Temperature and Pressure Sensor Interfaces for the ATTA

Experiment

Ashleigh Lonis

Columbia University REU 2012

Summary● Introduction to Dark Matter and Detection

What is Dark Matter? Xenon Experiment

● Introduction to ATTA Overview Laser Cooling and Trapping Techniques Current State of Project

● What I've Done Temperature Sensor Interfaces Pressure Sensor Interfaces

What is Dark Matter?● We don't know!

● Accounts for ~80% of the matter in the universe

● Probably WIMPs

Could be the lightest neutral particle predicted by SUSY

[Crvelin, H. 2011. EMC.com. Https://community.emc.com/people/ble/blog/2011/12/26/susy]

Dark Matter - Indirect Detection● WIMPs may be maybe their own anti-particle

● Detection might give clue about distribution of dark matter in our galaxy (and Universe!)

● Fermi Gamma-ray Space Telescope is one of the current detectors.

● Difficulties distinguishing gamma ray sources

[The Pair Telescope. 2010. Goddard Space Flight Center. http://imagine.gsfc.nasa.gov/docs/science/how_l2/pair_telescopes.html]

Direct Detection of Dark Matter

● Most detectors use cryogenic or scintillation techniques.

● Cryogenic detectors - cooled systems below 100 mK and detect the heat created during collision (Ge or Si).

● Scintillation detectors – use noble gases and detect the scintillation light.

● Both types of detectors typically operate in deep underground labs to reduce cosmic ray background.

Xenon

[Xenon Dark Matter Project. 2011. http://xenon.astro.columbia.edu/XENON100_Experiment/]

Xenon Sensitivity

[Xenon Dark Matter Project. 2011. http://xenon.astro.columbia.edu/XENON100_Experiment/]

Krypton Contamination● Xe is collected from the atmosphere and has normal

Kr contamination at the ppm scale.

● Difficult to remove the Kr from Xe since they are both noble gases (cannot be done with a getter)

● Achievable: ppt Krypton contamination level – (Xenon100 currently ~10 ppt, Xenon1T experiment will use ~ppt)

[Noble Gases. 2012. http://chemistry.about.com/od/elementgroups/a/noblegases.htm}

85Kr Contamination● In the atmosphere in very

low quantities● mostly due to nuclear bomb

testing, nuclear reactor accidents and nuclear waste treatment

● Half-life of ~10.7 years. ● Beta decays into 85Rb –

stable and filtered with the getter.

[Beta Decay Artistic. 2006. Commons.wikimedia.org]

Atom Trap Trace Analysis (ATTA)● Count the number of 84Kr atoms in a Xe gas sample.

● 84Kr is the most common Kr isotope ~57% abundance.

● Known ratio of 85Kr/Kr (~2 x 10-11) → 84Kr in Xe measurement can be used to infer 85Kr contamination

● Xenon1T should have ~105 85Kr atoms in 2400 kg Xe (assuming ppt Kr contamination)

ATTA Overview

[Image: Luke Goetzke]

Vacuum Gradient

● From 10-4 torr at the source to 10-9 torr in the MOT chamber.

● Low pressure in MOT chamber ensures that trapped atoms will stay trapped

Laser● Very narrow laser

bandwidth, locked on isotope-specific atomic transition -> keep laser in resonance with the moving atoms! (Doppler effect)

● Net cooling force: atoms absorb photons from one direction but spontaneously emit isotropically

[Laser Cooling. http://www.npl.co.uk]

● Currently using Ar instead of Kr to avoid contamination of equipment

● Ar and Kr have similar transition energy from a metastable level so the same laser can be used in testing and production stages of the apparatus (811.5 nm for Kr, 811.8 nm for Ar).

Metastable

ATTA

[Image: ATTA Group]

Metastable Source● Amplified 120 MHz rf signal creates a

plasma discharge through a Cu coil surrounding a AlN tube.

● Converts Kr/Ar atoms from the ground state to a metastable state.

Cold Finger● The inflowing gas is

cooled to ~160 K by a pulse tube refridgerator (PTR)

● Cooling the gas causes increased efficiency in slowing the atoms.

Ar from 6% (at 400 K) to 24% efficiency

Kr from 18% (at 400 K) to 59% efficiency

[Figure: Tae-Hyun Yoon]

Transverse Cooling

● Collimates the beam to increase capture efficiency

● 2-D Optical Molasses – using 6 MHz red detuned laser.

● Slows transverse velocity while keeping velocity along axis unchanged.

Zeeman Slower

● Slowing from ~250 m/s to 10 m/s: changing doppler shift, keep resonance to laser!

● Magnetic field gradient on axis→ Zeeman effect changes transition energy level (keeps laser in resonance)

Magneto Optical Trap (MOT)

● Two Anti-Helmholtz cois create a magnetic field with B=0 at the center

● 3-D Optical molasses – 6 MHz laser beams

[Du, X. Realization of Radio-Krypton Dating with an Atom Trap. p. 40]

MOT and Detection● While in the MOT, the atom(s) fluoresces giving off

approximately 107 photons/second/atom.

● Observe a 6% solid angle view of MOT.

● Avalanche photodiode (APD) to detect the fluorescent light – picking up approximately 104 photons/second

[Figure – ATTA Group]

Current State of ATTA

● Demonstrated that the MOT efficiently traps atoms.

● Fine tune the system to be able to detect single atoms trapped in the MOT (distinguish from background).

108 Trapped Ar atoms – false color[Figure – ATTA Group]

● Consumption rate ~1017 atoms/s

● MOT loading rate ~109 atoms/s

● System efficiency ~ 10-8

What I've Done Overview

● ATTA needs a program that will read and record all the data from their sensors

● Created LabVIEW code to read data from pressure sensors.

● Worked to create interfaces for the temperatures sensors

● Troubleshooting determined problems with temperature sensor output.

Micromega Temperature Controller

● Plan – design an interface from analog out to LabVIEW to read and record the measured temperature.

● Setpoints for output set to -190 (0 V) to 100° C (10 V)

● Analog output – showed around .5 V for every temperature that was measured.

● Confirmed with Omega engineer that the output was non-functional.

-190 -140 -90 -40 10 600

2

4

6

8

10 Micromega Temperature Controller

Temperature (C)

Vol

tage

(V

)

Omega CN7800 - Micromega Alternative

● 4 – Omega – CN7800 Temperature sensors in the lab used for temperature readings when baking the MOT chamber.

● Had been irreversibly modified to provide current to heating tapes

● Measured output signal and determined output was non-functional.

Pfeiffer MaxiGauge● Write LabVIEW code to log for a set timespan

and graph the pressures

● Needs to be visible from across the room and allow for individual separate files to be created.

LabVIEW Front Panel

● Large display can be easily read from across the room.

● 4 channel selections with error output

● Toggle between graph display of the different sensors and viewing more than one at a time

● Option to save certain data to a file.

Channel 2RF Discharge/Source

First Optical Molasses

Channel 2

LabVIEW Data – Channel 2

Channel 3

Red Lion

Channel 3 Data

LabVIEW Block Diagram

Red Lion PAX

● Attempted to create LabVIEW interface for the PAX.

● Created driver and LabVIEW VI● Tested PC connections, cables, and got a

null modem adapter – Still not interfacing

PAX Front Panel

PAX Block Diagram

Acknowledgements

● André Loose, Tae-Hyun Yoon, and Luke Goetzke for their great deal of help, knowledge, and patience.

● Professors Aprile and Zelevinsky for allowing me to work with their groups and making this experience possible.

● Professor Parsons and Amy Garwood for organizing the program and taking care of our needs while at Columbia.

● NSF and Columbia University for giving me the opportunity to be here

Questions?