Power and phase monitoring system for the lower hybrid phased array heating system on ATC machine Page: 4 of 20
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The end product of the monitoring system is
graphic computer output of forward and rEverse
power versus time for each waveguide in vi antenna
array (Fig. 1), and a series of plots of the courier
spectrum of the radiation fields in front of the
array in ni space (parallel to the toroidal
magnetic field on ATC). This output is tsed to
assist system tuning (an involved process of inter-
acting adjustments) and to evaluate theory.
Although directional couplers, tuners and
detection equipment are located on the ATC platform
to minimize errors due to carrier frequency drift,
temperature and load changes, a grounding problem
is created because of the stray ohmic heating fields
in the vicinity. Considerable caution is taken to
eliminate ground loops which would disturb mrasure-
ments. All detection electronics are en. c:wd in
an RFI shielded rack into which enters only K' t!t-
nals and 60 cycle power. Outputs are dif Vrontially
driven shielded twisted pairs.
RF System Outputs
Detore tuner feaw.Ad power
Before tuner reverse power
After tuner forward power
After tuner reverse power
After tuner quadrature
The Data Aquisition Services group at PPL has
built a 32 channel analog magnetic drum transient
recording system (Fig. 2) with a 100 Ki-'z bandwidth
and a 30 ms track length. Its differential inputs
are driven directly by the monitoring system outputs.
Since the drum is several hundred feet from the
machine platform, the twisted pairs are properly
terminated on both ends. The analog signals are
IN modulated before recording. When read back,
they are demodulated, filtered and digitized at a
software selectable but maximum rate of 1 point
every 10 us. One 20 ms experiment generates 64K
10 bit words when digitized at maximu: throughput.
The interface to the DAS-1800 computer (also
designed and constructed by DAS) cannot pass and
process this much data in-between events (90 sec.
apart) so a PDP-8/I, designated to the control of
data transfer, is used to block out a rch smaller,
software selectable, segment of data rxer a limited -
time span for transfer to the DAS-180.
A calibration pulse, generated rn the platform
and applied to each signal input, is freshly record-
ed on the drum each cycle and is used :z correct
gain and offset drift errors during arlysis.
Since the drum is a relatively r.::sy system
(30 mV rms noise at 100 SHz BW), a prcramable
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Reed, B.W. Power and phase monitoring system for the lower hybrid phased array heating system on ATC machine, article, January 1, 1975; New Jersey. (digital.library.unt.edu/ark:/67531/metadc869483/m1/4/: accessed November 14, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.