  We investigate the physical processes occuring in the multiphase gas of a
damped Ly\alpha system (DLA). We base our analysis on a high quality Keck HIRES
spectrum of the QSO J1211+0422 in which a DLA is detected at z=2.377. There is
little contamination of the high-ion (OVI, NV, CIV, SiIV) absorption, allowing
us to explore the properties of the highly ionized gas and its connection to
other gas-phases. The metallicity ([Z/H]=-1.41+/-0.08), HI column density (log
N(HI)=20.80+/-0.10), full-width velocity (\Delta(v_ neut)=70 km/s) and relative
abundances ([Si/Fe]=+0.23+/-0.05 and [N/Si]=-0.88+/-0.07) of this DLA are not
unusual. However, we derive the lowest CII* cooling rate in a DLA, l_c <
10^{-27.8} erg/s per H atom (3\sigma). Using this stringent limit, we show that
the neutral gas (confined at |v|<+39 km/s) must be warm and the star formation
rate is <7.1x10^{-3} M_odot/yr/kpc^2. Surprisingly, the gas shows strong,
complex absorption profiles from highly ionized gas whose kinematics appear
connected to each other and the low ions. The total amount of highly and weakly
ionized gas is very large with N(HII)/N(HI)>1.5. At |v|>+39 km/s, the gas is
fully and highly ionized (H+/H~1, N(CIV)>>N(CII), N(SiIV)>>N(SiII)). Based on
ionization models, OVI and NV are generally difficult to produce by hard
photons, while SiIV and CIV can be photoionized to a large extent. There is,
however, no evidence of OVI-bearing gas at T~10^6 K associated with this DLA.
In contrast, there is some evidence for narrow OVI, NV, and CIV components
(unexplained by photoionization), implying too low temperatures (T < 10^5 K)
for simple collisional ionization models to produce their observed column
densities. Stellar feedback is a possible source for producing the high ions,
but we cannot rule out accretion of non-pristine material onto the protogalaxy.
