J. P. Blewett

Orbits and fields in the helical wiggler

The ’’helical wiggler’’ is a device in which relativistic electrons pass through a transverse magnetic field whose direction revolves with distance along the beam axis. In this paper we discuss the electron orbits in this device. The field patterns and necessary current distributions are established. Finally, the question is treated as to whether this device can be incorporated into a storage ring without destroying the circulating beam. It is concluded that there is reason to expect satisfactory performance from helical wigglers in storage rings.

Synchrotron radiation - early history.

The scientific history of the work that led to the prediction and observation of synchrotron radiation goes back more than a century. This paper is a summary of that history.

Free Electron Laser Experiment at the NSLS 700 MeV Electron Storage Ring

A free electron laser experiment is described, to be performed with the 700 MeV electron storage ring of the National Synchrotron Light Source. The experiment is designed to study the parameters of the fel in an electron storage ring and the performance of this laser as a source of short wavelength radiation in the VUV region of the spectrum. The initial experiment will be carried out at a wave length of approximately 3000 Å, utilizing a permanent magnet undulator. For an average electron current of 1A distributed in three beam bunches, the small signal gain per pass (relative enhancement of the radiation intensity per electron bunch pass through the undulator) is calculated to be approximately 10%.

Radio‐Frequency System. Part IV—Accelerating Unit

The Cosmotron accelerating gap and its associated shield are driven by a broad‐band amplifier. The impedance level at the gap is raised to the point at which it can be driven by conventional power tubes, by loading the surrounding shield with ferromagnetic material. Extensive tests on loading materials led to the choice of nickel‐zinc ferrite. About 2800 pounds of ferrite are required. Techniques are described for fabrication and assembly of the ferrite structure, and for excitation of the gap by the power amplifier.

Radio‐Frequency System. Part I—Design Principles

The Cosmotron rf system must supply a 2000‐volt radio‐frequency accelerating signal across an insulated gap in the vacuum chamber. During the one‐second accelerating cycle the frequency must vary from about 370 kc to 4.2 Mc at a rate determined by the rate of change of the field in the gap of the Cosmotron magnet. Frequency is swept in an oscillator whose resonant circuit includes a ferrite‐loaded saturable inductor. The impedance of the gap and its associated shield is maintained by ferrite loading. A description is included of the sequence of control and switching operations in the rf system during a complete Cosmotron cycle.

Radio‐Frequency System. Part II—Frequency Control

Frequency control in the Cosmotron is based on a signal derived from a pickup loop in the magnet gap. This signal is integrated electronically and is then distorted in a nonlinear network to yield a control voltage for the saturable‐core oscillator. System constants are chosen such that the oscillator frequency has, at all times, the value associated with the instantaneous Cosmotron magnetic field. Dynamic frequency is measured by counting cycles for one millisecond at any desired time during the cycle. Tests on the present system indicate that it is adequate, but that several simplifications are possible.

Pole‐Face Windings. Part I—Design

At fields over 10 000 gauss the effects of saturation in the Cosmotron magnet cause deterioration of the field pattern which rapidly becomes serious enough to cause complete loss of the proton beam. This pattern can be restored adequately up to 14 000 gauss by passing current through single‐layer windings on the faces of the magnet poles. Peak correction current required at 14 000 gauss is about 300 amp per radial inch of each winding. The pole‐face winding returns are so arranged that the winding is almost completely decoupled from the main magnetizing winding. The windings and their power supplies are in place but are not yet energized. Several turns of the winding are used in a self‐powered correction for the distortion of the magnetic median surface at injection fields.

Magnet. Part I—Design

The magnet of the Cosmotron is designed to provide magnetic fields up to 14 000 gauss over a region roughly 9 in. by 30 in. surrounding the proton orbit of 30‐ft radius. The magnet is C‐shaped with the magnetic return inside the proton orbit. The magnet gap contour is shaped very precisely to accommodate and control the excursions of the proton beam from its stable orbit. The magnet is energized by current supplied to its water‐cooled coil from a 26 000‐kva motor‐flywheel‐generator set. Magnet parameters are tabulated, and the considerations which led to their choice are discussed.

Radio‐Frequency System. Part V—Properties of Ferromagnetic Ferrites

Ferromagnetic ferrites are used in numerous applications in the Cosmotron. For example, in the accelerating unit over a ton of ferrite is included. During the design of the Cosmotron, much information was required about the various electrical and magnetic properties of ferrites. Since this information was not available, a detailed program of investigation of ferrite properties has been carried out. Results are presented of dielectric properties and of magnetic properties as functions of frequency, dc and ac field strengths, and temperature. A general discussion is included of the behavior of electromagnetic waves in ferrite structures.

Recent Advances in Particle Accelerators

Publisher Summary This chapter elaborates the new ideas and progress on major particle accelerators throughout the world. The minimum overall length of linear accelerators for high energies has, in the past, been set by the maximum electric field that could be maintained without a breakdown between parts of the accelerating structure. In all, over 30 laboratories are studying, actively proposing, or constructing heavy ion machines. However, no mention has been made of the conversion of Columbias Nevis synchrocyclotron to higher energy and intensity operation. Also the new linac injector and pressurized preinjector for the 3-GeV proton synchrotron at Saclay, the high-intensity electron linac at MIT, the splendid new tandem accelerators developed by High Voltage Engineering, the Dynamitron accelerators developed by Radiation Dynamics, various high current electron accelerators for use as flash X-ray tubes, and many proposals for modification and improvement of existing accelerators have been either neglected or barely mentioned. A less technical but very readable source of information about current accelerator developments is the CERN Courier published monthly in French and English by CERNs Public Information Office.