Realization of a phase bunching effect for minimization of beam phase width in a central region of an AVF cyclotron

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• 作者：Nobumasa Miyawaki^a ; ^{miyawaki.nobumasa@jaea.go.jp} ; Mitsuhiro Fukuda^b ; Satoshi Kurashima^a ; Susumu Okumura^a ; Hirotsugu Kashiwagi^a ; Takayuki Nara^a ; Ikuo Ishibori^a ; Ken-ichi Yoshida^a ; Watalu Yokota^a ; Yoshiteru Nakamura^a ; Kazuo Arakawa^a ; Tomihiro Kamiya^a
• 关键词：AVF cyclotron ; Central region ; Beam phase
• 刊名：Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment
• 出版年：2011
• 出版时间：21 April 2011
• 年：2011
• 卷：636
• 期：1
• 页码：41-47
• 全文大小：718 K

文摘

A phase bunching effect has been achieved for the first time using a rising slope of the dee voltage waveform produced at the first acceleration gap between the RF shielding cover of the inflector and the puller in the new central region of the JAEA AVF cyclotron. The feasibility of the phase bunching effect in the central region for a two-dee system with a span angle of 86° in three acceleration harmonic modes was assessed by a simple geometrical analysis of particle trajectories and a three-dimensional beam orbit simulation using the calculated electric field and a measured magnetic field. The simulation indicated that the initial beam phase width of 40 RF degrees is compressed to 11 RF degrees (about 28 % of the initial phase width) in the second harmonic mode. A phase width of 1.5 RF degrees FWHM for a 260 MeV ²⁰Ne⁷⁺ beam accelerated in the second harmonic mode was observed when using a 4 mm phase slit gap. The phase width reduction was considerably enhanced by the bunching effect, compared with the beam phase width of 7.3 RF degrees FWHM in the same harmonic mode for a 10 MeV H⁺ beam accelerated in the original central region. The ratio of the beam current for the 1.5 RF degrees FWHM phase width with 4 mm phase slit gap restriction to the full beam current without the phase slit was drastically improved to 80 % , while the beam current was less than 1 % of the full beam when narrowing the phase slit gap to obtain the 7.3 RF degrees FWHM phase width in the original central region.