temperature and pressure sensor interfaces for the … block diagram acknowledgements andré loose,...
TRANSCRIPT
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?