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Pulse ch.rping effect on controlling th. transverse cavity oscillations in nonlinear bubble regime

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Ch.nese Ph.sics B 2017年第2期26卷 313-319页

作者： h.Vosough.an Z Riazi h.afarideh G Sarri Laser and Optic Institute Nuclear Science and Technology Research Institute Tehran Iran ph.sics and Accelerator Sch.ol Nuclear Science and Technology Research Institute Tehran Iran Department of Energy Engineering and Ph.sics Amirkabir University of Technology P. O. Box 15875-4413 Tehran Iran Sch.ol of Math.matics and Ph.sics The Queen's University of Belfast BT7 INN Belfast United Kingdom

Th. propagation of an intense laser pulse in an under-dense plasma induces a plasma wake th.t is suitable for th. acceleration of electrons to relativistic energies. For an ultra-intense laser pulse wh.ch.h.s a longitudinal size sh.rter th.n th. plasma wavelength. λp, instead of a periodic plasma wave, a cavity free from cold plasma electrons, called a bubble, is formed beh.nd th. laser pulse. An intense ch.rge separation electric field inside th. moving bubble can capture th. electrons at th. base of th. bubble and accelerate th.m with.a narrow energy spread. In th. nonlinear bubble regime, due to localized depletion at th. front of th. pulse during its propagation th.ough.th. plasma, th. ph.se sh.ft between carrier waves and pulse envelope plays an important role in plasma response. Th. carrier–envelope ph.se（CEP） breaks down th. symmetric transverse ponderomotive force of th. laser pulse th.t makes th. bubble structure unstable. Our studies using a series of two-dimensional（2D） particle-in-cell（PIC） simulations sh.w th.t th. frequency-ch.rped laser pulses are more effective in controlling th. pulse depletion rate and consequently th. effect of th. CEP in th. bubble regime. Th. results indicate th.t th. utilization of a positively ch.rped laser pulse leads to an increase in rate of erosion of th. leading edge of th. pulse th.t rapidly results in th. formation of a steep intensity gradient at th. front of th. pulse. A more unstable bubble structure, th. self-injections in different positions, and h.gh.dark current are th. results of using a positively ch.rped laser pulse. For a negatively ch.rped laser pulse, th. pulse depletion process is compensated during th. propagation of th. pulse in plasma in such.a way th.t results in a more stable bubble sh.pe and th.refore, a localized electron bunch.is produced during th. acceleration process. As a result, by th. proper ch.ice of ch.rping, one can tune th. number of self-injected electrons, th. size of accelerated bunch

关键词： bubble regime plasma wake field positively ch.rped laser pulse

Optimization and numerical simulation for th. extraction system of th. h.- multicusp ion source

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Ch.nese Ph.sics C 2014年第5期38卷 93-97页

作者： M.h.sseinzadeh.h.afarideh Nuclear Engineering and Ph.sics Department Amirkabir University of Technology

A new ion source h.s been designed and manufactured for th. CYCLONE30 accelerator, wh.ch.h.s a much.advanced performance compared with.th. original. It is expected th.t th. newly designed ion source extraction system will transport a very large percentage of th. beam with.ut deteriorating th. beam optics, wh.ch.is designed to deliver an h. beam at 30 keV. Th. accelerator assembly consists of th.ee circular aperture electrodes made of copper. Th. simulation study was focused on finding parameter sets th.t raise th. beam perveance as large as possible and wh.ch.reduce th. beam divergence as low as possible. Ion beams of th. h.gh.st quality are extracted wh.never th. h.lf-angular divergence is minimum, for wh.ch.th. perveance current intensity and th. extraction gap h.ve optimum values. Th. triode extraction system is designed and optimized by using CST software （for Particle Beam Simulations）. Th. ph.sical design of th. extraction system is given in th.s paper. From th. simulation results, it is concluded th.t it is possible to ach.eve th.s goal by decreasing th. th.ckness of th. plasma electrode, sh.rtening th. first gap, and adjusting th. acceleration electrode voltage.

关键词： multicusp ion source extraction electron tracking perveance angular divergence

Intelligent low-level RF system by non-destructive beam monitoring device for cyclotrons

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Ch.nese Ph.sics C 2016年第4期40卷 98-105页

作者： M.S.Sh.rifi Asadi Malafeh.M.Gh.rgh.reh.h. h.afarideh J.S.Ch.i Yoon Sang Kim Department of Energy Engineering&Ph.sics Amirkabir University of TechnologyTehranIran College of Information&Communication Engineering Sungkyunkwan UniversitySuwonKorea Sch.ot of Computer Science and Engineering Korea University of Technology and EducationCheonanKorea

Th. project of a 10 Me V PET cyclotron accelerator for medical diagnosis and treatment was started at Amirkabir University of Tech.ology in 2012. Th. low-level RF system of th. cyclotron accelerator is designed to stabilize acceleration voltage and control th. resonance frequency of th. cavity. In th.s work an Intelligent Low Level Radio Frequency Circuit or ILLRF, suitable for most AVF cyclotron accelerators, is designed using a beam monitoring device and narrow band tunable band-pass filter. In th.s design, th. RF ph.se detection does not need signal processing by a microcontroller.

关键词： accelerator destructive stabilize tunable resonant acceleration narrow adjust bunch.correction