R&D needed for feasibility demonstration of the machine
The objective of these R&D items is to show that the key machine parameters are not
unrealistic. In particular, a proof of existence of the basic critical constituents of the
machines should be available upon completion of the Ranking 1 R&D items.
TESLA Upgrade to 800 GeV c.m.
The Energy Working Group considers that a feasibility demonstration of the machine
requires the proof of existence of the basic building blocks of the linacs. In the case of
TESLA at 500 GeV, such demonstration requires in particular that s.c. cavities
installed in a cryomodule be running at the design gradient of 23.8 MV/m. This has
been practically demonstrated at TTF1 with cavities treated by chemical processing1.
The other critical elements of a linac unit (multibeam klystron, modulator and power
distribution) already exist.
- The feasibility demonstration of the TESLA energy upgrade to about 800 GeV
requires that a cryomodule be assembled and tested at the design gradient of
1Knowing that electropolished cavities sustain signficantly higher gradients than chemically polished cavities,
there is little doubt that cryomodules running at about 24 MV/m can be built.
35 MV/m. The test should prove that quench rates and breakdowns, including
couplers, are commensurate with the operational expectations. It should also
show that dark currents at the design gradient are manageable, which means
that several cavities should be assembled together in the cryomodule. Tests with
electropolished cavities assembled in a cryomodule are foreseen in 2003.
- The proposed choke-mode structures have not been tested at high power yet.
High power testing of structures and pulse compressors at the design parameters
are needed for JLC-C. Tests are foreseen at KEK and at the SPring-8 facility in
the next years.
- For JLC-X/NLC, the validation of the presently achieved performance (gradient
and trip rates) of low group velocity structures - but with an acceptable average
iris radius, dipole mode detuning and manifolds for damping - constitutes the
most critical Ranking 1 R&D issue. Tests of structures with these features are
foreseen in 2003.
- The other critical element of the rf system is the dual-moded SLED-II pulse
compression system. Tests of its rf power and energy handling capability at
JLC-X/NLC design levels are planned in 2003. As far as the 75 MW X-band
PPM klystron is concerned, the Working Group considers the JLC-X PPM-2
klystron a proof of existence (although tested only at half the repetition rate). A
similar comment can be made regarding the solid-state modulator tested
- The presently tested CLIC structures have only been exposed to very short
pulses (30 ns maximum) and were not equipped with wakfield damping. The
?²3rst Ranking 1 R&D issue is to test the complete CLIC structures at the design
gradient and with the design pulse length (130 ns). Tests with design pulse length
and with undamped structures are foreseen when CTF3 is available (April 2004).
- The validation of the drive beam generation with a fully loaded linac is foreseen
in CTF3. Beam dynamics issues and achieving the overall efficiency
- In the present CLIC design, an entire drive beam section must be turned off on
any fault (in particular on any cavity fault). CLIC needs to develop a mechanism
to turn off only a few structures in the event of a fault. At the time of writing
this report, there is no specific R&D program aimed at that objective but
possible schemes are being studied.