Temporal multiplexing for economical measurement of power versus time on NIF Page: 6 of 10
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The digitizer is mounted in a supporting VXI mainframe with power supply. There is room for a control card (local
computer), a communicatios cu anu a total of five digitizer cards, four of which will be the Tektronix TVS 645 and the
fifth, s glower TVS 641 for the backreflection measurement Including labor, the fiber bundles and the ae ...eron.s *t
projected cost is about $6200 per measurement. Fiber bundles are required to reduce speckle modulation, which would be
excessive if a single fiber were used. The fiber bundles are a major labor expense because optical delays of all 20 fibers must
be within 50 ps of each other in order not to affect the overall system rise time significantly. This requires a tedious
procedure of measuring and trimming each of the large number of fibers using an optical time-domain-reflectometer and then
hundlina and ddilng connectors and a protective shield
Preliminary evaluation of the digitizer gives indications that the device meets or exceeds all of the manufacturer's
specifications that we checked. Of concern was crosstalk among channels, which was specified at 30:1 (3 V on one channel
would produce less than 0.1 V on the other channels). During testing, we saw no crosstalk signal on three of the channels at
5 mV sensitivity when the fourth channel was driven with a +_ fast-ise pulse. Other tests sr -nI-uraging
results.
Comment: Although the specified risetime requirement is not met by the system described, and computer processing
wim nave to be used with some compromise in performance on dynamic range, it is likely that improvements in commercial
digitizers will be realized ie i;,B. ip ementat.n ,-n NIC A.. 1ncae. L...Ad...:.l 1. z wlIT al. w .s 11.-
digiizes. .., a,.. e a.iw .n- ai', llJL IL *i.ata~vtfl ,I'u i ru n *inciease inI uaiuwiuui LU 1.3 Jfl WtJrUIU allow US to
achieve our rise-time requirement. Although commercial manufacturers refuse to speculate on future improvements, one
manufacturer now has a 10 GS/s digitizer, and there are commercial RF amplifiers available with bandwidths of several Ghz.
slot 1&2 slot 3&4 slot S&6 sIot 7&8 slot 9&l slot 11
digitizer #1 digitizer #2 digitizer #3 digitizer #4 digitizer i5 communications
card
TVS 645 Card TVS 645 Card TVS 645 Card TVS 645 Card TVS 641Card
r- D1 - - ' .' ' I- r -J-', m II " I I I I .-To.....
I 2:1 : 2 &1 I I I "-
tr.n...rmor . tran:::rmnr r mform Connection
I II I
R1328U F _A
P L 1 \CKreYection I Zot 12
-U - iecronnir PDH
r1328U V I 1 I (see below) I power
PWt k supplies
R1328U chassis
138n roi iv V,..
P 11R1,7 9 I I { I 1 I
P -I-- 2KV I00V
- J to to
y FO bundles from OSPs Vac. Si.
for 16 beam lines PD5 PDS
Figure 4 PoerlhacLreflaetinn sonsor in a V1410 mainframe
3.5 Mainframe chassis
Figure 4 shows the block diagram for one complete system to measure three samples each of 16 beam lines, as well as
their hrkreflertinn. Al nfthe slprtrnnn rnmpnnnontc ore mnun .wt.Atin the Tektronix VXA10 manf-..a Tkhelenses,
fiberoptic delays and photodiodes (PD) are enclosed within two chassis below. The 50 S) photodiode outputs are fed to two-
to-one, coaxial-line, high-speed transformers with four identical 50 0 outputs, which drive each of the four inputs of one
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Thomas, S.; Boyd, B.; Davis, D.T. & Hall, B. Temporal multiplexing for economical measurement of power versus time on NIF, article, October 1, 1996; California. (https://digital.library.unt.edu/ark:/67531/metadc682209/m1/6/: accessed May 5, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.