C. Adolphsen

The Mark II silicon strip vertex detector

Abstract A silicon strip vertex detector consisting of 36 modules has been built and operated in the Mark II solenoidal detector at the Stanford Linear Collider. The construction of the detector modules, their performance tests, the stability and accuracy of their placement, and the precision alignment of the complete device prior to and after installation are discussed. We also describe the operation of the vertex detector, and we discuss the measurement of impact parameters of charged particle tracks in conjunction with the Mark II wire drift chambers.

Cavity BPM system tests for the ILC energy spectrometer

The main physics programme of the International Linear Collider (ILC) requires a measurement of the beam energy at the interaction point with an accuracy of 10-4 or better. To achieve this goal a magnetic spectrometer using high resolution beam position monitors (BPMs) has been proposed. This paper reports on the cavity BPM system that was deployed to test this proposal. We demonstrate sub-micron resolution and micron level stability over 20 h for a long BPM triplet. We find micron-level stability over 1 h for 3 BPM stations distributed over a long baseline. The understanding of the behaviour and response of the BPMs gained from this work has allowed full spectrometer tests to be carried out.

RF Distribution optimization in the main linacs of the ILC

The nominal design gradient in the main linacs of the International Linear Collider (ILC) is 31.5 MV/m for a beam current of 9.0 mA. However, the superconducting cavities built to date have demonstrated a range in sustainable gradient extending well below this goal, being limited by Q drop-off and quenching. For the current distribution of gradient limits in the RF cavities of the ILC linacs we have optimized the overall gradient of a 26 cavity RF unit, assuming the availability of various combinations of circulators and variable power tap-offs. One simple way of running such a unit is to set RF power, beam arrival time, and all loaded Q values so that the power is matched and the gradient in all cavities equals the gradient limit in the poorest performing cavity. One improvement strategy is to adjust the cavity couplings individually (possible, since circulators are assumed in the baseline ILC design) or in pairs (when circulators are not needed) using the movable antennae of the fundamental mode couplers. Another strategy is to use variable power tap-offs (VTOs) by which the RF power to succeeding pairs of cavities can be made to differ.

High power test of an X-band slotted-iris accelerator structure at NLCTA

The CLIC study group at CERN has built two X-band HDS (hybrid damped structure) accelerating structures for high-power testing in NLCTA at SLAC. These accelerating structures are novel with respect to their rf- design and their fabrication technique. The eleven-cell constant impedance structures, one made out of copper and one out of molybdenum, are assembled from clamped high-speed milled quadrants. They feature the same heavy higher-order-mode damping as nominal CLIC structures achieved by slotted irises and radial damping waveguides for each cell. The X-band accelerators are exactly scaled versions of structures tested at 30 GHz in the CLIC test facility, CTF3. The results of the X-band tests are presented and compared to those at 30 GHz to determine frequency scaling, and are compared to the extensive copper data from the NLC structure development program to determine material dependence and make a basic validation of the HDS design.

Converter-modulator design and operations for the "ILC" l-band test stand

To facilitate a rapid response to the International Linear Collider (ILC) L-band development program at SLAC, a spare converter-modulator was shipped from LANL. This modulator was to be a spare for the spallation neutron source (SNS) accelerator at ORNL. The ILC application requires a 33% higher peak output power (15 MW) and output current (120 Amp). This presents significant design challenges to modify the existing hardware and yet maintain switching parameters and thermal cycling within the semiconductor component ratings. To minimize IGBT commutation and free-wheeling diode currents, a different set of optimizations, as compared to the SNS design, were used to tune the resonant switching networks. Additional complexities arose as nanocrystalline cores with different performance characteristics (as compared to SNS), were used to fabricate the resonant boost transformers. This paper will describe the electrical design, modelling efforts, and resulting electrical performance as implemented for the ILC L-band test stand.

High-power coupler component test stand status and results

Fundamental power couplers for superconducting accelerator applications like the ILC are complicated transmission line assemblies that must simultaneously accommodate demanding RF power, cryogenic, and cleanliness constraints. When these couplers are RF conditioned, the observed response is an aggregate of all the parts of the coupler and the specific features that dominate the conditioning response are hard to determine. To better understand and characterize RF conditioning phenomena toward improving performance and reducing conditioning time, a high-power coupler component test stand has been built at SLAC. Operating at 1.3 GHz, this test stand was designed to measure the conditioning behavior of select components of the TTFIII coupler independently, including outer-conductor bellows, tube transitions, copper plating, surface preparations, and cold window geometries and coatings. A description of the test stand, the measurement approach, and a summary of the results obtained so far are presented.

ILC RF system R&D

The ILC linac group at SLAC is actively pursuing a broad range of R&D to improve the reliability and reduce the cost of the L-band (1.3 GHz) rf system. Current activities include the development of a Marx-style modulator and a 10 MW sheet-beam klystron, construction of an rf distribution system with adjustable power tap- offs and custom hybrids, tests of cavity coupler components to understand rf processing limitations, simulations of multipacting in the couplers and optimization of the cavity fill parameters for operation with a large spread of sustainable cavity gradients. Also, a prototype positron capture cavity is being developed for the ILC injectors. This paper surveys the results from the past year and notes related L-band R&D at other labs, in particular, that at DESY for the XFEL project.

A prototype energy spectrometer for the ILC at end station a in SLAC

The main physics program of the International Linear Collider requires a measurement of the beam energy with a relative precision of the order 10-4 or better. A magnetic spectrometer using high resolution beam position monitors (BPMs) has been proposed to achieve this goal. A prototype spectrometer chicane employing four dipole magnets is currently under development at the End Station A in SLAC, intending to demonstrate the required resolution and stability of this method and investigate possible systematic effects and operational issues. This contribution reports on the successful commissioning of the beam position monitor system and the resolution and stability achieved. Also, the initial results from a run with a full spectrometer chicane are presented.

Investigations of the wideband spectrum of higher order modes measured on tesla-style cavities at the FLASH LINAC

Higher Order Modes (HOMs) excited by the passage of the beam through an accelerating cavity depend on the properties of both the cavity and the beam. It is possible, therefore, to draw conclusions on the inner geometry of the cavities based on observations of the properties of the HOM spectrum. A data acquisition system based on two 20 GS/s, 6 GHz scopes has been set up at the FLASH facility, DESY, in order to measure a significant fraction of the HOM spectrum predicted to be generated by the TESLA cavities used for the acceleration of its beam. The HOMs from a particular cavity at FLASH were measured under a range of known beam conditions. The dipole modes have been identified in the data. 3D simulations of different manufacturing errors have been made, and it has been shown that these simulations can predict the measured modes.