  This paper presents a new technique to study the adsorption and desorption of
ions and electrons on insulating surfaces in the presence of strong electric
fields in cryoliquids. The experimental design consists of a compact cryostat
coupled with a sensitive electro-optical Kerr device to monitor the stability
of the electric fields. The behavior of nitrogen and helium ions on a
poly(methyl methacrylate) (PMMA) surface was compared to a PMMA surface coated
with a mixture of deuterated polystyrene and deuterated polybutadiene. Ion
accumulation and removal on these surfaces were unambiguously observed. Within
the precision of the data, both surfaces behave similarly for the physisorbed
ions. The setup was also used to measure the (quasi-)static dielectric constant
of PMMA at T = 70 K. The impact of the ion adsorption on the search for a
neutron permanent electric dipole moment in a cryogenic environment, like the
nEDM@SNS experiment, is discussed.
