What is an Atom Chip

Atom chip by RAL Space
Cold atom chip as a source for atom interferometer​. Credit: RAL Space, STFC, UKRI

If you follow physics or science news, you will know that a huge part of current physics research is in the field of particle physics. Scientists aim to understand and harness the power of atoms. In laboratories across the world, scientists have been using silicon circuitry to sense the effects of their experiments, with huge silicon detectors being commonplace. You will also find silicon circuitry in the driving circuits of things like magnets and lasers, but these instruments are usually large, as it only needs to fit in a lab. There is no need to minimise. There is also an upcoming exciting area of physics that uses all of these techniques to truly harness the power of the atom known as Cold Atoms. The world of cold atoms uses the concept of trapping small amounts of atoms in a very small area, and super cooling them very close to absolute zero. At this temperature the quantum effects of the atom take over, and can be observed and maybe even harnessed.

 Atom Chip
A close up of an atom chip by The Atom Chip Lab at Ben-Gurion University

This is where Atom chips come in. They are not the only way to practice cold atoms by any means, but it is becoming a popular method to practice the art. The popularity is down to how small the overall circuit is, and the lower amounts of instrumentation needed to drive it. That being said, they are also more temperamental, and much more sensitive to things like noise. The way to trap atoms in an area is to use electric, magnetic and optical fields, all these things have control of the location and activity of the atoms. Atom chips use these three fields to confine, control and manipulate the cold atoms. If you imagine a normal Integrated Circuit (IC), the electrons move through the surface, through things like transistors, capacitors and resistors. In Atom chips the atoms are trapped above the surface, and using forces that we can control, we manipulate their motion, and internal state. The electric, magnetic and optical fields come from small structures on the chip, sometimes protruding out.

Atom chip at Vienna University of Technology
Another example of an atom chip at TU Wien. Credit: Vienna University of Technology

The area that the atoms are held in is often around 1 micrometer squared, and the amount of atoms is around 10,000. This is a surprisingly small amount when you think about it, that’s the amount of students you would find at most universities. The atoms are held at a few hundred nano Kelvin, and due to their design are often well isolated from the warm solid state environment around it. This allows their quantum state to remain undisturbed for tens or even hundreds of seconds. This is partly the basis of modern Atomic clocks. In fact the atoms used are usually the same, strontium or cesium. When you see images of modern atomic clocks, there usually is some sort of atom chip controlling the cold atom cloud directly. This is down to the ease of both reducing the size and complexity of the clocks without impacting the resolution of the clock circuit itself.

Cold Atoms Lab ISS
An artists impression of the Cold Atoms Lab on the International Space Station. Using techniques similar to the ones mentioned here. Credit: NASA/JPL-Caltech

The basis of the trapping part of the circuit uses something known as a magnetic trap (sometimes known as a micro trap). Imagine a wire, for the moment we will imagine it it straight. When a current is induced through it a magnetic field is created around it, a bit like a tube moving round the wire at a certain distance. This is the red line on the diagram below. As you learnt in physics class, the intensity of that magnetic field is directly proportional to the current running through the wire. Control the current then we control the magnetic field. In a magnetic trap there is also another magnetic field induced across the entire experiment, that we can assume is constant and uniform. This is represented by the green line, and is called B. Although there is only one green line, The magnetic field ie everywhere, but the green line is the bit we really care about. Now it took me a while to visualise this, but these two magnetic fields interact, and add up. So if the wire magnetic field is travelling the same way as the field B at any point then the magnetic field gets stronger, if the magnetic field oppose then the field will get weaker at that point. This means there is a magnetic gradient across the entire experiment.

The point we care about is where the magnetic field is zero, meaning the wires magnetic field is equal to, and opposing the field B. As the magnetic field from the wire gets less as it gets further away from the wire, there is a point at a certain radius (R on the diagram) away from the wire where this is the case. The atoms used want to be in the lowest energy state, and are trying to get away from the magnetic field, so it will “seek out” the point with the minimum magnetic field. in this case, the point R distance away from the wire. The wire now has a single line of trapped atoms R distance away from it. Now imagine that wire is bent into a circle with a radius of R. All those atoms are no longer trapped in a line, but now at a single point in the center of the wire. In practice to get the required magnetic field strength it will be a coil rather than a single wire, but the concept is the same. You now have a collection of atoms trapped in a small area defined by you, to do an experiment. Most of the time the atoms are then super cooled with lasers, or trapped and compressed further. This allows experiments with Bose Einstein Condensates, and potential to make quantum “qbits” for quantum computers, but that is a post for another day.

Thank you for reading, take a look at my other posts if you are interested in space, electronics, physics or military history. If you are interested, follow me on Twitter to get updates on projects I am currently working on.

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Mars InSight Has Been Busy

insight selfie
This is NASA InSight’s first full selfie on Mars. It displays the lander’s solar panels and deck. On top of the deck are its science instruments, weather sensor booms and UHF antenna. Credit: Nasa/JPL-Caltech.

So I have talked previously about the launch of the latest lander on Mars, named Mars Insight. Launched on the 5th of May 2018 by an Atlas V 401 from Vandenberg AFB, it began its 6 month journey to the red planet. Travelling across 484 million km it landed on 26th of November 2018. It landed much like the Curiosity and Phoenix missions with a parachute decent and then using rockets to lower the lander onto the surface gently. The mass of the lander is about 358 kg, but due to the gravity on Mars being two thirds less it only weighs 134.6 kg on the surface. Just a few hours after touchdown the Mars Odyssey orbiter relayed signals indicating that the solar panels had successfully opened, generating power. The relayed signal also contained a pair of images of the landing site. For the next few weeks InSight checked the health of the on board systems and monitor the weather and temperature of the landing site.

InSights workspace
This mosaic, made of 52 individual images from NASA’s InSight lander, shows the workspace where the spacecraft will eventually set its science instruments. The lavender annotation shows where InSight’s seismometer and heat flow probe can be placed. Credit: NASA/JPL-Caltech

The images relayed were used to find the best area to place the Seismometer instrument. There was then some time for scientists to evaluate the information and pick the best spot to place the sensitive instrument. On the 19th of December Insight used its 8ft robotic arm to pick up the Seismometer from the deck of the lander, and place it on the ground nearby. The position picked was one fairly free of rocks, making the leveling process easier. There was then another set of a few weeks to adjust the cable and ensure the SEIS instrument was perfectly placed. Then the arm picked up a protective cover from the lander to place over the instrument. This is designed to minimise noise from the surrounding atmosphere, being introduced from huge temperature changes and wind vibrations. This will allow the seismometer to pick up the tiny tremors that the planet may have. This is the first time another planet has been studied this way, the only other planetary body being the Moon. Viking 1 and 2 had seismometers on board but design flaws meant the results were inconclusive.

Temperature is one of the biggest issues with a mission like this. On Mars the temperature can range over 90 degrees Celsius in just a single sol (Martian day). The protective cover is ringed with a thermal barrier and a section of chain mail around the bottom. The wind and thermal shield has been specifically designed for the environment to moderate the temperatures. JPL has a history dealing with Mars temperatures from the many missions it has sent there including the Phoenix lander, and the Curiosity rover. The SEIS instrument was provided by the French Space Agency CNES, and developed by the Institut de Physique du Globe de Paris, with JPL building the wind and thermal shield. There is also a great British part of the instrument with some of the silicon sensors designed and fabricated by Imperial College London. The microseismometers were designed to pick up the faintest seismic activity from the surface. Scientists from Oxford’s Department of Physics also supported the development, and the Rutherford Appleton Laboratory’s RAL Space worked closely with the team to develop the front electronics of the instrument as well as the space qualification.

SEIS instrument cutaway
Cutaway illustration showing interior components of SEIS. Credit: NASA/JPL-Caltech/CNES/IPGP
microseismometer
One of the microseismometer sensors, carved from a single piece of silicon 25mm square. Credit: Imperial College/T.Pike.

On the 12th of February the lander deployed the HP3 package onto the surface. Known as the Heat Flow and Physical Properties Package, it was placed about a meter away from the seismometer. The Idea of HP3 is to measure the heat flow through Mars’s subsurface, hopefully helping scientists to figure out how much energy it takes to build a rocky planet like Mars. An interesting instrument, it has a self-hammering spike, or mole, allowing it to burrow up to 5m below the surface. This is much deeper than any previous mission. Viking 1 only scooped down 8.6 inches, and the predecessor of Insight, Phoenix dug to 7 inches. The probe was provided by the German Aerospace Centre (DLR). A tether attached to the top of the mole features heat sensors to measure the temperature of the Martian subsurface. Heat sensors in the mole itself will measure the soils thermal conductivity (how easily the heat moves through the surface). The mole plans to stop every 50 centimetres to take the measurements, as the hammering creates friction, releasing heat that would likely impact the instruments readings. It is then heated up by 28 degrees Celsius over 24 hours, with the temperature sensors measuring how rapidly this happens.

A GIF of the Insight lander placing the instruments on the ground. Credit: NASA/JPL-Caltech

Along with the Insight lander, the launch also contained a new first, a pair of cubesats known as MarCO-1 and MarCO-2. The size of small suitcases the pair were the first cubesats to enter and work in deep space. The team nicknamed the WALL-E and EVE, and they functioned as communications relays during the insight landing, beaming back data from the decent, along with the first image. WALL-E also managed to capture its own great images of Mars as it soared past it. The mission cost was about $18.5 million, much less than most missions, and was designed by JPL as a technology demonstrator mission. Neither is still in contact with Earth, with WALL-E losing contact on the 29th of December 18, and EVA losing contact on the 4th of January 19. JPL says they will attempt to contact the pair again in the future, but it is unlikely. The MarCO satellites will still live on though, with some of the spare parts going towards other cubesat missions, including experimental radios, antennas and propulsion systems. They also pushed the idea of using commercial parts to develop the system.

MarCO
Engineer Joel Steinkraus uses sunlight to test the solar arrays on one of the Mars Cube One (MarCO) spacecraft at NASA’s Jet Propulsion Laboratory. Credit: NASA/JPL-Caltech
MarCO GIF
MarCO-B, one of the experimental Mars Cube One (MarCO) CubeSats, took these images as it approached Mars. Credit: NASA/JPL-Caltech

Just as an addition, there is a great comic that can be found here about Mars Insight, by the oatmeal. It is worth a quick read.

Thank you for reading, take a look at my other posts if you are interested in space, electronics, or military history. If you are interested, follow me on Twitter to get updates on projects I am currently working on.

Follow @TheIndieG
Tweet to @TheIndieG

Final Rokot Launches Sentinel 3B

What Sentinel 3B looks like
Artist’s view of what Sentinel 3B looks like when up in space, sadly there are not many images of it for real! Credit: ESA/ATG Medialab

On April 25th, 2018, at 17:57 UTC a Russian Rokot/Briz KM rocket launched from Site 133, pad 3 from Plesetsk Cosmodrome. Aboard was Sentinel 3B, an Earth observing satellite, part of Europe’s Copernicus environmental monitoring network. This marks the final commercial Rokot Launch, and the final Eurokot mission. There are some more Rockot launches planned for the Russian government though, after which it is reportedly that the repurposed missile launch system will be retired.

Sentinel-3B UC exit from MIK go to Launch pad
The Sentinel 3B being transported to the launchpad by the russian train system.

Sentinel 3B is a Thales Alenia Space Prima Bus satellite, designed to measure ocean temperatures, colour, surface height and the thickness of sea ice. While it is over land it can measure the height of rivers and lakes, monitor wildfires, provide maps of land use and monitor vegetation. The satellite has been designed for many uses. Created for the European Space Agency, the satellite will join Sentinel 3A in orbit to symmetrically monitor the Earth. The data will be primarily fed into the Copernicus Environmental Monitoring Service, where the applications can be developed from to use the data.

Sentinel 3B in integration
An image of the Sentinel 3B satellite just before it was sent off to Russia to be put on the Rokot. Credit ESA

The satellite carries many payloads to track the huge amount of data it is recording, these include:

  • OLCI (Ocean and Land Colour Instrument)
  • SLSTR (Sea and Land Surface Temperature Radiometer)
  • SRAL (Synthetic Aperture Radar Altimeter)
  • MWR (Microwave Radiometer)
  • DORIS
  • LRR (Laser Retroreflector)
  • GNSS (Global Navigation Satellite System)

Thales Alenia Space was the prime contractor, responsible for constructing the spacecraft and the SRAL instrument, as well as contributing to the supply of the SLSTR instrument. Many European companies were involved in supplying the SLSTR instrument, including SELEX Galileo, RAL (Rutherford Appleton Laboratory), Jena-Optronik, Thales Alenia Space, ABSL and ESA-ESTEC. EADS CASA Espacio was contracted to provide the MWR instrument. CNES was contracted to provide the DORIS instrument.

Mediterranean Sea
An image of the Mediterranean Sea taken by Sentinel 3A, the partner of Sentinel 3B, they will don the same job on opposite sides of the Earth. Credit: ESA