Abstract
Standard quadrupole beam-based alignment (BBA) techniques rely on orbit data and on the sequential variation of quadrupole and orbit corrector magnets (OCM). This results in time-consuming measurements of the order of several hours in most circular accelerators. Fast (10 kHz) beam position monitors (BPM) and OCMs with ac power supplies are routinely used in modern synchrotron light sources to drive fast orbit feedback systems. In this paper we show how they can be employed also to dramatically reduce the time for any quadrupole BBA to several minutes only, ensuring the same level of accuracy and precision. Moreover, conversely to the standard BBA, the new procedure accounts automatically for any level of betatron coupling, BPM roll and OCM tilt. In the case of the ALBA 3rd generation light source, the time for a complete measurement dropped from 5 hours to 10 minutes, a reduction by a factor 30. As further extension of this novel approach, an even faster skew quadrupole BBA was demonstrated in ALBA for the first time, taking advantage of the additional ac modulation of the skew quadrupole field. Results from this fully ac measurement are compared with those obtained via a traditional dc scan of the skew quadrupole.
Highlights
Aligning the beam centroid to the center of the magnetic elements is an efficient way to minimize unwanted multipole feed-down effects in particle accelerators
In this paper we present a fast beam-based alignment (BBA) (FBBA) beam position monitors (BPM)-to-quad method based on the parallel ac modulation of several orbit corrector magnets (OCM) at different frequencies and on the harmonic analysis of orbit data sampled at high frequency (10 kHz)
As any other BPM-to-quad BBA implementation, this method does not relies on the accelerator model knowledge so the effective orbit response matrix (ORM) Ryljy is unknown
Summary
Aligning the beam centroid to the center of the magnetic elements is an efficient way to minimize unwanted multipole feed-down effects in particle accelerators. The BPM-to-quad technique does not rely on the accelerator optics model but needs to scan the strength of one or several OCMs at every quadrupole change This is usually much more time consuming and it may give inaccurate results if the beam orbit has a pronounced angle at the quadrupole. In synchrotron light sources the quadrupole scan is typically performed step by step in a dc way and slow acquisition (10 Hz) orbit position data are analyzed, whereas the BBA of quadrupoles in the interaction regions of colliders is usually carried out via a continuous quadrupole gradient modulation and the harmonic analysis of turnby-turn BPM data In the literature the latter approach is referred to as k-modulation [5] and requires quadrupole power supplies with ac capabilities, presently not available in ALBA. This fully ac variant would further reduce the FBBA time by an additional factor two
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