Pepperpot Emittance Measurement System: Current Status Simon Jolly Imperial College FETS Meeting, 10/05/06

10/05/06Simon Jolly, Imperial College 2 Pepperpot Principle H - Ion Beam Tungsten screen Copper block Phosphor screen H - Beamlets Fast CCD Camera Beam segmented by tungsten screen. Drift length of ~12mm allows beamlets to expand. Beamlets produce image on phosphor screen. Copper block prevents beamlets from overlapping. CCD camera records image of light spots.

10/05/06Simon Jolly, Imperial College 3 FETS Pepperpot System (PJS) Complete Pepperpot assembly: Screen assembly produces beamlets and image on phosphor. Camera (+ lens) records phosphor image. Support structure “stolen” from previous system at RAL. Longitudinal motion from screw thread.

10/05/06Simon Jolly, Imperial College 4 Complete Pepperpot System Assembled Pepperpot System at IC Bellows Camera + lens Vacuum flange Pepperpot block + mount

10/05/06Simon Jolly, Imperial College 5 Pepperpot Calibration Images Calibration Images from setup at IC

10/05/06Simon Jolly, Imperial College 6 Pepperpot Data (run 1) Calibration ImageIon Source Background

10/05/06Simon Jolly, Imperial College 7 Run 1 Observations Ran with no platform voltage, varying extract voltage. An image was produced by the beam which the camera could record. An image appeared on the screen even when there was supposed to be NO BEAM (ie. platform voltage off) - very faint. This “background” beam behaved like it should ie. could be steered by changing exctract V and magnet I. With platform voltage at 35kV, image looks reasonable (no analysis yet) but much too faint: should be LOTS of light. Vacuum leak in main seal: clear when system dismantled.

10/05/06Simon Jolly, Imperial College 8 Pepperpot Data (Run 2) 1 Ion Source Background (run 1)Run 2: Platform 0kV

10/05/06Simon Jolly, Imperial College 9 Pepperpot Data (Run 2) 2 Run 2: Platform 5kVRun 2: Platform 10kV

10/05/06Simon Jolly, Imperial College 10 Pepperpot Data (Run 2) 3 Run 2: Platform 16.5kVRun 2: Platform 17.5kV

10/05/06Simon Jolly, Imperial College 11 Pepperpot Data (Run 2) 4 Run 2: Platform 25kVRun 2: Platform 35kV

10/05/06Simon Jolly, Imperial College 12 Beam Damage Pepperpot front plate (tungsten screen and aluminium mount) showing damage from beam impact. Note: the beam is larger than the exposed tungsten, even at this shorter z position.

10/05/06Simon Jolly, Imperial College 13 Run 2 Observations Ran with extract voltage & magnet current fixed & varied platform voltage. Could see effect of increasing platform voltage, as well as beam change shape with Kr gas. Interesting effects with platform voltage ~17kV: definite change in beam shape either side of this transition. Main image still very faint:  Current “good” at ~12mA from toroid.  Problems with phosphor: see Jürgen’s talk. Pepperplot plate too small: can still make measurements, but perhaps redesign with better tungsten plate & phosphor.

10/05/06Simon Jolly, Imperial College 14 Image Analysis Need a prediction of image centre and tilt: Use previous calibration image to relate image centre to ends of rulers. Use calibration image before each data run to mark ruler position and determine PP centre and tilt. Use “light box” data to record hole centres and sizes (till we have better data). Correlate hole positions to ruler measurement

10/05/06Simon Jolly, Imperial College 15 Next steps Complete calibration & analysis software in Matlab:  Need prediction of actual hole location before we can calculate emittance.  Alignment comes from “ruler” image: correlate to hole position using test data. Fix vacuum leaks (new seals/bellows). Make improved hole size measurements on tungsten screen. Improved tungsten screen with 50  m holes. Take some real data…