A controller for 97 MHz super-conducting QWR for NSC LINAC booster

Abstract

A resonator controller has been implemented to stabilize the amplitude and phase of rf fields in the super-conducting resonators of NSC LINAC. Due to reduced losses these resonators have intrinsic band width of the order of 0.1 Hz at 97 MHz whereas the vibration-induced center frequency changes are of the order of a few tens of hertz. In the control strategy followed, the resonator is made the frequency selective part of an oscillator. The phase lock is achieved by dynamically adding a phase shift in the oscillator. A slow tuner minimizes the slow drifts in the resonator center frequency. In this paper we present the control strategy, implementation details and performance obtained with this controller.

Improvement of accelerating gradients in niobium quarter wave resonators

“…During the cold test, the QWR was powered through a self-excited loop (SEL) [23] realized by an indigenously developed resonator control module [24]. The cold test nominally consisted of the following steps:…”

Piezoelectric actuator based phase locking system to improve the dynamics of the control scheme for a heavy ion superconducting linac

“…The resonator is made to operate at the peak of the resonance curve by changing the phase through loop phase shifter [8]. The amplitude of the RF field is stabilized using the amplitude feedback loop of the dynamic phase controller.…”

“…The bandwidth of these loops is about a few tens of kHz. Under these operating conditions the phase error signal is proportional to the frequency detuning [8]. The phase error signal is used for the closed loop control of the piezoelectric actuator based tuner.…”

“…During acceleration of heavy ion beams, all the resonators in the linac are independently phase locked at accelerating gradients which lead to about 6 W of wall losses dissipated in liquid helium at 4.2 K. This typically results in an accelerating gradient of 3-4 MV/m in CW mode. The control scheme for the QWR is based on the dynamic phase control using complex phasor modulator to control the high frequency microphonics, and a mechanical tuner to stabilize the mean resonant frequency [6][7][8]. The mechanical tuner in the QWR used helium gas to flex the niobium bellows located at the high voltage end of the resonator to tune the resonant frequency [2,3] [Fig.…”