Abstract
We have established and also implemented a nondestructive online monitoring system for measuring the stripper foil degradation, such as foil thinning and pinhole outbreak, for the first time during beam operation in a high-intensity proton accelerator. We aimed to achieve a realistic and longer lifetime of a stripper foil by ensuring proper uses and determining its end of usefulness without any failure. A stripper foil is used for negative hydrogen (${\mathrm{H}}^{\ensuremath{-}}$) stripping to proton (p) for multiturn charge-exchange injection in high-intensity proton accelerators. A longer foil lifetime is expected, while foil failure during operation should be avoided, as it reduces the accelerator availability and also has serious issues for regular accelerator maintenance. A proper use of the foil should also be ensured to minimize the replacement of the foil magazine, as it involves unhealthy radiation exposure to the workers. We have measured the partially stripped ${\mathrm{H}}^{0}$ and unstripped ${\mathrm{H}}^{\ensuremath{-}}$ charge fractions of the injection ${\mathrm{H}}^{\ensuremath{-}}$ beam out of the stripper foil to understand details of foil degradation, such as foil thinning and pinhole formation due to high-intensity beam irradiation, which are believed to be foil breaking signals. We used two independent beam monitoring devices and precisely measured both ${\mathrm{H}}^{0}$ and unstripped ${\mathrm{H}}^{\ensuremath{-}}$ charge fractions by each monitor. As a result, we obtained a detail of foil degradation during operation to determine a realistic end of its usefulness by successfully achieving a record of nearly 2 yr of operation with a single foil without any failures. The detailed measurement result of the foil degradation also gives strong feedback for producing stronger and durable stripper foils. The present research was done by using simple and ordinary beam diagnostic devices including a nondestructive one, which can be easily applied to overcome the stripper foil issues in any similar existing and next-generation further higher-intensity accelerators.
Highlights
The multiturn charge-exchange injection (CEI) of negative hydrogen (H−) is an effective way to increase the proton (p) beam intensity in synchrotrons or storage rings [1,2,3,4]
The present measurement and online monitoring of foil degradation during beam operation itself and, the understanding of the detailed progression of foil degradation are all conducted for the first time in any accelerators which run with the CEI stripping foil
The current transformer (CT) is used for online monitoring of the foil degradation. As both partially stripped H0 and unstripped H− fractions are ideally very small and practically hard to measure in an ordinary way, we utilized a fast Fourier transformation (FFT) analysis of the raw signal taken by the CT to identify even a small fraction of the beam corresponding to the chopping frequency of the injection H− beam, while the integrated beam profile yields measured by the multiwire profile monitor (MWPM) were used for that purpose
Summary
The multiturn charge-exchange injection (CEI) of negative hydrogen (H−) is an effective way to increase the proton (p) beam intensity in synchrotrons or storage rings [1,2,3,4]. A precise measurement of the detailed progression of stripper foil degradation, such as foil thinning and information on the pinhole outbreak during beam irradiation, is a superior way for determining a realistic end of usefulness of a foil to ensure proper uses without any failure for achieving a longer foil lifetime and for strong feedback to the next-generation durable foil production. We have established precise measurement methods and implemented a nondestructive online monitoring system for stripper foil degradation to ensure proper uses of the foil by determining its realistic end of usefulness as well as to achieve a longer foil lifetime without any failures. The present measurement and online monitoring of foil degradation during beam operation itself and, the understanding of the detailed progression of foil degradation are all conducted for the first time in any accelerators which run with the CEI stripping foil. The ppp for the MR is only 1.5 times
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