RF Commissioning of the SPIRAL2 RFQ in CW Mode and Beyond Nominal Field

The SPIRAL2 RFQ was recently successfully commissioned at nominal voltage of 114 kV, corresponding to 1.65 Kilpatrick factor. The paper describes limitations of the RFQ main subsystems, cavity conditioning difficulties, as well as changes implemented in the LLRF and automatic procedures to simplify turn on and operation of the whole system. INTRODUCTION The SPIRAL2 RFQ [1] is driven with four independent RF chains directly combined into the cavity. Cavity loss was estimated around 160-180 kW at highest operating voltage (~114 kV) and four 60 kW RF power chains were chosen to preserve the quadrant symmetry and to lead to realistic specifications for the circulators and amplifiers. Figure 1: RFQ RF system. The RFQ RF system is shown in Fig. 1. The LLRF defines the master/slave configuration chosen to synchronise the four chains. Master LLRF controls the amplitude and phase stability, while slave LLRF follow the incident power of the master chain. Master LLRF also measures the cavity detuning and provides tools to condition and power up the cavity as well as to recover voltage after sparks. The system is completed by the Tuning Control System (TCS) and by external devices for the Phase Looked Loop (PLL) driving mode and by the Local Control System (LCS, not shown).

[1]  R. Ferdinand,et al.  SPIRAL 2 RFQ DESIGN , 2004 .