High resolution monochromator systems using thermal gradient induced variable Bragg spacing

The vertical divergences of bending magnet and wiggler synchrotron sources are generally considerably larger than the acceptance angles of typical monochromator systems. This is particularly true at high energies (E greater than or equal to 14 keV) where the Darwin widths of perfect crystals are of the order 10-6 radians. By imposing a thermal gradient on the crystal, an efficient, wide acceptance angle monochromator can be obtained. The necessary condition being that the resulting d . sin theta is a constant across the beam. Gains in intensity of 3 to 100 can be realized relative to standard flat crystal systems. A number of possible designs are presented for both two and four crystal monochromator systems. The use of Si, Ge, and quartz monochromators are discussed