Combined-function electron storage rings

A combined-function lattice permits reduction of the RF power required for compensation of synchrotron radiation, compared to a separated- function machine of the same circumference. At the same time, the required beam aperture is slightly smaller, and the damping aperture is much larger. Damping of radial betatron oscillations is achieved by making the defocusing magnets slightly stronger than the focusing ones. (4 refs)

The impedance of layered vacuum chambers

USING AN ALGORITHM FOR THE CALCULATION OF ELECTRO-MAGNETIC FIELDS OF OSCILLATING CIRCULAR CYLINDRICAL BEAMS SURROUNDED BY ANY NUMBER OF ANNULAR LAYERS OF ARBITRARY MATERIAL PROPERTIES, WE CALCULATE THE TRANSVERSE RESISTIVE WALL IMPEDANCE OF THE BEAM SCREENS FOR THE LHC and FLHC, A LARGER HADRON COLLIDER. THESE CONSIST OF TUBES OF STAINLESS STEEL WITH THIN INSIDE LAYERS OF COPPER. THE RESULTS ARE COMPARED WITH THOSE OF AN APPROXIMATE ANALYTIC CALCULATION WHICH GIVES INCORRECT RESULTS WHEN THE SKIN DEPTH BECOMES SO LARGE THAT IT APPROACHES THE WALL RADIUS

Impedance of Layered Vacuum Chambers for Large Colliders

We calculate the transverse resistive wall impedance of the LHC beam screen, consisting of a tube of stainless steel with a thin inside layer of copper. For this we use an algorithm for the calculation of the electromagnetic fields of an oscillating circular cylindrical beam surrounded by any number of concentric layers of arbitrary material properties. The results for the impedance of the LHC beam screen and the growth rates of the resistive-wall instability are compared with earlier calculations using approximate formulae with wall penetration factors. The same algorithm is also used to estimate the impedance of a beam screen in a much larger machine, a Future Large Hadron Collider FLHC, where the penetration factor method would give incorrect results

On the Symmetry of the Impedance

The reciprocity theorem is used to prove the symmetry of the longitudinal impedance of an accelerating structure with respect to exchange of the coordinates of the leading and trailing particles. (2 refs)

Analysis of Shielding Charged Particle Beams by thin Conductors

We present an analysis of shielding of electromagnetic fields excited by beams of charged particles surrounded by thin conducting layers or metal stripes inside an external structure of finite length. The ability of shielding by a layer thinner than the skin depth is explained and expressions for the impedance are derived. A previous result[1] showing preferential penetration through the shielding layer at the resonant frequencies of the surrounding structure is verified, and extended to include finite resistivity of the outer structure. Integration over the spectrum of the beam bunch shows that penetration is (nearly) independent of the quality factors of the resonances. The transition of these results to those for a geometry of infinite length requires numerical evaluation

Shielding effects on coherent synchrotron radiation

A controversy concerning the shielding of coherent synchrotron radiation has existed for many years. Estimates of the reduction of radiated power by nearby conducting surfaces in LHC differ by several order of magnitude when one uses the expressions given in two of the major papers in the field. A clarification of this problem as well as the expected values for coherent synchrotron radiation in LEP and LHC are presented here

Energy Loss to Coaxial Vacuum Chambers in LEP and LHC

In many hig-energy storage rings the beam chamber is connected to a separate pump chamber by a metallic wall with many holes or slots whic permits passage of the rest gas. In LEP, the pump chamber contains a metallic 'negstrip' pump, and thereby becomes a coazial transmission line. Also in LHC, a coaxial line is formed by the 'liner' and the surrounding cold vacuum chamber which it shields from heating by sznchrotron radiation. Since the phase velocity of electro-magnetic fields in a coax line is close to light velocity, the fields will be almost in sznchronism with the particle beam and the pump chamber, which may result in a large resistive impedance and could lead to isntability, loss of beam energy, and excessive heating of the chamber walls. Here we estimate the rate of field buildup analytically, and in a subsequent report we will compare these results with numerical computations using 3-D computer codes. The results are tested for diagnostic purposes on a 'slot coupler' with short and wide holes designed to extract energy efficiency