R. Koontz

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>>

A solid state Marx type modulator for driving a TWT

This paper describes a solid state Marx type modulator design delivering an 11 kilovolt, 2-4 /spl mu/sec pulse to the cathode of an X-band driver TWT. Insulated gate bipolar transistors (IGBTs) are used as on/off switches to operate the Marx circuit in the energy storage capacitor partial discharge mode. With the aid of a passive compensation circuit, a very flat TWT cathode driver pulse is obtained. The 2 /spl mu/sec, 11 kV pulse amplitude is flat to 0.06%.

NLC klystron pulse modulator R&D at SLAC

The basic elements of a klystron pulse modulator are: a charging supply, a PFN with energy storage capacitors, a thyratron switch tube, and a pulse transformer. The design group mentioned above is working on the system requirements of an NLC modulator, is carrying out tests on components, and building a prototype NLC modulator of conventional, but optimized design. A PFN using Russian K15-10 type high energy density glass capacitors has been constructed and tested into a conventional pulse transformer and klystron load. Rise time is less than 400 nsec. Developmental work with thyratron manufacturers is being started. Similarly, R&D pulse transformers developed in cooperation with industry are being tested.

Pulse transformer R&D for NLC klystron pulse modulator

The authors have studied a conventional pulse transformer for the NLC klystron pulse modulator. The transformer has been analyzed using a simplified lumped circuit model. It is found that a fast rise time requires low leakage inductance and low distributed capacitance and can be realized by reducing the number of secondary turns, but it produces larger pulse droop and requires a larger core size. After making a tradeoff among these parameters carefully, a conventional pulse transformer with a rise time of 250 ns and a pulse droop of 3.6% has been designed and built. The transmission characteristics and pulse time-response were measured. The data were compared with the model. The agreement with the model was good when the measured values were used in the model simulation. The results of the high voltage tests using a klystron load are also presented.

Effects of temperature variation on the SLC linac RF system

The RF system of the Stanford Linear Collider in California is subjected to daily temperature cycles of up to 15/spl deg/C. This can result in phase variations of 15/spl deg/ at 3 GHz over the 3 km length of the main drive line system. Subsystems show local changes of the order of 3/spl deg/ over 100 meters. When operating with flat beams and normalized emittances of 0.3*10/sup -5/ m-rad in the vertical plane, changes as small as 0.5/spl deg/ perturb the wakefield tail compensation and make continuous tuning necessary. Different approaches to stabilization of the RF phases and amplitudes are discussed.

Design of a 50 MW klystron at X-band

This paper describes the design and performance of the XL-1 klystron; a 50 MW klystron operating at a frequency of 11.424 GHz for use on the SLAC Next Linear Collider Test Accelerator (NLCTA). Problems associated with the development of high-power rf sources for NLC, and the solutions implemented on XL-1 are discussed.

Accelerator and RF system development for NLC

An experimental station for an X-band Next Linear Collider has been constructed at SLAC. This station consists of a klystron and modulator, a low-loss waveguide system for RF power distribution, a SLED II pulse-compression and peak-power multiplication system, acceleration sections and beam-line components (gun, pre-buncher, pre-accelerator, focussing elements and spectrometer). An extensive program of experiments to evaluate the performance of all components is underway. The station is described in detail in this paper, and results to date are presented.<<ETX>>

Development of the pulse transformer for NLC klystron pulse modulator

We have studied a conventional pulse transformer for the NLC klystron pulse modulator. The transformer has been analyzed using a simplified lumped circuit model. It is found that a fast rise time requires low leakage inductance and low distributed capacitance and can be realized by reducing the number of secondary turns, but it produces larger pulse droop and core size. After making a tradeoff among these parameters carefully, a conventional pulse transformer with a rise time of 250 ns and a pulse droop of 3.6% has been designed and built. The transmission characteristics and pulse time-response were measured. The data were compared with the model. The agreement with the model was good when the measured values were used in the model simulation. The results of the high voltage tests are also presented.

Developments in the NLC modulator R&D program at SLAC

The NLC (Next Linear Collider) development effort continues to move forward from its initial Zero Design Report (ZDR). A major component of the NLC is the high power RF source, which is designed around the technology of the klystron. The NLC is conceptualized around 75 MW, PPM (periodic permanent magnet) focused klystrons and will use approximately 3300 klystrons in each of the two main linacs. Simple analysis has shown that operating two klystrons per modulator has both economic and configuration advantages. The physical design of the modulators is an integral part of the design of the tunnels, etc. Klystron spacing is dictated by the pulse compression regime. This paper presents the to-date results of the investigation efforts in energy storage, pulse transformers and efficiency. Future plans, including new technologies to pursue are discussed. SLAC is also continuously looking for new and novel approaches to either the modulator components or the overall modulator approach. SLAC and the DOE are attempting to use the SBIR program to help with industry development of the needed components and new ideas.

High dielectric constant materials for pulsed energy storage capacitors

A high dielectric constant coupled with a high dielectric strength is essential in producing high energy density, low inductance capacitors used in pulsed energy systems. The NLC (Next Linear Collider) which is envisioned as the next step in high energy physics research tools will employ several thousand pulsed klystron RF sources. The modulators for these klystrons require efficient, reliable energy storage capacitors. Collaboration with Russian scientists has made available to us information and capacitor samples based on the Tungsten-Bronze family which exhibit dielectric constants of over 1,000, and working voltage gradients in excess of 60 kV/cm. We are currently testing 10 nanofarad, 40 kV capacitor samples in pulsed modulator service manufactured at the GIRIKOND Institute in St. Petersburg, Russia. Dr. Galina Blokhina is the designer of these capacitors. The material is a solid solution of complex compounds of niobate dielectric. The Tungsten-Bronze-Type Crystals are bound in amorphous glass. The paper summarizes the theoretical studies of this material with a Russian and English bibliography, describes Dr. Blokhinas manufacturing processes, and presents the results of pulsed energy storage testing carried out at SLAG for the NLC R&D effort. It is the intent of this paper to spark interest in transferring this technology to the world community so that R&D in this area will expand and provide this technology to many users including the Parallel NLC project.