Fast SCR Thyratron Driver Page: 3 of 3
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C.05kV [
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Fig. 4: Voltage rises before and after 1-stage sharpener,
and saturating reactor voltage.
Fast turn-on diode D3 and transzorb D4 are used to limit
the anode reverse and forward blocking voltages. On the
output side, VR1, which consists of two series GE metal-
oxide varistors rated 180 joules at 1.2 kV each, clamps
down transient voltages while diode D5 blocks the
reverse current. To further reduce the chance of an SCR
failure by a soft turn-on due to high ground potentials,
which can sometimes build up on the gate after a rapid set
of thyratron fire-throughs, an active feedback scheme is
employed. A portion of the output voltage is gated
through U6 with the 120 ps command trigger pulse. A
thyratron arc that randomly occurs outside this timing
window would immediately turn on the SCR and shut off
the high voltage supply for a period of 1 second before
returning to normal operation.
For ease of manufacture and low assembling cost, all
connectors and electrical components were mounted on a
single 0.093 inches thick PC board. One exception was
the output HN connector that must be mounted directly
on the chassis for mechanical strength. The driver was
simply constructed by fitting together the PC board, front,
rear, and side panels of a standard 19 x 5.25 x 8 inches
rackmount chassis. Figure 5 shows a photograph of the
complete trigger generator PC board.
Fig. 5: Photograph of the complete driver on PC board.
3 PERFORMANCE
Jitter and long-term timing drift were measured with SR-
620 Universal Time Interval Counter. The test conducted-
-L
at 120 Hz with a sample size of 5000 shots. A typical
result of jitter distribution is shown in figure 6. The graph
displays a peak-to-peak jitter of 320 ps with standard
deviation or RMS jitter of 72 ps. Throughput delay,
defined as the timing difference (on rising edges at half
maximum) between the trigger input and the pulsed
output, is 580 ns. A 24-hrs run test at 200C temperature
excursion resulted in a timing drift of less than 3 ns.
0 FR11 - 5OG,170 rr-
Mean =R6 ps
Sigma J 072 p
3- -
Fi.Y: Hitora ofjitr .itrbtin
30
20
151
,5 -20 -15 -i 5 0 5 OIC 15 20 25
T-1 ex 10-1 bins= 50
Fig. 6: Histogram of jitter distribution.
The mean time to failure (MTTF) rate, which was
calculated based on actual data collected over several
years, is 195,000 hours. More detailed discussions of the
modulator reliability can be found in the report [5].
4 CONCLUSION
New thyratron drivers for the 244 SLAC klystron
modulators have been economically built and operated
since 1994. In several years of operation, these drivers
have contributed to the modulator stability and proven to
be very reliable.
5 ACKNOWLEDGMENTS
The author wishes to thank R. Cassel for his valuable
comments, A. Donaldson for support and editing help, and
the AMW crew for their hard work in bringing this project
to a successful completion.
6 REFERENCES
[1] T. Mattison et al.,"Status of the SLC Damping Ring Kicker
Systems", Proc. of the 1991 IEEE Particle Accelerator Conf.., San
Francisco, pp. 2955 - 7.
[2] M. Nguyen and R. Cassel, "Fast Thyratron Driver", Proc. of the
1991 IEEE Particle Accelerator Conf.., San Francisco, pp. 3153-5.
[3] G. N. Glasoe and J. V. Lebacqz, "Pulse Generators", New York
and London, 1948, McGraw-Hill Book Company, Inc.
[4] A. R. Donaldson et al., "Kicker Experience from SLC", Proc. of
the 1991 IEEE Particle Acc. Conf., San Francisco, pp. 3165 - 7.
[5] A. R. Donaldson , "SLAC Modulator System Improvements and
Reliability Results", Proc. of the 1998 International Power
Modulator Symposium, Rancho Mirage, pp. 74 - 9.
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Nguyen, M. N. Fast SCR Thyratron Driver, article, June 18, 2007; [Menlo Park, California]. (https://digital.library.unt.edu/ark:/67531/metadc881785/m1/3/: accessed April 24, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.