The beam transport line delivers the extracted Booster beam from the extraction point of the Booster to the target in the experimental area and also provides the required beam profile on the target. The transport line starts at the beginning of the D6 straight section of the Booster, and ends at the target which is located 100m downstream. The layout of the magnets which will be used to transport and shape the beam on target includes the following elements:

• The thick septum magnet, placed just after the Booster extraction point, bending the fraction of the beam that has been kicked by the thin septum at D3 by 8.2^o (143 mrad) to the left, thus extracting the beam from the Booster ring. The actual bend angle of the thick septum is 155 mrad since the beam enters the septum with a 12 mrad pitch towards the inside of the Booster ring.

• Two consecutive dipole magnets, each bending the beam by 10^o for a total of 20^o bend to the left to direct the beam into the second and final straight section of the BAF tunnel. The midpoint of the bend is about 33.4 m downstream of the beginning of the 100 m long beam transport line. The bending power of the dipoles matches that of the thick septum and allows the transport of protons up to a momentum of 3.9 GeV/c.

• Eight quadrupole magnets, two upstream of the 20^o bend and 6 downstream of the bend. The position of the first quad pair and the bend was optimized to have the beam free of dispersion after the 20^o bend, see the transport output for a typical beam tune here. Therefore the two 18D36 dipoles can run at constant current during the extraction process, although the beam momentum will vary by  0.5%. The long distance from the extraction point to the first quadrupole, 18.3 m, allowed us to keep the cross section of the penetration through the Booster tunnel shielding relatively small at 13" ID. This enables us to access the BAF tunnel from the bend downward while the Booster is running in high intensity proton mode for physics experiments at the AGS. The quadrupoles Q3 and Q4 provide a horizontal beam  at the location of the first octupole O1 and Q5 a vertical beam at O2 (see beam contours). The last three quadrupoles provide the desired beam size at the target location.

• Two octupole magnets 50cm long with 8.125" (206mm) aperture. The octupoles are placed downstream of the bend and provide beam shaping, in particular beam uniformity at the target. These magnets were designed specifically for BAF. They are needed to flatten the beam profile at the target location which otherwise would have a dominantly Gaussian shape. As the octupole term represents only one element in the Fourier expansion of the beam sprofile, the beam cannot be made perfectly flat, but the intensity is expected to be homogeneous to +- 5% over most of the beam width, see the typical beam profile at the target location. Further flattening of the beam in the center enhances the "octupole horns" near the beam edges, see the flat beam profiles. This may be a desirable tune for the irradiation of targets that fit well within the beam envelope and do not require the maximum intensity available.

• Ten trim magnets, two inside the Booster tunnel and eight in the BAF tunnel. The trim magnets in the Booster provide a kick of up to 0.5 mrad at the maximum proton momentum of 3.9 GeV/c. The eight identical trim magnets in the BAF tunnel provide a kick of up to 7 mrad at 3.9 GeV/c. Both types of trims are new designs.

Beamline drawings (6-7-2000):

• PDF file (222 kB)
• ACAD drawing (472 kB)

Beam optics, transport and Turtle outputs:

• transport output for a typical tune
• typical beam contours at O1 and O2
• typical beam profile in x at the target location
• typical beam profile in y at the target
• "flat" beam profile in x at the target
• "flat" beam profile in y at the target
• BNLMAD lattice and example strength file