Neutron Sciences 2008 Annual Report - 17.79 MB - Spallation ...

SNS accelerator complex.
Superconducting
Linac
b = 0.81
High-Energy
Beam Transport
a beam energy of 860 MeV, substantially lower than
the design energy of 1000 MeV, because some superconducting
cavities were out of service and the superconducting
resonators in the high-energy portion
of the linac were operating at 15–20% below their
design accelerating field. To correct these problems,
repairs were completed to two cryomodules and
associated superconducting cavities in the new SNS
repair, maintenance, and testing facilities. The repairs
will allow SNS to operate with 80 of 81 superconducting
cavities, providing a linac output energy of
about 930 MeV.
Accumulator Ring:
compresses the beam
to 700 nanoseconds
Ring-To-Target
Beam Transport
A potential superconducting cavity surface treatment
process was conducted in which a radio-frequency
plasma discharge was established in a superconducting
cavity. The measured accelerating field after
this “plasma cleaning” showed an increase of approximately
15% in cavity field, near the increase
required to boost linac output energy to the design
value of 1000 MeV. Next steps involve further development
of this technique to enable in situ plasma
cleaning of the installed superconducting cavities in
the linac tunnel.
FACILITY DEVELOPMENT 2008 ANNUAL REPORT
Modulators
The radio-frequency waves that power the linac’s accelerating
cavities are generated by klystrons, which
in turn are driven by high-voltage converter modulators
that provide 60 pulses of 10-megawatt power
per second. These are state-of-the-art pulsed power
devices with advanced solid-state, high-speed, highpower
switches.
Since the modulator system accounts for the largest
fraction of unscheduled down time, active efforts
are in progress to improve its reliability. During
2008, the modulator systems were improved to allow
operation at a full repetition rate of 60 pulses per
second. Additional diagnostic and protection systems
were built and installed to allow easier diagnosis and
to protect equipment in the event of failure. A full
replacement of problematic capacitors was initiated
in late 2008, measurably improving reliability in the
final month of 2008 operation.
Contact: Stuart Henderson (shenderson@ornl.gov)
Target
ORNL NEUTRON SCIENCES The Next Generation of Materials Research
59
FACILITY DEVELOPMENT