\author{
J.\ A.\ Ballin$^a$,
R.\ Coath$^b$,
J.\ P.\ Crooks$^b$,
P.\ D.\ Dauncey$^a$\thanks{Corresponding author},
A.-M.\ Magnan$^a$,
Y.\ Mikami$^c$\thanks{Current address: Institut Pluridisciplinaire Hubert CURIEN, 23 rue du loess - BP28, 67037 Strasbourg CEDEX 2, France.},
O.\ D.\ Miller$^c$,
M.\ Noy$^a$\thanks{Current address: CERN, CH-1211 Gen\`eve 23, Switzerland.},
V.\ Rajovic$^c$\thanks{Current address: Faculty of Electrical Engineering, University of Belgrade, Bulevar kralja Aleksandra 73, 11120 Belgrade, Serbia.},
M.\ Stanitzki$^b$,
K.\ D.\ Stefanov$^b$\thanks{Current address: Sentec Ltd, Cambridge, UK.},
R.\ Turchetta$^b$,
M.\ Tyndel$^b$,
E.\ G.\ Villani$^b$,
N.\ K.\ Watson$^c$,
J.\ A.\ Wilson$^c$,
Z.\ Zhang$^b$\\
\llap{$^a$}Department of Physics,
Blackett Laboratory,
Imperial College London,
Prince Consort Road,
London, U.K.\\
\llap{$^b$}PP Division,
STFC,
Rutherford Appleton Laboratory,
Chilton, Didcot, U.K.\\
\llap{$^c$}School of Physics and Astronomy,
University of Birmingham,
Edgbaston,
Birmingham, U.K.\\
\\
E-mail: \email{P.Dauncey@imperial.ac.uk}
}
