First Results from the use of Dual Harmonic Acceleration on the ISIS Synchrotron

The ISIS facility at the Rutherford Appleton Laboratory in the UK is currently the most intense pulsed, spallation neutron source. The accelerator consists of a 70 MeV H-linac H-linac H-linac and an 800 MeV, 50 Hz, rapid cycling, proton synchrotron. The synchrotron beam intensity corresponds to a mean current of 200 μA. The synchrotron beam is accelerated using six, ferrite loaded, RF cavities with harmonic number 2. Four additional, harmonic number 4, cavities have been installed to increase the beam bunching factor with the potential of raising the operating current to 300 μA. This paper reports on the hardware commissioning and the first beam tests.

INTRODUCTION

Currently, six two-gap RF cavities have been used to accelerate the ISIS synchrotron beam. With this arrangement ~ protons can be held in the synchrotron throughout the 10 ms accelerating cycle from 70 to 800 MeV during which the RF sweeps from 1.3 to 3.1 MHz. The maximum mean beam current which can be accelerated by the synchrotron is ~. The addition of a second harmonic component [1] to the RF waveform should allow the acceleration of higher currents by increasing the bunching factor. This component is provided by four second harmonic (2RF) cavities, one of which is shown schematically in figure 1. Figure 1: Schematic of a 2RF accelerating cavity