Temperature and Pressure Sensor Interfaces for the ATTA Experiment. Ashleigh Lonis Columbia University REU 2012

Transcription

1 Temperature and Pressure Sensor Interfaces for the ATTA Experiment Ashleigh Lonis Columbia University REU 2012

2 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

3 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 EMC.com.

4 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 Goddard Space Flight Center.

5 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.

6 Xenon [Xenon Dark Matter Project

7 Xenon Sensitivity [Xenon Dark Matter Project

8 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

9 85 Kr 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. 85 Beta decays into Rb stable and filtered with the getter. [Beta Decay Artistic Commons.wikimedia.org]

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

11 ATTA Overview [Image: Luke Goetzke]

12 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

13 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.

14 ATTA 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, nm for Ar). Metastable [Image: ATTA Group]

15 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.

16 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]

17 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.

18 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)

19 Magneto Optical Trap (MOT) Two AntiHelmholtz 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]

20 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]

21 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

22 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.

23 Micromega Temperature Controller 10 Micromega Temperature Controller Voltage (V) Temperature (C) 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. 60

24 Omega CN 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.

25 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.

26 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.

27 RF Discharge/Source Channel 2 First Optical Molasses Channel 2

28 LabVIEW Data Channel 2

29 Channel 3 Red Lion

30 Channel 3 Data

31 LabVIEW Block Diagram

32 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

33 PAX Front Panel

34 PAX Block Diagram

35 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

36 Questions?