R&D needed to finalize design choices and ensure reliability of the machine
These R&D items should validate the design of the machine, in a broad sense. They
address the anticipated difficulties in areas such as the architecture of the subsystems,
beam physics and instabilities, and tolerances. A very important objective is also to
examine the reliability and operability of the machine, given the very large number of
components and their complexity.
- To finalize the design choices and evaluate reliability issues it is important to
fully test the basic building block of the linac. For TESLA, this means several
cryomodules installed in their future machine environment, with all auxiliaries
running, like pumps, controls, etc. The test should as much as possible simulate
realistic machine operating conditions, with the proposed klystron, power
distribution system and with beam. The cavities must be equipped with their
final HOM couplers, and their relative alignment must be shown to be within
requirements. The cryomodules must be run at or above their nominal field for
long enough periods to realistically evaluate their quench and breakdown rates.
This Ranking 2 R&D requirement also applies to the upgrade. Here, the
objectives and time scale are obviously much more difficult.
- The development of a damping ring kicker with very fast rise and fall times
- For the TESLA damping ring particle loss simulations, systematic and random
multipole errors, and random wiggler errors must be included. Further dynamic
aperture optimization of the rings is also needed.
- The energy and luminosity upgrade to 800 GeV will put tighter requirements on
damping ring alignment tolerances, and on suppression of electron and ion
instabilities in the rings. Further studies of these effects are required.
- In the present TESLA design, the beams collide head-on in one of the IRs. The
trade-offs between head-on and crossing-angle collisions must be reviewed,
especially the implications of the present extraction-line design. Pending the
outcome of this review, the possibility of eventually adopting a crossing-angle
layout should be retained.
- The TESLA single tunnel configuration appears to pose a significant reliability
and operability risk because of the possible frequency of required linac accesses
and the impact of these accesses on other systems, particularly the damping
rings. TESLA needs a detailed analysis of the impact on operability resulting
from a single tunnel.
- The klystrons and modulators should be tested successfully at the nominal
100 Hz repetition rate.
- This should lead to the full test of the linac subunit, with beam. This will
include klystrons, modulator, pulse compression system, LLRF control and
several structures in their future environment.
- There must be a full test of the JLC-X PPM klystron at the specified repetition
rate of 120 or 150 Hz.
- These klystrons should be tested with the NLC modulator (at full specs and
including arcing tests) and form part of a linac subunit test. The latter should
also comprise the dual-moded SLED-II complete system, several damped and
detuned structures, installed in the accelerator environment (with temperature
control, for instance), and LLRF and controls systems. The test should be made
with beam. The present plan is to perform this sort of test with a full girder of
structures (some of them being detuned and damped) in 2004.
- Present tests have demonstrated the advantages of tungsten and molybdenum
irises in reaching the highest gradients in accelerator structures. These tests
should be pursued, possibly also with other materials, for application to CLIC
and possibly other machines.
- The very high power of the drive beam and its stability are serious concerns for
CLIC. The drive beam stability should be validated, and the drive beam
Machine Protection System, which is likely to be a complex system, should be
designed to protect the decelerator structures.
- The test of a relevant linac subunit with beam is required. This is one of the
purposes of CTF3, which should start operation in 2004.
xl ILC-TRC/Second Report
Ranking of Recommended R&D Issues
- The validation of the proposed multibeam klystron performance is needed to
finalize the design choices for the CLIC drive beam generation. This applies
particularly to the 3 TeV energy upgrade (long pulse).
Low Emittance Transport
- Calculations of the effects of coherent synchrotron radiation on the CLIC bunch
compressors must be performed.
- An extraction line design for 3 TeV c.m. must be developed.
Items Common to All Machines
- For all the damping ring designs, further simulation studies are needed to
understand the magnitude of the electron cloud effects and to explore possible
means of suppressing these effects. Experiments in existing rings are needed to
test the electron cloud simulations. Possible cures for the electron cloud
(including chamber coatings, superimposed magnetic fields, and gaps in the
bunch pattern) need to be experimentally investigated.
- Further simulations of the fast ion instability are also necessary. Experiments in
the ATF and other suitable rings are needed to test the predictions of
- Damping ring extraction kicker stability, required at the level of <10-3, is an
important issue. Continued studies including experiments with the ATF double
kicker system are needed.
- Finally, additional simulations of emittance correction in the damping rings are
needed, including the effects listed in Section 184.108.40.206. Additional experiments in
the ATF and other operating rings are needed to test the emittance
Low Emittance Transport
- For all low emittance transport designs, the static tuning studies, including
dynamic effects during correction, must be completed.
- The most critical beam instrumentation, including the intra-train luminosity
monitor, must be developed, and an acceptable laser-wire profile monitor must
be provided where needed in each design. A vigorous R&D program is
mandatory for beam instrumentation in general; it would be appropriate for a
collaborative effort between laboratories.
- A sufficiently detailed prototype of the main linac module (girder or cryomodule
with quadrupole) must be developed to provide information about on-girder
sources of vibration.
- A detailed evaluation of critical subsystem reliability is needed to demonstrate
that adequate redundancy is provided and that the assumed failure rate of
individual components has been achieved.
- The performance of beam based tuning procedures to align magnets and
structures must be demonstrated by complete simulations, in the presence of a
wide variety of errors, both in the beam and in the components.