Editing Linear particle accelerator (section)

== Concepts in development ==
Various new concepts are in development as of 2021. The primary goal is to make linear accelerators cheaper, with better focused beams, higher energy or higher beam current.

=== Induction linear accelerator ===
Induction linear accelerators use the electric field induced by a time-varying magnetic field for acceleration—like the [[betatron]]. The particle beam passes through a series of ring-shaped [[ferrite core]]s standing one behind the other, which are magnetized by high-current pulses, and in turn each generate an electrical field strength pulse along the axis of the beam direction. Induction linear accelerators are considered for short high current pulses from electrons but also from heavy ions.<ref>{{Cite web|date=2002-06-25|title=Heavy ions offer a new approach to fusion|url=https://cerncourier.com/a/heavy-ions-offer-a-new-approach-to-fusion/|access-date=2021-01-22|website=CERN Courier|language=en-GB}}</ref> The concept goes back to the work of [[Nicholas Christofilos]].<ref>{{Cite journal|last1=Christofilos|first1=N. C.|last2=Hester|first2=R. E.|last3=Lamb|first3=W. a. S.|last4=Reagan|first4=D. D.|last5=Sherwood|first5=W. A.|last6=Wright|first6=R. E.|date=1964-07-01|title=High Current Linear Induction Accelerator for Electrons|url=https://aip.scitation.org/doi/10.1063/1.1746846|journal=Review of Scientific Instruments|volume=35|issue=7|pages=886–890|doi=10.1063/1.1746846|bibcode=1964RScI...35..886C|issn=0034-6748|url-access=subscription}}</ref> Its realization is highly dependent on progress in the development of more suitable [[Ferrite (magnet)|ferrite]] materials. With electrons, pulse currents of up to 5 kiloamps at energies up to 5 MeV and pulse durations in the range of 20 to 300 nanoseconds were achieved.<ref>{{Cite journal|last=Fraas|first=H.|date=1989|title=Kern- und Elementarteilchenphysik. Von G. Musiol, J. Ranft, R. Reif und D. Seeliger, VCH Verlagsgesellschaft Weinheim, 1988, DM 128|url=http://adsabs.harvard.edu/abs/1989PhuZ...20...31F|journal=Physik in unserer Zeit|volume=20|issue=1|pages=31|doi=10.1002/piuz.19890200109|bibcode=1989PhuZ...20...31F|issn=0031-9252}}</ref>

=== Energy recovery linac ===
In previous electron linear accelerators, the accelerated particles are used only once and then fed into an absorber ''(beam dump)'', in which their residual energy is converted into heat. In an energy recovery linac (ERL), the accelerated in resonators and, for example, in [[undulator]]s. The electrons used are fed back through the accelerator, out of phase by 180 degrees. They therefore pass through the resonators in the decelerating phase and thus return their remaining energy to the field. The concept is comparable to the hybrid drive of motor vehicles, where the kinetic energy released during braking is made available for the next acceleration by charging a battery.

The [[Brookhaven National Laboratory]] and the [[Helmholtz-Zentrum Berlin]] with the project "bERLinPro" reported on corresponding development work. The Berlin experimental accelerator uses superconducting niobium cavity resonators. In 2014, three [[free-electron laser]]s based on ERLs were in operation worldwide: in the [[Thomas Jefferson National Accelerator Facility|Jefferson Lab]] (US), in the [[Budker Institute of Nuclear Physics]] (Russia) and at JAEA (Japan).<ref>{{Cite book|url=https://www.springer.com/gp/book/9783319143934|title=Synchrotron Light Sources and Free-Electron Lasers: Accelerator Physics, Instrumentation and Science Applications|date=2016|publisher=Springer International Publishing|isbn=978-3-319-14393-4|editor-last=Jaeschke|editor-first=Eberhard|language=en|editor-last2=Khan|editor-first2=Shaukat|editor-last3=Schneider|editor-first3=Jochen R.|editor-last4=Hastings|editor-first4=Jerome B.}}</ref> At the [[University of Mainz]], an ERL called MESA is expected to begin operation in 2024.
<ref>{{cite journal |last1=Hug |first1=Florian |last2=Aulenbacher |first2=Kurt |last3=Heine |first3=Robert |last4=Ledroit |first4=Ben |last5=Simon |first5=Daniel |title=MESA - an ERL Project for Particle Physics Experiments |journal=Proceedings of the 28th Linear Accelerator Conf. |date=2017 |volume=LINAC2016 |pages=313–316 |doi=10.18429/JACoW-LINAC2016-MOP106012 |url=https://inspirehep.net/literature/1633150 |access-date=18 August 2024}}</ref>

=== Compact Linear Collider ===
The concept of the [[Compact Linear Collider]] (CLIC) (original name CERN Linear Collider, with the same abbreviation) for electrons and positrons provides a traveling wave accelerator for energies of the order of 1 tera-electron volt (TeV).<ref>{{Cite book|last=Raubenheimer|first=T. O.|title=A 3 TeV e+e− linear collider based on CLIC technology|publisher=|year=2000|isbn=92-9083-168-5|location=Geneva|pages=}}</ref> Instead of the otherwise necessary numerous [[klystron]] amplifiers to generate the acceleration power, a second parallel electron linear accelerator of lower energy is to be used, which works with superconducting cavities in which standing waves are formed. High-frequency power is extracted from it at regular intervals and transmitted to the main accelerator. In this way, the very high acceleration field strength of 80 MV / m should be achieved.

=== Kielfeld accelerator (plasma accelerator) ===
In cavity resonators, the dielectric strength limits the maximum acceleration that can be achieved within a certain distance. This limit can be circumvented using accelerated waves in plasma to generate the accelerating field in [[Plasma acceleration|Kielfeld accelerators]]: A laser or particle beam excites an oscillation in a [[Plasma (physics)|plasma]], which is associated with very strong electric field strengths. This means that significantly (factors of 100s to 1000s ) more compact linear accelerators can possibly be built. Experiments involving high power lasers in metal vapour plasmas suggest that a beam line length reduction from some tens of metres to a few cm is quite possible.

===Compact medical accelerators ===
The LIGHT program (Linac for Image-Guided Hadron Therapy) hopes to create a design capable of accelerating protons to 200MeV or so for medical use over a distance of a few tens of metres, by optimising and nesting existing accelerator techniques <ref>{{Cite web| url=http://cdsweb.cern.ch/record/2314160/files/frb1io02.pdf| title =LIGHT: A LINEAR ACCELERATOR FOR PROTON THERAPY}}</ref> The current design (2020) uses the highest practical bunch frequency (currently ~ 3&nbsp;GHz) for a [[Radio-frequency quadrupole]]  (RFQ) stage from injection at 50kVdC  to ~5MeV bunches,  a  Side  Coupled  Drift  Tube  Linac  (SCDTL) to accelerate from 5Mev to ~ 40MeV and a Cell Coupled Linac (CCL) stage final, taking the output to 200-230MeV. Each stage is optimised to allow close coupling and synchronous operation during the beam energy build-up.
The project aim is to make proton therapy a more accessible mainstream medicine as an alternative to existing radio therapy.