Numbering in GRETINA

Here, we try to summarize the various numbering schemes with the GRETINA system; both geometry related and electronics related.  The majority of this is summarized in this project document.  The take-home message here -- book-keeping with GRETINA is critical!
Geometry within GRETINA


Hole Numbers in the Array
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There are 30 mounting positions for the full 4pi GRETA array; the GRETINA frame uses the hole-numbering convention envisioned for GRETA, with available hole numbers from 1-30, though with the current GRETINA frame, not all hole numbers are accessible (21 holes can be populated in total for the GRETINA hemispheres).  The hole numbers, and theta/phi positions relative are summarized in the table below.  Note the coordinate system convention: z-axis is beam; x-axis is gravity (pointing down), and y-axis is defined by right-hand-rule.

Mounting Position (Hole #) Theta (degrees) Phi (degrees)  Comments 
1 31.72  36  Not in GRETINA 
2 108 Not in GRETINA
3 180 Not in GRETINA 
4 251 Not in GRETINA 
5 323 Not in GRETINA 
6 58.28 72  West hemi 
7 144 West hemi 
8 216 East hemi 
9 288 East hemi 
10 360 Not in GRETINA 
11 90.00 18  West hemi 
12 54 West hemi 
13 90 Axial support
14 126 West hemi 
15 162 West hemi
16 198 East hemi 
17 234 East hemi 
18 270 Axial support 
19 306 East hemi 
20 342 East hemi 
21 121.72 36  West hemi 
22 108 West hemi 
23 180 Interferes in GRETINA 
24 252 East hemi 
25 324 East hemi 
26 148.28 72  West hemi 
27 144 West hemi 
28 216 East hemi 
29 288 East hemi 
30 360 West hemi 

Within each mounting hole, a quad can be mounted in only orientation, thus fixing the positions of the four individual crystals in each hole position.  The crystal-specific angles (to the front center of each crystal; (0, 0, 0) in the crystal coordinate frame) are summarized on pg. 4 of the numbering document.  

Okay -- but how do I know the hole number?

Aside from the fact that you hopefully know when analyzing an experiment where the GRETINA quads were mounted, the hole number information is encoded in the mode3 (raw) and mode2 (decomp) data streams.  The extraction of the hole number is summarized below.

Mode2 (Decomp) Data:
    In the mode2 data struct, the variable "crystal_id" can be decoded to get the hole number.  "crystal_id/4" gives the hole number, while "crystal_id%4" gives the crystal number within that hole (i.e. from 0-3, or 1-4 depending on how you want to count). 

Mode3 (Raw) Data:
    In the mode3, it's a little harder to get at the hole number; the value is encoded as part of hdr[1] (see data structure description).  The equivalent of "crystal_id" from mode2 is derived as "hdr[1] >> 6".  As above, the hole number is then "crystal_id/4", while "crystal_id%4" gives the crystal number within that hole (i.e. from 0-3, or 1-4 depending on how you want to count). 

Electronics within GRETINA


Segment Ordering in the Electronics
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For Q3-Q8 (and hopefully beyond) the connection between the electronics channel a segment is plugged into and the segment number is fairly straight forward.  Q1 and Q2 were early, so they're quirky.  Back to that later. 

First things first -- segment numbering in general.

Segment have two labeling schemes- segment number from 0-35 (or 1-36) and the layer-column scheme.  The layer-column scheme uses greek letters to denote layers (α, β, γ, δ, ε, φ) from the front of the crystal to the back, and numbers to denote wedges (1-6, where 1 is always on the inside of the quad overall, and numbering is counterclockwise when looking from the front of the detector.  See the picture on the right.

Here is the connection between the segment number and layer-column schemes:

Segment # Segment ID    Segment #  Segment ID 
α1   18 δ1
1 α2   19 δ2
2 α3   20 δ3
3 α4   21 δ4
4 α5   22 δ5
5 α6   23 δ6
6 β1   24 ε1
7 β2   25 ε2
8 β3   26 ε3
9 β4   27 ε4
10 β5   28 ε5
11  β6   29 ε6
12 γ1   30 φ1
13 γ2   31 φ2
14 γ3   32 φ3
15 γ4   33 φ4
16 γ5   34 φ5
17 γ6   35 φ6

In the GRETINA electronics, each crystal (40 signals = 36 segments + 4 copies of the CC) occupies one electronics bank, consisting of an IOC, and 4 x 10-channel digitizers.  The convention is to think of the electronics channels for a given bank as channels 0-39, in order.  Signals are connected with the first 9 channels on each board as segment and the tenth channel as a copy of the CC.  The mapping of electronics channel to segment # is as follows.  Note the differences in Q1 and Q2 (certain positions only) compared to ALL other quads.

Bank Electronics Channel Digitizer #  Board Channel #   Q1 Position 1/3 Segment #  Q2 Position 1/3 Segment # Q1 Positions 2/4;
Q2 Positions 2/4;
Q3-Q8 (Positions 1-4) Segment #
0 1 (α2) 0 (α1) 0 (α1)
1 8 (β3) 1 (α2) 1 (α2)
2 3 (α4) 2 (α3) 2 (α3)
3 4 (α5) 3 (α4) 3 (α4)
4 35 (φ6) 4 (α5) 4 (α5)
5 0 (α1) 5 (α6) 5 (α6)
6 7 (β2) 6 (β1) 6 (β1)
7 14 (γ3) 7 (β2) 7 (β2)
8 8 9 (β4) 8 (β3) 8 (β3)
9 CC1  CC1  CC1 
10 10 (β5) 9 (β4) 9 (β4)
11 1 29 (ε6) 10 (β5) 10 (β5)
12 2 30 (φ1) 11 (β6) 11 (β6)
13 3 13 (γ2) 12 (γ1) 12 (γ1)
14 20 (δ3)  13 (γ2) 13 (γ2)
15 15 (γ4) 14 (γ3) 14 (γ3)
16 16 (γ5) 15 (γ4) 15 (γ4)
17 23 (δ6) 22 (δ5) 16 (γ5)
18 24 (ε1) 17 (γ6) 17 (γ6)
19 CC2  CC2 CC2 
20 19 (δ2)  18 (δ1) 18 (δ1)
21 26 (ε3) 19 (δ2)  19 (δ2) 
22 21 (δ4) 20 (δ3) 20 (δ3) 
23 3 22 (δ5) 21 (δ4) 21 (δ4)
24 17 (γ6) 16 (γ5) 22 (δ5)
25 18 (δ1) 23 (δ6) 23 (δ6)
26 25 (ε2)  24 (ε1) 24 (ε1)
27 32 (φ3) 25 (ε2) 25 (ε2)
28 27 (ε4) 26 (ε3) 26 (ε3)
29 CC3 CC3  CC3 
30 28 (ε5) 27 (ε4) 27 (ε4)
31 11 (β6) 28 (ε5) 28 (ε5)
32 12 (γ1) 29 (ε6) 29 (ε6)
33 31 (φ2) 30 (φ1) 30 (φ1)
34 2 (α3) 31 (φ2) 31 (φ2)
35 33 (φ4) 32 (φ3) 32 (φ3)
36 34 (φ5) 32 (φ3) 32 (φ3)
37 5 (α6) 34 (φ5) 34 (φ5)
38 6 (β1) 35 (φ6) 35 (φ6)
39 CC4 CC4 CC4