Ranking 2

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.

TESLA

Energy

• 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 is needed.

Luminosity

Damping Rings

• 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. Machine-Detector Interface
• 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.

Reliability

• 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.

JLC-C

Energy

• 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.

JLC-X/NLC

Energy

• 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.

CLIC

Energy

• 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).

Luminosity

Low Emittance Transport

• Calculations of the effects of coherent synchrotron radiation on the CLIC bunch compressors must be performed. Machine-Detector Interface
• An extraction line design for 3 TeV c.m. must be developed.

Items Common to All Machines

Luminosity

Damping Rings

• 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 these simulations.
• 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 7.2.3.2. Additional experiments in the ATF and other operating rings are needed to test the emittance correction algorithms. 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.

Reliability

• 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.