Accelerator (61, 61') for accelerating charged particles, comprising: a capacitor stack - with a first electrode, which can be brought to a first potential, - with a second electrode, which is concentrically arranged with respect to the first electrode and can be brought to a second potential that differs from the first potential, - with at least one intermediate electrode, which is concentrically arranged between the first electrode and the second electrode and which can be brought to an intermediate potential situated between the first potential and the second potential, a switching device, to which the electrodes (33, 37, 39) of the capacitor stack are connected and which is embodied such that, during operation of the switching device, the electrodes (33, 37, 39) of the capacitor stack concentrically arranged with respect to one another can be brought to increasing potential levels, a first acceleration channel, which is formed by first openings in the electrodes (33, 37, 39) of the capacitor stack such that charged particles can be accelerated by the electrodes (33, 37, 39) along the first acceleration channel, a second acceleration channel, which is formed by second openings in the electrodes (33, 37, 39) of the capacitor stack such that charged particles can be accelerated by the electrodes (33, 37, 39) along the second acceleration channel, a device (55, 59) arranged in the center of the capacitor stack, by means of which it is possible to influence the accelerated particle beam in the interior of the capacitor stack, as a result of which photons (57, 57') that are emitted by the particle beam are created, wherein, as a result of the device (55, 59), an interaction with the accelerated particle beam is created, which interaction changes the energy, the speed and/or the direction of propagation, characterized in that a spacing of the electrodes (39, 37, 33) decreases toward the center. a capacitor stack - with a first electrode, which can be brought to a first potential, - with a second electrode, which is concentrically arranged with respect to the first electrode and can be brought to a second potential that differs from the first potential, - with at least one intermediate electrode, which is concentrically arranged between the first electrode and the second electrode and which can be brought to an intermediate potential situated between the first potential and the second potential, - with a first electrode, which can be brought to a first potential, - with a second electrode, which is concentrically arranged with respect to the first electrode and can be brought to a second potential that differs from the first potential, - with at least one intermediate electrode, which is concentrically arranged between the first electrode and the second electrode and which can be brought to an intermediate potential situated between the first potential and the second potential, a switching device, to which the electrodes (33, 37, 39) of the capacitor stack are connected and which is embodied such that, during operation of the switching device, the electrodes (33, 37, 39) of the capacitor stack concentrically arranged with respect to one another can be brought to increasing potential levels, a first acceleration channel, which is formed by first openings in the electrodes (33, 37, 39) of the capacitor stack such that charged particles can be accelerated by the electrodes (33, 37, 39) along the first acceleration channel, a second acceleration channel, which is formed by second openings in the electrodes (33, 37, 39) of the capacitor stack such that charged particles can be accelerated by the electrodes (33, 37, 39) along the second acceleration channel, a device (55, 59) arranged in the center of the capacitor stack, by means of which it is possible to influence the accelerated particle beam in the interior of the capacitor stack, as a result of which photons (57, 57') that are emitted by the particle beam are created, wherein, as a result of the device (55, 59), an interaction with the accelerated particle beam is created, which interaction changes the energy, the speed and/or the direction of propagation, characterized in that a spacing of the electrodes (39, 37, 33) decreases toward the center.