An electron storage ring to be used solely as o synchrotron radiation source has been designed for a maximum energy of 1.5 GeV, expandable to 2 GeV, and a maximum current of 1 A. High field superconducting sagnet wigKlers to serve as hard radiation ports have !>een Incorporated into the ring to make available a wide range of wavelengths for simultaneous experiments. The regular lattice consists of a series of small achromatic bends forming the arcs. The wiggler magnets are placed in low-c regions in the center of insertions separating these arcs. The arrangement minimizes the electron emittances and yields high source brightness, other machine parameters are dictated by experimental requirements and apparatus as well as by cost constraints.
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.
IntroductionPrevious six dimensional linac orbit calculations performed with a computer program, in which the beam bunch is described as collection of approximately 500 uniformly charged spheres,suggested the following conclusions.1 1. The beam can be matched to both the longitudinal and transverse admittances of the linac according to a simple prescription based on the ellipsoidal model.2. With beams from recently developed preinjectors focussed by sufficiently high quadrupole gradients in the beginning of the linac, output intensities up to several hundred milliamperes can be achieved.3. There is a considerable emittance growth in beams with brightness, B,f* of 109 and higher. This appears to be caused by non-linear space charge forces.Results 2 and 3 are consistent with experimental measurements carried out with the 50 MeV linacs at CERN2 and BNL,3 using high brightness pre injectors.It is the purpose of this paper to further investigate the nature and magnitude of space charge induced transverse emittance growth. As will be seen, the result of this study suggests that conventional bunching schemes do not yield optimal linac performance with regard to conservation of transverse emittance in bright beams. Calculations and ResultsAll calculations were done assuming a beam current of 100 mA. For this current the BNL preinjector provides a normalized transverse emittance of 0.09 n cm-mrad. Machine parameters of the BNL 200 MeV injector linac were used unless otherwise mentioned. Computer runs were made up to 10 MeV. Transverse emittances were calculated by a rms method. Calculations with transverse space-charge forcesIn order to obtain a qualitive or, at the most, a semi-quantitive understanding of the coupling effects which showed up in earlier numerical calculations the computer program was modified with * Work performed under the auspices of the U. S. Atomic Energy Commission. ** Defined as B = I . 10 6/½12E2, where I is the current in mA, E-rr is the normalized emittance in cm-mrad. respect to its treatment of space charge forces, quadrupole focussing forces and RF fields in the gap between drift tubes. These changes were motivated by the following considerations: Previous results eliminated longitudinal-transverse coupling through the RF field as major contributor to the observed emittance growth. Since magnet misalignment errors and magnet non-linearities are not included in the computer program, the observed increase in transverse phase space area must be caused by either space charge induced longitudinal-transverse or transverse-transverse coupling, or both. These effects were now separated by excluding longitudinal space charge forces in the motion code. Transverse space charge forces were calculated by assuming that each of the approximately 500 particles is an infinitely long and uniformly charged cylinder, the radius of which is determined by the requirement that all cylinders together fill up the x-y cross section of the beam.The bunched character of the beam was described by the use of a bunching fac...
Introduct ionThe distance between the 200-MeV linac and the 750-keV preinjector is designed to be approximately 8 m. A 200-mA beam with a phase-space area of 4.5 cm-mrad must be transported and bunched over this length with minimum loss in beam quality. As was first pointed out by Regenstreif,1 nonlinearities due to quadrupole fringing fields can cause serious emittance growth in low-energy transport channels. In order to design a satisfactory system an effort has to be made to keep this effect as small as possible.It is the purpose of this paper to describe how a suitable system was chosen and to show results on beam profiles and emittances along the system which were obtained from numerical beam dynamics calculations including fringing fields and spacecharge effects. Results obtained for two other, less desirable, systems are also shown.
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