The VLPC Cassette Top in the Baseline Approach

In the fiber tracker, scintillating fibers are arranged in ribbon layers. To form the Level 1 trigger, axial fibers have to be grouped in trigger sectors, narrow `phi' wedges encompassing fibers from all layers. This can be done either using a mixer box or patch panel somewhere en route from the tracker to the VLPC cryostat, or, as in the current baseline approach, without such a device. Routing the fibers from the axial CFT and CPS layers to the VLPC cassettes without a separate mixer box essentially means integrating the patch panel into the cassette top. This note is meant to help investigate the viability of this `mixerless' approach, by laying out the fiber connection scheme on top of the cryostat.

In this approach, detector ribbons connect to 256-fiber light guides running the full length to the VLPC cryostats. About two feet above the trigger cryostat, each light guide splits into 16 substrands of 16 fibers each. 64 16-fiber connectors plug into a single 1024-channel cassette. This is the connection scheme for the odd layers A, C, E, and G. For the even layers, there are a few complications. Some 8-fiber substrands are required, yielding light guide types with varying numbers of 8- and 16-fiber substrands (cf. Table 1). Connecting those to the cassette requires a few (on average, five per cassette) 8-fiber patches. These can be constructed using 'flying Y’ plugs above the cassette. The ‘Y’s are made from three 16-fiber connectors. Two half-populated connectors receive fibers from different ribbons and patch them via short (1-2’’) leads into a single 16-fiber connector, which then plugs into the cassette. Table 1 shows the basic trigger sector pattern of 480 fibers total. This pattern determines the light guide construction.

 

layer	trigger sector pattern	multiplier wrt layer A	total pattern width, in ribbons	number of different light guide types	number of ribbons per 8-cassette sector	number of substrands per light guide bundle
A	16-16	1	1	1	2	16
B	16-16-8	1.25	5	5	2.5	19-20
C	16-16-16	1.5	3	1	3	16
D	16-16-16-8	1.75	7	7	3.5	22-23
E	16-16-16-16	2	1	1	4	16
F	16-16-16-16-8	2.25	9	9	4.5	18-19
G	16-16-16-16-16	2.5	5	1	5	16
H	16-16-16-16-16-8	2.75	11	11	5.5	17-18
Total				36

For example, the five different B-layer light guide patterns are:

 Id                  pattern                                          # of substrands

B1:          (8-16-16)₁ … (8-16-16)₅-(8-16-16)₆-8-8             20
B2:   8-16-(8-16-16)₁ … (8-16-16)₅ -8-16-8                       20
B3:       8-(8-16-16)₁ … (8-16-16)₅-(8-16-16)₆-8                20
B4: 16-16-(8-16-16)₁ … (8-16-16)₅ -8-16                         19
B5:      16-(8-16-16)₁ … (8-16-16)₅-(8-16-16)₆                       19
 

Table 2 shows the connection pattern on the cassette top, for a sector of eight cassettes, one fifth of the detector. Each cassette holds two front-end boards with 512 trigger channels. Two columns of sixteen 16-fiber plugs correspond to one front-end board.

Within the connector space corresponding to one FE board, 16-fiber plugs are running left to right, and top to bottom. Plugs from Layer A occupy the first row. The light guide from detector ribbon A1 covers the first four cassettes, ribbon A2 the next four.

Plugs from layer H, which for trigger reasons has to be next to layer A on the FE board, occupy the next five and a half plug positions for each FE board. The last H-plug in each FE board shares the cassette top location with an 8-fiber substrand from layer B, using the ‘Y’ plug interface described above. As can be seen e.g. for the H2/H3 transition on the right FE board of cassette 3, occasionally the last eight fibers from one ribbon share a 16-fiber plug with the first eight fibers from the next ribbon in the same layer, which necessitates employing an additional ‘Y’ interface.

The last row, in module 8 of the cassettes, receives the signals from the axial strips of the central preshower detector. Indicated is the CPS octant number; substrands with odd numbers are coming from the left end of the detector, even substrands from the right. It makes sense to use 160-fiber light guide bundles for the CPS.

A FORTRAN program exists that creates both the cassette top layout and the labels for the clear waveguide substrands. These labels, which are to be applied to the waveguides at construction time, contain both the consecutive substrand number as well as the cassette top location where each substrand is to be plugged in. This should render making the fiber connections fairly easy and straightforward. A mock-up to test the feasibility of this approach in praxis has been built.

cassette 1

cassette 2

cassette 3

cassette 4

left FE board

right FE board

left FE board

right FE board

left FE board

right FE board

left FE board

right FE board

A1- 1

A1- 2

A1- 3

A1- 4

A1- 5

A1- 6

A1- 7

A1- 8

A1- 9

A1-10

A1-11

A1-12

A1-13

A1-14

A1-15

A1-16

H1- 1

H1- 2

H1- 7

H1- 8

H1-13

H1-14

H2- 2

H2- 3

H2- 8

H2- 9

H2-14

H2-15

H3- 3

H3- 4

H3- 9

H3-10

H1- 3

H1- 4

H1- 9

H1-10

H1-15

H1-16

H2- 4

H2- 5

H2-10

H2-11

H2-16

H2-17

H3- 5

H3- 6

H3-11

H3-12

H1- 5

H1- 6 B1- 1

H1-11

H1-12 B1- 4

H1-17

H2- 1 B1- 7

H2- 6

H2- 7 B1-10

H2-12

H2-13 B1-13

H2-18     H3 1

H3- 2 B1-16

H3- 7

H3- 8 B1-19

H3-13

H3-14  B2- 3

B1- 2

B1- 3

B1- 5

B1- 6

B1- 8

B1- 9

B1-11

B1-12

B1-14

B1-15

B1-17

B1-18

B1-20      B2 1

B2- 2

B2- 4

B2- 5

G1- 1

G1- 2

G1- 6

G1- 7

G1-11

G1-12

G1-16

G2- 1

G2- 5

G2- 6

G2-10

G2-11

G2-15

G2-16

G3- 4

G3- 5

G1- 3

G1- 4

G1- 8

G1- 9

G1-13

G1-14

G2- 2

G2- 3

G2- 7

G2- 8

G2-12

G2-13

G3- 1

G3- 2

G3- 6

G3- 7

G1- 5

C1- 1

G1-10

C1- 4

G1-15

C1- 7

G2- 4

C1-10

G2- 9

C1-13

G2-14

C1-16

G3- 3

C2- 3

G3- 8

C2- 6

C1- 2

C1- 3

C1- 5

C1- 6

C1- 8

C1- 9

C1-11

C1-12

C1-14

C1-15

C2- 1

C2- 2

C2- 4

C2- 5

C2- 7

C2- 8

F1- 1

F1- 2

F1- 6

F1- 7

F1-11

F1-12

F1-16

F1-17

F2- 4

F2- 5

F2- 9

F2-10

F2-14

F2-15

F2-19     F3 1

F3- 2

F1- 3

F1- 4

F1- 8

F1- 9

F1-13

F1-14

F1-18 F2 1

F2- 2

F2- 6

F2- 7

F2-11

F2-12

F2-16

F2-17

F3- 3

F3- 4

F1- 5 D1- 1

D1- 2

F1-10 D1- 5

D1- 6

F1-15 D1- 9

D1-10

F2- 3 D1-13

D1-14

F2- 8 D1-17

D1-18

F2-13 D2- 3

D2- 4

F2-18     D2- 7

D2- 8

F3- 5 D2-11

D2-12

D1- 3

D1- 4

D1- 7

D1- 8

D1-11

D1-12

D1-15

D1-16

D1-19 D2 1

D2- 2

D2- 5

D2- 6

D2- 9

D2-10

D2-13

D2-14

E1- 1

E1- 2

E1- 5

E1- 6

E1- 9

E1-10

E1-13

E1-14

E2- 1

E2- 2

E2- 5

E2- 6

E2- 9

E2-10

E2-13

E2-14

E1- 3

E1- 4

E1- 7

E1- 8

E1-11

E1-12

E1-15

E1-16

E2- 3

E2- 4

E2- 7

E2- 8

E2-11

E2-12

E2-15

E2-16

CPS1- 1

CPS1- 2

CPS1- 3

CPS1- 4

CPS1- 5

CPS1- 6

CPS1- 7

CPS1- 8

CPS1- 9

CPS1-10

CPS1-11

CPS1-12

CPS1-13

CPS1-14

CPS1-15

CPS1-16

cassette 5

cassette 6

cassette 7

cassette 8

left FE board

right FE board

left FE board

right FE board

left FE board

right FE board

left FE board

right FE board

A2- 1

A2- 2

A2- 3

A2- 4

A2- 5

A2- 6

A2- 7

A2- 8

A2- 9

A2-10

A2-11

A2-12

A2-13

A2-14

A2-15

A2-16

H3-15

H3-16

H4- 3

H4- 4

H4- 9

H4-10

H4-15

H4-16

H5- 4

H5- 5

H5-10

H5-11

H5-16

H5-17

H6- 4

H6- 5

H3-17

H3-18

H4- 5

H4- 6

H4-11

H4-12

H4-17

H4-18 H5 1

H5- 6

H5- 7

H5-12

H5-13

H5-18

H6- 1

H6- 6

H6- 7

H4- 1

H4- 2 B2- 6

H4- 7

H4- 8 B2- 9

H4-13

H4-14 B2-12

H5- 2

H5- 3 B2-15

H5- 8

H5- 9 B2-18

H5-14

H5-15 B3- 2

H6- 2

H6- 3  B3- 5

H6- 8

H6- 9  B3- 8

B2- 7

B2- 8

B2-10

B2-11

B2-13

B2-14

B2-16

B2-17

B2-19

B2-20  B3 1

B3- 3

B3- 4

B3- 6

B3- 7

B3- 9

B3-10

G3- 9

G3-10

G3-14

G3-15

G4- 3

G4- 4

G4- 8

G4- 9

G4-13

G4-14

G5- 2

G5- 3

G5- 7

G5- 8

G5-12

G5-13

G3-11

G3-12

G3-16

G4- 1

G4- 5

G4- 6

G4-10

G4-11

G4-15

G4-16

G5- 4

G5- 5

G5- 9

G5-10

G5-14

G5-15

G3-13

C2- 9

G4- 2

C2-12

G4- 7

C2-15

G4-12

C3- 2

G5- 1

C3- 5

G5- 6

C3- 8

G5-11

C3-11

G5-16

C3-14

C2-10

C2-11

C2-13

C2-14

C2-16

C3- 1

C3- 3

C3- 4

C3- 6

C3- 7

C3- 9

C3-10

C3-12

C3-13

C3-15

C3-16

F3- 6

F3- 7

F3-11

F3-12

F3-16

F3-17

F4- 3

F4- 4

F4- 8

F4- 9

F4-13

F4-14

F4-18

F5- 1

F5- 5

F5- 6

F3- 8

F3- 9

F3-13

F3-14

F3-18

F4- 1

F4- 5

F4- 6

F4-10

F4-11

F4-15

F4-16

F5- 2

F5- 3

F5- 7

F5- 8

F3-10 D2-15

D2-16

F3-15 D2-19

D3- 1

F4- 2 D3- 4

D3- 5

F4- 7 D3- 8

D3- 9

F4-12 D3-12

D3-13

F4-17 D3-16

D3-17

F5- 4 D4- 2

D4- 3

F5- 9 D4- 6

D4- 7

D2-17

D2-18

D3- 2

D3- 3

D3- 6

D3- 7

D3-10

D3-11

D3-14

D3-15

D3-18

D4- 1

D4- 4

D4- 5

D4- 8

D4- 9

E3- 1

E3- 2

E3- 5

E3- 6

E3- 9

E3-10

E3-13

E3-14

E4- 1

E4- 2

E4- 5

E4- 6

E4- 9

E4-10

E4-13

E4-14

E3- 3

E3- 4

E3- 7

E3- 8

E3-11

E3-12

E3-15

E3-16

E4- 3

E4- 4

E4- 7

E4- 8

E4-11

E4-12

E4-15

E4-16

CPS2-1

CPS2-2

CPS2-3

CPS2-4

CPS2-5

CPS2-6

CPS2-7

CPS2-8

CPS2-9

CPS2-10

CPS2-11

CPS2-12

CPS2-13

CPS2-14

CPS2-15

CPS2-16