摘要:

The beam tube vacuum requirements in future superconducting proton colliders that have been proposed or discussed in the literature—SSC, LHC, and ELN—are reviewed. The main beam tube vacuum problem encountered in these machines is how to deal with the magnitude of gas desorption and power deposition by synchrotron radiation while satisfying resistivity, impedance, and space constraints in the cryogenic environment of superconducting magnets. A beam tube vacuum model is developed that treats photodesorption of tightly bound H, C, and O, photodesorption of physisorbed molecules, and the isotherm vapor pressure of H2. Experimental data on cold tube photodesorption experiments are reviewed and applied to model calculations of beam tube vacuum performance for simple cold beam tube and liner configurations. Particular emphasis is placed on the modeling and interpretation of beam tube photodesorption experiments at electron synchrotron light sources. The paper also includes discussion of the constraints imposed by beam image current heating, the growth rate of the resistive wall instability, and single‐bunch instability impedance limits. © 1995American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.47297

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The problem of emittance growth due to random fluctuations of the magnetic field in a hadron collider is considered. It is shown that the transverse feedback system can suppress strongly the emittance growth. The main effect limiting a suppression degree is the betatron tube spread due to head‐on beam‐beam effects. A simple analytical model is considered. Its results are in a good coincidence with computer simulations. The dependencies of the emittance growth rate on noise spectral density, beam separation at the Interaction Point (IP), and value of beam separation at long‐range collisions are studied. The results are applicable to the Superconducting Super Collider. © 1995American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.47298

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

To achieve the goal of high luminosity in a proton synchrotron, one can either increase the beam intensity or lower the transverse emittance. This article, based on our design study for the Medium Energy Booster of the Superconducting Super Collider, contains an analysis of a few mechanisms that could possibly cause the transverse emittance to grow in a proton synchrotron. To ensure that the emittance growth is within a tolerable level, some feasible precautions are suggested. Their improvements on beam quality are also described. © 1995American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.47299

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The Superconducting Super Collider was designed to provide 108proton‐proton collisions per second in each of four detectors, about 1.7 collisions per bunch crossing. This collision rate requires a luminosity of 1033cm−2s−1, a value that can be attained only by strict control of beam emittance in each accelerator in the chain. Emittance control must start with an understanding of the causes of emittance growth as a guide to beam dynamics design. Manufacture, installation, commissioning, and operation of every component of the machine must be accomplished with emittance control as one of the objectives. This paper describes the actions taken to assure tht the linac output emittance is within the design goals of 0.3 &pgr;‐mm‐mrad (rms, normalized, transverse) and <0.89×106&pgr;‐eV‐s (rms, longitudinal). © 1995American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.47300

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

A feedback microprocessor has been built for the Tevatron. It has been constructed to be applicable to hadron colliders in general. Its inputs are realtime accelerator measurements, data describing the state of the Tevatron, and ramp tables. The microprocessor software includes a finite‐state machine. Each state corresponds to a specific Tevatron operation and has a state‐specific Tevatron model. Transitions between states are initiated by the global Tevatron clock. Each state includes a cyclic routine, which is called periodically and where all calculations are performed. The output corrections are inserted onto a fast Tevatron‐wide link from which the power supplies will read the real time corrections. We also store all of the input data and output corrections in a set of buffers that can easily be retrieved for diagnostic analysis. In this paper we describe this device and its use to control the Tevatron tunes as well as other possible applications. © 1995American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.47301

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Persistent currents in superconducting accelerator magnets are caused by the magnetization of the superconducting filaments in the field of the magnet itself. The magnetized filaments create additional field distortions that can have an important effect on the beam dynamics. During the initial operation of the Tevatron as a colliding beam accelerator, the chromaticities at the injection energy were found to be time‐dependent, leading to instabilities and particle loss during injection and at the start of acceleration. Laboratory measurements on single Tevatron dipoles indicated that these effects were due to time‐dependent, persistent‐current phenomena. Using additional laboratory measurements and beam observations, we have developed a set of procedures to compensate the time‐dependent chromaticities due to persistent currents. Application of these procedures has eliminated all problems caused by time‐dependent, persistent‐current effects. We will discuss the general problem of persistent‐current distortions in superconducting accelerators, as well as the laboratory measurements, beam observations, and successful implementation of the correction schemes. While these procedures have worked well, they do have limitations that will be discussed, as will possible future improvements and implications for future projects. © 1995American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.47302

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The imaging of synchrotron radiation (SR) has been suggested as a technique for providing a continuous, non‐interfering monitor of the beam profile in the Collider rings at the Superconducting Super Collider. A closer examination has raised questions concerning the applicability of SR imaging in this case because of the diffraction broadening of the image, the requirements for axial space and location in the lattice, and the complexity of the system. We have surveyed the known, alternative, minimal interference techniques for measuring beam size and have evaluated them for possible Collider usage. We conclude that of the approaches that appear feasible, all require at least some development for our usage and that the development of an electron beam probe offers the best promise. We recommend that flying wires be used for cross‐checking and calibrating the electron beam probe diagnostic and for luminosity measurements when the highest accuracy is required, but flying wires should not be used as the primary diagnostic because of their limited lifetime. © 1995American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.47303

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

In this discussion we present a description of imaging using an opaque obstruction with a circular cross section (such as a sphere) as the optical imaging element. Image formation is discussed in terms of the convolution product of the point spread function of the system and the optical intensity distribution of the object. It is shown how this convolution product can be efficiently accomplished in the frequency domain using digital technqiues. The emphasis of this report is placed on the numerical generation of the transfer function of the optical system. An analytical example of imaging using this technique with a standard 3‐bar target as the object is presented. Experimental verification of the analytical results is also given. © 1995American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.47304

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The echo effect has been known for many years in such diverse branches of physics as nuclear magnetic resonance, optics, plasmas, and fluids. It has been pointed out that the echo phenomenon should also be observable in hadron accelerators. If a beam is injected off‐center, and the betatron oscillations of its centroid are permitted to damp out by nonlinearity‐induced decoherence, a subsequent quad kick should, after a delay, transiently restore those betatron oscillations in the form of an echo signal. This article presents beam phase‐space portraits of the evolution of the echo, as well as detailed analytical calculations that permit estimation of the maximum echo amplitude attainable for a given initial beam offset. One of the analytic results is a numerically useful summation formula that also reveals a regular multiple‐echo train subsequent to the first echo signal. © 1995American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.47305

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Reducing the emittance of the proton beams of the Superconducting Super Collider (SSC) could result in major cost savings. The beam size is proportional to the square root of the emittance. Smaller emittance therefore implies smaller beam size, which leads to a smaller required dynamic aperture for the magnets, which would lead to large cost reduction. The luminosity (L) of any collider isL=&ggr;f0BN1N2/4&egr;N&bgr;*, whereN1andN2are the numbers of protons per bunch in the clockwise and counterclockwise directions, respectively, and &egr;Nis the normalized emittance of the beams. A lower beam emittance allows one to use lower values ofN1andN2to achieve the same luminosity. Lower values ofN1andN2will lead to cost savings throughout the SSC complex, as less stringent beam loading requirements will be placed on the source, the linac, and the Low Energy Booster (LEB), and less synchrotron heating and gas desorption will ocur in the collider, reducing the demands of cryogenic and vacuum systems. Lower requiredNalso raises the possibility of a proton antiproton option at the SSC, which would entail the use of a single Collider ring, resulting in additional savings. This paper will evaluate many of the important issues relevant to electron cooling of proton beams for the SSC. It will be shown that there are several possible options for electron cooling at the SSC. All options require technological progress before they become feasible, and care must be taken to avoid proton beam instability and resonant crossing. But should the technological hurdles be passed, electron cooling may provide the means to greatly reduce the cost of a future high energy physics Collider. © 1995American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.47307

出版商:AIP    

年代:1995

数据来源: AIP