Status of Beam loss Monitoring on CTF3 Results of Tests on LINAC and PETS as R&D for TBL Anne Dabrowski Northwestern University Thibaut Lefevre CERN CTF3 Collaboration Meeting 24 November 2004

Beam loss monitoring on CTF3 Goal –Map Beam Loss, both in amplitude and within the pulse time along the LINAC and PETS. To What precision?? –Better than % level (accuracy of BPM’s ~ %) –For a nominal beam current in the LINAC of 3.5Amps, we need to be sensitive to a beam loss of at least 35mA, as measured by the BPM’s –Want to provide detailed information about the losses along the girder that the BPM’s can’t provide. R&D for TBL: –Experience on the LINAC will teach us more about the beam loss environment This is a very different environment from the high electron / proton flux environment for what the chambers were initially developed for. –Future … want at least the ‰ level, to measure beam loss in TBL For nominal beam current in the TBL of 35 Amps, we need to be sensitive to a beam loss of at least 35mA.

Beam Loss from GEANT 3.21 simulation Radius (cm) Energy (MeV) Flux (1/cm 2 /s) Number of particles / 25 MeV electron gammas Charged particles M. Wood note 061, (2004) 25 MeV Electron beam plots scaled to 1‰ of the beam loss, which is 35mA at nominal CTF intensity Beam Loss induced at 30mrad with the y axis

Beam Loss from simulation … cont Radius (cm) 0 Energy (MeV) 100 M. Wood CTF3 note 061, (2004) 25 MeV electrons100 MeV electrons Energy (MeV) 25 Flux (1/cm 2 /s) Dominated by low energy photons Radius (cm) Radial distribution of beam loss Energy Distribution of secondary particles at a distance of 100 cm from beam loss

Example of typical photon cross with metal as a function of photon energy τ, atomic photo-effect (electron ejection, photon absorption); Photons cross sections dominate at low energy The photon production cross section, and the interaction cross section with matter make this the dominant process at low energy

Design of Detector Tested in October –SEM (vacuum) gas sealed, radiation hard, high rate chamber. Since the environment is dominated by photon and secondary emission cross-sections, these processes provide a signal higher than ionization. The SEM is the main chamber, and the SIC (helium/Argon filled) is almost equivalent device. Installed 48 detectors along the LINAC –Faraday Cup tested as cross-calibration device (Aluminum block sensitive to charged particles) SEM SIC F. cup Chamber mounted in metal box for shielding

‘Gallery’ Timing & 100MHz ADC’s 0-2kV Power supply Cables Patch Panel Beam position monitor Accelerating structure Quadrupoles e-e- ‘Tunnel’ Amplifier card HV distribution On each Girder, we have 3 setup stations along z T. Lefevre

Chambers Installed in CTF3 to give Installed 3 Chambers and 1 Faraday Cup (for online calibration) per Girder Total of 48 detectors After the quadrupleMiddle of second cavity Middle of first cavity Example below of Setup: Girder 5 ~30 MeV electrons (Similar setups on Girders 6,7,8,10,11,12) Mechanical Support for detectors Freedom to mount device at chosen height along support

Setup sensitivity to beam loss along Girder Just after the quadruple Middle of the first cavity Middle of the second cavity Beam current before and after the accelerating structure for one pulse of the beam measure by BPM ~0.25A lost (~50nC per pulse) ~0.2% (~100pc) of beam loss measured ~0.6% (~250pC) of beam loss measured ~0.08% (~40pC) of beam loss measured Nominal beam Optics, Girder 5 ~ 30 MeV Electron beam

Chambers calibrated using the Faraday cup 0.25 A of beam loss Less than A beam loss [between % and ‰] Current lost measured by beam position monitors Chambers Sensitive to beam loss as measured by beam position monitors between the % and ‰ level. For greater sensitivity, currently improving shielding, and finding the balance between signal collected and time resolution … Signals in the chambers and Faraday Cup Linear response between SIC and Faraday Cup BPM’s insenstive to beam loss! But beam loss seen by Faraday Cup / Chamber setup This is based on the BPM’s being well calibrated … must check this … re-do plots with signals after 12 Nov (day when BPMS were re-calibrated) … this analysis in PROGRESS. … ready in a few hrs

Example of Beam loss on Girder 7 Loss is less than % level on BPM Signal from the sic visible Calibration from Faraday Cup

Regions of Low beam loss ?? Girder 12 … Energy ~ 150 MeV From Simulation, beam loss is more collimated … difficult to measure this loss, unless it is directed right at detector. A PMT detector was installed in the 1 st Cavity, together with a Faraday Cup. PMT measure beam loss … when current is low … this example collects pC of charge / pulse Change PMT voltage, depending of sensitivity required PMT have relatively low dynamic range within a gain Signal from PMT With offline calibration Online (x400) Signal from Faraday Cup in the noise

PMT used Hamamatsu R7400U series At a given voltage the dynamic range is limited

Current Choices for Detectors for TBL DetectorIntensity RangePriceSuitability Faraday Cup (Aluminium Block) Charged particles, limited at the per mil level Must increase the size to stop high energy particles 20 chf without connectors No high voltage needed SEMCharged particles and photons 500 chf??No high voltage needed PMTSensitive to low losses Dynamic range for a given voltage limed to 3 orders of magnitude 610 chfRequires High voltage Sensitive to photons in the machine, not related to the beam pulse

Summary  This has been a valuable exercise to learn about beam loss environment in LINAC … to translate to the TBL.  Chambers are sensitive to beam loss along the girder …. Additional monitoring complementary to BPM available today!  Chambers are most sensitive to Photo-electric / Secondary emission signal … fast time resolution, and no need to apply voltage  Faraday Cup provides an online calibration for the charge particle signal …  For TBL, beam currents will be 10X larger … but we need to investigate all possible devices to find the best range of sensitivity to beam loss

Slides about PETS work

Summary of main features from Simulation 25 MeV e + beam with losses of ‰ 3.5A beam current (assume pulse 200ns) Secondary Particle:Flux(cm -2 s -1 )Flux(cm -2 pulse -1 )must check this with Thibaut Photos(0.1-1)x10 12 (0.2-2)x10 5 e + /e - (0.5-4) x10 11 (1.0-8) x MeV e + beam with losses of ‰ 3.5A beam current Secondary Particle:Flux(cm -2 s -1 )Flux(cm -2 pulse -1 ) Photos(0.1-1)x10 14 (0.2-2)x10 7 e + /e - (0.5-4) x10 12 (1.0-8) x10 5 Photon production is > 1 order of magnitude > electrons Maybe include this ????

Argon Plateau – sensitivity to ionization? This shows that the beam loss is constant … last measurement shows effect of the Geiger regime Geiger regime