COLLECTION OPTICS WITH THE HORN TYPE FOCUCING ELMENT MADE WITH SEPARATE CONDUCTORS
We describe the device for focusing of charged particles by the system of separated conductors which follow the parabolic profile. Basically this is a horn-type focuser, but with the individual conductors instead of continuous surface. This device allows substantial reduction of fabrication cost with the same focusing properties as the continuous parabolic surface. We recommend this “bird-cage” type system for focusing pions/muons in the projects under discussion in many Laboratories around the World. OVERVIEW Necessity for good quality secondary beams is well argumented topic for the high energy physics [1]-[3]. The horn-like focusing elements (lenses) are broadly in use in many laboratories for collection of secondary particles in the proton lines. One example of usage of miniature copy of such lens for collection of positrons is known from Budker INP [4]. For collection of pions the horns reach sized of ~0.5 m in diameter and ~2 m long [5]. Fabrication of thin wall parabolic surface of this scale represents substantional technological difficulties. Typically it is fabricated from solid billets of 40-6061-T6 Aluminum with typical lengths of 40 cm [5]. Three segments are electron beam welded together. Typical thickness of the parabolic wall is around 2mm. In all horn-like focusing devises the secondary beams running through material of paraboloid. In this publication we made a proposition to approximate continuous surface of paraboloid with limited number of separate conductors. This approach delivers significant simplifications in technology of fabrication. The payoff for this-a distortions of trajectories can be made acceptable as the angular spread of secondary beams is significant. Any way it is comparable with divergences obtained as a result of multiple scattering in material of paraboloid.
Fermilab Neutrino - Horn Focussing System
The study of neutrino physics at Fermilab in the 15-foot bubble chamber and in electronic counter detectors is being actively and agressively pursued. To increase the flux of neutrinos through the detectors over the entire neutrino energy spectrum, a high efficiency horn-focussed beam was developed. The horn system is well known for its high acceptance and hi hly achromatic focussing of charged particles 4 produced at the production target into a low divergence beam. This meson beam is allowed to decay in a 400 m long vacuum region producing neutrinos and muons. The muons are absorbed from the beam by using 1 Km of earth allowing the filtered neutrino beam to pass through the experimental detectors. This report covers the equipment and results of the focussing region.
Review of the frontier workshop and Q-slope results
Abstract Over the last few years, significant progress has been made to produce field emission free niobium surfaces. Nowadays, the major limitation towards achieving the critical field in radio-frequency (rf) superconducting cavities made of bulk niobium of high purity is represented by the so-called “high field Q -slope” or “ Q -drop”. This phenomenon is characterized by a sharp decrease of the cavity quality factor, in absence of field emission, starting at a peak surface magnetic field of the order of 100 mT. It has been observed that these losses are usually reduced by a low-temperature “in situ” baking, typically at 100–120 °C for 24–48 h. Several models have been proposed to explain the high field Q -slope and many experiments have been conducted in different laboratories to validate such models. A three-day workshop was held in Argonne in September 2004 to present and discuss experimental and theoretical results on the present limitations of superconducting rf cavities. In this paper, we will focus on the high field Q -slope by reviewing the results presented at the workshop along with other experimental data. In order to explain the Q -drop and the baking effect we will discuss an improved version of the oxygen diffusion model.