PROGRESS TOWARDS AN OPEN MIDPLANE SEPARATION DIPOLE P. Wanderer, BNL with R. Gupta, A. Ghosh, N. Mokhov HHH-AMT 12 November 2004

LARP at BNL Magnet activity – look at open midplane dipole for LHC IR upgrade with “dipole first” optics and block coils Other activities – Beam instrumentation for present LHC Accelerator physics Superconductor development Superconductor, magnet testing for other US labs working on LARP

Interaction Region Upgrade Quad or Dipole first? Single bore or twin bore? Large crossing angles with superbunches or crab cavities? Long range (parasitic Beam-Beam collisions?

D1 parameters for this IR Bdl = 15T x 10m  Nb3Sn If block coils  R&W or W&R coils Coil apertures studied: 84, 160, 120 mm Field quality – typical δB/B ~10-4 Magnet & cryo system tolerant of beam heating 9 kW (4.5K)  fully open midplane + absorber at temperature >> 4.5K

Some design challenges Any “dipole-first” D1: large forces, stored energy, radiation heating Open midplane, block coils less efficient than cosθ coils Good field quality harder to achieve Weak vertical support of coil

Issues for R&D program Goal: design, build, test proof-of-principal model LARP main effort is IR quadrupole  limited resources

POP design phase – June 04 Design for 10m dipole-first D1 June, 2004 LARP review Achieved 10-4 FQ, reasonable strain on conductor =>”proof of principal” design Complex coil ~ 50% of radiation deposited in cold mass coil aperture 160 mm ~ 1m yoke OD => $$$ to build 10m length => $$$ to build Needed resources inconsistent with LARP’s focus on quad

Dipole Design Status, Ramesh Gupta, BNL Navigation of Lorentz Forces (1) A new and major consideration in design optimization Vertical Component of the Lorentz Force Density Vertical Lorentz force density in certain designs ~Zero vertical Lorentz force density line Since there is no downward force on the lower block (there is slight upward force), we do not need much support below it, if the structure is segmented. The support structure can be designed to deal with the downward force on the upper block using the space between the upper and the lower blocks. This allows the lower block to move closer to midplane to improve field quality. LAPAC Meeting, June 16-17, 2004 Dipole Design Status, Ramesh Gupta, BNL

Dipole Design Status, Ramesh Gupta, BNL Navigation of Lorentz Forces (2) (Transferring vertical forces between blocks) Design with 50 mm midplane gap: Blocks must be strategically segmented to minimize maximum stress build-up, navigate Lorentz forces, minimize peak fields and optimize field quality. Vertical force comes from the horizontal component of the field : Ly = Jz X Bx. “Block A” with height more than that of “Block B” straightens field lines that reduce Bx and the downward force on “Block B” by ~50%. A B The task is to demonstrate that it is possible to satisfy all of the above requirements at the same time. Note: There is a plenty of space for support structure below “Block A” Moving Block A upward also minimizes the secondary energy deposition from target. LAPAC Meeting, June 16-17, 2004 Dipole Design Status, Ramesh Gupta, BNL

Power (mW/g) at L = 5m, 10m N. Mokhov – LARP Napa Oct 04

Design Progress – October 04 Relax design parameters: Horizontal aperture 120 mm Field quality – δB/B ~10-3 Separate D1 into two magnets, D1a, D1b D1a: ~84mm aperture, develop fully under LARP D1b: develop only proof-of-principal design More details on next slide

Starting Point and some estimates on D1A Parameters (to be iterated) Design Goal: An open Midplane design with large horizontal and small vertical aperture that includes a warm absorber inside the cold-mass to avoid a major upgrade in CERN cryogenic facility and to remove ~9KW at an affordable cost. D1A (to be developed under LARP): Horizontal Aperture : ~70 mm Magnet Length : ~ 5 meter Quench Field : 15+T Yoke outer radius: ~400 mm (or a rectangular yoke with smaller vertical size?) A preliminary design presented at Port Jeff in 9/2003 D1B (NOT to be developed under LARP): Horizontal Aperture : ~140 mm Magnet Length : ~ 5 meter Quench Field : ~13T Yoke outer radius: ~600 mm Note: D1B may have similar Lorentz forces as D1A

Overall Parameters of the Reduced Aperture Open Midplane Dipole Preliminary Design Outer Yoke Radius : 600 mm to 700 mm (old value 1 meter) Horizontal Coil Spacing : 120 mm (old value 160 mm) Vertical Coil Spacing : 30 mm (old value 50 mm) Field errors: 2.10-3, projected to be 5.10-4 with more optimization at +/- 50 mm (old value 5.10-5 at +/- 36 mm) Quench Field: ~14.5 T (old value ~15 T) Conductor requirements: ~60% of previous design The above magnet is much smaller than before. However, it still has a significant size. LARP Collaboration Meeting, Oct. 19-21, 2004 Dipole for LHC IR Upgrade - Ramesh Gupta

A Lower Cost Open Midplane Dipole Proposal At present, the aperture of D1 is determined by the requirements at the far end of IP. We propose dividing each D1 in two dipoles D1A and D1B. We also propose to develop only D1A under LARP. D1A will be shorter and will have lower aperture. One can also consider raising field in D1A and reducing in D1B. This will balance Lorentz forces better between D1A (higher field, lower aperture) and D1B (lower field, larger aperture). Beam Trajectory LARP Collaboration Meeting, Oct. 19-21, 2004 Dipole for LHC IR Upgrade - Ramesh Gupta

A Proposal to Build D1A Under LARP A lower aperture, lower length, lower cost, open midplane racetrack coil dipole that while developing and proving the basic technology, also gets used in LHC IR upgrade (half length magnet) * Coil aperture * (full length magnet) Coil aperture Good field aperture Beam Trajectory Good field aperture Consider increasing the field in the first D1 (D1A), and also consider using HTS there. HTS has a potential to generate higher fields and can tolerate higher heat loads, as well. LARP Collaboration Meeting, Oct. 19-21, 2004 Dipole for LHC IR Upgrade - Ramesh Gupta

A Similar Layout Was Considered for VLHC Beam optics reasons were different, but magnet design reasons were partly similar. First Magnet (D1A): Higher field, lower aperture, taking help of HTS. Second Magnet (D1B): Lower field, larger aperture, based entirely on Nb3Sn. Given the time frame of LHC IR Upgrade, we would consider HTS. However, we won’t make the design contingent on that. LARP Collaboration Meeting, Oct. 19-21, 2004 Dipole for LHC IR Upgrade - Ramesh Gupta

Hardware Progress – October 04 Better understanding of conductor – flux jumps, RRR New winding machine for reacted Nb3Sn Successful test of ten-turn, common coil dipole (DCC016) Plan to use LBL subcoils (L ~ 30 cm) Use BNL ten-turn fixtures, with spacers, to assemble subcoils

Dipole Design Status, Ramesh Gupta, BNL Technology Development Tests Sub-scale Coils in Open Midplane Structure Short coils made and pre-tested for other applications can be used in an open midplane configuration to examine the basic technological issues. (BNL/LBL collaboration). The support structure for this open midplane dipole test will be designed such that it: Produces similar deflections (after the 1st test with ~zero deflection) Allows variation in pre-stress Allows variation in vertical separation Max. stress in actual magnet: Horizontal = 150-200 MPa Vertical = 90-100 MPa LAPAC Meeting, June 16-17, 2004 Dipole Design Status, Ramesh Gupta, BNL

Looking ahead - 1 Assemble subcoils for test of open midplane concept. (Assemble and test in ~ a year?) Plan intermediate steps Experiments with magnets, especially preload Minimum & maximum preload Model magnet features

Looking ahead - 2 Determine parameters for D1a + D1b Aperture, length, field quality  accelerator physics Radiation heating  LHC cryo ops, heating calculations Design, build, test proof-of-principle model This program will be reviewed in mid-December