Spatial resolution of a GEM readout TPC using the charge dispersion signal

A large volume Time Projection Chamber (TPC) is being considered for the central charged particle tracker for the detector for the proposed International Linear Collider (ILC). To meet the ILC-TPC spatial resolution challenge of ~100 microns with a manageable number of readout pads and channels of electronics, Micro Pattern Gas Detectors (MPGD) are being developed which could use pads comparable in width to the proportional-wire/cathode-pad TPC. We have built a prototype GEM readout TPC with 2 mm x 6 mm pads using the new concept of charge dispersion in MPGDs with a resistive anode. The dependence of transverse resolution on the drift distance has been measured for small angle tracks in cosmic ray tests without a magnetic field for Ar/CO2 (90:10). The GEM-TPC resolution with charge dispersion readout is significantly better than previous measurements carried out with conventional direct charge readout techniques.Comment: 5 figures, 10 page

Realization of One-Way Electromagnetic Modes at the Interface Between Two Dissimilar Metals

We calculate the dispersion relations for electromagnetic waves propagating at the interface between two dissimilar Drude metals in an external magnetic field B parallel to the interface. The propagating modes are bound to the inteface and travel perpendicular to B. In certain frequency ranges, the waves can propagate in one direction only. The frequency range for these one-way modes increases with increasing B. One group of modes occurs at moderate frequencies, between the lower and upper plasma frequencies of the two metals. The other occurs at much lower frequencies, between their lower and upper cyclotron frequencies. We discuss possible ways to realize such modes in real materials, including dissimilar superconductors.Comment: 10 pages, 3 figure

Electrically controlled Bragg resonances of an ambichiral electro-optic structure: oblique incidence

The Pockels effect can increase the effective birefringence of ambichiral, electro--optic rejection filters made of materials with a $\bar{4}2m$ point group symmetry, when a dc electric field is applied parallel to the axis of nonhomogeneity. The reflectances and the transmittances of such an ambichiral structure for obliquely incident plane waves is solvable through a boundary-value problem that is formulated using the frequency-domain Maxwell equations, the constitutive equations that contain the Pockels effect, and standard algebraic techniques for handling 4x4 matrix ordinary differential equations. The Bragg resonance peaks, for different circular-polarized-incidence conditions, blueshift as the angle of incidence increases. These blueshifts are unaffected by the sign of the dc electric field.Comment: 11 page