High Power Arbitrary RF Pulse Shaping Tests with NG-LLRF and Cool Copper Collider Prototype Structure

TL;DR

The paper addresses the need for highly flexible, per-pulse RF envelope control in accelerator LLRFs. It demonstrates a direct RF sampling NG-LLRF implemented on RFSoC that can synthesize and measure arbitrary RF pulses entirely in the digital domain. Through high-power tests on a Cool Copper Collider prototype structure, it validates square, linear-phase ramp, phase-reversal, and pulse-train envelopes up to $16.45\ \mathrm{MW}$, and shows precise phase control and rapid phase flips relevant to SLED-based compression. Architecture and cost analyses indicate scalable deployment for the collider (~$22\ \mathrm{M}$ total, ~$1{,}000$ per RF channel) with substantial reductions in analogue hardware. The work thereby supports programmable accelerator concepts by enabling real-time, digitally implemented RF shaping and beam-loading compensation at high power.

Abstract

RF pulse modulation techniques are widely applied to shape RF pulses for various types of RF stations of particle accelerators. The amplitude and phase modulations are typically implemented with additional RF components that require drive or control electronics. For the RF system-on-chip (RFSoC) based next generation LLRF (NG-LLRF) platform, which we have developed in the last several years, RF modulation and demodulation are fully implemented in the digital domain. Therefore, arbitrary RF pulse shaping can be realized without any additional analogue components. We performed a range of high-power experiments with the NG-LLRF and a prototype Cool Copper Collider (C\(^3\)) structure. In this paper, the RF field measured at different stages with different pulse shapes and peak power levels up to 16.45 MW will be demonstrated and analyzed. The high precision pulse shaping schemes of the NG-LLRF can be applied to realize the phase modulation for a linear accelerator injector, the phase reversal for a pulse compressor, or the modulation required to compensate for the beam loading effect.

Figures (9)

• Figure 1: The conceptual block diagram of a single NG-LLRF module for C$^3$. The NG-LLRF system has 16 RF inputs and 16 outputs. All the RF inputs are utilized and only 4 of the RF outputs are used to drive the 4 accelerators for half of a cryo-module.
• Figure 2: The schematics of high-power test setup for testing the NG-LLRF with C-band high-power test stand and a C$^3$ prototype structureliu2025high.
• Figure 3: The magnitude and phase of baseband pulses from high power test stand driven by RF pulses modulated with square and linear phase ramp envelope. The pulse width is about 500 ns and the peak power injected to the prototype structure is around 16.45 MW.
• Figure 4: The magnitude and phase of baseband pulses from high power test stand driven by RF pulses modulated with square and linear phase ramp envelope. The pulse width is about 1 $\mu$s and the peak power injected to the prototype structure is around 5.2 MW.
• Figure 5: The magnitude and phase of baseband pulses from high power test stand driven by RF pulses modulated with square and square wave with phase reversal every 250 ns envelopes. The pulse width is about 500 ns and the peak power injected to the prototype structure is around 16.45 MW.