An improved diode for forming an intense electron beam and propagating theeam. The diode includes a cathode having a bore, and a rod-shaped anode having a medial tapered section which extends, approximately coaxially, through the bore of the cathode. The anode tapers at or near the cathode and is formed from electrically conductive material. The cathode is made from a material which rapidly emits electrons during the early stage of an applied voltage pulse. The electrons strike the anode and form a plasma thereon. Sufficient anode current and the formation of sufficient anode plasma affect the magnetic and electric fields to pinch the electrons closer to each other and to force the electron beam to propagate along the anode and away from the cathode and voltage supply. The tapered section of the anode increases the velocity of the pinch and the density of the electron beam.