Multipole components and their minimization in deflecting cavities with standard type couplers

Deflecting cavities are used in particle accelerators for the manipulation of charged particles by deflecting or crabbing (rotating) them. For short deflectors, the effect of the power coupler on the deflecting field can become significant. The particular power coupler type can introduce multipole rf field components and coupler-specific wakefields. Coupler types that would normally be considered like standard on-cell coupler, waveguide coupler, or mode-launcher coupler could have one or two rf feeds. The major advantage of a dual-feed coupler is the absence of monopole and quadrupole rf field components in the deflecting structure. However, a dual-feed coupler is mechanically more complex than a typical single-feed coupler and needs a splitter. For most applications, deflecting structures are placed in regions where there is small space hence reducing the size of the structure is very desirable. This paper investigates the multipole field components of the deflecting mode in single-feed couplers and ways to overcome the effect of the monopole component on the beam. Significant advances in performance have been demonstrated. Additionally, a novel coupler design is introduced which has no monopole field component to the deflecting mode and is more compact than the conventional dual-feed coupler

High gradient testing of an X-band crab cavity at XBOX2

CERN’s Compact linear collider (CLIC) will require crab cavities to align the bunches to provide effective head-on collisions. An X-band quasi-TM11 deflecting cavity has been designed and manufactured for testing at CERN’s Xbox-2 high power standalone test stand. The cavity is currently under test and has reached an input power level in excess of 40MW, with a measured breakdown rate of better than 10-5 breakdowns per pulse. This paper also describes surface field quantities which are important in assessing the expected BDR when designing high gradient structures

A Wideband Conical Beam Cylindrical Dielectric Resonator Antenna

The letter proposes a novel cylindrical dielectric resonator antenna (DRA) geometry with low radiation Q-value facilitating wide band operation with conical radiation patterns. The DRA is fed by a microstrip transmission line with a vertical strip that is attached to the DRA surface. At optimum dimensions and position of the vertical strip on the horizontal microstrip, the DRA exhibits an impedance bandwidth ( $vert {rm S}_{11}vert < - 10$ dB) of {sim}35hbox{%} at the centre frequency of 3 GHz. Measured radiation patterns are conical in shape and are stable with moderate gain across the matching band

Microstripline fed Half-Cylindrical Dielectric Resonator Antenna for 2.4 GHz WLAN application

A compact half-cylindrical dielectric resonator antenna (DRA) made from a high-permittivity (εr = 69) ceramic material is investigated. A microstrip transmission line excites the DRA. The DRA shows broad and stable radiation characteristics across a matching band of 2.32 to 2.5 GHz with peak gains of 5.5 dBi in the elevation plane and 3.6 dBi in the azimuth plane. The results lead us to propose this DRA for 2.4-GHz WLAN (2.4 to 2.484 GHz) applicatio

CLIC crab cavity design optimisation for maximum luminosity

The bunch size and crossing angle planned for CERN's compact linear collider CLIC dictate that crab cavities on opposing linacs will be needed to rotate bunches of particles into alignment at the interaction point if the desired luminosity is to be achieved. Wakefield effects, RF phase errors between crab cavities on opposing linacs and unpredictable beam loading can each act to reduce luminosity below that anticipated for bunches colliding in perfect alignment. Unlike acceleration cavities, which are normally optimised for gradient, crab cavities must be optimised primarily for luminosity. Accepting the crab cavity technology choice of a 12 GHz, normal conducting, travelling wave structure as explained in the text, this paper develops an analytical approach to optimise cell number and iris diameter

Prototype Development of the CLIC Crab Cavities

CLIC will require two crab cavities to align the beams to provide an effective head-on collision with a 20 mdeg crossing angle at the interaction point. An X-band system has been chosen for the crab cavities. Three prototype cavities have been developed in order to test the high power characteristics of these cavities. One cavity has been made by UK industry and one has been made using the same process as the CLIC main linac in order to gain understanding of breakdown behaviour in X-band deflecting cavities. The final cavity incorporates mode-damping waveguides on each cell which will eventually contain SiC dampers. This paper details the design, manufacture and preparation of these cavities for testing and a report on their status

Status of the CLIC-UK R&D; Programme on Design of Key Systems for the Compact Linear Collider

Six UK institutes are engaged in a collaborative R&D; programme with CERN aimed at demonstrating key aspects of technology feasibility for the Compact Linear Collider (CLIC). We give an overview and status of the R&D; being done on: 1) Drive-beam components: quadrupole magnets and the beam phase feed-forward prototype. 2) Beam instrumentation: stripline and cavity beam position monitors, an electro-optical longitudinal bunch profile monitor, and laserwire and diffraction and transition radiation monitors for transverse beam-size determination. 3) Beam delivery system and machine-detector interface design, including beam feedback/control systems and crab cavity design and control. 4) RF structure design. In each case, where applicable, we report on the status of prototype systems and performance tests with beam at the CTF3, ATF2 and CesrTA test facilities, including plans for future experiments