UK News from CERN Issue 77

 

Issue 77 contents

Simulation of the modulation process

Making waves for future accelerators

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The AWAKE experiment has achieved a major milestone towards a technique that could revolutionize particle accelerator design.

Metal after treatment

LESS is more

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Pioneering laser technology developed in the UK could boost the performance of the Large Hadron Collider.

Analysing event displays

That looks weird…

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Citizen scientists seem to have the edge on sophisticated computer algorithms.

Particle Zoo

Christmas stocking fillers

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Need some last minute ideas for your Christmas list?

Organiser

Dates for the diary

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Dates and deadlines for 2017.


 

Making waves for future accelerators

Simulation of the modulation process

Graphic from a simulation of the modulation process. Proton are shown in red, electric fields in dark blue and the laser pulse, used to ionize a Rubidium vapour and create a plasma, in green. The strong modulation of the proton bunch is seen when comparing the proton distribution ahead of and behind the laser pulse. The bunching of the protons leads to the creation of large electric fields.
(Credit: AWAKE/CERN)

 

The AWAKE experiment has achieved a major milestone towards a technique that could revolutionize particle accelerator design.

The AWAKE collaboration has reached a major milestone; in the final week of CERN's accelerator operations for 2016, it has observed strong modulation of high-energy proton bunches in plasma, signalling the generation of very strong electromagnetic fields. This is a significant step towards the goal of using the proton-driven plasma wakefield technique to accelerate electrons.

The facility was successfully commissioned between June and November and is the first experiment to investigate the use of plasma wakefields driven by proton beams to accelerate charged particles (see UKNFC26).

The experiment injects a "drive" bunch of protons from CERN’s SPS accelerator into a plasma column created by ionising a gas with a laser. When this bunch interacts with the plasma, it splits into a series of smaller bunches, in a process called self-modulation. As these shorter bunches move through the plasma, they generate a strong wakefield. It is signals of the self-modulation process that the AWAKE team has observed, and from which it can infer the creation of the wakefield.

The next step, which AWAKE has yet to demonstrate, is to inject a second beam of electrons, the “witness” beam, in the right phase behind the proton beam. This witness beam "feels" the wakefield and is accelerated, just as a surfer accelerates by riding a wave.

The use of plasma to accelerate particles is a potential alternative to traditional accelerating methods that rely on radiofrequency electromagnetic cavities. It has long been known that plasmas are capable of supporting very strong electric fields. The challenge for researchers is to understand the best way to take advantage of this capability to create ‘same size’ particle accelerators with much higher energies, or much smaller (and cheaper) accelerators with the same energy than we have today. To put this into context, with existing technology a linear collider generating TeV energies would be 30-50km long. Using proton-driven plasma wakefield techniques, the length would be just a few kilometres.

This exciting development, the culmination of three years of intense preparation, opens a new era of particle accelerator development at CERN and worldwide.

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LESS is more

Pioneering laser technology developed in the UK could boost the performance of the Large Hadron Collider to new levels of efficiency, and become an integral part of future high energy particle accelerators.

The technology for the surface modification of metals known as LESS (Laser Engineered Surface Structures) for this specific application is the result of a collaboration between the University of Dundee and STFC.

Dundee and STFC have now entered into partnership with CERN to use the new technology, which is aimed at clearing the `electron cloud’ that develops in the LHC and limits the range of experiments that it can handle.

“Large particle accelerators such as the Large Hadron Collider suffer from a fundamental limitation known as the `electron cloud’,” explains Amin Abdolvand, Dundee’s Chair of Functional Materials and Photonics. “This cloud of negative particles under certain condition may degrade the performance of the primary proton beams that circulate in the accelerator, which is central to its core experiments.

“Current efforts to limit these effects involve applying composite metal or amorphous carbon coatings to the inner surfaces of the LHC vacuum chambers. These are expensive and time consuming processes that are implemented under vacuum.”

Steel before it has been re-engineered using lasers

Metal before treatment
(Credit: University of Dundee)

Steel after it has been re-engineered using lasers

Metal after treatment
(Credit: University of Dundee)

 

As part of the High Luminosity LHC upgrade project, a new solution is needed to reduce the electron cloud problem to much lower levels than would be expected with the current technology.

The LESS method has shown potential to reduce the electron cloud to unprecedentedly low levels. It involves using lasers to manipulate the surface of metals, and relies on understanding how different metal surfaces react when they are subjected to varying levels of laser fluence or intensity.

Tests have shown that it is possible to reformulate the surface of the metals in the LHC vacuum chambers to a design that under a microscope resembles the type of sound padding seen in music studios. The surface can trap electrons, keeping the chambers clear of the cloud. Initial tests at the Super Proton Synchrotron, the LHC injector, have shown the LESS method is very effective at controlling the electron yield, as electron clouds have been fully eradicated.

“The LESS method should yield many successful applications in the future,” says Peter McIntosh (STFC), “this is just one opportunity that will have a dramatically positive impact for the LHC and its High Luminosity configuration.

“Through close working interaction between ASTeC vacuum scientists and Dundee University laser specialists, a real breakthrough in suppression of secondary emission yield performance has been accomplished, which could have widespread implications for high electro-magnetic field environments, where breakdown limitations are of particular concern, such as for sensor systems and applications in satellite and aerospace technologies.

“We expect it will prove to be an innovative solution for CERN.”

Michael Benedikt, Head of the Future Circular Collider study at CERN, said “The LESS solution could be easily integrated in the design of future high-intensity proton accelerators; the method is scalable from small samples to kilometre-long beam lines.”

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That looks weird…

Citizen scientists seem to have the edge on sophisticated computer algorithms.

This article by Katarina Anthony is reprinted by kind permission of the ATLAS collaboration.

Analysing event displays

Analysing event displays on the HiggsHunters website.
(Credit: ATLAS Experiment/CERN)

 

HiggsHunters is the first mass-participation citizen science project for the Large Hadron Collider, allowing non-experts to get directly involved in physics analysis. Since its launch in 2014 on the Zooniverse platform, over 30,000 people from 179 countries have participated in the project. Their work has led to the project’s first publication on arXiv.

Citizen scientists are asked to examine ATLAS event displays, looking for ‘off-centre vertices’ where several tracks intersect away from the central collision point. These events may indicate the presence of a new long-lived particle; such a discovery would be extremely significant to the scientific community.

The recently-released paper shows the results of over 1.2 million event display classifications. “We found the collective ability of our volunteers to be excellent,” says Alan Barr, ATLAS physicist who led the creation of the project (University of Oxford). “Our citizen scientists are very good at pattern recognition by eye, and are able to spot ‘weird’ or unusual events that wouldn’t otherwise have been identified. In fact, for certain particle types, they were even able to identify ‘off-centre vertices’ better than existing computer algorithms.”

These results help to cement the scientific viability of citizen science projects in high-energy physics. “Even without making a discovery, our volunteers have made a great contribution,” says Barr. “We hope to feed back their results to improve our existing analysis algorithms.”

Given the success, there’s plenty of opportunity for further papers from HiggsHunters.

Interested in becoming a sharp-shooting Higgs hunter? Join the project’s thriving community by visiting HiggsHunters.

The HiggsHunters project was developed by the University of Oxford, New York University and the ATLAS Experiment, in collaboration with Zooniverse.

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Christmas stocking fillers

Need some last minute ideas for your Christmas list? Here’s some suggestions!

Particle Zoo

(Credit: Quercus)

First up is ‘The Particle Zoo: The Search for the Fundamental Nature of Reality’. Let Gavin Hesketh (UCL and ATLAS) be your guide through the extraordinary subatomic world of antimatter, ghostly neutrinos, strange-flavoured quarks and time-travelling electrons, gravitons and glueballs, mindboggling eleven-dimensional strings and the elusive Higgs boson itself.

Undoubtedly the must-have popular physics book of 2016, it’s available online or at any good bookshop.

 

Hello Kitty

(Credit: Sanrio)

Admittedly, the next suggestion does require you to be able to navigate a Japanese website or even go to Japan, but it will definitely be worth the effort!

The association leading the campaign to have the International Linear Collider built in Japan has collaborated with Hello Kitty to bring you a range of impossibly cute promotional merchandise. Complete with a Lagrangian ‘L’ bow, specs and a pocketful of pens, Science Kitty is perched on an ILC cryomodule.

Who says high energy physics can’t be cute? This will be the T-shirt for summer 2017, so get yours now!

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Dates for the diary

Organiser

(Credit: Pixabay)

 

Dates and deadlines for 2017

Contents

Science and Technology Facilities Council Switchboard: 01793 442000