Conference Paper

Room temperature accelerator structures for linear colliders

Stanford Linear Accelerator Center, Menlo Park, CA
DOI: 10.1109/PAC.2001.988264 Conference: Particle Accelerator Conference, 2001. PAC 2001. Proceedings of the 2001, Volume: 5
Source: IEEE Xplore

ABSTRACT Early tests of short low group velocity and standing wave
structures indicated the viability of operating X-band linacs with
accelerating gradients in excess of 100 MeV/m. Conventional scaling of
traveling wave traveling wave linacs with frequency scales the cell
dimensions with λ. Because Q scales as λ1/2,
the length of the structures scale not linearly but as λ3/2
in order to preserve the attenuation through each structure. For
the NLC we chose not to follow this scaling from the SLAC S-band linac
to its fourth harmonic at the X-band. We wanted to increase the length
of the structures to reduce the number of couplers and waveguide drives
which can be a significant part of the cost of a microwave linac.
Furthermore, scaling the iris size of the disk-loaded structures gave
unacceptably high short range dipole wakefields. Consequently, we chose
to go up a factor of about 5 in average group velocity and length of the
structures, which increases the power fed to each structure by the same
factor and decreases the short range dipole wakes by a similar factor.
Unfortunately, these longer (1.8 m) structures have not performed nearly
as well in high gradient tests as the short structures. We believe we
have at least a partial understanding of the reason and will discuss it
below. We are now studying two types of short structures with large
apertures with moderately good efficiency including: 1) traveling wave
structures with the group velocity lowered by going to large phase
advance per period with bulges on the iris, 2) π mode standing wave

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    ABSTRACT: The next-generation linear collider will require high-power microwave sources and accelerating systems vastly more challenging than its predecessor, the Stanford Linear Collider (SLC). Cost efficiency will demand high accelerating gradient to achieve beam energies five to ten times greater than in the SLC. Luminosity goals 10,000 times greater than the SLC demand efficient creation of the highest possible beam power without degradation of beam emittance. The past decade of R&D has demonstrated the feasibility of two technical approaches for building a 500-GeV center-of-mass system (cms) collider with attractive options for future upgrade. The TESLA R&D program offers the prospect of 1.3-GHz superconducting rf (srf) linacs with 23.4 MV/m gradient that can be upgraded later to 35 MV/m gradient by doubling the number of klystrons and the cryo-plant, to reach 800 GeV cms [1]. The Next Linear Collider (NLC) and Japanese Linear Collider (JLC) R&D programs offer the prospect of 11.4-GHz room-temperature linacs that can later be extended to 1 TeV by doubling the number of structures and klystrons, and to 1.5 TeV by additionally increasing gradient or length [2-4]. Both programs offer a 500-GeV linear collider project start within the next few years (2-3 years for TESLA, 3-4 years for NLC) based on available technology validated by experiments at several complementary test facilities. Both offer their upgrades as a result of further progress in R&D that is already underway.
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    ABSTRACT: The NLC/JLC collaboration focuses its major effort on X-band linac technology which is the main part of a 1 TeV electron-positron linear collider. Both SLAC and KEK have pursued R&D for a TeV linear collider over 15 years with the acronyms NLC (Next Linear Collider) and JLC (Japan Linear Collider). The two teams assumed X-band (11.424 GHz) warm linac technology for the main linac, although R&D for technology at C-band (5.712 GHz) has also been optionally undertaken at KEK. The collaboration between SLAC and KEK is focused on the X-band linac technology and low-emittance beam generation study [1] at the ATF (Accelerator Test Facility) damping ring of KEK. In this collaborative framework, however, many other laboratories have also contributed: BINP (Protvino, Russia), Postech (Korea), IHEP and Tsinghua University (Beijing), LLNL, LBNL and recently FNAL (USA), and several universities worldwide. Since 1998, 8 meetings have been held for the International Study Group (ISG), through which NLC and JLC are getting much closer in the design features and R&D directions. The report below summarizes is the recent R&D status on X-band accelerating structures and RF power source together with some interesting results of the most-up-to-date beam monitors developed at the ATF damping ring.
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    ABSTRACT: As part of the Next Linear Collider (NLC) collaboration, the NLC structures group at Fermilab has started an R&D program to fabricate NLC accelerator structures in cooperation with commercial companies in order to prepare for mass production of RF structures. To build the Next Linear Collider, thousands accelerator structures containing a million cells are needed. Our primary goal is to explore the feasibility of making these structures in an industrial environment. On the other hand the structure mass production requires "industrialized" microwave quality control techniques to characterize these structures at different stages of production as efficiently as possible. We developed several automated set-ups based on different RF techniques that are mutually complementary address this problem.

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