Facility Diagnostic Beamlines
Contact J.C. Bergstrom
The function of the Facility Diagnostic Beamlines (FDB) are to determine various stable-beam qualities, to determine unstable beam characteristics, and to facilitate studies of the transverse and longitudinal beam dynamics.
- Photon beam size in both planes, and the photon angular spread.
These quantities define the photon beam emittance, and hence the intrinsic brightness of the source point. - Use the photon measurements (visible and x-ray) to deduce the electron beam size, phase-space ellipse and emittance. Deduce the first and second moments of the beam distribution in the transverse plane.
- Photon source-point positional stability. This provides a measure of transverse beam instabilities.
- Determine the x-y emittance coupling.
- Determine the longitudinal emittance of the electron beam (energy spread and bunch length). Deduce the first and second moments of the beam distribution in the longitudinal direction.
- In a single-bunch mode, machine studies include:
- RF bunch purity
- Bunch length vs. current
- Energy spread vs. current
- Bunch length vs. RF voltage
- Transverse beam size vs. current, which provides a measure of the ring impedance.
- Diagnostics of head-tail instabilities
- In a multi-bunch mode, machine studies include some of the items above, plus the following:
- Diagnostics of coupled-bunch instabilities
- Diagnostics of longitudinal instabilities using a dispersive source-point
- Bunch-phase stability re the cavity RF
- Measure transient beam motion following injection, before the beam has damped. This will assist in optimizing the injection system, which is especially crucial for a top-up mode of operation. Note that the FDB must operate during injection (unlike the other beamlines).
- Measure the transverse bunch extent on a turn-by -turn basis immediately following injection. This will assist in matching the Twiss parameters of the injected beam to those of the ring (“beam matching”). Studies suggest that matching the vertical (y) b-function is especially important for maximizing the capture efficiency. These remarks also apply to the Booster.
- Measure the circulating beam energy by employing the method of Resonant Depolarization. This well-known technique yields the absolute energy (mean), with relative accuracies of 10 -4 to 10 -5 being achievable.
In order to comply with the above requirements, the FDB needs both visible synchrotron radiation (OSR) and x-ray (XSR) capabilities. The OSR and XSR source points are located within two different dipole magnets.
OSR – Optical Synchrotron Radiation
OSR source point:
| βx = 1.06 m | αx = 0.53 m |
| βy = 25.68 m | αy = -4.814 m |
| η x = 0.062 m | η x ¢ = 0.023 m |
| σx = 166 mm | σ x ¢ = 145 mm |
| σy = 63.0 mm | σy ¢ = 2.45 mm |
| εx = 18.2 nm-rad | εy = 0.18 nm-rad (assuming 1% coupling) |
Nominal wavelength of the synchrotron radiation is 600 nm.
CCD
- resolution diameter 70 µm, dominated by the depth-of-field limit and the diffraction limit
- emittance measurements down to 13 nm-rad horizontally and 0.23 nm-rad vertically
Streak Camera
- 2 ps resolution for turn by turn and single bunch studies
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Streak camera images of 8 ps (1σ) bunches. |
XSR – X-Ray Synchrotron Radiation
XSR source point:
| βx = 0.745 m | αx = 0.503 m |
| βy = 27.06 m | αy = -3.113 m |
| ηx = 0.127 m | η x ¢ = -0.152 m |
| σx = 189 mm | σx ¢ = 239 mm |
| σy = 64.7 mm | σy ¢ = 2.39 mm |
| εx = 18.2 nm-rad | εy = 0.18 nm-rad (assuming 1% coupling) |
Nominal wavelength of the synchrotron radiation is 0.10 nm which corresponds to 12 keV radiation.
A YAG crystal is used to convert x-rays to visible light.
CCD
- 0 – 100 µm pinhole, optimal slit-width of 25 mm yields a resolution of about 23 µm
- emittance measurements down to 0.06 nm-rad vertically
- is not able to stream real-time data to external applications such as EPICS or Matlab
- a second CCD with this functionality will be installed in the near future, providing access to such variables as beam centroid, position and rotation
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Beamspot at XSR |
Last modified: 2012-01-19 17:01:31