Abstract
Non-perturbative measurements of low-intensity charged particle beams are particularly challenging to beam diagnostics due to the low amplitude of the induced electromagnetic fields. In the low-energy antiproton decelerator (AD) and the future extra low energy antiproton rings at CERN, an absolute measurement of the beam intensity is essential to monitor the operation efficiency. Superconducting quantum interference device (SQUID) based cryogenic current comparators (CCC) have been used for measuring slow charged beams in the nA range, showing a very good current resolution. But these were unable to measure fast bunched beams, due to the slew-rate limitation of SQUID devices and presented a strong susceptibility to external perturbations. Here, we present a CCC system developed for the AD machine, which was optimised in terms of its current resolution, system stability, ability to cope with short bunched beams, and immunity to mechanical vibrations. This paper presents the monitor design and the first results from measurements with a low energy antiproton beam obtained in the AD in 2015. These are the first CCC beam current measurements ever performed in a synchrotron machine with both coasting and short bunched beams. It is shown that the system is able to stably measure the AD beam throughout the entire cycle, with a current resolution of .
Highlights
The non-perturbative detection and measurement of charged particle beams is an important aspect for different fields and applications relying on low-intensity beams
The main design challenges were to adapt the cryogenic current comparators (CCC) monitor to cope with the high slew-rate of the antiproton decelerator (AD) beam current while retaining its superior current resolution, to have a cryogenic system design so that the level of liquid helium in the monitor’s cryostat is kept constant without the need for periodic liquid-helium refills, with the cooling power provided by a cryocooler, and to optimise the mechanical performance by minimising the transmission of vibrations to the CCC
A CCC monitor optimised for the AD and extra low energy antiproton (ELENA) rings at CERN has been implemented and first measurements with beam have been carried out
Summary
The non-perturbative detection and measurement of charged particle beams is an important aspect for different fields and applications relying on low-intensity beams. Beams [3, 4], hadron cancer therapy [5], mass spectroscopy [6] or ion implantation in semiconductor fabrication [7] All these areas would profit from an online non-perturbing beam intensity measurement with absolute calibration. At injection the beam is composed of 4 bunches, each with a length of 4st = 30 ns, assuming a Gaussian longitudinal shape. This is the moment when the current slew-rate reaches its highest value. While Schottky-noise based monitors are very inaccurate when measuring low-intensity DC beams, and present a strong bunch length dependency for bunched beams [9], these can not be calibrated for an absolute measurement
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