The High-Energy Light-Ion eXperiment (HELIX) is designed to measure the
fluxes of light cosmic-ray nuclei at energies of a few GeV per nucleon.
The primary goal is to study the evolution of the ratio of Be-10
to Be-9 between 0.2 GeV/n and 3 GeV/n. The former is a radioactive 'clock
isotope' while the latter is stable, so the ratio contains information about
how far and through what the cosmic rays have been propagating. Better
knowledge of our local environment within the Galaxy has become important
in understanding the increase with energy of the positron flux seen in
new data from the AMS-02 detector installed on the International Space
Station. Is it from dark-matter annihilation or from more conventional
HELIX is a balloon-borne detector based on a 1 T superconducting solenoid.
A drift chamber will be used to measure particle momenta while time-of-flight
counters will determine the velocities at low energies. At higher energies
a ring-imaging Cherenkov counter based on aerogel tiles and silicon
photomultipliers will take over. A 14-day circumpolar flight launched
from McMurdo Station on the coast of Antarctica has been scheduled for
the 2019/20 season.