Resonant cavity accelerators

Resonant cavity accelerators consist of several resonant cavities in series energized by a single S-band klystron using a microwave power distribution system.51 Another type consists of a single VHF cavity energized by a triode tube that is less expensive than klystron. The resonant frequency of the latter is about 110 MHz, which is well... 

Other types of indirect accelerators are vhf resonant cavities and linear induction accelerators, such as travelling wave linacs, standing wave linacs, resonant cavity accelerators and linear induction accelerators [1]. 

A standing wave (SW) microwave linear accelerator consists of a linear array of resonant cavities that are energized by a common source of microwave power. These cavities are nearly isolated by webs with small-diameter apertures, and the high-energy electron beam passes through these apertures. However, they are coupled through intermediate cavities, which stabilize the microwave phase relationship between the accelerating cavities. 

The new accelerator at Brookhaven is based on an RF photocathode gun with one or more resonant cavities in which microwaves create transient electric fields up to 1 MeV cm [104], A pulse of laser light is used for generating photoelectrons which are accelerated to 9 MeV in a distance of 30 cm. The laser pulse can also be used as the analyzing light source this means it is closely synchronized with the electron pulse. The time resolution of the electron pulse is therefore that of the laser pulse, so that subpicosecond pulse radiolysis is possible. A similar system is planned at Argonne National Laboratory [146],... 

To exploit the capabilities of fast lasers, a new picosecond Laser-Electron Accelerator Facility (LEAF) has been recently developed at Brookhaven National Laboratory. In this facility, schematically shown in Figure 1, laser light impinging on a photocathode inside a resonant cavity gun merely 30 cm in length produces the electron pulse. The emitted electrons are accelerated to energies of 9.2 MeV within that gun by a 15 MW pulse of RF power from a 2.9 GHz klystron. The laser pulse is synchronized with the RF power to produce the electron pulse near the peak field gradient (about 1 MeV/cm). Thus the pulse length and intensity are a function of the laser pulse properties, and electron... 

A Rhodotron is an electron accelerator based on the principle of recirculation of a beam in successive passes through a single coaxial cavity resonating in the VHP frequency range. This large-diameter cavity operates with a relatively low microwave field, which makes it possible to achieve continuous wave (CW) acceleration of electron beams to high energies. 

The electron gun is located at the outer wall of the accelerating cavity, and the electrons are injected into the cavity at a voltage of abouf 35-40 kV. The cavify is cooled by a water jacket on the inner coaxial conductor and at the end flanges and by discrefe water channels along the outer diameter. The system is designed to operate with a 2 MW cooling tower up to an outside temperature of 35°C (95°F). Therefore, no water chiller is required. The RF amplifier defects and follows changes in fhe resonant frequency of the cavity so that accurate control of the cavity temperature is not required. 

A microwave technique for measuring the decay of electrons in pulse irradiated gases is described. The technique involves the measurement of the change in resonant frequency of a microwave cavity caused by a change in the complex conductivity within the cavity when electrons are present Single pulses of 3 Mev. electrons from a Van de Graaff accelerator are used to ionize the gas. Electron densities as low as 107 cm. 3 (total dose 0.3 rad at 10 ton) can be measured accurately. In the absence of diffusion the method can be used to study electron loss by electron capture or electron-ion recombination for pressures as low as 1 ton and as high as at least 200 ton. The potential of the technique is illustrated by results obtained with pulse-irradiated air. 

The radio frequency quadrupole (RFQ) is used to accelerate protons and heavier ions. It uses four parallel electrodes around the beam axis as shown in O Fig. 50.20. The RFQs operate at high frequencies, typically from tens to hundreds of MHz. The electrodes, which are called vanes, are placed in a cavity forming a resonant structure. The adjacent electrodes have opposite charges. From the end, the RFQ looks like an electric quadrupole. This arrangement of electric field focuses the beam in one plane and defocuses it in the other one. Since the electric field oscillates, a net focusing effect can be obtained along the length of the vanes. 

At about the same time, L. Ornstein and myself were working on an experiment connected with the original idea of coherent acceleration. We hoped to obtain a burst of (x-waves sufficiently powerful to accelerate, by means of radiation pressure, a plasma bunch to relativistic energies. Since there were no [x-wave generators that could produce such a burst — we proposed a method that we hoped would achieve it. Imagine a cavity in which a particular resonant mode is excited. The volume of the cavity is then rapidly reduced, e.g., by a piston moving axially (Fig. 1). 

Mi etron A microwave vacuum tube oscillator in which microwaves in a number of cavity resonators interact with bunched electrons in motion rotating or rectihnearly. The basic electron motion is formed by the appUed accelerating electric fields and the DC magnetic fields. 

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