1. Cryogenic Distillation of Underground Argon Henning O. Back – Princeton U. 2/14/14 Henning Back - Princeton University 1

2. Low radioactivity argon Low-Radioactivity Argon is a National Resource with uses in many fields – calibration gas for argon radiometric dating – proportional counter gas for National Security – target for dark matter detectors 1) Briefly summarize the current state of the program, discussing what has been learned and what are the remaining issues. Atmospheric Argon (AAr)Underground Argon (UAr) Contain beta emitter 39 Ar at a concentration of 10 -18 Radioactivity of AAr = 1 Bq/kg Concentration of 39 Ar is at least 150 times less than AAr Radioactivity of UAr < 7mBq/kg Important Note: We are the only source for this gas in usable amounts 2/14/14 Henning Back - Princeton University 2

3. Program Goals Prove ability to produce detector grade argon from an underground source on a large scale Provide Darkside-50’s underground argon target Demonstrate ability to produce underground argon for ton scale experiments 1) Briefly summarize the current state of the program, discussing what has been learned and what are the remaining issues. 2/14/14 Henning Back - Princeton University 3

4. Underground Argon Source Carbon Dioxide well in SW Colorado – contains ~500 ppm argon Princeton operates an extraction plant to produce crude argon mix from CO 2 Crude mix: – Argon (4-6%) – Helium (50-90%) – Nitrogen (5-45%) – Trace contaminants CO 2 CH 4 C 2 H 6 C 3 H 8 … Gas is shipped to Fermilab for further processing and purification 1) Briefly summarize the current state of the program, discussing what has been learned and what are the remaining issues. 2/14/14 Henning Back - Princeton University 4

5. Initial purification plan at FNAL Great Initial Success First commissioning with atmospheric argon (from Airgas) – input mix: 6% Ar, 55% He, 44% N 2 – output: 100% Ar, <500ppm N 2 Issues started with Colorado gas and with greater production rates Waste Cryogenic Distillation Column (CDC) Input Product Booster Transportation cylinder racks 1) Briefly summarize the current state of the program, discussing what has been learned and what are the remaining issues. 2/14/14 Henning Back - Princeton University 5

6. Plant Expansion 1) Briefly summarize the current state of the program, discussing what has been learned and what are the remaining issues. 2/14/14 Henning Back - Princeton University 6

7. Plant systems Helium Separator Waste Stream Argon Capture Contaminant Freeze Out Distillation 1) Briefly summarize the current state of the program, discussing what has been learned and what are the remaining issues. 2/14/14 Henning Back - Princeton University 7

8. Waste Purification Process Stream Condenser Booster Helium Separator (CB) Condenser Booster Helium Separator (CB) Input Product Waste CB Charcoal Trap (CBCT) CB Charcoal Trap (CBCT) Input Product Waste CDF Organics Cold Traps Input Product Waste CDC Charcoal Trap CDC Charcoal Trap Product Input Waste Cryogenic Distillation Column (CDC) Input Product Vent pumped out Buffer Volume Transportation cylinder racks Booster #1 1) Briefly summarize the current state of the program, discussing what has been learned and what are the remaining issues. Oct-Nov 2013 UAr Purification Colorado gas 5% Ar, 6% N 2, 89% He ~150,000 liters Colorado gas 5% Ar, 6% N 2, 89% He ~150,000 liters After He separation 40% Ar, 60% N 2 ~12,000 liters After He separation 40% Ar, 60% N 2 ~12,000 liters Final Product ~100% UAr 6.5 kg Final Product ~100% UAr 6.5 kg 2/14/14 Henning Back - Princeton University 8

9. Distillation product gas concentrations RGA N 2 limit ~300 ppm Final cylinder consumed at hour 11:25 RGA N 2 limit reached about 12 hours after final cylinder consumed 1) Briefly summarize the current state of the program, discussing what has been learned and what are the remaining issues. 2/14/14 Henning Back - Princeton University 9

10. Final Product Purity 1) Briefly summarize the current state of the program, discussing what has been learned and what are the remaining issues. 2/14/14 Henning Back - Princeton University 10

11. Remaining issues Methane contaminated gas – We have about 12 kg of Argon (purified or in crude mix) that contains too much methane – Takes very long to replace with gas from Colorado – Can be removed through distillation (Chem. E. models say it is easier than Ar/N 2 distillation) Final polishing – Distillation does not quite produce detector grade Ar – Gettering is required to go from ~100 ppm N 2 to <1ppb – Gettering system is being assembled at PAB 1) Briefly summarize the current state of the program, discussing what has been learned and what are the remaining issues. 2/14/14 Henning Back - Princeton University 11

12. Program scope Produce UAr target mass for Darkside-50 Keep plants in operational condition continuously – Requires skilled operators (Min. 3) Currently have three (EXPERIMENT) – Make immediate repairs when issues arise Requires technician manpower on short notice (FNAL) Use Distillation Column to remove methane (R&D) – Total amount of methane < 100 grams – requires: Design and operating parameters (FNAL & Chem. E. from PNNL) Engineering for safety review issues (FNAL) Technician to installed required plumbing (FNAL) Test and Commission with atmospheric argon and methane mix (EXPERIMENT) Install final gettering system – requires: Engineering – Design and safety review (FNAL) Technician – assemble system, leak check (FNAL) Electrician – system uses 480 VAC compressor (FNAL) Test and Commissioning (EXPERIMENT) 2) What is the proposed scope of the R&D program for the next two years, and what resources are required for that program? 2/14/14 Henning Back - Princeton University 12

13. Compared with other programs We are the only ones extracting significant masses of Underground Argon radiometric dating programs also extract underground Argon, but at much smaller amounts And, the sole supplier of UAr to programs requiring low radioactivity argon – Dark matter Darkside DEAP – Low-level radioactivity detection Argon radiometric dating (calibration gas) – Argonne – ATTA – Heidelberg, Germany – ATTA – Bern, Switzerland – gas proportional counters(?) National Security – PNNL – gas for proportional counters Radio-dating gas samples Our gas – 10 racks 4000 psi each 3) Compare the program with similar programs worldwide. Are we doing leading work in this area? Inches Feet 2/14/14 Henning Back - Princeton University 13

14. Generic R&D or Project Specific? Developing a supply of low radioactivity argon is a generic R&D program with many interested parties Providing the target for the Darkside-50 experiment is project specific 4) Which parts of the program should be considered generic R&D and which parts should be considered project specific? 2/14/14 Henning Back - Princeton University 14

15. New projects at the lab? Being the sole supplier of low radioactivity argon is its own project If Darkside-G2 passes the Dark Matter detector down select then it will require 5 tons DEAP is another dark matter detector that is interested in low radioactive argon on the ton scale (3.6 tons) With the availability of low radioactive argon the low level radioactivity measurement field could expand 5) Will this research likely result in new projects at the lab? 2/14/14 Henning Back - Princeton University 15

16. Summary 1)Briefly summarize the current state of the program, discussing what has been learned and what are the remaining issues. The Fermilab UAr purification systems have successfully produced pure underground argon. However, we need to keep the plant running, develop methane distillation, and perform final polishing 2)What is the proposed scope of the R&D program for the next two years, and what resources are required for that program? Prove ability to produce detector grade argon from an underground source on a large scale Provide Darkside-50’s underground argon target Demonstrate ability to produce UAr for ton scale experiments 3)Compare the program with similar programs worldwide. Are we doing leading work in this area? There are not any comparable programs. We are the sole supplier for programs interested in low radioactivity argon. 4)Which parts of the program should be considered generic R&D and which parts should be considered project specific? Developing supply of low radioactivity argon is a generic R&D program Providing the target for Darkside-50 is project specific 5)Will this research likely result in new projects at the lab? Sole provider of low radioactivity argon is its own program Darkside G2 and DEAP are ton scale dark matter detectors Low-level radioactivity field could expand with available low radioactivity argon 2/14/14 Henning Back - Princeton University 16