  The Antiproton Decelerator of CERN began operation in 1999 to serve
experiments for studies of CPT invariance by precision laser and microwave
spectroscopy of antihydrogen ($\bar{\rm H}$) and antiprotonic helium
($\bar{p}{\rm He}^+$). The first 12 years of operation saw cold $\bar{\rm H}$
synthesized by overlapping clouds of positrons ($e^+$) and antiprotons
($\bar{p}$) confined in magnetic Penning traps. Cold $\bar{\rm H}$ was also
produced in collisions between Rydberg positronium atoms and $\bar{p}$.
Ground-state $\bar{\rm H}$ was later trapped for up to $\sim 1000$ s in a
magnetic bottle trap, and microwave transitions excited between its hyperfine
levels. In the $\bar{p}{\rm He}^+$ atom, UV transitions were measured to a
precision of (2.3-5) $\times$ $10^{-9}$ by sub-Doppler two-photon laser
spectroscopy. From this the antiproton-to-electron mass ratio was determined as
$M_{\bar{p}}/m_e=$1836.1526736(23), which agrees with the p value. Microwave
spectroscopy of $\bar{p}{\rm He}^+$ yielded a measurement of the $\bar{p}$
magnetic moment with a precision of 0.3%. More recently the magnetic moment of
a single $\bar{p}$ confined in a Penning trap was measured with a higher
precision, as $\mu_{\bar{p}}=-2.792845(12)$$\mu_{\rm nucl}$ in nuclear
magnetons. Other measurements include the energy loss of 1-100 keV $\bar{p}$
traversing conductor and insulator targets; the cross sections of <10 keV
$\bar{p}$ ionizing gas targets; and the cross sections of 5-MeV $\bar{p}$
annihilating on target foils via nuclear collisions. The biological
effectiveness of $\bar{p}$ beams destroying cancer cells was measured as a
possible method for radiological therapy. New experiments under preparation
attempt to measure the gravitational acceleration of $\bar{\rm H}$ or
synthesize $\obar{\rm H}^+$.
