the output of the PFN/Blumlein must be impedance-matched to this load. Any mismatch causes ringing on the flat-top or an extended fall time. Therefore, the entire pulse generator, from the switch to the output connector, is designed as a matched transmission line system. To achieve the required fast fall time, an additional "crowbar" or shorting switch is often placed across the output and triggered immediately after the main pulse ends, actively clamping the output to zero volts.

Stability and synchronization are paramount. The pulse amplitude directly sets the kick angle. The supply must exhibit long-term drift of less than 0.05% per day. This is achieved through ultra-stable charging supplies and temperature-controlled components. The timing of the pulse relative to the RF master clock of the accelerator must have picosecond-level jitter to ensure the kick is applied to the exact intended bunch. The trigger for the main switch is derived from this master clock through low-jitter delay generators and is transmitted via fiber-optic cable to the floating high-voltage platform of the pulser. The system includes extensive diagnostics, often sampling the output pulse with a high-bandwidth capacitive divider and digitizing it for every shot, allowing for real-time amplitude and timing feedback to the control system. This high-voltage fast pulse power supply is a masterpiece of precision timing and high-voltage engineering, acting as the definitive gatekeeper that directs multi-million-dollar particle beams with nanosecond accuracy.