transfer function for separation dipoles
DESCRIPTION
Transfer Function for Separation Dipoles. Frank Zimmermann LHCCWG 12.07.2006. Discussions with O. Bruning, S. Fartoukh, M. Giovannozzi. the problem. D1-D2 transfer function errors can have a significant effect on closed orbit during squeeze (10 units → 3 s orbit change at triplet) - PowerPoint PPT PresentationTRANSCRIPT
Transfer Function for Separation Dipoles
Frank Zimmermann
LHCCWG 12.07.2006
Discussions with O. Bruning, S. Fartoukh, M. Giovannozzi
the problem
D1-D2 transfer function errors can have a significant effect on closed orbit during squeeze (10 units → 3 orbit change at triplet)
local correction requires careful analysis and distinction between
• D1/D2 transfer function errors• Triplet alignment errors• Triplet gradient errors with crossing-angle bump
offsets
[O. Bruning, Chamonix XII]
D2 D2D1 D1
common BPMsseparate BPM
separate BPM
BPM distances to IP: 21.35, 31.53, 58.32, 151.14 m
IR1 layout
original procedure
• triplet alignment optics with low- quads off to define straight line with 6 or 8 BPMs;
• k-modulation of individual Q1, Q2 or Q3 magnets to find offsets w.r.t. to reference line from BPMs
• differences in the lines for beam1 and beam2 indicates D1/D2 transfer line error
• after correcting D1/D2 powering error obtain reference line for triplet alignment
[O. Bruning, Chamonix XII]
LHC triplet alignment optics
[A. Verdier, LHC PN 325, 2003]requires about half the nominal emittance for aperture reasons;x&y tunes lower by 1 unit, if IR1 & 5 both use this optics
•correct incoming beam upstream of D2 for zero offset and angle
•adjust D1 on one side to steer beam on 0-slope trajectory through the IP
•then look at other side
•and/or adjust D1 and D2 together to get both beams on the same orbit?
“refined” procedure (?)
S. Fartoukh, M. Giovannozzi, F.Z.
problems
• low- quads: misalignment of mechanical & magnetic axes 0.1-0.2 mm in x, 0.5 mm in y; beam needs to be steered through the mechanical center!
• BPM offsets may cause error of up to 5 rad (?), compared with total deflection angle of 1.5 mrad; this is larger than desired precision of 3x10-4
• BPMs might have different offsets for beam1 and beam2 (?)
S. Fartoukh, M. Giovannozzi, F.Z.
questions
• in which aspect is the D1/D2 transfer function effect any different from other closed-orbit errors of the two beams, and why does it need to be treated differently?
• do we want to measure transfer functions with beam at 450 GeV and at 7 TeV?
• do we want to use alignment optics?; if yes, with which beam and which BPM resolution?
• alignment optics at injection to define straight reference line for both beams (BPM readings)
• K-modulation to measure quad misalignments and align where necessary
• apply 2-beam orbit correction across IR region; include D1 and D2 as additional correctors
I propose following procedure