Abstract
Optical methods for non-invasive beam diagnostics of high current H− ion accelerators have been developed in recent years. Such laserwires typically measure a 1D beam profile and/or 2D transverse emittance from the products of photo-detached ions as a laser beam is scanned across the H− beam. For laser pulse durations (∼80 ns) longer than the RF period (∼3ns), the detector integrates many complete bunches, enabling only transverse beam monitoring. This paper presents a new technique to capture a series of time resolved transverse emittance measurements along the bunch train. A fast (∼10 ps) pulsed laser photo-detaches ions within each bunch and is synchronised to sample consecutive bunches at certain longitudinal positions along each bunch. A fast detector records the spatial distribution and time-of-flight of the neutralised H0, thus both the transverse and longitudinal emittance are reconstructed. We present simulations of a time varying pulsed laser field interacting within an H− bunch, and estimate the yield, spatial and time distributions of H0 arriving at the detector. We summarise the design of a recently funded longitudinal laserwire being installed in FETS at RAL, UK.
Highlights
Non-invasive laserwires to measure the transverse profile and emittance of high intensity hydrogen ion beams have been demonstrated at several accelerators including SNS [1] and CERN’s LINAC4 [2,3,4,5,6,7,8]
Collection of the liberated electrons by a Faraday cup or similar detector enables the 1D profile to be determined as the laser is scanned across the beam, while a spatially sensitive downstream detector records the neutralised H0 enabling the 2D transverse emittance (x, x′) to be reconstructed
In 2017, a dual station laserwire system was designed and permanently implemented at LINAC4 [8], with each station consisting of two orthogonal laserwires, an electron detector and a crossed pair of diamond strip detectors
Summary
Non-invasive laserwires to measure the transverse profile and emittance of high intensity hydrogen ion beams have been demonstrated at several accelerators including SNS [1] and CERN’s LINAC4 [2,3,4,5,6,7,8]. In this paper we propose a combination of the above techniques with a time-of-flight method, to enable 6-dimensional bunch parameters of high intensity H− beams to be measured by a single non-invasive laserwire instrument.
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