Compact Free Electron Laser for Medical Applications.
Annual technical rept. 30 Sep 91-29 Sep 92,
MASSACHUSETTS INST OF TECH CAMBRIDGE RESEARCH LAB OF ELECTRONICS
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The 70-period Microwiggler has been tuned. A novel iterative tuning regimen was employed which involves perturbing the tuning profile at selected points in order to produce an empirical Taylor expansion matrix relating the magnetic field profile described as a 140-dimensional vector consisting of the peak amplitude of each half-period to the tuning resistor profile described as a 140-dimensional vector consisting of the length of the tuning resistor of each half-period. The resulting matrix equation is then numerically inverted to produce a list of resistor adjustments which to first order will produce a flat field amplitude profile. Some field error invariably will remain, however, due to non-linear saturation effects and measurement error in the matrix entries. The process is then repeated until the errors in the field profile are of the same magnitude as the errors inherent in the field measurement system. Experience has shown that this regimen converges very rapidly, with 3-4 iteration required to reduce field errors from 2.5 RMS untuned to 0.08 RMS. Tuning, therefor can be accomplished in 3-4 working days during most of which time the Microwiggler system runs unattended under computer control.
- Medical Facilities, Equipment and Supplies
- Lasers and Masers