Submergible Acoustic Transducers for Superheated Fluid Dark Matter Experiments

1. Submergible Acoustic Transducers for Superheated Fluid Dark Matter Experiments • Abstract: • Submergible Acoustic Transducers for the PICASSO Dark Matter Experiment  IUSB is developing acoustic transducers for the PICASSO dark matter detection experiment. The transducers will detect the explosive phase transition of a superheated fluid target caused by dark matter interactions with the nuclei of the fluid. Future large scale detectors will likely require that the transducer be inside the pressure chambers. The low power of piezoelectric crystals and long transmission lines outside the pressure vessels require integrating the transducers with preamplifiers. The entire package must be able to survive the hostile environment and not contribute significant radioactive background. This talk will discuss the design and performance of the first version of this device. Edward R Behnke Indiana University South Bend Supported in part by NSF grant 02555472 and Indiana University South Bend. The Joint Meeting of Pacific Region Particle Physics Communities Honolulu, Hawaii October 29-November 3

2. The PICASSO Collaboration Project in Canada to Search for Supersymmetric Objects F. Aubin, M. Auger, G. Azuelos, P. Doane, G. Giroux M.-H. Genest, R. Gornea, R. Guénette, Y. Landry, C. Leroy, L. Lessard, J.P. Martin, M. -C. Piro, N. Starinsky, V. Zacek Université de Montréal, Canada U. Wichoski, Laurentian University B. Beltran, K. Clark, X. Dai, C. Storey, C. Krauss, C. Hearns, A. Noble, C. Storey Queens University, Canada J. Bocan, S. Pospisil, J. Sodomka, I. Stekl IEAP-Czech Technical University in Prague, Czech Republic E. Behnke, W. Feighery, I. Levine, N. Vander Werf Indiana University South Bend, USA F. d’Errico Yale University, USA S. Kanagalingam and R. Noulty Bubble Technology Industries, Canada MOU with Universidade de Lisboa, Universite Paris 6&7 (SIMPLE Collaboration)

3. COUPP the “Chicagoland Observatory for Underground Particle Physics” University of Chicago Juan Collar, Keith Crum, Smriti Mishra,, Brian Odom, Nathan Riley, Matthew Szydagis Indiana University South Bend Ed Behnke, Ilan Levine (PI), Nate Vander Werf Fermilab Peter Cooper, Mike Crisler, Martin Hu, Erik Ramberg, Andrew Sonnenschein, Bob Tschirhart

4. Superheated fluid transition detection • The basic method is to watch and or listen for a phase transition from fluid to gaseous. • The phase transition has detectable frequency content from audio to as much as 200 kHz, the majority of the signal is in the audio spectrum or below 20 kHz. • Sensitivity of the active detector fluid is related to temperature. The superheated range is from about 0 degrees C to near 60 degrees C.

5. Superheated techniques are temperature dependant, less recoil energy is required at higher temperatures adding to the count rate.

6. Overview of Experiments • PICASSO – small droplets of superheated fluid in a carrier gel. Can detect multiple bubbles per pressure cycle. • COUPP – large volume of superheated fluid in pressure vessel. Single event per compression cycle.

7. How do observe events • PICASSO: we listen for explosive phase transitions using only piezo transducers. • COUPP: we watch the active fluid for the start of a bubble using a camera while listening with a piezo transducer.

8. Pressure / Environmental Demands • Compression cycles are about 200 psi. • PICASSO uses a corrosive and possibly conductive gel to suspend the superheated droplets. This places a requirement on the encapsulant to be a good insulator, both electrically and mechanically. Currently COUPP uses a non-conductive fluid in one detector and a conductive fluid in another.

9. Recoiling 19F creates microscopic vapour cavities. If Rcavity>R ”critical”, Phase transition irreversible. ~Half thermal PE released acoustically Adjust pressure (and superheat) Temp Control Metastable Superheated Freon droplet, suspended in gel Freon bubble WIMP/19F elastic scatter Freon bubble Acoustic sensor, preamp, daq

10. Acoustic Signal PICASSO Bubble Events Wave Form: Magnitude of acquired signal as function of time. From Americium spiked detectors Frequency composition Frequency composition of same event. Characteristic peaks near 80 KHz and 160 KHz not observed in noise events!

11. Pre-Amps • We have chosen to use a JFET LT1792 op amp with very low noise 6 nV/root Hz as the preamp. We have set the frequency response to about 250 kHz which is above the expected signal (frequency response is a function of gain).

12. Encapsulants • Needs • Optically Clear (for camera) • Acoustically clear. • Radioactively quiet • Usable thru the temperature range. • Easy to use. • Good insulator. • Two part resin and epoxies. • Acrylic • We chose a two part resin from MAS used to manufacture fiberglass boats as a stand-in till we perfect the acrylic technique.

13. Potting • Construct mold out of materials that the encapsulant does not adhere to. • Vacuum strip the resin to allow bubble free pour. • Rough sand • Dip in resin to form clear final surface.

14. COUPP Camera

15. COUPP Submergible Transducer with Preamplifier

16. Summary • We have all the pieces tested for the next generation transducer for the detector. • We need to choose a new piezo or a set of piezo to allow proper frequency response. • We need to perfect the acrylic technique if possible.