Solenoidal transport of low-voltage (≤ 20 kV) sheet beams

This paper investigates solenoidal transport and show that it is not only feasible but preferred for certain types of devices. In particular, interest in low-voltage (<20 kV), high-power (~10 kW) W-band amplifiers has led to design an extended interaction klystron (EIK) that employs a solenoidal (~9 kG) transport configuration using permanent magnets. The much stronger magnetic field that can be achieved with a solenoidal magnet configuration allows significantly higher perveance beams to be transported, and simulations show excellent beam stability with essentially no current loss over distances of several diocotron growth lengths (typically several cm for millimeter-wave (MMW) device parameters). Semi-empirical scaling laws have been developed that relate the critical beam parameters (voltage, current density, emittance, and aspect ratio) and projected amplifier performance (power and efficiency) to the magnetic focusing strength. The implications of these relationships for the design of compact, low-voltage MMW amplifiers will be presented, and a permanent magnet solenoidal field configuration suitable for a MMW EIK will be described.