The CERN Linear Electron Accelerator for Research

What is CLEAR?

The primary focus for the The CERN Linear Electron Accelerator for Research (CLEAR) is general accelerator R&D and component studies for existing and possible future machines at CERN, based on a broad internal and external user community. The program covers two of the top priorities identified by the European Strategy for Particle Physics, namely the prototyping and validation of accelerator components for the upgrade of the Large Hadron Collider and its injector chain, and studies of high-gradient acceleration methods. The latter cover X-band studies for linear accelerators and also novel concepts as plasma and THz acceleration. CLEAR also provides unique training possibilities, as well as irradiation test capability, of which is worth mentioning a collaboration with the European Space Agency (ESA).

The facility proposal document is available on cds.

View on Beam Instrumentation Test Stand at CLEAR


The Beam Line

The CLEAR facility is hosted by the CLEX experimental area at CERN - building 2010. The CLEAR Beam Line is built on the basis of CALIFES, previously used at CTF3 as Probe Beam injector for testing the CLIC Two Beam Acceleration concept.

On the spectrometer at the end of the CALIFES injector is placed the VESPER (see its official web page): a test stand for irradiation studies.

The layout of the linear accelerator and VESPER is as follows (note that beam travels from right to left):

CALIFES Injector line

The 2nd part of the line, which contains most of the experiments:

Experimental line layout

Legend for the layouts above is:

Layout legend

Various other versions of the drawing above can be found at ; if used in publications please cite K. Sjobak et al, "Status of the CLEAR Electron Beam User Facility at CERN", in proceedings of IPAC2019 (Melbourne), May 2019, MOPTS054, doi:10.18429/JACoW-IPAC2019-MOPTS054, .

Technical Drawings of the facility are available on request.

Beam Parameters

The beam parameters at the end of the linac are summarised in the following table:

Beam parameter (end of linac) Value range
Energy 60 - 220 MeV
Bunch charge 0.01 - 1.5 nC
Normalized emittances 3 um for 0.05 nC per bunch
20 um for 0.4 nC per bunch (in both planes)
Bunch length ~100 um - 1.2 mm
Relative energy spread < 0.2 % rms (< 1 MeV FWHM)
Repetition rate 0.8 - 10 Hz
Number of micro-bunches in train 1 - 150
Micro-bunch spacing 1.5 or 3.0 GHz

CLEAR Beam Structure

Beam line MAD-X Lattice

The MAD-X sequence of the present beam line is available on the official CERN Gitlab Optics Repository.