R.D. Ruth

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>>

Accelerator Physics Measurements at the Damping Ring

Besides the optics measurements described elsewhere, machine experiments were done at the SLC damping ring to determine some of its parameters. The synchrotron radiation energy loss which gives the damping rates was measured by observing the RF-voltage dependence of the synchronous phase angle. The emittance was obtained from the synchrotron light monitor, scraper measurements and by extracting the beam through a doublet and measuring its size for different quadrupole settings. Current dependent effects such as parasitic mode losses, head tail instabilities, synchrotron and betatron frequency shifts were measured to estimate the impedance. RF-cavity beam loading and its compensation were also studied and ion collection was investigated. All results agree reasonably well with expectations and indicate no limitations to the design performance.

Progress at SLAC on high-power rf pulse compression

Rf pulse compression is a technique for augmenting the peak power output of a klystron (typically 50--100 MW) to obtain the high peak power required to drive a linear collider at a high accelerating gradient (typically 200 MW/m is required for a gradient of 100 MV/m). The SLED pulse compression system, with a power gain of about 2.6, has been operational on the SLAC linac for more than a decade. Recently, a binary pulse-compression system with a power gain of about 5.2 has been tested up to an output power of 120 MW. Further high-power tests are in progress. Our current effort is focused on prototyping a so-called SLED-II pulse-compression system with a power gain of four. Over-moded TE[sub 01]-mode circular waveguide components, some with novel technical features, are used to reduce losses at the 11.4-GHz operating frequency.

Status of the SLC Damping Rings

Electron beams of full design energy 1.21 GeV and nearly full design intensity 4×1010 particles/pulse (design 5×1010) have been extracted from the Stanford Linac and successfully stored in the electron damping ring. Beams of less intensity have been extracted from the ring and reinjected into the Linac. The present intensity limits are not thought to be fundamental. The operating experience with the electron ring and the status of the construction of the positron ring will be discussed.