Commissioning of the CLAS12 Torus Detector Magnet at Jefferson Laboratory Cesar Luongo Thomas Jefferson National Accelerator Facility Newport News, Virginia, USA G. Biallas, K. Bruhwel, R. Fair , P. Ghoshal, D. Kashy , S. Mandal, J. Matalevich, M. Mestayer, R. Miller, R. Rajput-Ghoshal , C. Rode, N. Sandoval, G. Young Thomas Jefferson National Accelerator Facility , Newport News, VA, USA 2016 Applied Superconductivity Conference Denver, CO, USA September 4-9, 2016

Outline Overview of Jefferson Lab and the Hall B-CLAS12 Upgrade The CLAS12 Torus Detector Magnet Coil Fabrication Magnet Installation Commissioning of the Torus Magnet Administrative Steps and Safety Reviews Phases of Commissioning Leak-checking and vacuum pumping Cooldown Magnet energization Field mapping

Jefferson Lab Located in Newport News, VA Pre-eminent Nuclear Physics accelerator facility in the USA 800 staff, 1400 users and collaborators from 30 countries $338M Upgrade from 6 GeV to 12GeV of the accelerator (SRF) along with 1 new Experimental Hall and 2 of 3 existing Halls being upgraded (2006-2017) (CD1 – CD4b) 8 superconducting magnets are part of the 12 GeV upgrade $70M Upgrade of Hall B includes the CLAS12 Torus Detector Magnet

CLAS12 Detector System

CLAS12 Torus in Hall B Distribution Box (DBX) – Feeds Torus and Solenoid Torus Cryo Service Tower (TST) Connection to Refrigerator Chimney (Cryo interface) Cryoduct (bus leads) ~ 10m Very thin coils/cryostats 6 coils electrically in series Conduction-cooled with SHe Coils hydraulically in series, re-cooled by counterflow 1 atm He in thermosyphon mode LN2 (shield) circuits also in thermosyphon mode Torus Magnet

Coil Fabrication Coils shipped from Fermilab were instrumented and cryostated (in assembly –line manner) at JLab. Cold-tested (80K) for thermal and insulation performance JLab provide conductor, Fermilab wound and impregnated the coils (6 + 2) MT-24: S. Krave et al. , “Overview of Torus Magnet Coil Production at Fermilab for the Jefferson Lab 12 GeV Hall B Upgrade, “IEEE Trans. Appl. Supercon. 26(4), 4102705, 2016

Installation Coils installed via “spit” (rotisserie) method Coils attached to spit hub one by one “Hex beams” attached and assembly rotated Method allows for all the coil-to-coil electrical and hydraulic connections to be made in a consistent (horizontal) position from the subway balcony Assembly can be rotated for welding VJ as needed MT-24: C. Luongo et al. , “The CLAS12 Torus Detector Magnet at Jefferson Lab, “IEEE Transactions on Applied Superconductivity 26(4), 4500105, 2016

Installation Installation complete ~ April 30, 2016 Applying MLI Splices between coils Welding the vacuum jacket Installation complete ~ April 30, 2016

Commissioning: Administrative steps and safety reviews Pressure System Review Internal JLab review (Engineering Division) to ensure all piping and vessel components comply with ASME codes (design, manufacturing, procurement, and documentation) Magnet and its Cryo service tower: March 24 Cryogenic Distribution System: May 24 Experimental Readiness Review (ERR) – Magnet Cooldown Internal/External review (Physics Division) to ensure all operating procedures have been prepared, reviewed, and approved. That there is a hand-over plan in place, and that all documentation is in order prior to transferring operational responsibility to Physics (hand-over) ERR Part I: April 13 ERR Part II: June 27 Final approval for hand-over to Physics (and release to start magnet cooldown): August 5 Cooldown ERR 1 Cooldown ERR 2 Power-Up ERR Pressure Review 1 Pressure Review 2

Vacuum P&ID Turbo (top) Single vacuum space Roots blower Turbo (bottom)

Commissioning: Leak Checking and Vacuum Pumping Pumping Port on TST Vacuum Instrumentation Rack Turbo Roots Blower

Commissioning: Leak Checking and Vacuum Pumping Leak-checking of internal circuits (He and N2) Leak-checking of vacuum jacket, plus fixes (feedthroughs, welds, etc.) Vacuum jacket completed in early May, leak-checking phase lasted ~ 6 weeks. Continuous pumping since mid-June. Decrease at ~ 10-7 Torr/hr An RGA was connected, most of pump-out was water (>85%) A de-watering strategy was devised and implemented Multiple pump-and-purge cycles (no apparent help) Run up to 10 A through the coils, maintain temperature < 325K (~320K) Flow warm N2 through the thermal shield circuits using the heated U-Tube (3 kW) and keep inlet temperature < 350K Once system was warm pumping speed increased 30-50% ROR tests done before and during warming cycle showed water release increased by a factor of 3 (accelerated de-watering) After ~ 2 weeks of warming cycle, pressure started to decrease Warming disconnected (but took another ~2 weeks for system to thermalize back to room temperature) ~ 0.5x10-4 Torr reached on all internal gauges after ~ 3 mos. of pumping

Commissioning: Leak Checking and Vacuum Pumping Pump-and-purge cycles Pressure in vacuum space (Torr) De-watering Cycle Start of Cooldown Days of continuous vacuum pumping

Cooldown: Simplified diagram of hydraulic circuits * Pressure Relief Valves Not Shown

Commissioning: Cooldown Cooldown proceeds by independently cooling the shields and the cold mass Shields are floating from each other and the cold mass, so they could potentially be cooled at any rate (as long as cold mass is not cooling too fast) Shield circuit is cooled by 80K gas, inlet temperature controlled by 3kW heater to adjust cooling rate Helium circuits cooled via warm helium “split” into two circuits, one of them running through heat exchanger in LN2 (80K). Fraction of “split” controls helium inlet temperature to cold mass Max allowable delta-T between coils and hex beams (supports) is 45 K Controls set to keep this delta-T to ~ 10 K (alarm at 30 K) Controls set so that cold mass cools at ~ -0.5 K/hr (alarm at -2 K/hr) N2 shield cooled independently consistent with above control actions After shields are below 100K, start introducing liquid nitrogen in shields After cold mass is at 80 K, switch cooling mode and introduce liquid helium into buffer dewar to continue cooldown process down to 4 K

Commissioning: Cooldown Status Cooldown started on Aug. 12 - Coils currently at ~ 180K Shield cooling starts Temperature (avg.), K Days since beginning of cooldown

Commissioning: Magnet Energization Magnet energization expected to start by mid to late September Step 1: Low current polarity and instrumentation checks. Inductance measurements Step 2: test of Fast Dump and QD from 500 A Step 3: Conditioning ramp-up to 3800 A with wait/evaluate at 3000 A

Commissioning: Field Mapping Field mapping expected to start in October Field quality requirements: ± 0.1% in toroidal direction, ± 1% in other two directions Mapper consists of temporary attachments (surveyed) and carbon fiber tubes with 3-axis hall probes and stepper motor translation Mapping of hub and in four locations across each sector (25 lines in total) Mapper shown accurate to within ± 0.01% Mapping to take ~ 1 week

Summary Magnet installation successfully completed in April 2016 A series of 5 safety and readiness reviews carried out in parallel to commissioning, all successfully passed Torus Magnet Commissioning Leak checks (internal cryo circuits and vacuum jacket) Vacuum pumping Cooldown (@ 180 K) Magnet energized (early October) Field mapped (mid October) Turnover to Physics (late October)

BACK-UPS

Torus Technical Parameters DESIGN VALUE Magnet Type Toroidal Field Geometry Number of Coils 6 Coil structure Double pancake Number of turns per pancake 117 Number of turns per coil 234 Conductor SSC outer dipole (36 strands) soldered in Cu channel Nominal current (A) 3770 Ampere turns 5.3E6 Peak Field (T) 3.58 Peak Field Location Inner turn near warm bore adjacent to cooling tube B-Symmetry 99.9% Bdl @ nominal current (Tm) 2.78 @ 5 degree , 0.54 @ 40 degree Inductance (H) 2.00 Stored Energy (MJ) 14.2 Warm bore  (mm) 124 Total weight (Kg) 26,000 Cooling mode Supercritical He with indirect conduction Supply temperature (K) 4.6 Temperature margin (K) Min 1.58 (@5.3 K) to Generation temperature 6.878 Turn to Turn Insulation 0.003” E-Glass Tape ½ Lap

Chronology of Torus CCM production, cryostating, and installation Coil in storage Coil installed in Hall B FNAL JLab Cryostat Factory Hall B 08/14 09/14 10/14 11/14 12/14 01/15 02/15 03/15 04/15 05/15 06/15 07/15 08/15 1 2 3 4 5 6 10 20 30 Weeks Coil # Evidence of Learning Curve From start of production at Fermi to Coil installed in Hall B: First Coil: 30 weeks Last Coil: 20 weeks While maintaining safety and quality

Torus Magnet – Coil + Cryostat Design 4K Cooling Tube ½” ID Shield Out of Plane Support Copper cooling sheets 0.050” total thickness (x2 sheets) Double Pancake Coil 234 turns 80K Cooling Tube 3/8” ID FNAL 6061 T6 Aluminum Heat shield 3.2mm thick JLab