Coreless SQUID-based cryogenic current comparator for non-destructive intensity diagnostics of charged particle beams

Abstract

We report on a novel concept and prototype development of a coreless SQUID-based charged-particle beam monitor as a non-destructive diagnostic tool for accelerator facilities. Omitting the typically used pickup coil with a high magnetic permeability core leads to a significant improvement in low-frequency noise performance. Moreover, a revised shielding geometry allows for very compact and rather lightweight device designs. Based on highly sensitive SQUIDs featuring sub-micron cross-type Josephson tunnel junctions, our prototype device exhibits a current sensitivity of about 6 pA Hz−1/2 in the white noise region. Together with a measured shielding factor of about 135 dB this opens up the way for its widespread use in modern accelerator facilities.

Influence of Mechanical Deformations on the Performance of a Coaxial Shield for a Cryogenic Current Comparator

“…Let us note that a coreless variant will be considered throughout this work, with the exception of section V-F where the case of CCCs with a magnetic core is briefly discussed. Indeed, within a coreless framework, the numerical setting can be simplified by integrating the CCC itself in the pickup loop (see section II-B for more details), as shown in Fig 1 . This variant was selected in the folded-coaxial CCC shield presented in [5].…”

“…While this paper focuses on the shield itself, let us briefly discuss the dependence between the change of magnetic flux in the SQUID of the CCC and the current I to be measured. This can be achieved by following for instance the magnetic circuit approach discussed in [5] 4 . It is however important to stress that this requires not only the mutual inductance M but also the self inductance L of the pickup coil.…”

“…Nonetheless, as this variation does not modify the shield itself, our conclusions about η and the coaxial CCC shield damping remain unchanged. Let us also note that CCCs with highly magnetic permeable materials suffer from temperature dependent drifts and low-frequency noise caused by flipping of individual magnetic domains inside the core material [5].…”

“…This component is magnetically coupled with a pickup loop and (optionally) a highly permeable core. Depending on the geometry of the shield and on the location of the pickup coil, different variants can be built, such as the (folded-)coaxial [4], [5], [6], the ring [7] or the overlapped tube [8] CCC shields just to name a few. Among the applications of those CCCs, let us mention that overlapped tube variants have been successfully used in metrological applications, such as the accurate measurement of resistances for instance (see e.g.…”

“…[9] and references therein). On the other hand, ring and folded-coaxial CCCs can be used, for example, in the non-perturbative measurement of low-intensity charged particle beams, as encountered in particle accelerator facilities [5], [10]. In this paper, we will focus on the simplest configuration, namely the coaxial one, as sketched in Fig.…”