Honeycomb drift chamber

As mentioned in the previous sections, the tilted Enge spectrometer combined with the splitter magnet lost its original symmetry of the optics and it is essential to measure the particle incident angle as well as its position at the exit of the spectrometer. In order to achieve momentum resolution of 4$\times$10$^{-4}$ (FWHM), position and angular resolutions of 100$\mu$m and 2 mr (rms), respectively, are required for trajectories incident angles of which vary more than 50 degrees. Furthermore, the detector should stand for singles rate as high as 10 MHz.

A drift chamber with honeycomb cell structure is to be employed to meet above requirements.

表 13: Honeycomb drift chamber parameters

layer configuration	xx' uu' xx' vv' xx' (u,v $\pm 30^\circ$ tilt)
effective volume	$12^H \times 100^W \times 30^T cm$
cell size	honeycomb (hexagon) with side 5 mm
anode wire	tungsten $\phi$ 20$\mu$m
shield/field wire	aluminum $\phi$ 80$\mu$m

The effect of multiple scattering was studied with the GEANT simulation. Angular spreads for various gases are listed in Table 14. Standard Ar + C$_2$H$_6$(50/50) gas barely satisfies the requirement and possibility to use a He-based gas will be investigated.

表 14: Multiple scattering effects for the scattered electrons

Gas	Angular spread (mrad, rms)
He	0.84
Ar	1.90
Ar + C$_2$H$_6$ (50/50)	1.90

Figure 35 shows an isochrome drift lines for one honeycomb cell calculated with the Garfield program.