Minutes of the CLIC Meeting - 12 September 2003
Agenda:
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Latest news from
1) X-Band R&D at SLAC
2) The work being done by the US LC Steering Group
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Speaker:
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Dave Burke
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Dave gave an update of
the latest NLC results and presented the work being done by the US LC Steering
Group. First, he recalled the present NLC design with the new dual-mode
SLED II pulse compression parameters. Then he presented the tests of the
accelerating cavities with the goal to reach less than one breakdown per
10 hours at 65 MV/m, in particular the results of the new 'H-series'
with damping slots and damping manifolds. The tests indicate that the damping
slots have no direct influence on the breakdowns but a small indirect effect:
The small losses they induce require a slightly higher power with the disadvantage
of having more energy stored in the structure.
In their tests, the breakdown rate increases by a factor 10 per about 8 MV/m
increase in the gradient, relatively independent from structure type and
pulse length. The trip history shows so-called 'spitfests': a trip is followed
by more breakdowns with a higher rate than usual, probably caused by a deposition
of melted Cu that is processed away subsequently. Lowering the gradient
to 60 MW/m make the spitfests disappear, increasing the gradient provokes
that the majority of trips occurs with short intervals.
Breakdowns are located typically in the first cells with a high accelerating
gradient. Accordingly, the field profile along the structures was changed
to lower the gradient in the first cells. Dave mentioned that the structures
are fully annealed at 1020°C at the end of assembly. This increases
the grain size which leads to a lower breakdown rate.
Then Dave presented the SLED II baseline test with the goal of reaching
450 MW during 400 ns. The solid state modulator is on-line and drives
4 klystrons, the delay lines have passed microwave 'cold tests'. The next
goal is to install a complete module with 8 structures (a/λ=0.17) with fixed
power splitters in NLCTA. First Permanent Magnet Focused (PPM) klystrons exist
now with the nominal parameters.
Finally, he presented the US LC evaluation based on a list of physics requirements
developed by the USLCSG Physics and Detector Subcommittee. Two technology
options are to be developed: a warm option, based on the design of the NLC
Collaboration, and a cold option, similar to the TESLA design at DESY. The
TESLA design was modified to reach an upgrade energy of 1 TeV, the initial
gradient was chosen as 28 MV/m for 500 GeV. The different designs
are being compared in terms of cost & schedule, siting (either California
or Illinois, not far from Fermilab), availability and risk.
copy of his transparencies (pdf format)
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Frank
Tecker - Last updated 15-09-2003