In impulsive flares, the streaming 10-100 keV electrons, that are
seen by the type III radio bursts and hard X-rays they produce,
form velocity distributions that are unstable for production of
hydrogen electromagnetic ion cyclotron (EMIC) waves [
Temerin and Roth 1992]. The frequencies of these
waves lie between the gyrofrequencies of H and of 
He. The
rare isotope 
He is the only species whose gyrofrequency lies
in this range to resonantly absorb these waves. The waves are
only produced in a regions of high magnetic field near the base
of the corona where the Alfv‚n speed is >2000 km/s. The
acceleration is extremely efficient, in fact, the observed number
of 
He ions in space requires the acceleration of >10% of
the 
He in a typical flare volume near the base of the corona
[ Reames 1993].
Heavy ions probably interact with other wave modes produced
below the 
He gyrofrequency [ Miller and Viñas 1993],
and their enhancements are more modest [see Mason et al 1986;
Reames et al. 1994]. The similar enhancements of Ne, Mg and
Si suggest that those species have similar gyrofrequencies. This
only occurs if acceleration begins at a plasma temperature of
3 MK [ Reames et al 1994].
Acceleration of the ions we observe at 1 AU probably occurs on
open magnetic field lines, but there is gamma-ray evidence that
the ions are accelerated on closed loops by the same mechanism.
The broad gamma-ray lines, produced by ions in the energetic
beam, show the same pattern of heavy-element enhancements and the
low proton/
He ratio (
1.0) that is seen in the 
He-rich
events at 1 AU [ Murphy et al 1991]. Unfortunately,
the 
He/
He ratio itself cannot be measured with gamma-ray
line spectroscopy.
The particles accelerated in gamma-ray events at the Sun can
produce intense particle events with hard spectra near Earth
[ Van Hollebeke, McDonald and Meyer
1990]. Partly because of the small longitude cone, however, they
are relatively rare. Some well-connected events also show the
presence of both impulsive and gradual components, with
Fe/O
1 early in the event falling to Fe/O
0.1 later in
the gradual phase of the event [ Reames 1990b].