Saltdome Shower Array: A GZK neutrino Detector For High Energy Physics & Particle Astrophysics

1. Saltdome Shower Array: A GZK neutrino Detector For High Energy Physics & Particle Astrophysics Part II: Salt Domes & Detector Details Peter Gorham With help from Gary Varner University of Hawaii at Manoa SalSA presentation, DOE HQ

2. What is needed for a GZK n detector? • Standard model EeV GZK n flux: <1 per km2 per day over 2p sr • Interaction probability per km of water = 0.2% • Derived rate of order 0.5 event per year per cubic km of water or ice  A teraton (1000 km3 sr) target is desirable! Problem: how to scale up from current water Cherenkov detectors? • One solution: exploit the Askaryan effect: coherent radio Cherenkov emission • Particle showers in solid dielectric media yield strong, coherent radio pulses • Neutrinos can shower in many radio-clear media: air, ice, rock-salt, etc. • Economy of scale for a radio detector (antenna array + receivers) is very competitive for giant detectors SalSA presentation, DOE HQ

3. Antenna array Saltdome Shower Array (SalSA) concept Salt domes: found throughout the world Qeshm Island, Hormuz strait, Iran, 7km diameter 1 2 3 Depth (km) 4 • Halite (rock salt) • La(<1GHz) > 500 m w.e. • Depth to >10km • Diameter: 3-8 km • Veff ~ 50-350 km3 w.e. • No known background • >2p steradians possible 5 Isacksen salt dome, Ellef Ringnes Island, Canada 8 by 5km 6 7 • Rock salt can have extremely low RF loss, as radio-clear as Antarctic ice • ~2.4 times as dense as ice • typical:50-100 km3 water equivalent in top ~3.5km =>300-600km3 sr w.e. SalSA presentation, DOE HQ

4. U.S Gulf coast salt domes • Salt origin: Shallow Jurassic period sea, 200-150M yrs old, inshore Gulf coast area dried ~150 Myrs ago • Formed fairly uniform evaporite beds ~1 km thick or more, known as ‘Louann’ salt: • 94-98% halite (NaCl) • 2-6% anhydrite (Calcium sulfate) • Trace Mg, Sr, dissolved gases, 10-40 ppm trapped brine • Salt density (2.2) < rock (2.6) • plasticity at 10-15km depth leads to ‘diapirism’ : formation of buoyant extrusions toward surface • Diapirism for Louann salt ceased 50-100 Myrs ago, left stable salt diapirs all over the Gulf coast New Orleans Hockley salt Dome & mine Houston SalSA presentation, DOE HQ

5. Gulf coast salt domes • 1.5 - 8 km sectional axes, circular to highly elliptical • vertical extent from near surface to 10 km depths common • Source of oil & gas trapped on flanks: • impermeability of salt compared to sediments SalSA presentation, DOE HQ

6. Examples of Gulf coast halite purity SalSA presentation, DOE HQ

7. Halite & anhydrite • Pure NaCl crystals are theoretically lossless to RF via absorption • Crystal lattice defects are only mechanism for loss • Rayleigh & Mie scattering lead to attenuation over 100’s of m • Measured in situ bulk attenuation lengths can be several hundred m or more in many salt domes, but not all (Weeks Island--water intrusion) • Chief impurity: anhydrite (anhydrous gypsum or alabaster) • Also known to have ultra-low loss at radio frequencies • Expectations: typical Louann salt will have at least several hundred meter attenuation length if water content is low (<300 ppm) • Core samples indicate low water content in 80-90% of domes SalSA presentation, DOE HQ

8. Halite-anhydrite salt dome structure • Morton Salt mine, Grand Saline Salt dome, TX • ~98% pure halite, 2% anhydrite • Anhydrite banding evident, nearly vertical from deformation of original salt beds • Produces negligible effects on radio propagation SalSA presentation, DOE HQ

9. In situ salt dome measurements of attenuation SalSA presentation, DOE HQ

10. Borehole radar on dome flank • Pine Prairie dome, LA northern extreme of Louisiana salt dome region • Holser et al 1972 used dipole & helix antennas at 230MHz in a 5” diameter sonde to map the flank of the dome (1 microsec pulses) • Most data within 150m of edge of dome (impurities increase close to flank) • Flank location confirmed by retrieved samples when flank was intercepted • Good data & SNR to 8000 foot depths, until flank was pierced SalSA presentation, DOE HQ

11. Salt Dome Selection & Phase I Prototype • Inputs: Surveys in 1970’s, 1980’s for Nuclear Waste Repository sites • Stringent requirements with similar needs to SalSA, large, stable dome with dry salt, no economic usage • Richton (MS) and Vacherie (LA) domes both have excellent DOE salt core reports • Keechi Dome in TX also appears to have no oil or gas interests • Select 3-5 salt domes, drill 1500’ borehole with 300-500 ft of salt penetration, continuous core • Use chemical & loss-tangent measurements on core, plus borehole radar to assess initial salt quality • Choose best of initial domes that meet requirements for three or four deep (3km) boreholes, to install a prototype SalSA (‘Salsita’) • 1-2 years’ operations to establish proof-of-concept, and discover or confirm small sample of GZK neutrino events, then propose full array SalSA presentation, DOE HQ

12. Current Salt Dome candidate ranking SalSA presentation, DOE HQ

13. Richton Dome • Richton Dome has excellent seismic, gravity & sulfur exploration (unsuccessful) measurements of salt body SalSA presentation, DOE HQ

14. Richton Dome area • Land use primarily industrial forest • Plum Creek Land Mgmt contacted, lease option negotations ongoing SalSA presentation, DOE HQ

15. Mechanics of land use & drilling • Land use & rights studies underway, will have agreements in place for initial phase as pre-requisite for proposal • Mineral rights owner/leaseholders will retain asset rights if oil, gas, sulfur, etc. is discovered (unlikely but not excluded) • Surface rights owners will receive “damages” for 1 acre drilling site, and lease agreements for duration of project • Depends on land usage, rural land: $1-2K damages typical per well • Typical $1-2K/yr lease for small well-head site (~100 sq. ft.) & right of way • Will negotiate contracts for “options” on leases for proposal • Baker-Hughes INTEQ has expressed interest in cost-sharing agreement for prototype phase • Mississippi Office of Geology is supporting Richton dome SalSA studies SalSA presentation, DOE HQ

16. Drilling salt domes • Shallow holes: a modest rig possible, 20-40’ truck-mounted; water-well driller capable • Deep holes require large derricks, 130’ high typical, and a 1 acre site • Bore is drilled through surface layers and “caprock” to about 1000’ depth into salt, and must be cased with steel liner above salt • Salt is hermetic and needs no casing or liner, is easily drilled • Requires oil-based drilling fluids to avoid brine formation • Borehole remains OPEN after drilling, probably for decades at a 4” bore, and is backfilled with fluid providing hydrostatic pressure head • Ergo: Strings will be repairable, recoverable, can be upgraded! SalSA presentation, DOE HQ

17. Drilling Salt Domes • Drilling costs preliminary estimates $120-150K per 1500’ bore, $250-350K per 3.5 km deep hole • 4 shallow & 3-4 deep holes: $1.2M-$2M including casing and cores • Capital cost of dedicated drill rig ($0.8-1M) would be justified for full SalSA, but not at this stage • rig can be sold at termination of drilling, capital re-invested in project (eg., Don Thomas at UH has done similar) • Damage & lease costs: • Damages of order $20K in initial year • Lease costs expected to be of order $20K per yr for 3 years • Negotiations for lease options in progress SalSA presentation, DOE HQ

18. String instrumentation: “node” configuration • Antennas (copper cylinders) are cheap, “controller nodes” (receiver, digitizers, data transmitters, & pressure housing) costly, THUS: • Use many (12) antennas per controller node to optimize sensitivity • 12 nodes of 12 antennas each is current choice • $100-$150K estimated per string cost with no new technology • pressure-compensated controller system to be demonstrated SalSA presentation, DOE HQ

19. Fat dipole results in salt 120 MHz 180 MHz • 4” diameter by 30 inch length, copper • Usable from 50MHz to 1 GHz (better than model predicts) • Single mode from 50-350MHz Gain, dB 50 ohm feedpoint coupling 530 MHz 370 MHz SWR (predicted) SWR (measured) Frequency, Hz/MHz SalSA presentation, DOE HQ

20. Basic string architecture NEMA 3R 38" x 21" x17" String 12 nodes armor tape Insulated conductors Stainless tube Fibers Node = 12 antennas and center housing SalSA presentation, DOE HQ

21. GEISER (Giga-bit Ethernet Instrumentation for SalSA Electronics Readout) • GEISER Philosophy • Set low threshold • Fill Gb/s ethernet link • Event build at surface • Pure digital transmission • Trigger/Event building • No custom, fast trigger • Exploit telecomm • Event building on PC farm SalSA presentation, DOE HQ

22. GEISER Data flow • GEISER approach: • Digitize the “mud” in downhole • Pan for gold at the surface Trigger packets sent via FM/local radio 4-deep analog buffering: Node/String Time stamps 100ms latency/hit >99.999999…% livetime @ 1.5kHz Event request Digital Cell system for data collection Data Transfer RF in Continuous Hold at 1.5kHz (>2.4s) 64kb/event 1.6kHz (100baseT) 16kHz (GbitEthernet) Internal FPGA Buffer RAM SalSA presentation, DOE HQ

23. In hole digitization Digitizer n’ Readout, In-situ Transient Observation in Salt [D’RITOS] 3rd generation switched-capacitor array (SCA) architecture • Massively parallel ADCs • 50ms conversion • 7x256 samples/event • 50ms readout (40MHz) • 100ms total latency 6 4-deep analog buffering for each antenna channel Reference timing Channel SalSA presentation, DOE HQ

24. Readout board D’RITOS HV-lvDC regulation on separate board LNA, 2nd-stage amps LNA, 2nd-stage amps Trigger, bi-directional fiber-link RF conns SalSA presentation, DOE HQ

25. Radio Cherenkov testbed system • Goal: to detect first coherent radio Cherenkov emission signals of natural origin, from muon-bremsstrahlung showers • Standard hodoscope tagging combined with antenna array • SalSA instrument development: up to 196 antenna channels! Salt, 25 tons Liquid Scintillation counters (MACRO) Antenna layer Shown exposed SalSA presentation, DOE HQ

26. First Observation of Cosmic-ray muon- generated Radio Cherenkov signals • Average of ~10K events selected for showers, out of 230K (2mo. data) • Signal antennas & time determined by track fit from scint. Counter • Backgrounds taken from out-of-cone and out-of-time data • We see strong enhancement due to ensemble of ~200 GeV muon bremsstrahlung showers SalSA presentation, DOE HQ

27. Summary • The SalSA concept • intellectual fruit of two OJI awards, Saltzberg & Gorham • Strong HEP motivation to study & use GZK neutrinos • We have gone about as far as we can without a prototype array • Salsita will position us for a full-scale proposal within 2 years • Capable of discovery and/or confirmation of GZK flux • Pathfinder for full scale detector, built around the prototype • We solicit your advice & guidance! • OJI awards have mentored us both to this stage • We offer SalSA as a next generation Energy Frontier HEP instrument SalSA presentation, DOE HQ

28. Neutrino Flavor/Current ID ~2 km • Charged/neutral current & flavor ID possible on subset of SalSA events • At least 20% of GZK CC events will get first order flavor ID • For non-SM high neutrino cross sections, NC events can interact twice 1018 eVnm SalSA presentation, DOE HQ