Linac4 BPMs: issues after 3MeV tests

1. Linac4 BPMs: issues after 3MeV tests • Beam observables: • position H&V, intensity, phase variation, TOF, energy • Contents: • Results and issues already solved • Issues in progress • MD list for open issues CERN, Beam Coordination Committee. BPMs for Linac4: issues. 27 june 2013 Michael Ludwig for the BPML4 team slide1

2. Results and Issues already solved • position precision is very good, results from SVD analysis with Linac2 beam: <10um at 50mA p+Linac2 • Run theoretical calibration with good confidence • Electronics noise bashed successfully (now: ~10uA beam): grounding improved • Measurements contributing to 3MeV understanding: • Found 2MHz oscillation of the beam, coming from the source (plasma generation frequency). • Losses on 3rd pickup: beam touching the pipe/PUelectrodes due to beam size and steering • Slit postitonmeasurement intensity<1% => out of specs • Chopping amplitude gives V position deflection: A=50%=>beam touches lower V electrode CERN, Beam Coordination Committee. BPMs for Linac4: issues. 27 june 2013 Michael Ludwig for the BPML4 team slide2

3. Results and Issues already solved (2) • Centering beam on SEM (using spectrometer bending) reveals off-center beam: line issue • TOF configuration issue found and solved for 3rd pickup: realistic results with ~1% variation. TOF looks good, encouraging. • FEC Software stable production mode, ergonomic GUIs in progress. Mathematica interface (1), MD scripting interface • (1): see https://edms.cern.ch/file/1289924/1/rdaMathApplication_v3.pdf CERN, Beam Coordination Committee. BPMs for Linac4: issues. 27 june 2013 Michael Ludwig for the BPML4 team slide3

4. BPML4: Issues in progress • Short cables force short calibration pulses, calibration precision was ~10% shot-by-shot. Will improve with longer cables and calibration precision-averaging • Attenuator settings for the BPMs: not tested yet with beam • Timing jitter phase between RF gun start and ADC start sampling is not fully stable. Similar symptom observed with BCT. No show stopper, but should be understood & fixed for serious TOF. • Don’t fully understand transfer impedance Zt : simulation and measurement disagree by ~x2 • Zt depends on dp/p and on the beam size for beta <<1: need to quantify relatively • Electronics saturation above 2.5Vpp CERN, Beam Coordination Committee. BPMs for Linac4: issues. 27 june 2013 Michael Ludwig for the BPML4 team slide4

5. BPML4: MD lists for open issues • We need to do: • Classical steering exercise with beam: fine scanning • Some energy scanning to qualify TOF fully: error estimates • Some intensity scanning (source?) to detect normalization errors and quantify them • Better definition of beam “head” and “tail” from OP: ROI settings just estimated until now, but can do much better. • We need a dipole at entry of test bench & pencil beam • Should do a full optics scan: “permutations of quads, dipoles”, record all currents and BCT, BPM. Need just 3 shots per setting, should be powerful, should confirm optics model, get ready for ABS later. CERN, Beam Coordination Committee. BPMs for Linac4: issues. 27 june 2013 Michael Ludwig for the BPML4 team slide5

6. BPML4: Proposals &Conclusions • Proposals & Conclusions • Should have one full crate with 8 BPMs installed soon: had no chance until now. We’ll split some signals and get close to this in L4. • BPM crates must be inside faraday cage (OK with 352.2MHz): interventions, final setup, grounding • we didn’t have enough beam time for the BPM system in the 3MeV test stand: very little systematic data taking • BPML4 progressed a lot nevertheless CERN, Beam Coordination Committee. BPMs for Linac4: issues. 27 june 2013 Michael Ludwig for the BPML4 team slide6