[{"command":"settings","settings":{"ajaxPageState":{"theme":"hm_theme","theme_token":"bhlK3V3vjkcGKLm5rkewUVUJmyRHZFDV9fzrj-GgN5w","libraries":"eJwDAAAAAAE"},"ajaxTrustedUrl":{"form_action_p_pvdeGsVG5zNF_XLGPTvYSKCf43t8qZYSwcfZl2uzM":true},"pluralDelimiter":"\u0003","user":{"uid":0,"permissionsHash":"2af85631393b514cbde3779a1f71d92618d53b94b54ea1960d28b2e2d121ff12"}},"merge":true},{"command":"openDialog","selector":"#drupal-modal","settings":null,"data":"\u003Cdiv id=\u0022republish_modal_form\u0022\u003E\u003Cform class=\u0022modal-form-example-modal-form ecl-form\u0022 data-drupal-selector=\u0022modal-form-example-modal-form\u0022 action=\u0022\/en\/article\/modal\/6881\u0022 method=\u0022post\u0022 id=\u0022modal-form-example-modal-form\u0022 accept-charset=\u0022UTF-8\u0022\u003E\u003Cp\u003EHorizon articles can be republished for free under the Creative Commons Attribution 4.0 International (CC BY 4.0) licence.\u003C\/p\u003E\n \u003Cp\u003EYou must give appropriate credit. We ask you to do this by:\u003Cbr \/\u003E\n 1) Using the original journalist\u0027s byline\u003Cbr \/\u003E\n 2) Linking back to our original story\u003Cbr \/\u003E\n 3) Using the following text in the footer: This article was originally published in \u003Ca href=\u0027#\u0027\u003EHorizon, the EU Research and Innovation magazine\u003C\/a\u003E\u003C\/p\u003E\n \u003Cp\u003ESee our full republication guidelines \u003Ca href=\u0027\/horizon-magazine\/republish-our-stories\u0027\u003Ehere\u003C\/a\u003E\u003C\/p\u003E\n \u003Cp\u003EHTML for this article, including the attribution and page view counter, is below:\u003C\/p\u003E\u003Cdiv class=\u0022js-form-item form-item js-form-type-textarea form-item-body-content js-form-item-body-content ecl-form-group ecl-form-group--text-area form-no-label ecl-u-mv-m\u0022\u003E\n \n\u003Cdiv\u003E\n \u003Ctextarea data-drupal-selector=\u0022edit-body-content\u0022 aria-describedby=\u0022edit-body-content--description\u0022 id=\u0022edit-body-content\u0022 name=\u0022body_content\u0022 rows=\u00225\u0022 cols=\u002260\u0022 class=\u0022form-textarea ecl-text-area\u0022\u003E\u003Ch2\u003EPlasma accelerators could overcome size limitations of Large Hadron Collider\u003C\/h2\u003E\u003Cp\u003EIf you know what a particle accelerator is, you probably think first of the Large Hadron Collider (LHC) \u2013 that gargantuan ring on the Franco-Swiss border that smashes protons and ions together, exposing the secrets of the subatomic world.\u003C\/p\u003E\u003Cp\u003EBuilt by the European lab CERN, the LHC accelerates particles to the kinds of speeds found during the eruption of the early universe. To do so, it needs a very, very big circumference \u2013 27 kilometres.\u003C\/p\u003E\u003Cp\u003EYet the LHC is already finding limits to what it can explore. Physicists want even more powerful accelerators \u2013\u0026nbsp;but building one much bigger than the LHC is hard to contemplate.\u003C\/p\u003E\u003Cp\u003EDr Ralph Assmann, a leading scientist at the German particle physics lab DESY, believes a completely different approach is needed. He thinks accelerators can be powerful, yet up to 1,000 times smaller, if they are based on a strange type of matter known as a plasma \u2013 a cloud of negative electrons and positive ions.\u003C\/p\u003E\u003Cp\u003E\u2018Plasma accelerators provide a path to energies beyond the LHC,\u2019 he said. \u2018Particle physicists must take this opportunity very seriously.\u2019\u003C\/p\u003E\u003Cp\u003E\u003Cstrong\u003ESwing\u0026nbsp;\u0026nbsp;\u0026nbsp;\u0026nbsp;\u0026nbsp;\u0026nbsp;\u0026nbsp;\u0026nbsp;\u0026nbsp;\u0026nbsp;\u0026nbsp;\u0026nbsp;\u0026nbsp;\u0026nbsp;\u0026nbsp;\u0026nbsp;\u0026nbsp;\u0026nbsp;\u0026nbsp;\u0026nbsp;\u0026nbsp;\u0026nbsp;\u0026nbsp;\u0026nbsp;\u0026nbsp;\u0026nbsp;\u0026nbsp;\u0026nbsp;\u0026nbsp; \u003C\/strong\u003E\u003C\/p\u003E\u003Cp\u003EConventional accelerators work by sending charged particles through oscillating electromagnetic fields. By switching back and forth, these fields kick the particles to an incrementally higher energy with every cycle \u2013 a bit like pushing a child on a swing.\u003C\/p\u003E\u003Cp\u003E\u003Cblockquote class=\u0022tw-text-center tw-text-blue tw-font-bold tw-text-2xl lg:tw-w-1\/2 tw-border-2 tw-border-blue tw-p-12 tw-my-8 lg:tw-m-12 lg:tw--ml-16 tw-float-left\u0022\u003E\n \u003Cspan class=\u0022tw-text-5xl tw-rotate-180\u0022\u003E\u201c\u003C\/span\u003E\n \u003Cp class=\u0022tw-font-serif tw-italic\u0022\u003E\u0026#039;Particle physicists must take this opportunity very seriously.\u0026#039;\u003C\/p\u003E\n \u003Cfooter\u003E\n \u003Ccite class=\u0022tw-not-italic tw-font-normal tw-text-sm tw-text-black\u0022\u003EDr Ralph Assmann, Leading Scientist, DESY\u003C\/cite\u003E\n \u003C\/footer\u003E\n\u003C\/blockquote\u003E\n\u003C\/p\u003E\u003Cp\u003EThe trouble with this approach is that the individual kicks \u2013 which are generated by electrical components \u2013\u0026nbsp;can only be so powerful, or the field itself will break down. High energies therefore demand lots and lots of soft kicks, which is why conventional accelerators get so big.\u003C\/p\u003E\u003Cp\u003EPlasmas, however, can sustain much bigger fields. Nearly 40 years ago, physicists discovered that if a laser pulse or a particle beam is sent into a plasma, it is possible to momentarily separate the negative and positive charges, generating a field of some 100 billion volts per metre.\u003C\/p\u003E\u003Cp\u003EAny electrons stranded in the wake of this separation are propelled forwards. The effect, like a surfer riding a wave, is known as plasma wakefield acceleration.\u003C\/p\u003E\u003Cp\u003EIn recent years, the energies accessible with plasma wakefield accelerators have risen sharply. Scientists like Dr Assmann want to increase these energies, but also to improve the stability and quality of the electron beams coming out of the accelerator.\u003C\/p\u003E\u003Cp\u003E\u003Cstrong\u003EHost of applications\u003C\/strong\u003E\u003C\/p\u003E\u003Cp\u003EThat would make plasma accelerators suitable for particle physics but also a host of other applications, including cancer treatment, medical diagnostics, security scanners and the study of advanced materials. Conventional accelerators already help with these applications, but their size and cost means that demand currently far outstrips supply.\u003C\/p\u003E\u003Cp\u003EDr Assmann is coordinating a project, EuPRAXIA, to come up with a design for the world\u2019s first plasma wakefield accelerator with an energy of five giga-electronvolts (GeV) that can actually be used for research. That is less than one-thousandth the energy of the LHC but, as Dr Assmann points out, you have to walk before you can run.\u003C\/p\u003E\u003Cp\u003E\u2018Clearly, high-field accelerators, like plasma accelerators, (are) the logical long-term solution for advancing the energy frontier in particle physics,\u2019 he said. \u2018But it will require a realistic and sustained approach.\u2019\u003C\/p\u003E\u003Cp\u003E\u003Cfigure role=\u0022group\u0022 class=\u0022@alignleft@\u0022\u003E\n\u003Cimg alt=\u0022A two-storey design limits the length of the 5 GeV EuPRAXIA plasma accelerator facility, although it could extend to 35-250m depending on what applications are added downstream. Diagram not to scale. Image credit - Horizon\u0022 height=\u0022787\u0022 src=\u0022https:\/\/horizon-magazine.eu\/research-and-innovation\/sites\/default\/files\/hm\/PlasmaAccelerator-01.png\u0022 title=\u0022A two-storey design limits the length of the 5 GeV EuPRAXIA plasma accelerator facility, although it could extend to 35-250m depending on what applications are added downstream. Diagram not to scale. Image credit - Horizon\u0022 width=\u0022983\u0022\u003E\n\u003Cfigcaption class=\u0022tw-italic tw-mb-4\u0022\u003EA two-storey design limits the length of the 5 GeV EuPRAXIA plasma accelerator facility, although it could extend to 35-250m depending on what applications are added downstream. Diagram not to scale. Image credit - Horizon\u003C\/figcaption\u003E\n\u003C\/figure\u003E\n\u003C\/p\u003E\u003Cp\u003EWith 40 labs and universities on board, EuPRAXIA will have to answer key questions, such as whether all the accelerated electrons should come from the plasma, or whether additional electrons should be fed into the machine. The design is expected to be completed towards the end of next year.\u003C\/p\u003E\u003Cp\u003EEuPRAXIA is not the only plasma accelerator project in town, however. At CERN, a powerful wakefield accelerator called AWAKE has already been built, but with a twist \u2013\u0026nbsp;it uses a proton beam to drive it.\u003C\/p\u003E\u003Cp\u003E\u003Cstrong\u003EBigger impact\u003C\/strong\u003E\u003C\/p\u003E\u003Cp\u003EProtons are more than 1,800 times more massive than electrons, which means they have a much bigger impact when it comes to dividing the charges in a plasma. According to Dr Edda Gschwendtner, the CERN project leader of the AWAKE experiment, that means a proton-driven plasma accelerator could accelerate electrons to high energies in just a single stage, rather than multiple stages, as is often proposed.\u003C\/p\u003E\u003Cp\u003EAWAKE takes the proton beam from one of CERN\u2019s existing accelerators, and in the last two years has successfully created strong plasma wakefields. This year, the goal is to actually accelerate electrons in that wakefield to energies exceeding 1 GeV.\u003C\/p\u003E\u003Cp\u003E\u003Cfigure role=\u0022group\u0022 class=\u0022@alignleft@\u0022\u003E\n\u003Cimg alt=\u0022The AWAKE experiment uses a proton beam to create a strong plasma wakefield. Image credit - CERN\u0022 height=\u0022960\u0022 src=\u0022https:\/\/horizon-magazine.eu\/research-and-innovation\/sites\/default\/files\/hm\/cern_accelerator_0.jpg\u0022 title=\u0022The AWAKE experiment uses a proton beam to create a strong plasma wakefield. Image credit - CERN\u0022 width=\u00221440\u0022\u003E\n\u003Cfigcaption class=\u0022tw-italic tw-mb-4\u0022\u003EThe AWAKE experiment uses a proton beam to create a strong plasma wakefield. Image credit - CERN\u003C\/figcaption\u003E\n\u003C\/figure\u003E\n\u003C\/p\u003E\u003Cp\u003EIn years to come, Dr Gschwendtner wants to boost AWAKE\u2019s output to several tens of GeV. That would be enough to probe certain theoretical proposals of today\u2019s particle physics \u2013\u0026nbsp;dark photons, for instance, which some physicists believe could constitute the dark matter that predominates in the universe.\u003C\/p\u003E\u003Cp\u003EPlasma accelerators still have a long way to go before they can out-perform the likes of the LHC. But when conventional accelerators are so big and costly, Dr Gschwendtner believes they could be the only way forward.\u003C\/p\u003E\u003Cp\u003E\u2018New technologies must be developed,\u2019 she said. \u2018Plasma wakefield acceleration is a very promising novel accelerator technique.\u2019\u003C\/p\u003E\u003Cp\u003E\u003Cem\u003EThe research in this article has received EU funding. 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