A test accelerator for the next linear collider

Proceedings of International Conference on Particle Accelerators

The design for the Next Linear Collider (NLC) at SLAC is based on two 11.4 GHz linacs operating at an unloaded acceleration gradient of 50 MV/m increasing to 85 MV/m as the energy is increased from 1/2 TeV to 1 TeV in the center of mass[1]. During the past several years there has been tremendous progress on the development of 11.4 GHz (X-band) RF systems. These developments include klystrons which operate at the required power and pulse length, pulse compression systems that achieve a factor of four power multiplication and structures that are specially designed to reduce long-range wakefields. Together with these developments, we have constructed a 1/2 GeV test accelerator, the NLC Test Accelerator (NLCTA). The NLCTA will serve as a test bed as the design of the NLC is refined. In addition to testing the RF system, the NLCTA is designed to address many questions related to the dynamics of the beam during acceleration, in particular the study of multibunch beam loading compensation and transverse beam break-up. In this paper we present the status of the NLCTA and the results of initial commissioning.

1994

This paper describes the current SLAC R&D program to develop room tem~rature accelerator structures for the Next Linear Collider (NLC). me s~ctures are designd to operate at 11.4 GHz at an accelerating gradient in the range of 50 to 100 MV/m. In the past year a 26 cm constant-impedance traveling-wave section, a 75 cm constant-im~dmce traveling- wave section, and a 1.8 m traveling-wave section with detuned deflecting modes have been high-power tested. The paper presents a brief description of the RF test setup, the design and manufacturing details of the structures, and a discussion of test results includlng field emission, RF processing, dark current spwtrum and RF breakdown. Experimental Setup ., Accelerator structures descriti in this paper were dl testi in the Accelerator Structure Test Area (ASTA) facility located

Proceedings Particle Accelerator Conference, 1995

In this paper, we present the parameters and layout of the Next Linear Collider (NLC). The NLC is the SLAC design of a future linear collider using X-band RF technology in the main linacs. The collider would have an initial centerof-mass energy of 0.5 TeV which would be upgraded to 1 TeV and then 1.5 TeV in two stages. The design luminosity is > 5 10 33 cm 2 sec 1 at 0.5 TeV and > 10 34 cm 2 sec 1 at 1.0 and 1.5 TeV. We will brie y describe the components of the collider and the proposed energy upgrade scenario.

2000

An electron/positron linear collider with a center-of-mass energy between 0.5 and 1 TeV would be an important complement to the physics program of the LHC in the next decade. The Next Linear Collider (NLC) is being designed by a US collaboration (FNAL, LBNL, LLNL, and SLAC) which is working closely with the Japanese collaboration that is designing the Japanese Linear Collider (JLC). The NLC main linacs are based on normal conducting 11 GHz rf. This paper will discuss the technical difficulties encountered as well as the many changes that have been made to the NLC design over the last year. These changes include improvements to the X-band rf system as well as modifications to the injector and the beam delivery system. They are based on new conceptual solutions as well as results from the R&D programs which have exceeded initial specifications. The net effect has been to reduce the length of the collider from about 32 km to 25 km and to reduce the number of klystrons and modulators by a factor of two. Together these lead to significant cost savings.

2004

Designs for a future TeV scale electron-positron Xband linear collider (NLC/GLC) require main linac units which produce and deliver 450 MW of rf power at 11.424 GHz to eight 60 cm accelerator structures. The design of this rf unit includes a SLED-II pulse compression system with a gain of approximately three at a compression ratio of four, followed by an over-moded transmission and distribution system. We have designed, constructed, and operated such a system as part of the 8-Pack project at SLAC. Four 50 MW X-band klystrons, running off a common 400 kV solid-state modulator, drive a dualmoded SLED-II pulse compression system. The compressed power is delivered to structures in the NLCTA beamline. Four 60 cm accelerator structures are currently installed and powered, with four additional structures and associated high power components available for installation late in 2004. We describe the layout of our system and the various high-power components which comprise it. We also present preliminary data on the processing and initial high-power operation of this system.

2000

During the initial phase of operation, the linacs of the Next Linear Collider (NLC) will contain roughly 5000 X-Band accelerator structures that will accelerate beams of electrons and positrons to 250 GeV. These structures will nominally operate at an unloaded gradient of 72 MV/m. As part of the NLC R&D program, several prototype structures have been built and operated at the Next Linear Collider Test Accelerator (NLCTA) at SLAC. Here, the effect of high gradient operation on the structure performance has been studied. Significant progress was made during the past year after the NLCTA power sources were upgraded to reliably produce the required NLC power levels and beyond. This paper describes the structures, the processing methodology and the observed effects of high gradient operation.

1995

A description of the original CLIC two-beam scheme is given in . The overall layout of the 1 TeV machine is shown in . The main linac consists of normal conducting travelling wave accelerating structures operating at a frequency of 30 GHz and a gradient of 80 MV/m. One in ten of these sections have an asymmetric geometry and act as microwave quadrupoles for BNS damping. For multi-bunch operation damped and/or detuned structures would be required. The 30 GHz RF power is supplied by transfer structures which extract energy from a 3 GeV high-intensity electron drive linac running parallel to the main linac in the same tunnel. The transfer structure consists of a 11.5 mm diameter circular beam tube coupled through two diametrically-opposite ≈5mm wide slots to two periodicallyloaded rectangular waveguides. Each 50 cm long section produces two simultaneous 11.6 ns long 44.6 MW power pulses which drive two accelerating structures. This output power corresponds to 95% of the energy extracted from the beam. Two full-length (84 cell) constant impedance undamped accelerating section have been tested to an average accelerating gradient of 94 MV/m without any signs of breakdown and the periodically-loaded output waveguides of a full-length transfer structure have withstood 60 MW of 30 GHz RF power without breakdown but the structure itself has not yet been tested with a bunched beam Prototype diamond machined discs with the asymmetric geometry required for microwave quadrupole sections have been successfully produced by industry, and studies of damped structures for multibunch operation are underway. High gradient tests have also been made at SLAC on a 26-cell CERN-built X-band section . Average accelerating gradients of 125 MV/m (a peak surface field of 285 MV/m) were obtained after 10 7 shots at 60 Hz with a pulse length of 150 ns. After conditioning, the dark current was 2µA at 50 MV/m and 150µA at 80 MV/m.

Acta Physica Polonica B, 1999

The CLIC study of high-energy (0.5-5 TeV), high-luminosity (1034-1035cm-2{s}-1) e± linear collider is presented. Beam acceleration using high-frequency (30 GHz) normal-conducting structures operating at high accelerating fields (100 to 200 MV/m) significantly reduces the length and, in consequence, the cost of the linac. Based on new beam and linac parameters derived from a recently developed set of 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 (TBA) 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 results from the CLIC Test Facility (CTF), assessing the feasibility of the scheme, are described.}

2004

Designs for a future X-band linear collider (NLC/GLC) require an rf unit that can produce 450 MW to feed eight 60 cm accelerator structures. The implementation of this rf unit is envisioned to include a dual-moded SLED-II pulse compression system, with a gain of approximately three at a compression ratio of four, followed by an overmoded transmission and distribution system. We describe the tunnel layout plan for these rf systems. The design, construction, and operation of a prototype system are a focus of the 8-Pack project at SLAC. In its initial phase last fall, powered by four 50 MW X-band klystrons sharing a common 400 kV solid-state modulator, the SLED-II system delivered to a set of loads 400 ns pulses of up to 580 MW. In the next phase, this power will be delivered to the NLCTA beamline and distributed between several structures, through which a bunch train will be accelerated. We describe the layout of this system and the functionality of various overmoded, high-power components which comprise it. We also present data on the cold testing, processing and initial operation of the system, which is setting high-power records in pulsed rf.

2004

The accelerator structure groups for NLC (Next Linear Collider) and GLC (Global Linear Colliders) have successfully collaborated on the research and development of a major series of advanced accelerator structures based on room-temperature technology at Xband frequency. The progress in design, simulation, microwave measurement and high gradient tests are summarized in this paper. The recent effort in design and fabrication of the accelerator structure prototype for the main linac is presented in detail including HOM (High Order Mode) suppression and design of HOM couplers and fundamental mode couplers, optimized accelerator cavities as well as plans for future structures.