James R Pogge

Beam in gap measurements at the SNS front-end

The pulsed beam in the SNS accelerator has a fine time structure which consists of 695 ns long mini-pulses separated by 250 ns gaps in order to minimize transient beam losses in the accumulator ring which could arise during the ring extraction kicker rise time. This time structure is provided by a two stage Front End chopping system which must reduce the beam current in the gap to a level of 10/sup -4/ of the nominal current in order to satisfy requirements on the ring extraction losses. A Beam-in-Gap measuring system based on H/sup -/ stripping using Nd-YAG laser was developed and tested during the SNS Front-End commissioning period. This paper describes the Beam-in-Gap measurement system design and measured performance.

The Spallation Neutron Source Beam Commissioning and Initial Operations

The Spallation Neutron Source (SNS) accelerator delivers a one mega-Watt beam to a mercury target to produce neutrons used for neutron scattering materials research. It delivers ~ 1 GeV protons in short (< 1 us) pulses at 60 Hz. At an average power of ~ one mega-Watt, it is the highest-powered pulsed proton accelerator. The accelerator includes the first use of superconducting RF acceleration for a pulsed protons at this energy. The storage ring used to create the short time structure has record peak particle per pulse intensity. Beam commissioning took place in a staged manner during the construction phase of SNS. After the construction, neutron production operations began within a few months, and one mega-Watt operation was achieved within three years. The methods used to commission the beam and the experiences during initial operation are discussed.

SNS Ring and RTBT Beam Current Monitor

The SNS Diagnostics Group has implemented Beam Current Monitors (BCM) for the Ring and RTBT (Ring to Target Beam Transferline). In the Ring, the BCM must handle a thousand‐fold increase of intensity during the accumulation, and in the RTBT, the BCM must communicate the integrated charge of the beam pulse in real‐time for every shot to the target division for correlation with the produced neutrons. This paper describes the development of a four channel solution for the Ring BCM and the use of FPGA for the RTBT BCM to deliver the total charge to the target over a fiber optic network. Both system versions are based on the same commercial digitizer board.