Accuracy improvement in the isochronous mass measurement using a cavity doublet
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Accuracy improvement in the isochronous mass measurement using a cavity doublet X. Chen1,2 · M. S. Sanjari1 · J. Piotrowski3 · 1 · Yu. A. Litvinov1,4 · F. Nolden1 · P. Hulsmann ¨ 1 M. Steck · Th. St¨ohlker1,5
© Springer International Publishing Switzerland 2015
Abstract The accuracy of the isochronous mass measurement in a storage ring is subject to the isochronous condition γ = γt . It is obvious that this condition cannot be fulfilled for all kinds of nuclides since their velocities certainly differ from each other. However, the non-isochronicity effect can be corrected for by additionally measuring transverse positions of charged particles in the ring. To this end, we outline in this paper the correction method with an arrangement of a cavity doublet, which consists of a position cavity and a reference cavity. Keywords Storage ring · Isochronous mass spectrometry · Non-isochronicity correction · Schottky resonator
1 Introduction Heavy-ion storage rings have proven to be powerful tools for various experimental programs in atomic and nuclear physics (see e.g. [1]). The mass measurement of unstable nuclides, Proceedings of the 6th International Conference on Trapped Charged Particles and Fundamental Physics (TCP 2014), Takamatsu, Japan,1-5 December 2014. X. Chen
[email protected] 1
GSI Helmholtzzentrum f¨ur Schwerionenforschung, 64291 Darmstadt, Germany
2
Ruprecht-Karls-Universit¨at Heidelberg, 69120 Heidelberg, Germany
3
AGH University of Science and Technology, 30-059 Krak´ow, Poland
4
Max-Planck-Institut f¨ur Kernphysik, 69117 Heidelberg, Germany
5
Helmholtz-Institut Jena, 07743 Jena, Germany
X. Chen et al.
for example, is one of the valuable achievements with the usage of storage rings (see e.g. [2, 3]). The principle is based on the differential approximation to the first order γ 2 dv d(m/q) df = −αp + 1− 2 . (1) f (m/q) v γt Here αp and γt are machine parameters which are called momentum compaction and transition energy, respectively. They are related by γt2 = 1/αp . The momentum compaction describes the relative change of path length of a particle in the ring versus the relative change of its magnetic rigidity. By deliberately tuning the ion optics of the ring such that γt = γ , which is called isochronous condition, the revolution frequency f of the nuclide is only determined by its mass-to-charge ratio m/q. This is the theoretical basis for the isochronous mass measurement in the ring. In reality the revolution frequency, or equivalently the revolution period, can be measured by a Schottky resonator accompanied with FFT (Fast Fourier Transform), or by a TOF detector. Having identified nuclides in a spectrum, the peak location shows the revolution frequency (period), while the peak width indicates the associated error and determines the mass-resolving power. The correct determination of locations and widths is critical to the trustworthy mass evaluations in the succeeding procedures. However, the isochronous condition can only be satisfied within a small momentum region, also known as isoc
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