Can lightly-ionized atoms be accelerated to relativistic speeds with current technology?

In relativistic heavy-ion collisions, you're usually interested in reactions with much higher energy than the kilo-eV scale of a few dozen bound electrons. A typical RHI collision will have something like 10,000 particles in the final state, so a few dozen bound electrons in the initial state won't make much difference either.

What does make a difference is the charge-to-mass ratio. A massive, charged particle in an electric field will have an acceleration $a$ that obeys $$ F = ma = qE,quadtext{or}quad a = Efrac qm. $$ By "stripping" all the electrons from a nucleus you get a much larger $q/m$, and so you get more energy per ion for the same electric field $E$. That's what the high-energy, quark-gluon plasma folks are after.

However, there are other applications where you might want a singly-ionized nucleus — for instance, to use for atomic or molecular spectroscopy, perhaps loaded into a Penning trap. In that case, between your ion source and your accelerator you have to have some magnetic steering of the beam, which separates the beam by species with different $q/m$. If you went to a nuclear structure laboratory and asked for a beam of singly-ionized calcium at $frac34c$, they would probably say "calcium-40? -44? -48? or one of the rare or unstable calciums?"

Searching the web for "ion beam spectroscopy" finds

• an old review article which says that "fast ion beams" typically have energies of 10–10⁵ eV.

• at the recently-closed Holifield rare-isotope accelerator an ion spectroscopy facility "… with negatively- as well as positively-charged ions … of exotic nuclei like, e.g., ⁷⁹Cu and ⁸⁵Ga … [at] energies of about 200 keV." This facility was probably for nuclear spectroscopy, rather than electronic transitions, but the inner-shell electrons in heavy atoms are fast and can have a big effect on nuclear properties.

• a recent conference proceeding describes spectroscopy of a $lambda approx 600,mathrm{nm}$ transition in Ar⁺ ions in a 20 keV beam.

The argon-ion beam should appeal to your interest in special relativity. The ion beam wasn't dramatically relativistic, having $gamma-1 = frac{text{kinetic energy}}{mc^2} approx frac12times10^{-6}$. But the transition frequency was measured with a precision ${Deltanu}/{nu} approx 6times10^{-10}$. A change in beam energy of 1 eV, about one part in 10⁴, changed the frequency of the resonance by nearly fifty times the experimental uncertainty. This is the power of precision experiments, that there are complementary ways to access the stranger corners of the world: by going there directly, where the strange effects are obvious, or by looking very carefully where the strange effects are subtle. The argon-ion paper has some very interesting references.