Flux Return

The steel flux r( turn surrounds the coil and detector while allowing beam passage at the detector c( nt( rline. It sui)i)orts the detector components within, provides a more uniform and effi( ient magnetic field volume, and acts as tin raeliator lor tin hadron ( alorinn t( r. The end caps are movable to allow acc( ss to d( t( ctor components within. 

Tin barrel and endcai)s will sit on supports that allow accurate positioning of the eletector with respect to the beam axes. This motion can be provided by hydraulic jacks on Hillman rollers, in the manner of the SLD sui)pe rt system. 

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A familiar type of cyclically operated solenoid electromagnet is the Franz separator, a well-known continuous pe of solenoid separator manufactured by Kriipp-Sol. An enclosed flux return-frame solenoid design for cyclic and continuous use is built by Sala International Inc. 

The approximation is valid for particles with radii greater than 10 pm. The corresponding mass flux returning to the earth surface due to sedimentation is given by... 

The result given in Eq. (155) is correct for a single-well potential. For a doublewell potential in which the energy loss in each of the two wells is Au, A, one must revise the integral equation to take into consideration the flux returning from each one of the wells. As shown by Melnikov (85,86), this then leads to the deceptively simple result for the depopulation factor ... 

When both are present, flux returns to base levels (Muhanunad et al., 2004). We have previously seen similar effects with other combinations of additives on absorption of jet fuel hydrocarbons (Baynes et al., 2001 Riviere et al., 1999). 

Fig. IX.G.2 Two-dimensional simulations of the 48D48 spectrometer magnet. The figures show a simulation of an x-z slice of the magnet at beam height (top figure) and 20 cm above the beam height (bottom figure). Because the simulations are done in 2-D, some 3-D effects, such as the flux return lines in the iron, are not correct.

On the exit side of the 48D48, a split field clamp design in which the flux returns back to the yoke will be used. This design leaves a large open region above and below the beam line which allows room for the deflected K beam to exit near the bottom of the magnet gap, and has minimal interference with the back drift chambers near the top of the magnet gap. 

Other requirements of a general nature are that any particle identification system must not compromise either charged particle or photon resolution, that detector elements must be radiation hard to a level not previously encountered in e e detectors, and that detector elements and data acquisition systems must cope with unprecedentedly high rates. A valuable improvement in overall efficiency can be obtained by finely segmenting the magnet flux return to allow the identification of low momentum muons. 

The motivation for thoroughly instrumenting the magnet flux return is twofold ... 

The flux return design consists of 20-24 plates of 1 steel with 1 instrumented gaps. The detectors are larocci tubes with strip readout operated in limited streamer mode. Individual layers are read out, to ascertain the range of the candidate particle. 

For 7r/e and 7r//z separation as well as K/p separation in the 1-1.4 GeV/c region and above 2.7 GeV/c, one needs additional information lower-momentum electrons are identified by dE/dx, while higher-momentum electrons can be identified by pattern recognition in the electromagnetic calorimeter the instrumented flux return is employed for muon identification antiprotons leave a clear signature in the electromagnetic calorimeter. 

A variety of tradeoffs govern the design of the solenoidal coil and steel flux return of the detector. The optimization of the magnetic field value (1 or 1.5 Tesla), the choice of normal or superconducting technology for the coil and the instrumentation of the flux return to extend the physics capability of the detector are all involved. We will discuss the technical choices inv olved in arriving at an actual design these involve cost as well as physics performance. 

An instrumented flux return can serve as a calorimeter for detection and to extend effective tt/// separation to lower than usual momenta. In this regard, the larger thickness of a normal coil in interaction lengths becomes a consideration. 

Because the steel of the flux return and the instrumentation is highly segmented, the flux return adds two important capabilities to the detector. First, it extends muon detection to momenta below 1 GeV/c, by exploiting the small difference in range between /i s and tt s [1]. This is of value in improving efficiency both for reconstructing semi-leptonic B decays and for lepton tagging in CP violation experiments. Second, the flux return can... 

Thcise studies flo not, however, take into account the material of the coil between the Csl and the flux return, which is small only in the case of the superconducting coil. The extra material introduced by a normal coil will reduce the hadron detection efficiency substantially. 

Figure 6.7. Position resolution for 2 GeV/c interacting A J s detected in the segmented flux return.

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