Depressed collector/ribbon electron beam analyzer for a diffraction radiation generator

A diffraction radiation generator comprising:

• an open resonator including a diffraction grating extending between opposite ends of the open resonator;
• beam forming means for generating a ribbon electron beam, which is disposed adjacent one end of the open resonator and which includes a cathode and an anode;
• a collector, spaced from an opposite end of the open resonator, for receiving the ribbon beam;
• at least two conductive elements disposed between the open resonator and the collector and having respective slits therethrough to accommodate the ribbon beam, the at least two elements including a first element adjacent the open resonator and a last element adjacent the collector;
• beam directing means for directing the ribbon beam generated by the beam forming means across the diffraction grating and through the slits of the at least two elements to the collector;
• and
• voltage supply means for supplying direct voltages to the cahode, the anode, the at least two elements, and the collector, respectively, wherein the cathode voltage is the lowest or most negative voltage, the first element voltage is lower than the diffraction grating voltage, the voltage of each remaining element is lower than the voltage of the adjacent preceding element, and the collector voltage is lower than the last element voltage such that heating of the collector is minimized and the operating efficiency of the generator is increased.

A diffraction radiation generator comprising:

• an open resonator;
• a metallic diffraction grating disposed within the open resonator;
• beam forming means for generating a ribbon electron beam, which is disposed on one side of the open resonator and which includes a cathode and an anode;
• first voltage supply means for supplying direct voltages to the cathode, the anode, and the diffraction grating, respectively, wherein the anode voltage and the grating voltage are positive relative to the cathode voltage;
• beam directing means for directing the ribbon beam along a path extending through the open resonator across the diffraction grating;
• and
• a depressed collector/beam analyzer assembly which comprises
• a collector for receiving the ribbon beam, which is disposed in the beam path on an opposite side of the open resonator,
• at least two electrically conductive elements disposed between the open resonator and the collector and having respective slits disposed in the beam path to accommodate the ribbon beam directed therethrough by the beam directing means, said at least two elements including a first element adjacent the open resonator and a last element adjacent the collector,
• second voltage supply means for supplying selected adjustable direct voltages to the collector and the at least two elements, respectively, and
• current measuring means for measuring the collector current;
• wherein said assembly serves as a depressed collector when the voltages supplied by the second voltage supply are selected such that the first element voltage is negative relative to the grating voltage, the voltage of each remaining element is negative relative to the voltage of the adjacent preceding element, and the collector is negative relative to the voltage of the last element and is positive relative to the cathode voltage;
• and
• wherein said assembly serves as a ribbon electron beam analyzer when the voltages supplied by the second voltage supply means are selected such that the collector and the first element are maintained at approximately anode voltage, a series of selected voltages are sequentially supplied to the second element over a voltage range extending from a voltage above the cathode voltage which does not change the collector current to a voltage below the cathode voltage at which the collector current is zero, and any remaining elements are maintained at approximately anode voltage, the measured collector current at each selected second element voltage indicating the number of electrons in the ribbon beam having a velocity greater than the velocity corresponding to the selected second element voltage.

A method of generating coherent radiation, comprising the simultaneous steps of:

• applying direct voltages to a cathode and an anode of an electron gun to generate a ribbon electron beam, the anode voltage being greater, i.e., more positive, than the cathode voltage;
• directing the ribbon beam along a path extending over a metallic diffraction grating within an open resonator and through aligned slits in at least two electrically conductive elements to a collector, the at least two elements including a first element adjacent the open resonator and a last element adjacent the collector;
• applying a direct voltage to the diffraction grating which is greater than the cathode voltage so as to cause the generation of coherent radiation within the open resonator;
• applying a direct voltage to the first element which is less than the diffraction grating voltage to create an electric field along the beam path between the diffraction grating and the first element causing deceleration of the electrons forming the ribbon beam;
• applying a direct voltage to each remaining element which is less than the voltage applied to the adjacent preceding element to create an electric field along the beam path between each remaining element and the adjacent preceding element causing further deceleration of the electrons forming the ribbon beam;
• and
• applying a direct voltage to the collector which is greater than the cathode voltage and less than the last element voltage to create an electric field along the beam path between the last element and the collector causing final deceleration of the electrons forming the ribbon beam such that heating of the collector is minimized and the operating efficiency of the generator is increased.