Erk Jensen

A 3 TeV

A possible design of a multi-TeV e+e- linear collider is presented. The design is based on the CLIC (Compact Linear Collider) two-beam technology proposed and developed at CERN. Though the study has shown that this technology is applicable to a linear collider with centre-of-mass energies from 500 GeV or less up to 5 TeV, the present report focuses on the nominal energy of 3 Te V. First, a short overview is given of the physics that could possibly be done with such a collider. Then, the description of the main-beam complex covers the injection system, the 30 GHz main linac, and the beam delivery system. The presentation of the RF power source includes the beam-generation scheme, the drive-beam decelerator, which consists of several 625 m long units running parallel to the main linac, and the power-extraction system. Finally, brief outlines are given of all the CLIC test facilities. They cover in particular the new CLIC test facility CTF3 which will demonstrate the feasibility of the power production technique, albeit on a reduced scale, and a first full-scale single-drive-beam unit, CLICI, to establish the overall feasibility of the scheme.

e^+ e^-

Accelerating structures with strong transverse-mode damping are required in both the 30 GHz CLIC main linac and the 3 GHz CTF3 drive-beam accelerator. Damping via slotted irises has been investigated for both structures. The transverse wake, the effect of the slots on the fundamental-mode parameters such as Q, sensitivity to tolerances, and surface-field enhancements have been computed. Terminating loads have been designed and machining studies to obtain rounded slot edges have been made. A 32-cell prototype 3 GHz structure is being fabricated for the drive beam accelerator of CTF3.

Linear Collider Based on CLIC Technology

50 MW power sources at 937 MHz will be needed to accelerate the CLIC drive beams. We present a novel MBK concept with a large number of beamlets; this allows for small single beam perveance and high efficiency. The MBK features disc‐shaped RF circuits operated in a whispering‐gallery mode — a configuration permitting both high interaction impedance and easy spurious mode damping.

Slotted-iris structure studies

The design of klystrons has long been a manual process guided by experience. However, with well-defined specifications and sufficiently rapid simulation methods, it is a good candidate process for automatic optimization techniques. In this paper, such a technique is evaluated and refined using klystron specific techniques, leading to several designs (with different tradeoffs between efficiency and size) each of a structure comparable with the SLAC B-factory klystrons. The most efficient of which, while only 1% more efficient, is 17.1% shorter.

CLIC 50 MW L‐Band Multi‐Beam Klystron

The FCC-ee is a high-luminosity, high-precision e+e− circular collider, envisioned in a new 80100 km tunnel in the Geneva area. It is envisaged to operate the collider with centre of mass energies ranging from 90 GeV for Z production to 350 GeV at the tt threshold. With a constant power budget for synchrotron radiation, the FCC-ee RF system must meet the requirements for both the highest possible accelerating voltage and very high beam currents with the same machine, albeit possibly at different stages. Beam-induced higher order mode power will be a major issue for running at the Z pole, and will have a strong impact on the RF system design. Iterations are ongoing on RF scenarios and staging, choice of cavities and cryomodule layout, RF frequency and cryogenic temperature.

Automatic Optimization of a Klystron Interaction Structure

The HL-LHC upgrade will use deflecting (or crab) cavities to compensate for geometric luminosity loss at low β* and non-zero crossing angle. A local scheme with crab cavity pairs across the IPs is used employing compact crab cavities at 400 MHz. Design of the cavities, the cryomodules and the RF system is well advanced. The LHC crab cavities will be validated initially with proton beam in the SPS.

The RF system for FCC-ee

The CLIC (Compact Linear Collider) multi‐lateral study group based at CERN is studying the technology for an electron‐positron linear collider with a centre‐of‐mass energy up to 5 TeV. In contrast to the International Linear Collider (ILC) study which has chosen to use super‐conducting cavities with accelerating gradients in the range of 30–40 MV/m to obtain centre‐of‐mass collision energies of 0.5–1 TeV, the CLIC study aims to use a normal‐conducting system based on two‐beam technology with gradients of 150 MV/m. It is generally accepted that this change in technology is not only necessary but the only viable choice for a cost‐effective multi‐TeV collider. The CLIC study group is studying the technology issues of such a machine, and is in particular developing state‐of‐the‐art 30 GHz molybdenum‐iris accelerating structures and power extraction and transfer structures (PETS). The accelerating structure has a new geometry which includes fully‐profiled RF surfaces optimised to minimize surface fields, and h...

Crab Cavity Development

The Finite Differences Method and the Finite Element Method are the two principally employed numerical methods in modern RF field simulation programs. The basic ideas behind these methods are explained, with regard to available simulation programs. We then go through a list of characteristic parameters of RF structures, explaining how they can be calculated using these tools. With the help of these parameters, we introduce the frequency-domain and the time-domain calculations, leading to impedances and wake-fields, respectively. Subsequently, we present some readily av ailable computer programs, which are in use for RF structure design, stressing their distinctive featur es and limitations. One final example benchmarks the precision of different codes for calculating the eigenfrequency and Q of a simple cavity resonator.

Normal Conducting CLIC Technology

Modern RF structures make great demands on both materials and fabrication techniques. In addition to high required precision, they need to be compatible with ultra high vacuum, high power RF and the presence of particle b eams. We introduce materials compatible with these demands and summarize their relevant characteristics. Methods of forming and joining follow, again with emphasis on those suited fo r the fabrication of accelerating structures, and we point out their limitations. We mention different tests which will be designed into the fabrication process, and describe in some detail the testing of the RF properties of accelerating structures. The following overview is non-exhaustive and limited to normalconducting structures; many of the examples relate to a possible next-generation linear collider.

Computational Tools for RF Structure Design

After a short overview of a general approach to cavity design, we sketch the derivation of waveguide modes from plane waves and of cavity fields from waveguide modes. The characteristic parameters describing cavities and their performance are defined and explained. An equivalent circuit is introduced and extended to explain beam loading and higher order modes. Finally travelling- and standing-wave multi-gap cavities are introduced using the Brillouin diagram.