CW Performance of the Triumf 8 Meter Long RFQ for Exotic Ions

TL;DR

This paper reports on the design, construction, and successful high-power operation of an 8-meter CW RFQ for accelerating exotic ions, demonstrating stable operation and effective beam acceleration.

Contribution

It introduces a novel 8-meter long RFQ with unique design features and confirms its performance through extensive testing and beam validation.

Findings

Achieved stable CW operation at 75 kW and 100 kW power levels.

Confirmed RF and beam dynamics through successful beam tests.

Demonstrated effective mitigation of field emission issues.

Abstract

The ISAC 35 MHz RFQ is designed to accelerate ions of A/q up to 30 from 2keV/u to 150keV/u in cw mode. The RFQ structure is 8 meters long and the vane-shaped rods are supported by 19 rings spaced 40 cm apart. An unusual feature of the design is the constant synchronous phase of -25; the buncher and shaper sections are eliminated in favor of an external multi-harmonic buncher. All 19 rings are installed with quadrature positioning of the four rod electrodes aligned to +/- 0.08 mm. Relative field variation and quadruple asymmetry along the 8 meters of the RFQ was measured to be within +/- 1%. Early operation at peak inter-electrode voltage (75kV) was restricted by the rapid growth of dark currents due to field emission; the nominal operating power of 75 kW increased to 100 kW in a few hours. A program of high power pulsing, followed by cw operation have all but eliminated the problem leading to a successful 150 hour test at full power. Successful beam test results confirm beam dynamics and rf designs.