Difference between revisions of "List of changes since the 2006 HallD Tagging Spectrometer and Photon Beamline Review"
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# '''minimum deliverable electron beam current''' -- in 2006 this requirement was set at 100 pA. After further simulation work, it was determined that this requirement could be relaxed to 1 nA. | # '''minimum deliverable electron beam current''' -- in 2006 this requirement was set at 100 pA. After further simulation work, it was determined that this requirement could be relaxed to 1 nA. | ||
# '''change to a one-dipole tagging spectrometer''' -- in 2006 the tagger design called for two identical 3m magnets in series to disperse the post-bremsstrahlung electrons and divert the electron beam into the dump. Since then the decision has been made to build a single 6m dipole instead of the 3m pair. | # '''change to a one-dipole tagging spectrometer''' -- in 2006 the tagger design called for two identical 3m magnets in series to disperse the post-bremsstrahlung electrons and divert the electron beam into the dump. Since then the decision has been made to build a single 6m dipole instead of the 3m pair. | ||
| − | # '''change in the width and shape of the tagger magnet poles''' -- in 2006 the tagger dipoles had poles of dimensions 310 x 45 cm<sup>2</sup> with a simple 45° chamfer of width 1.5 cm around the edges facing the gap. The dimensions of the modified single-magnet pole are 600 x 41 cm<sup>2</sup> | + | # '''change in the width and shape of the tagger magnet poles''' -- in 2006 the tagger dipoles had poles of dimensions 310 x 45 cm<sup>2</sup> with a simple 45° chamfer of width 1.5 cm around the edges facing the gap. The dimensions of the modified single-magnet pole are 600 x 41 cm<sup>2</sup> with a two-step chamfer approximating a Rogowski contour. |
| − | # '''reduction in dimensions of the tagger dipole''' -- in 2006 the | + | # '''reduction in outer dimensions of the tagger dipole''' -- in 2006 the outer dimensions of the tagger dipole magnets were 109.0 cm x 141.0 cm in transverse cross section. In the final design the outer dimensions of the magnet in the transverse plane are 99.8 cm x 129.0 cm. |
Revision as of 10:28, 14 June 2010
In January 2006 the lab held an external review of the Hall D Tagging Spectrometer and Beam Line. The list below represents an attempt to collect in one place all of the changes to the tagger and photon beam line that have taken place since then, up until the PAC report in summer 2010.
- electron beam dump -- in 2006 the electron beam dump was located in an out-building that was connected to the tagger hall by a buried beam pipe. The present civil design now has the electron beam dump located in the tagger hall, which has been extended in the south-east direction to accommodate it.
- electron beam emittance -- in 2006 the horizontal emittance of the 12 GeV electron beam predicted by ray-tracing simulations was 1 x 10-8 m-r. Since then, a bug in the simulation was corrected, leading to a reduced estimate of 5 x 10-9 m-r. The emittance requirement for GlueX has remained fixed at the 2006 value of 10-8 m-r, but the improved outlook has caused some other requirements to be relaxed -- see next item.
- virtual beam spot size at the collimator -- in 2006 this requirement was an upper bound of 500 microns. Based on interactions with CASA and further simulations, it was determined that this requirement could be relaxed to 600 microns without substantial impact on the photon beam characteristics.
- radiator crystal size requirement -- in 2006 the requirement on the transverse dimension of the diamond crystal radiator was set at 8 mm minimum in order to contain the electron beam spot out to 2 standard deviations. Since then a new configuration has been found of the electron beam lattice that reduces the horizontal beam spot size to 1 mm rms. Based on this, the minimum transverse diamond radiator size requirement has been reduced to 4 mm.
- electron beam halo requirement -- in 2006 we set a conservative requirement of 10-6 on the fraction of the current that resides in the tails (outside the central Gaussian peak) of the electron beam. Considerable work has been done since that time on refining this specification and simulating the impact of halo on tagger performance. The new halo specification requires that no more than 5 x 10-5 of the electron beam current lie outside a cylinder of radius 5 mm centered on the nominal beam axis.
- minimum deliverable electron beam current -- in 2006 this requirement was set at 100 pA. After further simulation work, it was determined that this requirement could be relaxed to 1 nA.
- change to a one-dipole tagging spectrometer -- in 2006 the tagger design called for two identical 3m magnets in series to disperse the post-bremsstrahlung electrons and divert the electron beam into the dump. Since then the decision has been made to build a single 6m dipole instead of the 3m pair.
- change in the width and shape of the tagger magnet poles -- in 2006 the tagger dipoles had poles of dimensions 310 x 45 cm2 with a simple 45° chamfer of width 1.5 cm around the edges facing the gap. The dimensions of the modified single-magnet pole are 600 x 41 cm2 with a two-step chamfer approximating a Rogowski contour.
- reduction in outer dimensions of the tagger dipole -- in 2006 the outer dimensions of the tagger dipole magnets were 109.0 cm x 141.0 cm in transverse cross section. In the final design the outer dimensions of the magnet in the transverse plane are 99.8 cm x 129.0 cm.
