Design and Testing of a Prototype Beam Absorber for the PXIE MEBT

Abstract

One of the goals of the PXIE program at Fermilab [1] is to demonstrate the capability to form an arbitrary bunch pattern from an initially CW 162.5 MHz H-bunch train coming out of an RFQ. The bunch-by-bunch selection will take place in the 2.1 MeV Medium Energy Beam Transport (MEBT) [2] by directing the undesired bunches onto an absorber that needs to withstand a beam power of up to 21 kW, focused onto a spot with a ~2 mm rms radius. A prototype of the absorber was manufactured from molybdenum alloy TZM, and tested with an electron beam up to the peak surface power density required for PXIE, 17W/mm 2 . Temperatures and flow parameters were measured and compared to analysis. This paper describes the absorber prototype and key testing results.

Design and Testing of a Prototype Beam Absorber for the PXIE MEBT

“…After correcting for systematic errors associated with thermocouple mounting (see [5]), simulations agreed well with measurements, and tended to under-predict the observed temperature rise by 3-10%.…”

“…A variety of optical filters of varying central wavelength were used to separate OTR (broad band and light intensity linear with current) from thermal radiation (typically longer wavelength and light intensity strongly non-linear with surface temperature). These methods are further described in [5].…”

“…Temperatures within the absorber body are monitored by an array of thermocouples. A more comprehensive description of the prototype, testing methods and results is given in [5].…”

“…Predicted surface temperatures were compared to temperature estimates calculated from thermal radiation. As described in [5], fitting parameters used in the radiation calculations were adjusted to optimize fit with FEA simulation, so any agreement better than the inherent uncertainty of the optical measurement (±150K) is, to some extent, enforced. However, some encouragement is taken from the similarity with which analysis and measurement reconstruct fine structure within the temperature profile.…”