We describe the construction and operation of an x-ray beam size monitor (xBSM), a device measuring e + and e − beam sizes in the CESR-TA storage ring using synchrotron radiation. The device can measure vertical beam sizes of 10 − 100 µm on a turn-by-turn, bunch-by-bunch basis at e ± beam energies of ∼ 2 GeV. At such beam energies the xBSM images x-rays of ≈1-10 keV (λ ≈ 0.1 − 1 nm) that emerge from a hard-bend magnet through a single-or multiple-slit (coded aperture) optical element onto an array of 32 InGaAs photodiodes with 50 µm pitch. Beamlines and detectors are entirely in-vacuum, enabling single-shot beam size measurement down to below 0.1 mA (2.5 × 10 9 particles) per bunch and inter-bunch spacing of as little as 4 ns. At E b = 2.1 GeV, systematic precision of ∼ 1 µm is achieved for a beam size of ∼ 12 µm; this is expected to scale as ∝ 1/σ b and ∝ 1/E b . Achieving this precision requires comprehensive alignment and calibration of the detector, optical elements, and x-ray beam. Data from the xBSM have been used to extract characteristics of beam oscillations on long and short timescales, and to make detailed studies of low-emittance tuning, intra-beam scattering, electron cloud effects, and multi-bunch instabilities.

We describe the design and performance of optical elements for an x-ray beam size monitor (xBSM), a device measuring e + and e − beam sizes in the CESR-TA storage ring. The device can measure vertical beam sizes of 10 − 100 µm on a turn-by-turn, bunch-by-bunch basis at e ± beam energies of ∼ 2 − 5 GeV. X-rays produced by a hard-bend magnet pass through a single-or multiple-slit (coded aperture) optical element onto a detector. The coded aperture slit pattern and thickness of masking material forming that pattern can both be tuned for optimal resolving power. We describe several such optical elements and show how well predictions of simple models track measured performances.

We describe operation of the CESR-TA vertical beam size monitor (xBSM) with e ± beams with E b =4 GeV. The xBSM measures vertical beam size by imaging synchrotron radiation x-rays through an optical element onto a detector array of 32 InGaAs photodiodes with 50 µm pitch. The device has previously been successfully used to measure vertical beam sizes of 10 − 100 µm on a bunch-by-bunch, turn-by-turn basis at e ± beam energies of ∼2 GeV and source magnetic fields below 2.8 kG, for which the detector required calibration for incident x-rays of 1-5 keV. At E b = 4.0 GeV and B=4.5 kG, however, the incident synchrotron radiation spectrum extends to ∼20 keV, requiring calibration of detector response in that regime. Such a calibration is described and then used to analyze data taken with several different thicknesses of filters in front of the detector. We obtain a relative precision of better than 4% on beam size measurement from 15-100 µm over several different ranges of x-ray energy, including both 1-12 keV and 6-17 keV. The response of an identical detector, but tilted vertically by 60 • in order to increase magnfication without a longer beamline, is measured and shown to improve x-ray detection above 4 keV without compromising sensitivity to beam size. We also investigate operation of a coded aperture using gold masking backed by synthetic diamond.

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The use of water-cooling channels in silicon x-ray monochromators for the Cornell High Energy Synchrotron Source (CHESS) high power wiggler beamlines has been studied by finite element analysis. The efficiency from channels of different dimensions, ranging from 25 mm to 2 mm width and 5 mm depth, has been calculated. The new crystals are designed to replace the indirect cooled monochromators currently used at CHESS wiggler stations. At typical operation parameters of 150 mA electron current at 5.3 GeV and a gap of 40 mm, the 24-pole wiggler at CHESS provides an x-ray beam with a total power of 2.7 kW at the monochromator. Procedures have been developed for fabrication of internally cooled crystals using a silver-glass dye attach paste. Tests of a new crystal with a conventional x-ray source revealed very small amounts of residual strain. Experiments with synchrotron radiation are scheduled in the near future.