C. Adolphsen

A multi-moded rf delay line distribution system for the next linear collider

The Delay Line Distribution System (DLDS) is an alternative to conventional pulse compression, which enhances the peak power of rf sources while matching the long pulse of those sources to the shorter filling time of accelerator structures. We present an implementation of this scheme that combines pairs of parallel delay lines of the system into single lines. The power of several sources is combined into a single waveguide delay line using a multi-mode launcher. The output mode of the launcher is determined by the phase coding of the input signals. The combined power is extracted from the delay line using mode-selective extractors, each of which extracts a single mode. Hence, the phase coding of the sources controls the output port of the combined power. The power is then fed to the local accelerator structures. We present a detailed design of such a system, including several implementation methods for the launchers, extractors, and ancillary high power rf components. The system is designed so that it can handle the 600 MW peak power required by the NLC design while maintaining high efficiency.

The Next Linear Collider Test Accelerator

During the past several years, there has been tremendous progress on the development of the RF system and accelerating structures for a Next Linear Collider (NLC). Developments include high-power klystrons, RF pulse compression systems and damped/detuned accelerator structures to reduce wakefields. In order to integrate these separate development efforts into an actual X-band accelerator capable of accelerating the electron beams necessary for an NLC, we are building an NLC Test Accelerator (NLCTA). The goal of the NLCTA is to bring together all elements of the entire accelerating system by constructing and reliably operating an engineered model of a high-gradient linac suitable for the NLC. The NLCTA will serve as a testbed as the design of the NLC evolves. In addition to testing the RF acceleration system, the NLCTA is designed to address many questions related to the dynamics of the beam during acceleration. In this paper, we will report on the status of the design, component development, and construction of the NLC Test Accelerator.<<ETX>>

Processing studies of X-band accelerator structures at the NLCTA

RF processing studies of 1.8-m X-band (11.4 GHz) traveling wave structures at the Next Linear Collider Test Accelerator (NLCTA) have revealed breakdown-related damage at gradients lower than expected from earlier tests with standing wave and shorter, lower group velocity traveling wave structures. To understand this difference, a series of structures with different group velocities and lengths are being processed. In parallel, efforts are being made to improve processing procedures and to reduce structure contaminants and absorbed gases. This paper presents results from these studies.

Wakefield and beam centering measurements of a damped and detuned X-band accelerator structure

We present wakefield measurements of a prototype Next Linear Collider (NLC) accelerator structure that was built with dipole mode damping and detuning to suppress the long-range transverse wakefield induced by a beam. In addition, we describe beam centering tests that use as a guide the dipole power coupled out of the structure for damping purposes.

RF processing of X band accelerator structures at the NLCTA

During the initial phase of operation, the linacs of the Next Linear Collider (NLC) will contain roughly 5,000 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 and 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.

Parameters of the SLAC Next Linear Collider

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 center-of-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/spl times/10/sup 33/ cm/sup -2/ sec/sup -1/ at 0.5 TeV and >10/sup 34/ cm/sup -2/ sec/sup -1/ at 1.0 and 1.5 TeV. We will briefly describe the components of the collider and the proposed energy upgrade scenario.

Vibration studies of the Stanford Linear Accelerator

Vibration measurements of the linear accelerator structures in the SLC linac show a 1 micron RMS vertical motion. This motion reduces to 0.2 micron RMS motion when the cooling water to the accelerator structures is turned off. The quadrupoles have 250 nanometer RMS vertical motion with the accelerator structure cooling water on and 60 nanometer motion with it off. These results together with measurements of the correlations as a function of frequency between the motions of various components are presented.

Flat beam studies in the SLC Linac

The Stanford Linear Collider (SLC) was recently converted to flat beam operation (/spl gammaspl epsivsub x/=10 /spl gammaspl epsivsub y/), producing a factor of two increase in luminosity. In this paper we review the results of flat beam studies in the SLC Linac. In summary, the injected beams from the damping rings had invariant horizontal emittances as low as 30 mm-mrad and invariant vertical emittances as low as 2 mm-mrad. The emittances measured at the end of the linac after tuning for 3/spl times/10/sup 10/ particles are about 5 to 8 mm-mrad vertically and 40 to 50 mm-mrad horizontally. Flat beam operation began 3/17/93.<<ETX>>

Dispersion and betatron matching into the linac

In high-energy linear colliders, the low-emittance beam from a damping ring has to be preserved all the way to the linear accelerator (LINAC), in the LINAC and to the interaction point. In particular, the ring-to-LINAC (RTL) section of the SLAC Linear Collider (SLC) should provide an exact betatron and dispersion match from the damping ring to the LINAC. A beam with a nonzero dispersion shows up immediately as an increased emittance, while with a betatron mismatch the beam forms filaments in the LINAC. Experimental tests and tuning procedures have shown that the linearized beta matching algorithms are insufficient if the actual transport line has some unknown errors not included in the model. Also, adjusting quadrupole strengths steers the beam if it is offset in the quadrupole magnets. These and other effects have led to a lengthy tuning process, which in the end improves the matching, but is not optimal. Different ideas are discussed to improve this matching procedure and make it a more reliable, faster, and simpler process.<<ETX>>

Beam loading compensation in the NLCTA

In the design of the Next Linear Collider (NLC), multibunch operation is employed to improve efficiency at the cost of substantial beam loading. The RF pulse that powers the accelerator structures will be shaped to compensate for the effect of the transient loading along the bunch train. This scheme has been implemented in the Next Linear Collider Test Accelerator (NLCTA), a facility built to test the key accelerator technology of the NLC. In this paper we describe the compensation method, the techniques used to measure the energy variation along the bunch train, and results from tests with NLC-like beam currents.