# Physics in Perspective 2013 An enrichment course for sixth-formers and college students Monday 18th February

Michael Faraday worked here at the Royal Institution (but probably behind a different desk and with no video camera)

Five things you should never do with a particle accelerator

Dr Suzie Sheehy, Rutherford Appleton Laboratory, Oxford

The lecture

http://en.wikipedia.org/wiki/Particle_accelerator

Particle accelerators are some of the most advanced machines on the planet. They incorporate an impressive range of cutting-edge technology to do what seems like a simple job: to give subatomic particles energy. So what would happen if we tried to use them in unexpected ways? With the help of demonstrations, accelerator physicist Dr Suzie Sheehy discussed her top five things that one should never do with a particle accelerator – and a few things you definitely should.

The Large Hadron Collider is the biggest particle accelerator at the moment with a circumference of 27km but there are in fact about 26,000 particle accelerators in the world.

A neutron cannot be accelerated in a particle accelerator as it isn’t charged. Similarly a gold atom cannot be accelerated unless it is ionised.

Energy is also required in a particle accelerator.

Static electricity is an excess of electric charge within or on the surface of a material. The charge remains until it is able to move away by means of an electric current or electrical discharge. Static electricity is named in contrast with current electricity, which flows through wires or other conductors and transmits energy.                                                                                                                               A static electric charge is created whenever two surfaces come into contact and separate, and at least one of the surfaces has a high resistance to electrical current (and is therefore an electrical insulator). The effects of static electricity are familiar to most people because people can feel, hear, and even see the spark as the excess charge is neutralized when brought close to a large electrical conductor (for example, a path to ground), or a region with an excess charge of the opposite polarity (positive or negative). The familiar phenomenon of a static shock–more specifically, an electrostatic discharge–is caused by the neutralization of charge.

http://en.wikipedia.org/wiki/Static_electricity

Positive and negative charges attract each other (like charges repel).

The above picture shows Dr Sheehy and a volunteer showing that rubbing a material can remove or deposit electrons from its surface. It can then be attracted to a surface with the opposite charge (like hair).

The above picture on the left shows a Van de Graaff generator with a set of metal pie cases placed on the top (these represent the particles). The above picture on the right shows the pie cases flying off in all directions. This happened because the pie cases and the Van de Graaff all had the same charge and repelled each other.

http://en.wikipedia.org/wiki/Van_de_Graaff_generator

The above pictures are of Dr Sheehy’s model particle accelerator. The bowl consists of metal strips. Some are connected to a high voltage supply to provide a repelling force to the charged ball. The other strips are connected to the Earth but the ball continues moving when it touches them because of momentum.

You need to be able to control the particles in a particle accelerator.

Fundamental particles don’t change charge so the voltage must be changed (change speed). Magnets are used for control (change direction).

You need to be able to collide particles in an accelerator and you need to be able to detect the products from these collisions.

You couldn’t put your pet in the accelerator as they aren’t charged and they can’t live in a vacuum.

Look what happens to a marshmallow “rabbit”.

The picture below on the left is model rabbit made from marshmallows. The picture below centre shows Dr Sheehy placing the model into container that can have the air removed. The picture below on the right shows how a vacuum causes the marshmallow model to expand.

The above picture shows what happens to the poor model when the air pressure returns to normal.

Your head is actually too big to fit into the apparatus in which the particles move but if it could fit then the beam of 100 billion protons would go straight through your head. Each beam carries about 300 Mega joules of energy and this is enough to melt nearly 500 kg of copper when the start temperature is 2 kelvin.

http://lhc-machine-outreach.web.cern.ch/lhc-machine-outreach/beam.htm

A low energy beam can be stopped by water.

The picture below shows Walton carrying out experiments in his accelerator. Luckily for him the beam had such low energy that he was ok.

http://www-outreach.phy.cam.ac.uk/camphy/cockcroftwalton/cockcroftwalton7_1.htm

http://en.wikipedia.org/wiki/Cockcroft%E2%80%93Walton_generator

http://en.wikipedia.org/wiki/Ernest_Walton

http://en.wikipedia.org/wiki/John_Cockcroft

http://en.wikipedia.org/wiki/Bragg_peak

http://en.wikipedia.org/wiki/Proton_therapy

Protons are more easily directed than X-rays which means they can be sent directly to the tissue that needs treatment without effecting surrounding healthy tissue.

Difficult as the beam just passes through things.

http://en.wikipedia.org/wiki/Nuclear_transmutation

http://www.world-nuclear.org/info/Current-and-Future-Generation/Thorium/

http://en.wikipedia.org/wiki/Thorium

http://en.wikipedia.org/wiki/Thorium-based_nuclear_power

http://en.wikipedia.org/wiki/Accelerator-driven_sub-critical_reactor

http://en.wikipedia.org/wiki/Subcritical_reactor

The Accelerator-driven subcritical reactor is a nuclear reactor design discussed by the Accelerator Programme in UK which would be formed by coupling a substantially subcritical nuclear reactor core with a high energy proton accelerator. It would use Thorium as a fuel, which is more abundant than the Uranium and Plutonium in the Earth’s crust.

The extra neutron needed for achieving criticality would be provided by an external source – a Particle Accelerator. One of the main benefits for the use of such a reactor would be the relatively short life of the high toxic nuclear waste, which would be in the range of several hundreds of years as opposed of the several millions of years of the existing nuclear reactor types. At the moment this isn’t possible as the equipment isn’t powerful enough.

Now what is Dr Sheehy doing with a bunch of bananas?

She is going to show that bananas are radioactive due the presence of potassium 40.

Electron particle pasteurisation is not done in the UK but any products that are irradiated have to be labelled.

At the end of the lecture Dr Sheehy was asked which type of accelerator was better – linear or circular.

There are less synchrotron energy losses in a circular accelerator and a circular accelerator takes up less space.

There are less energy losses in a linear accelerator.

How to find black holes with lasers

Dr Andreas Freise, University of Birmingham

In 1916, Einstein – as a consequence of his new theory of gravity – predicted the existence of gravitational radiation (ripples in the fabric of space–time that propagate at the speed of light). Today, the hunt for such gravitational waves has sparked a new field of fundamental and instrumental science, using kilometre-sized telescopes that exploit laser technology. These new instruments are now in operation and close to observing Einstein’s prediction for the very first time. The observation of gravitational waves has the potential to change dramatically our understanding of the universe; we will be able to “hear” some of the most violent events in cosmic history, including black holes colliding in the centre of galaxies and the first fraction of a second after the Big Bang.

http://www.bbc.co.uk/news/technology-18341684

A laser guide star is created by a powerful laser beam illuminating the sodium layers of the atmosphere. It is used to obtain the best possible image of a celestial object from the Earth by correcting the distortion caused by the turbulence of the atmosphere, which makes stars twinkle and the image blurry and improving resolution.

The above picture is of the Australian Square Kilometre Array Pathfinder, or ASKAP. It is CSIRO’s new radio telescope at the Murchison Radio-astronomy Observatory (MRO) in Mid-West region of Western Australia. The Wajarri Yamatji people are the traditional owners of the land on which the observatory lies. Construction on ASKAP began in late 2009 and was completed in 2012.

ASKAP’s combination of fast survey speed and high sensitivity allows astronomers to answer some fundamental questions about the creation and early evolution of our Universe, and to test theories of cosmic magnetism and predictions from Einstein’s theory of general relativity.

ASKAP is an important technology demonstrator for the international Square Kilometre Array (SKA) project, a future international radio telescope that will be the world’s largest and most sensitive. In addition, ASKAP’s home, the MRO, was selected as the central site for major components of SKA telescope infrastructure in Australia. SKA telescope will also be deployed in southern Africa.

The telescope was launched on 5 October 2012, becoming the world’s fastest radio telescope. Scientists hope to use information from the array to survey the universe including the mapping of black holes and to explore the origins of galaxies.

http://en.wikipedia.org/wiki/Australian_Square_Kilometre_Array_Pathfinder

http://en.wikipedia.org/wiki/Square_Kilometre_Array

The beauty of the Square Kilometre Array is that the observer can be anywhere.

http://www.ligo.org/

http://en.wikipedia.org/wiki/LIGO

LIGO, which stands for the Laser Interferometer Gravitational-Wave Observatory, is a large-scale physics experiment aiming to directly detect gravitational waves of cosmic origin. These waves were first predicted by Einstein’s general theory of relativity in 1916, when the technology necessary for their detection did not yet exist. Gravitational waves were indirectly suggested to exist when observations were made of the binary pulsar PSR 1913+16, for which the Nobel Prize was awarded to Hulse and Taylor in 1993.

The above picture is LIGO Livingston Observatory (LLO) corner region in aerial view.

But what are gravitational waves?

96% of the universe is unknown made up of dark energy and dark matter.

http://en.wikipedia.org/wiki/Dark_energy

http://en.wikipedia.org/wiki/Dark_matter

http://en.wikipedia.org/wiki/Gravitational_wave

http://en.wikipedia.org/wiki/Theory_of_relativity

http://en.wikipedia.org/wiki/Introduction_to_general_relativity

http://en.wikipedia.org/wiki/General_relativity

In physics, gravitational waves are ripples in the curvature of spacetime which propagate as a wave, travelling outward from the source. Predicted to exist by Albert Einstein in 1916 on the basis of his theory of general relativity, gravitational waves theoretically transport energy as gravitational radiation. Sources of detectable gravitational waves could possibly include binary star systems composed of white dwarfs, neutron stars, or black holes. The existence of gravitational waves is possibly a consequence of the Lorentz invariance of general relativity since it brings the concept of a limiting speed of propagation of the physical interactions with it. Gravitational waves cannot exist in the Newtonian theory of gravitation, in which physical interactions propagate at infinite speed.

http://en.wikipedia.org/wiki/Mathematics_of_general_relativity

The Einstein field equations (EFE) are the core of general relativity theory. The EFE describe how mass and energy (as represented in the stress-energy tensor) are related to the curvature of space-time (as represented in the Einstein tensor). In abstract index notation, the EFE reads as follows:

where is the Einstein tensor, is the cosmological constant,  is the speed of light in a vacuum and   is the gravitational constant, which comes from Newton’s law of universal gravitation. Forces are limited by the speed of light

The picture below is an analogy of Einstein’s ideas about gravity (a mass in a rubber sheet). According to general relativity, the observed gravitational attraction between masses results from their warping of space and time. Mass creates the curvature of time and space. The “elastic” produces waves and changes in the gravitational field.

Two-dimensional projection of a three-dimensional analogy of spacetime curvature described in general relativity.

L is the luminosity.

http://en.wikipedia.org/wiki/Binary_star

http://en.wikipedia.org/wiki/Supernova

http://en.wikipedia.org/wiki/Pulsar

http://en.wikipedia.org/wiki/Accretion_disc

http://en.wikipedia.org/wiki/Black_hole

Binary systems are the most common arrangement of stars. Supernovae acceleration is believed to generate gravitational waves.

The picture below left is an artist’s impression of gravitational waves emerging from a black hole.

When a big boat moves through water, the water has to get out of the way to make space for the boat. The water has to curve around the boat! When the water moves out of the way, it makes ripples or waves on the surface.

Like a boat moving through water, massive objects moving through space make ripples or waves in space. A massive star or black hole moving through space causes waves in space. We call these waves gravitational waves.

http://spaceplace.nasa.gov/ligo-g-waves/

If you click on the above link you can “hear” a gravitational wave. As the rotational period increases the pitch increases.

Newton was right when we consider an apple falling from a tree but wrong when we consider cosmology.

Gravitational Wave detection

h = amplitude of the wave

http://www.gwoptics.org/ Tools for detecting gravitational waves

http://www.sr.bham.ac.uk/gwgroup/

http://en.wikipedia.org/wiki/Interferometry

http://en.wikipedia.org/wiki/Michelson_interferometer

Interferometry refers to a family of techniques in which waves, usually electromagnetic, are superimposed in order to extract information about the waves.

The Michelson interferometer is the most common configuration for optical interferometry and was invented by Albert Abraham Michelson. An interference pattern is produced by splitting a beam of light into two paths, bouncing the beams back and recombining them. The different paths may be of different lengths or be composed of different materials to create interference fringes on a back detector. Michelson, along with Edward Morley, used this interferometer in the famous Michelson-Morley experiment (1887) in a failed attempt to demonstrate the effect of the hypothetical “aether wind” on the speed of light. Their experiment left theories of light based on the existence of a luminiferous aether without experimental support, and served ultimately as an inspiration for special relativity.

The emergence of a new science

In the above picture on the right there is only one Dr Freise. He moved about a lot.

The GEO600 project aims at the direct detection of gravitational waves by means of a laser interferometer of 600 m arm length. Gravitational waves are extremely small ripples in the structure of spacetime caused by astrophysical events like supernovae or coalescing massive binaries (neutron stars, black holes). They have been predicted by Albert Einstein in 1916, but not yet directly observed.

http://outreach.ego-gw.it/index.php?option=com_content&view=article&id=102&Itemid=94&lang=it

http://en.wikipedia.org/wiki/Virgo_interferometer

The Virgo is a gravitational wave detector in Italy, which commenced operations in 2007. It is one of a handful of the world’s major experiments working towards the observation of gravitational waves.

The Virgo is a gravitational wave detector in Italy, which commenced operations in 2007. It is one of a handful of the world’s major experiments working towards the observation of gravitational waves.

Virgo is a massive Michelson laser interferometer made of two orthogonal arms, each three kilometres long.

The top right picture shows the VIRGO control room in 2003.

https://www.advancedligo.mit.edu/ The Next Step in Gravitational Wave Astronomy

The Advanced LIGO project will completely upgrade the three U.S. gravitational wave interferometers, bringing these instruments to sensitivities that should make gravitational wave detections a routine occurrence.

……. And a Nobel prize?

http://outreach.ego-gw.it/index.php?option=com_content&view=article&id=102&Itemid=94&lang=it

In principle arm cavities are rather simple objects, consisting of just two mirrors and a space between them. In reality one has to carefully choose the characteristics of the arm cavities:

Detector sensitivity and bandwidth;

Actual arm cavity design sets constraints for other subsystems;

Design of other subsystems sets constraints for the arm cavity design.

dcc.ligo.org/public/0037/G080523/000/G080523-00.ppt

The Einstein Telescope

http://en.wikipedia.org/wiki/Einstein_Telescope

Einstein Telescope or Einstein Observatory, is a future third generation gravitational wave detector, currently being designed by different institutions in the European Union. It will be able to test Einstein’s Theory of General Relativity in strong field condition and realize precision gravitational wave astronomy.