ZGOUBI USERS' GUIDE - HEP

76 4 DESCRIPTION OF THE AVAILABLE PROCEDURES@w>w>>ww>>>CHAMBR: Long transverse aperture limitationCHAMBR causes the identification, counting and stopping of particles that reach the transverse limits of the vacuumchamber. The chamber can be either rectangular (IFORM = 1) or elliptic (IFORM = 2). The chamber is centered at ², ²and has transverse dimensions o å¨ and o}r¨ such that any particle will be stopped if its coordinates Œ"[ satisfyorif IFORM qŽ8þ¨ŽKv¨ ² ² The conditions introduced with CHAMBR are valid along the optical structure until the next occurrence of the keywordCHAMBR. Then, if ¤;¨ þ¨the chamber ends and information is printed concerning those particles that have been stopped.v¨q the aperture is possibly modified by introducing new values of ², ², å¨ and v¨ , or, if> > Ž q if IFORM @ ² ² The testing is done in optical elements at each integration step, between the EFB’s. For instance, in QUADRUPO therewill be no testing from w § Š to 0 and from §„¨ to § ¨ § Œ , but only from 0 to § ¨ ; in DIPOLE, there is no testing aslong as the ENTRANCE EFB is not reached, and testing is stopped as soon as the EXIT or LATERAL EFB’s are passed.¤;¨ In polar coordinate optical elements stands for the radial coordinate (e.g. with DIPOLE, see Figs. 3C and 10). There-, and having a radial acceptancefore, centering ² 1 22CHAMBR at simulates a chamber curved with1 2radius 1. The testing is done in ESL (DRIFT) at the beginning and the end, and only for positive drifts. There is noo þ¨testing in CHANGREF.When a particle is stopped, its index IEX (see OBJET and section 4.6.8) is set to the value -4, and its actual path length isstored in the array SORT for possible further statistical purposes.