The longitudinal charge distribution of bunches accelerated in the Stanford Linear Collider (SLC) linac will strongly affect the performance of the Collider. Bunch lengths are chosen in a balance between the deleterious effects of longitudinal and transverse wakefields. The former impacts on the beam energy spread whereas the latter is important to the transverse emittance. Two bunch length measurement ports have been installed in the SLC linac: one in the injector region and one after the emittance damping ring to linac reinjection point. These ports utilize a fused quartz Cerenkov radiator in conjunction with an electrooptic streak camera to permit real time monitoring of single s-band buckets with a resolution of several picoseconds. The design of the radiators and light collection optics is discussed with an emphasis on those issues important to high resolution. Experimental results are presented.

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Real Time Bunch Length Measurements in the SLC Linac

Publisher Summary This chapter describes the technology that enables the investigation of radiation chemical phenomena at picosecond and femtosecond timescales. It particularly focuses on ultrafast studies using ionizing radiation, primarily electron beams, as the excitation source. Particle accelerators of every size and type consist of two major components, which are a particle source which is sometimes called an injector, and an acceleration stage. The job of the injector is to generate a particle beam with the desired position momentum relationship for acceptance into the acceleration section. Ultrafast accelerators require an injection system that deposits the entire electron bunch in a single RF period. The electron pulse is generated by gating the thermionic cathode of an electrostatic electron gun on and off within a few nanoseconds. Another type of injector developed in recent years for ultrafast accelerators is the radio-frequency photocathode electron gun. Radio-frequency (RF) photocathode electron guns consist of one or more conducting resonant cavities that are filled with several megawatts of microwave power to create transient electric field gradients of 80 to 100 MV/m.

Accelerators for ultrafast phenomena

The decade that opened in 1950 witnessed dramatic changes in the experimental study of the kinetics of chemical reactions. It started with the description of an apparatus for directly following light-induced processes on millisecond time scales (1) and closed with the announcement of the development of the use of pulses of high energy electrons of a few microseconds duration for studying radiation chemical changes (2–4). In between, the use of rapid jumps of temperature (5) and pressure (6) was applied to the study of the kinetics of chemical equilibrium. All these methods, and related ones developed since that time, rely on the imparting of a momentary burst of energy to a chemical system, in consequence of which the system leaves its initial equilibrium state. The return of the system to equilibrium is subsequently monitored by a technique that is amenable to a high degree of time resolution. The use of pulses of photons and electrons to disturb a system differs fundamentally from the use of temperature and pressure jumps: In the latter case the system moves only a small way from equilibrium, the change in equilibrium position depends upon the temperature and pressure dependence of the thermodynamic properties of the equilibrium state, and no new species are involved.

Instrumentation for the Generation and Detection of Transient Species

* Laboratoire de Chimie Physique-ELYSE, UMR CNRS-UPS, Bât. 349, Universite Paris-Sud, 91405 Orsay, France. † Chemistry Department, Brookhaven National Laboratory, Upton, NY 11973, USA. ‡ Advanced Science Research Center, Japan Atomic Energy Agency, 2–4 Shirakatashirane, Tokai, Naka, Ibaraki 319-1195, Japan. § Department of Nuclear Engineering and Management, School of Engineering, The University of Tokyo, Hongo 7-3-1, Bunkyo-ku, Tokyo 113-8656, Japan. ¶ Nuclear Professional School, School of Engineering, The University of Tokyo, 2-22 Shirakata Shirane, Tokai, Naka, Ibaraki 319-1188, Japan. || The Institute of Scientific and Industrial Research, Osaka University, 8-1 Mihogaoka, Ibaraki, Osaka 567-0047, Japan. ** CREST, Japan Science and Technology Agency, c/o Osaka University, 8-1 Mihogaoka, Ibaraki, Osaka 567-0047, Japan. †† E-mail: wishart@bnl.gov Chapter 5

Ultrafast Pulse Radiolysis Methods

Picosecond pulse radiolysis system at nuclear engineering research laboratory, University of Tokyo

We describe the technique and the results of a measurement of the width of a fine structure pulse from our L‐band electron linear accelerator. The pulse width was measured by measuring the width of the Cerenkov light pulse generated by the electron beam using a streak camera–TV camera–computer system. With very low beam currents, a pulse width of 20 psec (FWHM) was measured, while at higher beam currents a pulse width of 27 psec was measured showing a space‐charge effect. In addition, a broad energy spectrum for the electrons or improper focusing into a 270° bending magnet was also shown to increase the pulse width of the beam after it had traversed the magnet.

S. Gordon

Papers

Optimization of isolated electron pulses in the picosecond range from a linear accelerator using a streak camera–TV diagnostic system