THE PEP-14 DATA ACQUISITION SYSTEM

THE M P - 1 4 DATA ACQUISITIOS STSTEH P. B. Madden, D . B a s s e t , 5 . J . F r e e d a a n , ?> A. H a r r i s , C. P . Horna, H. J . Lnaty, J* H a p o l l t a n o , V. V n i l l e a i n Lawrence Berlceley L a b o r a t o r y , B e r k e l e y , C a l i f o r n i a 9 4 7 2 0 Stanford U n i v e r s i t y , Stanford, C a l i f o r n i a 94305 and U n i v e r s i t y o f B e w a i l , H o n o l u l u , H a w a i i 9 6 8 2 2 ABSTRACT He have d e v e l o p e d a r e a l t i m e s o f t w a r e a y s test f o r t h e VAX 1 1 / 7 8 0 which employs t e n p r o c e s s e s c o o p e r a t i n g c o n c u r r e n t l y i n t h e t a s k o f d a t a a c q u i s i t i o n and o n l i n e a n a l y s i s f o r t h e Free Quark S e a r c h e x p e r i m e n t a t t h e new c o l l i d i n g b e a a s t o r a g e r i n g facility (FEP) l o c a t e d a t t h e S t a n f o r d L i n e a r A c c e l e r a t o r C e n t e r - The s y s t e m u t i l i z e s most o f t h e r e s o u r c e s a v a i l a b l e t o t h e a p p l i c a t i o n s programmer under VAX 1 1 / 7 8 0 VMS I n c l u d i n g inter­ p r o c e s s communication v i a m a i l b o x , g l o b a l e v e n t f l a g c l u s t e r , and mapped g l o b a l s e c t i o n , and l a w r i t t e n p r i m a r i l y I n FORTRAN IV PLUS w i t h t i n e c r i t i c a l p o r t i o n s In MACR0-11* A d i s c u s s i o n o f t h e s y s t e m a r c h i t e c t u r e . I m p l e m e n t a t i o n and performance c o m p r i s e s t h e body of t h i s a r t i c l e - INTRODUCTION The Stanford L i n e a r A c c e l e r a t o r Center (SLAC) l a a national research f a c i l i t y o p e r a t e d f o r t h e U> S. Department of Energy b y Stanford U n i v e r s i t y f o r t h e p u r p o s e o f performing e x p e r i m e n t s I n h i g h e n e r g y physics* Designed and c o n s t r u c t e d In a j o i n t effort i n v o l v i n g t h e Lawrence B e r k e l e y Laboratory and SLAC, t h e P o s i t r o n E l e c t r o n P r o j e c t (PEP) i s nearinft c o m p l e t i o n and s e v e r a l new e x p e r i m e n t a l d e t e c t o r s a r e under development to fully exploit the researcn p o t e n t i a l o f t h i s new machine* Specifically, PEP-14 d e s i g n a t e s o n e o f t h e s e detectors and t h e Free Quark Llearch i t I s d e s i g n e d to accomplish* Developed by p h y s i c i s t s from t h r e e I n s t i t u t i o n * i n a c o l l a b o r a t i v e e f f o r t t h e s o f t w a r e system h a s p r o ­ v e n I t s e f f e c t i v e n e s s a f t e r s e v e r a l months o f u s e , and r e p r e s e n t s o n e o f t •>. f i r s t f u l l implementa­ t i o n s a t FEP o f an o n l i n e s y s t e m d e s i g n e d specifi­ cally f o r t h e VAX 11/780* Although o u r d i s c u s s i o n here i s n e c e s s a r i l y a p p l i c a t i o n dependent, the a r c h i t e c t u r e d e s c r i b e d b e l o w l a q u i t e f l e x i b l e and conforms r e a d i l y to many s e t s o f Bystta: r e q u i r e ­ ments* HARDWARE CONFIGURATION readout i s v i a delay ] i n e (four per chamber). Several l a y e r s o f counters on each s i d e o f t h e I n t e r a c t i o n r e g i o n a r e a l s o used t o measure time o f f l i g h t Information* CAHAC The CAHAC s y s t e m r e q u i r e d t o s u p p o r t t h e d e t e c t o r configuration described above i n c l u d e s about 8 0 0 channels o f analog to d i g i t a l converters (ADC's) and 2 5 0 c h a n n e l s o f t i m e t o d i g i t a l c o n v e r t e r s (TDCs)- Additionally, there i s specialized elec­ t r o n i c s a s s o c i a t e d w i t n t h e anode w i r e and d e l a y l i n e r e a d o u t i n t h e MWPC's. The s y s t e m requires two CAHAC o r a n c h e s which i n t e r f a c e v i a SLAC b u i l t branch d r i v e r s through t h e SLAC Trunk UNIBUS D r i v e r (STUD) t o t h e VAX. ( 1 ) The c y c l e time f o r t h e CAHAC I n t e r f a c e i s 4 m i c r o s e c o n d s and a f u l l readout o f d a t a from t h e d e t e c t o r (about 1700 32 b i t words) r e q u i r e s about 10 m i l l i s e c o n d s * VAX 11/780 The configuration of the V X employed by PEP-14 for A software development, data acquisition, hardware t e s t i n g , and i f f l i n e analysis i s given belou* V X 11/780 cpu A Floatlsg point accelerator One megabyte: of physical memory One RF06 disk arive Two TtT-77 magnetic tape drives One V R A E l i n e printer E S T C Two G I N L visual display units R H E L The PEP-14 V X i s one of s i x purchased by PEP to A support the online computing needs of experimental­ ists. Since V X 11/760 V S provides a f a c i l i t y for A M concurrent programming in r R R N IV and a f u l l set O T A of software development t o o l s , the V X 11/780 A is Ideally suited to t h i s task. Additionally, vith i t s 32 b i t word s i z e and virtual memory operating system the V X 11/780 Is also capable of handling A much of the o f f l i n e s c i e n t i f i c computing required by experimenters at SLAC* Detector The PEP-14 d e t e c t o r I s e s p e c i a l l y d e s i g n e d t o l o o k f o r e l e m e n t a r y p a r t i c l e s produced i n e l e c t r o n - p o s i t r o n c o l l i s i o n s a t PEP which have an e l e c t r i c c h a r g e l e s s than t h a t o f t h e e l e c t r o n - o n e d i s t i n ­ g u i s h i n g f e a t u r e o f t h e f r e e quark* The a p p a r a t u s c o n s i s t s o f two i d e n t i c a l s e c t i o n s , arranged on o p p o s i t e s i d e s o f t h e i n t e r a c t i o n r e g i o n , each c o n ­ taining five multi-wire proportional chambers (MWPC's), n i n e l a y e r s of s c i n t i l l a t i o n counters, and one l a y e r o f Cerenkov c o u n t e r s * I t employs 456 p h o t o - m u l t i p l i e r tubes to measure t h e e n e r g y d e p o ­ s i t e d by t h e charged p a r t i c l e s t r a v e r s i n g t h e s c i n ­ tillators and r o u g h l y 1800 c h a n n e l s o f anode readout i n the t e n KVPC's. The M P W C cathode aiSTRiECTlC-, ^ ':'-