Beam Stability in the Drive-Beam Decelerator of CLIC Using Structures of High-Order Symmetry

The RF power necessary to accelerate the main beam of the Compact Linear Collider (CLIC) is produced by decelerating a high-current drive beam in Power Extraction and Transfer Structures (PETS). The reference structure is not cylindrically symmetric but has longitudinal waveguides carved into the inner surface. This gives rise to a transverse component of the main longitudinal mode which can not be damped, in contrast to the transverse dipole wake- field. The field is non-linear and couples the motion of the particles in the two planes. Limits of the stability of the decelerated beam are investigated for different structures

Design of a 3 GHz Accelerator Structure for the CLIC Test Facility (CTF 3) Drive Beam

For the CLIC two-beam scheme, a high-current, long-pulse drive beam is required for RF power generation. Taking advantage of the 3 GHz klystrons available at the LEP injector once LEP stops, a 180 MeV electron accelerator is being constructed for a nominal beam current of 3.5 A and 1.5 microsecond pulse length. The high current requires highly effective suppression of dipolar wakes. Two concepts are investigated for the accelerating structure design: the "Tapered Damped Structure" developed for the CLIC main beam, and the "Slotted Iris - Constant Aperture" structure. Both use 4 SiC loads per cell for effective higher-order mode damping. A full-size prototype of the TDS structure has been built and tested successfully at full power. A first prototype of the SICA structure is being built.Comment: Contribution to Linac 2000 Conference, TUA16 (Poster

A Multi-Drive Beam Scheme for Two-Beam Acceleration in a TeV Linear Collider

The Compact Linear Collider (CLIC) study of an e+/e- linear collider in the TeV energy range is based on Two-Beam Acceleration (TBA) in which the overall RF power needed to accelerate the beam is extracted from high intensity relativistic electron beams, the so-called drive beams. Due to the high beam power, acceleration and transport of the drive beams in an efficient and reliable way is specially challenging. An overview of a potentially effective scheme is presented. It is based on the generation of trains of short bunches, accelerated in low frequency c.w. superconducting cavities, stored in an isochronous ring and combined at high energy by funneling before injection by sectors into the drive linac. The various systems of the complex are discussed as well as the beam dynamics all along the process. An original method has been specially developed to stabilize such an intense beam during deceleration and RF power production in the drive lina

Design of a chopper line for the CERN SPL

The SPL (Superconducting Proton Linac), a 2.2 GeV linac for high-intensity applications under study at CERN, requires a fast chopping at low energy of the H . beam. The most stringent demands on the chopper come from the operation of a Neutrino Factory, which requires 44 MHz bunch frequency in the accumulator ring and in the muon bunch rotation. This imposes a chopper structure with fast rise and fall times, below 2 ns, to remove 3 consecutive 352 MHz bunches out of every 8. An improved design of the standard travelling-wave chopper structure has been analysed and tested on a prototype. Additional effort has gone into the design of a pulse generator or power amplifier capable of providing the required rise and fall times. Since short rise times and high chopper voltages are conflicting requirements, the maximum voltage has been limited to 500 V per plate. A prototype driver has been built and tested. A very compact beam line design is proposed, which is still compatible with the low chopper voltage. The line houses the chopper structure and the dump, provides the separation between chopped and unchopped beam, and matches both from the RFQ and to a DTL. Effects of space charge and of varying beam parameters are analysed. In particular, the influence of the beam energy at the chopper on the line components is discussed in detail. A diagnostic line designed to perform the measurements necessary to validate this set-up is also described

A new method of RF power generation for two-beam linear colliders

In this paper we discuss a new approach to two-beam acceleration. The energy for RF production is initially stored in a long-pulse electron beam which is efficiently accelerated to about 1.2 GeV by a fully loaded, conventional, low frequency (~1 GHz) linac. The beam pulse length is twice the length of the high-gradient linac. Segments of this long pulse beam are compressed using combiner rings to create a sequence of higher peak power drive beams with gaps in between. This train of drive beams is distributed from the end of the linac against the main beam direction down a common transport line so that each drive beam can power a section of the main linac. After a 180-degree turn, each high-current, low-energy drive beam is decelerated in low-impedance decelerator structures, and the resulti ng power is used to accelerate the low-current, high-energy beam in the main linac. The method discussed here seems relatively inexpensive is very flexible and can be used to accelerate beams for lin ear colliders over the entire frequency and energy range

CLIC: a Two-Beam Multi-TeV e±e\pm Linear Collider

The CLIC study of a high-energy (0.5 - 5 TeV), high-luminosity (1034 - 1035 cm-2 sec-1) e+e- linear collider is presented. Beam acceleration using high frequency (30 GHz) normal-conducting structures operating at high accelerating fields (150 MV/m) significantly reduces the length and, in consequence, the cost of the linac. Using parameters derived from general scaling laws for linear colliders, the beam stability is shown to be similar to lower frequency designs in spite of the strong wake-field dependency on frequency. A new cost-effective and efficient drive beam generation scheme for RF power production by the so-called "Two-Beam Acceleration" method is described. It uses a thermionic gun and a fully-loaded normal-conducting linac operating at low frequency (937 MHz) to generate and accelerate the drive beam bunches, and RF multiplication by funnelling in compressor rings to produce the desired bunch structure. Recent 30 GHz hardware developments and CLIC Test Facility (CTF) results are described

Conceptual design of the SPL II: A high-power superconducting H−H^- linac at CERN

An analysis of the revised physics needs and recent progress in the technology of superconducting RF cavities have led to major changes in the speci cation and in the design for a Superconducting Proton Linac (SPL) at CERN. Compared with the rst conceptual design report (CERN 2000012) the beam energy is almost doubled (3.5 GeV instead of 2.2 GeV), while the length of the linac is reduced by 40% and the repetition rate is reduced to 50 Hz. The basic beam power is at a level of 45MW and the approach chosen offers enough margins for upgrades. With this high beam power, the SPL can be the proton driver for an ISOL-type radioactive ion beam facility of the next generation (`EURISOL'), and for a neutrino facility based on superbeam C beta-beam or on muon decay in a storage ring (`neutrino factory'). The SPL can also replace the Linac2 and PS Booster in the low-energy part of the CERN proton accelerator complex, improving signi cantly the beam performance in terms of brightness and intensity for the bene t of all users including the LHC and its luminosity upgrade. Decommissioned LEP klystrons and RF equipment are used to provide RF power at a frequency of 352.2 MHz in the lowenergy part of the accelerator. Beyond 90 MeV, the RF frequency is doubled to take advantage of more compact normal-conducting accelerating structures up to an energy of 180 MeV. From there, state-ofthe- art, high-gradient, bulk-niobium superconducting cavities accelerate the beam up to its nal energy of 3.5 GeV. The overall design approach is presented, together with the progress that has been achieved since the publication of the rst conceptual design report

The SPL (II) at CERN, a Superconducting 3.5 GeV H- Linac

A revision of the physics needs and recent progress in the technology of superconducting (SC) RF cavities have triggered major changes in the design of a SC H-linac at CERN. With up to 5MW beam power, the SPL can be the proton driver for a next generation ISOL-type radioactive beam facility (âEURISOLâ) and/or supply protons to a neutrino () facility (conventional superbeam + beta-beam or -factory). Furthermore the SPL can replace Linac2 and the PS booster (PSB), improving significantly the beam performance in terms of brightness, intensity, and reliability for the benefit of all proton users at CERN, including LHC and its luminosity upgrade. Compared with the first conceptual design, the beam energy is almost doubled (3.5GeV instead of 2.2 GeV) while the length is reduced by 40%. At a repetition rate of 50 Hz, the linac reuses decommissioned 352.2MHz RF equipment from LEP in the low-energy part. Beyond 90MeV the RF frequency is doubled, and from 180MeV onwards high-gradient SC bulkniobium cavities accelerate the beam to its final energy of 3.5GeV. This paper presents the overall design approach, together with the technical progress since the first conceptual design in 2000