Hybrid Dipoles how to triple the energy of LHC Peter McIntyre, Al McInturff, Akhdiyor Sattarov Texas A&M University Returning coals to Newcastle, a generation after Fred Asner’s pioneering dipole…

Large Hadron Collider 27 km circumference tunnel at CERN ATLAS detector CMS detector

LHC is a tool for discovery in high energy physics Higgs sector Supersymmetry / Supergravity New gauge couplings The Higgs boson and the spectrum of sparticles should be discovered at LHC, unless… The flood of precise data from astrophysics suggests that the gauge fields of nature may be far more complex than the picture of the Standard Model + Supergravity Can we extend the energy reach for direct discovery of new gauge fields?

Hadron colliders are the only tools that can directly discover gauge particles beyond TeV Predicting the energy for discovery is perilous. Example: for a decade after discovery of the b quark, we ‘knew’ there should be a companion t quark. But we couldn’t predict its mass. Predictions over that decade grew (with the limits) 20  40  80  120 GeV 4 colliders were built with top discovery as a goal. Finally top was discovered at Fermilab – 175 GeV! In the search for Higgs and SUSY, will history repeat?

Evolution of the gluon spectrum Dutta 2004 Tevatron LHC Tripler 3 x  s  2 x mass scale

The reach of a hadron collider is set by its size and its magnets Protons circulate in a ring of dipoles that bend and quadrupoles that focus them: LHC dual dipole: NbTi superconductor, 8 T field

Higher field requires new superconductor, handling immense stress loads NbTi Nb 3 Sn Bi-2212 Nb 3 Sn Cost today:NbTi$100/kg Nb 3 Sn$1,000/kg Bi-2212$10,000/kg

Stress management Lorentz stress results from the magnetic field created by the coil reacting back on each turn of cable in the coil. The stress accumulates through the lateral thickness, just as gravitational stress accumulates from the loads on all floors of a building. In a building, we manage the stress by intercepting it with floors, transferring it the walls, and passing it to the foundation. In dipoles we are doing the same! Laminar spring decouples stress between windings. Laminar spring provides channel for He cooling within windings. (a goal in NED) Laminar spring provides LOCAL expansion joint within windings during reaction bake – compatible for long magnets.

To push to higher field, use high-performance superconductor and limit coil stress Nb 3 Sn: 14 Tesla dipole Bore field14.1 T Current12.6 kA Maximum Coil Stress120 MPa Superconductor cross section29 cm 2

TAMU is developing 14 Tesla Nb 3 Sn dipole using stress management, flux plate, bladder preload

Coil winding Ti mandrel to preserve preload through cooldown. Inconel ribs, laminar springs transfer stress between windings.

Reaction bake 650 C for a week Argon atmosphere purge throughout coil Same furnace can bake 875 C in O 2 purge for Bi-2212 and maintain separate purges of Ar in Nb3Sn, O 2 in Bi-2212 windings We can react a 3 m long dipole in this furnace!

Splice leads Nb 3 Sn to NbTi Lead is supported in rigid frame anchored into winding superstructure, spliced to a pair of NbTi leads. Same technique can be used for Bi-2212.

Vacuum impregnation Horizontal orientation, multiple flow paths assure full impregnation We can impregnate a 3 m long dipole in this retort!

Bladder preload 1. Preload flux return against Al tube to make stiff wall. 2. Preload coil assembly against flux return to remove soft modulus. Preloads are delivered using S.S. bladders: Heat magnet to 80 C, pressurize bladders with Wood’s metal (2,000 psi) Cool to freeze in preload.

J c in Nb 3 Sn: 3000 A/mm 2 available today I strand in Bi-2212: 500 A in 0.8 mm  x1.4 what is available today Showa, Supramagnetics consider it a reasonable goal Now grade the conductor: Bi-2212 in highest field windings, Nb 3 Sn in lower field windings 3 Nb 3 Sn windings 2 Bi-2212 windings 32 cm beam tube separation Dual dipole (ala LHC) Bore field 24 T Max stress in superconductor130 MPa Superconductor x-section: Nb 3 Sn28 cm 2 Bi cm 2 Cable current25 kA Beam tube4x6 cm 2

Stress <150 MPa, Strain <.002 Stored energy 7 MJ/m

All Bi-2212 windings from a single cable in each layer All Bi-2212 windings on each layer are from one piece of cable –transitions made in ends –leads spliced to NbTi cable pairs Nb 3 Sn Bi-2212 continuous transitions

Control flux return size using NbTi trim NbTi trim windings without fringe trim with fringe trim

Magnet issues Nb 3 Sn windings must be reacted at 650 C in Ar atmosphere for a week to form the superconducting phase. Bi-2212 windings must be reacted at 850 C in O 2 atmosphere for ~10 minutes (partial melt). How to do both on one coil??? Wind Bi-2212 inner windings, do heat treat. Control fast excursion to partial melt using ohmic heating in coil itself. Then wind Nb 3 Sn outer windings, stress management structure isolates the ventilation of the two regions React the Nb 3 Sn with Ar purge, hold O 2 purge on Bi Quench protection - Bi-2212 highly stable, very different quench strategy from that with all-Nb 3 Sn dipoles.

Accelerator Issues Synchrotron radiation : power/length critical energy –Use photon stop: Instead of intercepting photons at ~10 K along dipole beam tube, intercept between dipoles on room-temperature finger. –Soft X-rays actually easier to trap that hard UV LHC: E = 7 TeV P = 0.22 W/mE c = 44 eV (hard UV) scatters LHC Tripler: E = 20 TeV P = 14 W/mE c = 1.2 keV (soft X-ray) absorbs!

Synchrotron damping J n = damping partition: J x ~ J y ~1, J E ~2 LHC:  J n = 53 hours,  E =   ~ 26 h LHC Tripler:  J n = 2.2 hours,  E =   ~ 1 h! This may be enough damping to help push luminosity. Stacking of new beam on old every few hours?

Beam separation in dual dipoles –Requires special dipoles to make beams cross at intersect. –D1, D2 must be 1.5 times longer LHC:  x = 20 cm Tripler  x = 32 cm

Tripler Injection –Must transfer beam from LHC to Tripler –Transfer at ~5 TeV – requires only 4:1 dynamic range for Tripler Suppress problems from magnetization multipoles, snap-back –Requires use of secondary straight sections –A tight fit for many functions

Magnets are getting more efficient! NbTi Nb 3 Sn Bi-2212

LHC Tripler Cost? Cost of high-field magnets: $ ~ half superconductor, half structure Neither Nb 3 Sn nor Bi-2212 have ever been produced in large-scale manufacture Nb 3 Sn today ~$1,000/kg. Tripler needs 550 tons –Nb 3 Sn will soon be manufactured for ITER –Goal of DOE HEP conductor development program ~ $300/kg- projected Nb 3 Sn cost = $165 M Bi-2212 today ~$2,000/kg.Tripler needs 1000 tons –2 Bi-2212 manufacturers project large-volume price ~$700/kg- projected Bi-2212 cost = $700 M

Questions for Today Is the physics of pp collisions at at high luminosity sufficiently compelling to justify technology development that would make it possible? Are there any accelerator issues that would make the Tripler unfeasible even if the magnets could be built? If we want to have the option of a Tripler upgrade after the end of first long run of LHC (10 years from now), we must start technology development today!

Plan for R&D Use existing 2-winding coil modules developed for Texas A&M high-field dipoles Make inner winding from Bi-2212 cable No new structures, direct comparison with all-Nb 3 Sn

Development objectives Develop fast excursion to 850 C in Bi-2212 heat treat – verify that we can get I c in winding Develop isolated gas flow in inner, outer windings – verify that we can keep I c Develop Bi-2212/NbTi splices – lead technology Preload and test hybrid single-pancake assembly – validate stress management Build and test TAMU5 – demonstrate parity with all-Nb 3 Sn at transition field strength

We are asking DOE to support the necessary magnet technology R&D Increase TAMU base funding to support Bi-2212 effort Invite SBIR proposals from Bi-2212 wire manufacturers to improve conductor –Increase I c to 500 A for 0.8 mm wire –Decrease filament size, improve Ag grain size to reduce bridging –Include ferromagnetics in Ag matrix (break coherence) Include Bi-2212 wire in DOE Conductor Development Program –Need Bi-2212 strand for magnet R&D Include Tripler R&D within LARP agenda We need CERN to evaluate whether it wants to see the Tripler option developed If so, tell DOE!