1. 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

2. 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

3. 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 ( ) (CD1 – CD4b)
8 superconducting magnets are part of the 12 GeV upgrade
$70M Upgrade of Hall B includes the CLAS12 Torus Detector Magnet

4. CLAS12 Detector System

5. 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

6. 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), , 2016

7. 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), , 2016

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

9. 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

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

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

12. 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

13. 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

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

15. 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

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

17. 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

18. 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

19. 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)

20. BACK-UPS

21. 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%
nominal current (Tm)
5 degree , 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 K) to Generation temperature 6.878
Turn to Turn Insulation
0.003” E-Glass Tape ½ Lap

23. 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

24. 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