• H. Okamoto, K. Ito, H. Sugimoto
  HU/AdSM, Higashi-Hiroshima
• H. Higaki
  Hiroshima University, Higashi-Hiroshima
• S.M. Lund
  LLNL, Livermore, California

S-POD (Sim­u­la­tor for Par­ti­cle Orbit Dy­nam­ics) is a table­top, non-neu­tral plas­ma trap sys­tem de­vel­oped at Hi­roshi­ma Uni­ver­si­ty for fun­da­men­tal beam physics stud­ies. The main com­po­nents of S-POD in­clude a com­pact ra­dio-fre­quen­cy quadrupole trap, var­i­ous AC and DC power sup­plies, a vac­u­um sys­tem, a laser cool­er, sev­er­al di­ag­nos­tics, and a com­pre­hen­sive com­put­er con­trol sys­tem. A large num­ber of ions, pro­duced through the elec­tron bom­bard­ment pro­cess, are cap­tured and con­fined in the RFQ trap to em­u­late col­lec­tive phe­nom­e­na in space-charge-dom­i­nat­ed beams trav­el­ing in pe­ri­od­ic lin­ear fo­cus­ing lat­tices. This unique ex­per­i­ment is based on the iso­mor­phism be­tween a one-com­po­nent plas­ma in the lab­o­ra­to­ry frame and a charged-par­ti­cle beam in the cen­ter-of-mass frame. We here em­ploy S-POD to ex­plore the co­her­ent be­ta­tron res­o­nance in­sta­bil­i­ty which is an im­por­tant issue in mod­ern high-pow­er ac­cel­er­a­tors. Ion loss be­hav­iors and trans­verse plas­ma pro­files are mea­sured under var­i­ous con­di­tions to iden­ti­fy the pa­ram­e­ter-de­pen­dence of res­o­nance stop­bands. Ex­per­i­men­tal ob­ser­va­tions are com­pared with PIC sim­u­la­tion re­sults ob­tained with the WARP code.

• H. Sugimoto, K. Ito, H. Okamoto
  HU/AdSM, Higashi-Hiroshima
• S.M. Lund
  LLNL, Livermore, California

Res­o­nant in­sta­bil­i­ties of ion plas­mas con­fined in a lin­ear Paul trap are stud­ied using the par­ti­cle-in-cell code WARP. Trans­verse two-di­men­sion­al model is em­ployed to save com­put­ing time and per­form sys­tem­at­ic in­ves­ti­ga­tions. Both ap­plied and self-field forces are cal­cu­lat­ed with a bound­ary con­di­tion as­sum­ing a quadrupole elec­trode struc­ture. A large num­ber of sim­u­la­tions were car­ried out with rms matched plas­mas to clar­i­fy char­ac­ter­is­tics of the in­sta­bil­i­ty caused by lin­ear and non­lin­ear co­her­ent res­o­nances. Stop band dis­tri­bu­tions pro­duced by the sim­u­la­tion runs are con­sis­tent with the­o­ret­i­cal pre­dic­tion. These re­sults are also com­pared to ex­per­i­men­tal re­sults ob­tained from Hi­roshi­ma Uni­ver­si­ty Paul trap that is de­vel­oped to study beam dy­nam­ics. It is shown that the stop band dis­tri­bu­tions of both nu­mer­i­cal and ex­per­i­men­tal re­sults are good agree­ment each other. We con­firmed from these re­sults that co­her­ent res­o­nances are ex­cit­ed when one of the co­her­ent tunes is close to a half in­te­ger.