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

2. 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

3. 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?

4. 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

5. 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

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

7. 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

8. 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

9. 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

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

11. 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

12. 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

13. 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: , projected to be with more optimization at +/- 50 mm
(old value 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 , 2004
Dipole for LHC IR Upgrade - Ramesh Gupta

14. 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 , 2004
Dipole for LHC IR Upgrade - Ramesh Gupta

15. 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 , 2004
Dipole for LHC IR Upgrade - Ramesh Gupta

16. 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 , 2004
Dipole for LHC IR Upgrade - Ramesh Gupta

17. 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

19. 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 = MPa
Vertical = MPa
LAPAC Meeting, June 16-17, 2004
Dipole Design Status, Ramesh Gupta, BNL

20. 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

21. 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