LINAC 4 source & LEBT measurement results L4 BI Review 18-Oct-2011 F. Roncarolo U.Raich, B.Cheymol BE-BI L.M. Hein BE-ABP Many thanks to many other colleagues

Contents Source and LEBT test stand introduction Diagnostics park Emittance meter bias rings optimization SEM grid, BCT and emittance measurement examples Beam parameters and LEBT line characterization to date Transmission RFQ matching BI L4 review - 18 Oct 2011 F. Roncarolo

Introduction Diagnostics Test stand installed since 2010 Operated with 35 keV H- and 45 keV Protons (tests still on-going) BI L4 review - 18 Oct 2011 Diagnostics Faraday’s Cup + SEM grid (H+V) after 1st solenoid SEM grid (H) in spectrometer line Beam Current Transformer between two solenoids Emittance-Meter slit&grid (H+V) Faraday Cup integrated in SEM grid tank Will remain in the Linac4 tunnel LEBT F. Roncarolo Used at different stages during the test stand and then Linac 4 tunnel commissioning

LEBT Final configuration BCT Faraday’s Cup H+V SEM grid BI L4 review - 18 Oct 2011 F. Roncarolo

LEBT Commissioning Stages Source Emittance meter Faraday’s Cup Faraday Cup + SEM Grid Sol. 1 Sol. 2 Slit SEM grid Completed with 35 keV H- and 45 keV Protons 1 Faraday’s Cup BI L4 review - 18 Oct 2011 2 Completed with 45 keV Protons 3 RFQ Input F. Roncarolo 4 Stage 4 just completed Now: will re-check stage 1 while re-arranging LEBT to host RFQ (Jan 2011) Beam Current Transformer (BCT)

Faraday Cup and BCT Beam Current Transformer Read-out with 2 channels CH1: Fast relative charge evolution CH2: Average charge with time and total charge in 400us pulse Down to 10ns sampling period BI L4 review - 18 Oct 2011 (more details in L.Søby’s talk) 500 us Beam Pulse Calibration Pulse of known (variable) amplitude Faraday’s Cup F. Roncarolo Retractable Read-out via scope ADC readout possible, sampling 250 kHz

Source Emittance-Meter SEM grid read-out 250kHz Stepping motors to allow coarse + fine position tuning SEM Grid V BI L4 review - 18 Oct 2011 SLITs SEM Grid H Single stainless steel blade with 2 slits F. Roncarolo

Slit & Grid Principle For each slit position  profile monitor gives beamlet divergence Scanning slit position  transverse phase space reconstruction  emittance @ Linac 4 emittance-meter: Profile monitor = SEM grids driven by stepping motors Profile measurement resolution can be enhanced by programming small SEM grid steps for each slit position BI L4 review - 18 Oct 2011 F. Roncarolo

Emittance-Meter: bias rings SEM grid wire signal determined by SE electrons generated by H- (or p) traversing the wire Secondary electrons are also generated @ Slit Faraday’s Cup and can reach the wires, perturbing the measurement BI L4 review - 18 Oct 2011 The system is equipped with 2 guard rings The polarization of the two guard rings and of the Faraday’s cup with DC bias voltages minimizes the measurement perturbance The bias configuration has been simulated with CST MWS and verified with measurements Faraday’s cup plate F. Roncarolo

Emittance-Meter: bias rings simulations Configuration considered initially: VP1>0 , VP2<0 according to simulations didn’t work, net field distribution lets many electrons emerging from P1 and the cup to reach the SEM grid + 500 V BI L4 review - 18 Oct 2011 Electrons trajectories as simulated by CST Microwave Studio Faraday’s Cup P1 P2 F. Roncarolo + 1200 V - 500 V Configuration proposed after simulations: VP1,VP2, VCUP > 0 minimizes perturbation due to FC and P1 electrons biasing the FC forbids charge measurements at the same time as emittance measurements

Emittance-Meter: bias rings setup with beam During Emittance Measurement -all biases > 0 clearly optimizes the wire signal During Beam charge measurement at the Faraday’s Cup (H- 35 keV) -Need VP2 < 0 to retain secondary electrons that would escape the CUP BI L4 review - 18 Oct 2011 F. Roncarolo All well in agreement with MWS simulations

Emittance-Meter Measurement Example (I) Emittance-meter measurement after 1st solenoid X’ H3+ H0 H2+ Protons BI L4 review - 18 Oct 2011 X F. Roncarolo 45 keV Proton source: different charge states produced by the source are focused differently as they pass through the solenoid

Emittance-Meter Measurement Example (II) Transverse distribution vs Source RF power Profiles extracted from Emittance Measurements (phase space projection on HOR axis) BI L4 review - 18 Oct 2011 F. Roncarolo

Emittance-Meter off-line analysis BI Expert Off-line Analysis GUI Working: Phase space and profile plots Histogram of wire signal levels Background subtraction based on thresholding RMS emittance calculation Under development Precise emittance evaluation via Scubexx algorithms BI L4 review - 18 Oct 2011 F. Roncarolo

Emittance measurements after 1st solenoid Effect of threshold and comparison between H- and Protons Threshold:  cut all wire signals below xx % of maximum wire signal  background subtraction BI L4 review - 18 Oct 2011 Source exit, 20 kW RF power F. Roncarolo Measurement result very much dependent on off line data treatment….

‘Exotic’ profile measurements Profile Measurement performed after the second solenoid by measuring the Emittance meter FC current while scanning the slit position BI L4 review - 18 Oct 2011 F. Roncarolo This particular measurement proved Source reproducibility (red and blue measurements taken in different days) beam-solenoid misalignment (beam centroid depends on Solenoid current)

Energy Spread Measurement SEM grid monitor used for 45 keV proton beam, spectrometer line ON-LINE (same low and high level software for LEBT and Spectro line SEM grids) OFF-LINE BI L4 review - 18 Oct 2011 SEM grid profile that allowed determining the beam energy spread to be ~ +- 170eV after 1st solenoid F. Roncarolo Beam Size Evolution along pulse

LEBT Transport Measurements Phase space distributions as measured at the source exit (before LEBT) and at the LEBT exit HOR VER BI L4 review - 18 Oct 2011 Grey: measured at the source exit Colored: measured after LEBT and reconstructed at source exit with theoretical optics F. Roncarolo

RFQ Matching Phase space distributions as measured and simulated (matched) at the RFQ input HOR VER Grey: nominal beam to match RFQ input Colored: measured for RFQ input BI L4 review - 18 Oct 2011 F. Roncarolo Best RFQ matching is achieved with Solenoid 1 settings that don’t give best transmission along LEBT (see also next slide)

LEBT Transmission Measurements In general : Solenoid 1 used to optimize transmission Solenoid 2 used to optimize RFQ input matching Current [mA] BI L4 review - 18 Oct 2011 Sol1 [A] Sol2 at 300A F. Roncarolo Best LEBT Transmission Best RFQ Matching

Summary / Outlook Source and LEBT test stand operated for two years Commissioning stages with 45 keV proton source almost completed Beam parameter and optics characterization depended heavily on diagnostics Faraday’s cup and BCT to validate transmission Emittance meter to validate matching to nominal optics Spectrometer SEM grid to measure energy spread Test stand served also for diagnostics commissioning in visage of 3 MeV test stand and Linac4 permanent systems BCT mechanics, electronics and acquisition software Emittance meter acquisition software and offline analysis BI L4 review - 18 Oct 2011 F. Roncarolo

BI L4 review - 18 Oct 2011 SPARE F. Roncarolo

LEBT transmission table RF-Power Source 21kW 30kW 40kW 48kW 60kW 2.32V/1.32V-1.36V 2.48V/1.48V 2.6V/1.6V 2.68V/1.64V 2.78V/1.76V Configuration No Iris 11mm 05mm Sol1-Sol2-Steerers    580-330-1000 15.1 0.8 0.2 23.2 0.9 27.5 1.1 29.1 1.2 29.9 600-330-1000 17.5 26.6 30.4 1.3 31.1 1.4 32.1 0.3 600-340-1000 17.6 1 30.3 620-330-1000 17.9 27.9 1.6 29.5 1.9 30.6 620-340-1000 28 1.5 29.6 30.5 620-350-1000 18 1.7 645-340-1000 17.1 25.5 2 0.4 26.7 2.3 25.1 2.6 2.7 640-350-1000 17 25.6 0.5 25.2 640-360-1000 26.5 24.5 24.6 685-355-1--0.25 00 10.8 3.8 13.6 4.4 13.8 5.5 12.8 5.8 12.6 685-365-1--0.25 00 10.2 12.7 5.4 11.7 11.5 5.6 685-375-1--0.25 00 9.3 0.7 11.4 4.5 11.6 5.3 10.7 5.2 10.5 700-355-1--0.25 00 8.4 4.8 10.4 6.9 10 7.8 2.1 8 BI L4 review - 18 Oct 2011 F. Roncarolo Beam current in mA Beam Current saturation at ~50kW Beam core is stable populated (?), as in case of 700A Sol1 most of the beam is scraped and only the core is leaved. The change of RF-Power does not mainly influence FC2 readings.