Test facilities for future linear colliders Page: 3 of 7
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30 GHz power generation include (i) raising the gradient
in the accelerating section to reduce the effect of wakefields
(ii) making shorter bunches using a magnetic bunch com-
pressor (iii) building a new 100 nC/bunch rf gun.
CLIC Alignment Test Facility. An active alignment test
facility has been built in an unused underground tunnel at
CERN to study the feasibility of making controlled submi-
cron displacements and to try out alignment systems.
The structures to be aligned, dummy accelerating sec-
tions for the moment, are supported by V-blocks on 1.4-
m-long silicon carbide girders. The ends of two adjacent
girders sit on a common platform which ensures continuity
of position between units.
The platforms are activated by three stepping-motor-
driven precision jacks (two in the vertical plane for vertical
displacement and axial rotation, and one in the horizon-
tal plane). The setup is equipped with linear and angular
displacement transducers (0.1 pm and 10 p-rad resolution
respectively) and is piloted remotely from a small com-
puter. After deliberate misalignments of 1 mm, the system
which is programmed for automatic alignment with respect
to the transducers, settles back to nominal positions within
< 1 pm.
The CESTA Test Facility. A collaboration to study
the use of an FEM to create the CLIC drive beam exists
between CERN and the Centre d'Etudes Scientifiques et
Techniques d'Aquitaine (CESTA) in Bordeaux. The aim
is to use a helical wiggler to bunch a beam from an in-
duction linac, and in a later phase to use this beam to
generate power in a CLIC transfer structure. A prelimi-
nary experiment to measure the bunching produced by a
helical wiggler using the beam from a gun-diode is already
The MIT Test Facility. CERN is collaborating with MIT
to test CLIC prototype components. MIT has a gun- diode
driven FEL that produces 20-ns-long, 60 MW power pulses
at 33 GHz. This facility is at present being used to test a
25-cell prototype CLIC accelerating section.
IV. The SBLC: the S-Band Test Facility
Among the different design studies for a next generation
e+e linear collider, the SBLC approach follows the con-
cept of a relatively low rf-frequency wrf and a moderate
accelerating gradient g. In the SBLC, conventional travel-
ing wave accelerating structures at 3 GHz are used running
at a gradient of 17 MV/m. The SBLC linear collider study
is pursued at DESY in the frame of an international collab-
oration with institutes in China, France, Germany, Japan,
Netherlands, Russia, and USA contributing to the techni-
cal R&D and/or the design of the 500 GeV collider.
The goal of the SBLC test facility under construction at
DESY is to construct and test the basic components re-
quired for the 2 x 250 GeV linear accelerators. The test
linac consists of an injector providing bunch trains similar
to those to be used in the collider. Two 150 MW klystrons
(built by SLAC) power four 6-m-long accelerating struc-
tures. A beam diagnostics station is foreseen to measure
bunch to bunch offsets as well as single and multibunch
energy-spread. The injector provides a 6 A pulse out of a
90 kV gun with a duration of 2 ns. This pulse is compressed
longitudinally by more than a factor of 200 resulting in a
bunch length of ~ 3 mm. Although longer than the final
design bunch length, this value is sufficient to study most
multibunch and beam dynamics effects. The subharmonic
cavities and the vacuum system will be assembled and in-
stalled during 1994 and be commissioned early 1995.
Recently, the first klystron has reached its full design pa-
rameters in rf tests at SLAC. Conventional line-type mod-
ulators are foreseen for pulsing the klystrons. As an alter-
native solution a hard tube switching device is also under
study at DESY. A klystron test stand for the 150 MW
klystron with water loads and further required infrastruc-
ture is under construction.
The design of the accelerating sections concentrates on
the first series production of 5.2-m-long structures for the
DESY injector linac, which are very similar to the test
facility structures. Nine-hundred cells for 6 sections (from
overall 14) have been ordered from industry and are being
brazed at DESY. Horizontal or vertical brazing, vacuum-
or hydrogen-atmosphere ovens or inductive heating are still
being investigated. A cup-tuning machine to match the
structure for the accelerating wave after brazing and before
final installation is now operating.
Low power test models of the symmetric high power cou-
plers have been manufactured and matched to an accelerat-
ing structure while the high power versions are scheduled
autumn 1994. Different types of additional couplers re-
quired for the HOM damping and/or measurement of the
beam induced higher order mode power are being investi-
gated. After brazing and tuning, the sections for the test
facility will be mounted on different types of temperature
insensitive girders (glass ceramics, carbon fiber composite
and heat shielded stainless steel) to keep the six meters of
copper waveguide straight within 15 ym rms. Every girder
is equipped with micromovers at both ends to allow for
f1.5 mm offset in both directions.
Magnets, structure supports, and precision movers, as
well as methods to compensate ground vibrations, are in-
vestigated. The design of the linac quadrupoles completely
decouples the coil windings from the iron yoke, which au-
tomatically minimizes the vibration effects due to cooling
water flow. Although the effects which have been described
before will not affect the final emittance in the test acceler-
ator, feedback systems and control loops will be tested on
the supports and girders, which have been designed to fit
the tunnel requirements and the minimum height for final
V. TESLA: The TESLA Test Facility Linac
The TESLA (5] approach uses a superconducting RF sys-
tem to accelerate the beam to high energy. The important
issues that need to be addressed in the Tesla Test Facil-
ity Linac (TTFL) are somewhat different than those in the
normal conducting case. There are both cost and technical
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Ruth, R.D. Test facilities for future linear colliders, article, December 1, 1995; Menlo Park, California. (digital.library.unt.edu/ark:/67531/metadc619423/m1/3/: accessed August 18, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.