saltdome shower array: a gzk neutrino detector for high energy physics & particle astrophysics

SalSA presentation, DOE HQ 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


What is needed for a GZK detector?

Standard model EeV GZK flux: <1 per km2 per day over 2 srInteraction 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 pulsesNeutrinos 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


Saltdome Shower Array (SalSA) concept

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Depth (km)

Halite (rock salt)• L(<1GHz) > 500 m w.e.• Depth to >10km• Diameter: 3-8 km• Veff ~ 50-350 km3 w.e.• No known background• >2 steradians possible

Antenna array

Qeshm Island, Hormuz strait, Iran, 7km diameter

Isacksen salt dome, Ellef Ringnes Island, Canada 8 by 5km

Salt domes: found throughout the world

• 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 =>300-600 km3 sr w.e.


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

Houston New OrleansHockley salt Dome & mine


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


Examples of Gulf coast halite purity

Salt dome Sample depth, ft halite % anhydrite %

Splindletop, TX 2676 94.83 5.17

Sour Lake, TX 7290 92.48 7.52

Saratoga, TX -- 96.79 3.21

McFaddin, TX 2645 98.47 1.53

Hull, TX 706 92.15 7.85

Moss Bluff 4566 96.02 3.98

High Island, LA 3359 89.63 10.37

Grand Saline, TX Various, mine hor. 98.0 2.0

Hockley, TX 1200, estimated avg. 95.0 5.0

Avery Island, LA Mine horizon 98.73 1.2

Cypress Creek, MS

1720-1876, 8 samples 95.61 3.97

Richton, MS 1120-1270, 8 samples

94.08 5.41

Port Barre, LA -- 99 1


Halite & anhydrite

Pure NaCl crystals are theoretically lossless to RF via absorptionCrystal 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


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


In situ salt dome measurements of attenuation

Location Freq., MHz

Loss coefficient Attenuation length

Method reference

Pine Prairie salt dome, LA

230 <0.0042 per m (best)<0.0105 (typical)<0.016 (worst case)

>235m>94m>66m

GPR, from salt dome flank reflections, 150-200m typical one way,very close to flank

Holser et al. 1972

Cote blanche salt dome, LA

440 <0.0033 per m >300m GPR, 1245m path, derived

Stewart & Unterberger 1976

Hockley dome, TX 440 <0.005 per m >200m GPR, derived from reflections, 350m 1-way

Hluchanek 1973

“saltdome in N. Germany”

22.5 0.0027 per m ~370m Dual borehole, 470m separation

Nickel et al. 1983

Hockley dome, TX 150300750

<0.0039 per m<0.0047 per m<0.0041 per m

>256m>213m>243m

Transmit & receive through salt column, 40m thick

Gorham, Saltzberg et al. 2001


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


Salt Dome Selection & Phase I Prototype

Inputs: Surveys in 1970’s, 1980’s for Nuclear Waste Repository sitesStringent 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 reportsKeechi 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 qualityChoose 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


Current Salt Dome candidate ranking

Rank DomeUS

State

Volume to 3.5km depth

[cubic km salt]

Maximum aperture [cubic km steradians

water equiv.] (a)

Positive Notes Negative Notes

1 Richton MS 50.0 684.4 220 360

Shallow, extensively mapped, no oil or gas production. Salt core analysis shows 94% halite 5%

anhydrite. Good drainage, flat cap region. Huge body of ONWI survey

literature. Industrial forestry on most of cap.

Numerous dropped projects. Plans for LPG storage caverns could revive?

2 Vacherie LA 45.4 621.7 240 300

3500' core taken by DOE, salt analysis done; very low water

content in salt; shallow cap. Large body of ONWI survey literature

some potential for flooding on dome crest?

3 Keechi TX 32.7 447.3 90 900No oil or gas, good drainage

around dome, good access. Near Palestine, TX

Little survey work. Sloping cap; requires >1000m bores on flank

4 Hainesville TX 39.2 536.5 366 400Well mapped; circular, flat cap, very large, sparsely populated

Extensive oil/gas production (53 wells); Several LPG storage caverns.

5 Chacahoula LA 38.7 529.8 370 1000No oil directly on cap (in 1961),

sparse population expected.

Extensive oil/gas prod, S flank densely producing. In "Bubbling Bayou."

Sloping cap, requires 1000m bores on flank. Probable LPG storage caverns

6 Butler TX 21.1 289.3 10 450Shallow cap. Near Palesine, TX.

Good access roads. Minimal oil or gas production.

Sandstone quarry on flank. Two or more gas storage caverns in 1984.

Potential for flooding.

7 Cypress Creek MS 15.0 205.8 396 400Extensively mapped by DOE. Flat cap. DOE salt core analysis gives

94% halite 6% anhydrite.

Oil & gas wells on S and W flanks. Some potential for flooding on cap

region.

NOTES:(a) Assumes 2 pi steradians solid angle acceptance for all of volume (consistent with simulations), density of 2.18 g/cc for salt.(b) Minimum depth is shallowest salt from surface; average is over all of crest needed to instrument the dome for a SalSA.

Salt crest mininmum (left) and average

(right) depths [m] (b)


Richton Dome

Richton Dome has excellent seismic, gravity & sulfur exploration (unsuccessful) measurements of salt body


Richton Dome area

Land use primarily industrial forest

Plum Creek Land Mgmt contacted, lease option negotations ongoing


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 wellTypical $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


Drilling salt domes

Shallow holes: a modest rig possible, 20-40’ truck-mounted; water-well driller capableDeep 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 saltSalt is hermetic and needs no casing or liner, is easily drilled

Requires oil-based drilling fluids to avoid brine formationBorehole remains OPEN after drilling, probably for decades at a 4” bore, and is backfilled with fluid providing hydrostatic pressure headErgo: Strings will be repairable, recoverable, can be upgraded!


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 yearLease costs expected to be of order $20K per yr for 3 yearsNegotiations for lease options in progress


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 sensitivity12 nodes of 12 antennas each is current choice$100-$150K estimated per string cost with no new technologypressure-compensated controller system to be demonstrated


Fat dipole results in salt

4” diameter by 30 inch length, copperUsable from 50MHz to 1 GHz (better than model predicts)Single mode from 50-350MHz

120 MHz

370 MHz

180 MHz

530 MHz

Frequency, Hz/MHz

SWR (predicted)

SWR (measured)

Gain, dB

50 ohmfeedpointcoupling


Basic string architecture

String12 nodes

Node = 12 antennas and center housing

tape

Stainless tube

armor

Insulatedconductors

Fibers

NEMA 3R 38" x 21" x17"


GEISER (Giga-bit Ethernet Instrumentation for SalSA Electronics

Readout)

GEISER PhilosophySet low thresholdFill Gb/s ethernet linkEvent build at surfacePure digital transmission

Trigger/Event buildingNo custom, fast triggerExploit telecomm Event building on PC farm


GEISER Data flow

GEISER approach:Digitize the “mud” in downholePan for gold at the surface

Digital Cell system for data

collection

Internal FPGA Buffer RAM

100ms latency/hit>99.999999…% livetime @ 1.5kHz

RF inContinuous 64kb/event

1.6kHz (100baseT)16kHz

(GbitEthernet)

Trigger packets sent via FM/local

radio

Node/String Time stamps

Event request

Data Transfer

4-deep analog buffering:

Hold at

1.5kHz(>2.4

)


In hole digitization

3rd generation switched-capacitor array (SCA)

architecture

Digitizer n’ Readout, In-situ Transient Observation in Salt

[D’RITOS]

4-deep analog buffering for each antenna channel

Reference timing

Channel

6

Massively parallel ADCs• 50ms conversion • 7x256 samples/event• 50ms readout (40MHz)• 100ms total latency


Readout board

Trigger, bi-directional fiber-link

D’RITOS

LNA, 2nd-stage amps

LNA, 2nd-stage amps

RF conns

HV-lvDC regulation on separate board


Radio Cherenkov testbed system

Goal: to detect first coherent radio Cherenkov emission signals of natural origin, from muon-bremsstrahlung showersStandard hodoscope tagging combined with antenna arraySalSA instrument development: up to 196 antenna channels!

Salt, 25 tons

Antenna layerShown exposed

Liquid Scintillation counters (MACRO)


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. CounterBackgrounds taken from out-of-cone and out-of-time dataWe see strong enhancement due to ensemble of ~200 GeV muon bremsstrahlung showers


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 yearsCapable 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


Neutrino Flavor/Current ID

Charged/neutral current & flavor ID possible on subset of SalSA eventsAt least 20% of GZK CC events will get first order flavor IDFor non-SM high neutrino cross sections, NC events can interact twice

Charged current (SM: 80%)

Neutral current (SM: 20%)

e 25% hadronic + 75% EM shower at primary vertex; LPM on EM shower

Single hadronic shower at vertex

25% hadronic at primary, 2ndary lepton showers, mainly EM


25% hadronic at vertex, 2ndary lepton showers, mainly hadronic


~2 km

1018 eV

saltdome shower array: a gzk neutrino detector for high energy physics & particle astrophysics

Documents

impermeability of salt

salt column

typical louann salt

diameter isacksen salt

salt dome flank reflections

world rock salt

grand saline salt dome

cote blanche salt dome