Bunch to bunch beam profile measurements provide a valuable tool to control the injection lines to the SPS. A fast profile monitor based on a 2.5 µm Mylar coated with Aluminium Optical Transition Radiation (OTR) radiator, has been developed, installed and tested in the transfer line between the PS and SPS. The OTR beam image is focused onto a fast Linear Multianode Photo Multiplier Tube and the associated electronics sample and store profiles every 25 ns. The paper describes the detector design, the electronic processing, and presents the results of different measurements made with bunches of 109-1011 protons at 26 GeV, and bunches of 106 Pb82 ions at 5.11 GeV/u

Ferioli, G

Gras, J J

Hiller, H

Jung, R

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EUROPEAN ORGANIZATION FOR NUCLEAR RESEARCHCERN    SL DIVISIONGeneva, SwitzerlandAugust, 1999CERN SL-99-043  BIBEAM PROFILE MEASUREMENTS AT 40 MHz IN THE PS TOSPS TRANSFER CHANNELFerioli, G.; Gras, J.J; *Hiller, H.; Jung, R.CERN – Geneva – CH*Bruun & Sorensen (France)AbstractBunch to bunch beam profile measurements provide a valuable tool to control theinjection lines to the SPS.A fast profile monitor based on a 2.5 µm Mylar coated with Aluminium OpticalTransition Radiation (OTR) radiator, has been developed, installed and tested in thetransfer line between the PS and SPS.The OTR beam image is focused onto a fast Linear Multianode Photo Multiplier Tubeand the associated electronics sample and store profiles every 25 ns.The paper describes the detector design, the electronic processing, and presents the resultsof different measurements made with bunches of 109-1011 protons at 26 GeV, and bunchesof 106   Pb82 ions at 5.11 GeV/u.Presented at DIPACChester – 16-18 May 1999BEAM PROFILE MEASUREMENTS AT 40 MHz IN THE PS TO SPSTRANSFER CHANNELG. Ferioli, J.J. Gras, *H. Hiller, R. JungCERN, Geneva, Switzerland - *Bruun & Sørensen (France)AbstractBunch to bunch beam profile measurements provide avaluable tool to control the injection lines to the SPS.A fast profile monitor based on a 2.5µm Mylar coatedwith Aluminium Optical Transition Radiation (OTR)radiator, has been developed, installed and tested in thetransfer line between the PS and SPS.The OTR beam image is focused onto a fast LinearMultianode Photo Multiplier Tube and the associatedelectronics sample and store profiles every 25ns.The paper describes the detector design, the electronicprocessing, and presents the results of differentmeasurements made with bunches of 109-1011 protons at 26GeV, and bunches of 106   Pb82 ions at 5.11 GeV/u.1. INTRODUCTIONIn the transfer line between PS and SPS different types ofbeams have to be monitored for a good injection in theSPS. For the Fixed Target operation 2 injections of2*1013p at 14 GeV and 10.5 µs long are extractedhorizontally in 5 PS turns. With the ions, 4 injections of 16bunches of 1.5*106 Pb82 ions each at 5.11 GeV/u andspaced by 140 ns are used.In view of the use of the SPS as LHC injector oneinjection of 16 bunches of 109 protons each at 26 GeV andspaced by 140 ns, is presently used for preliminary testsand, from this year one injection of 83 bunches spaced by25 ns will be tested. For all beams the rms vertical andhorizontal sizes are measured by Secondary EmissionGrids (SEG) and OTR Beam Television Profiles (BTP).The SEG electronics integrates all the signals comingfrom the grids for each injection at intervals defined by themaster timing and gives only a single H/V profile. TheCCD camera, used in the BTP monitor, integrates thesignals during a TV frame (20ms), and the associatedprocessing system computes a single H/V projection and a2-Dimensional representation [1]. In both cases theevolution of the position, relative intensity, and profiles ofthe different bunches or structures is lost.A new fast system able to acquire H/V profiles ofbunches spaced by 25ns has been developed, installed inthe transfer line and tested with different beams.2. THE EXPERIMENTAL SET UPMany OTR radiators made of 12 µm Titanium or 25 µmMylar coated with 2 µm of Aluminium are currently usedin the transfer lines to the SPS. These screens generatelight, which reproduces the time structure of the beam andbunches spaced by 25ns can be analyzed [2].The intensity of the OTR radiation, generated by ion orproton bunches injected in the SPS, is high enough toprovide good diagnostics with a CCD camera or aPhotomultiplier.Figure 1: Schematic view of the monitor set-upThe measurement station (Fig. 1) uses a standard BTVSPS tank, where an OTR radiator is placed at 45º withrespect to the beam. The radiation, through a window onthe vacuum chamber and a set of neutral density filters, isfocused by a 75 mm objective onto a Multianode PhotoMultiplier Tube (MPMT).This MPMT (type: Hamamatsu R5900U) with theproximity focusing dynode structure preserves the spatialdistribution of intensity between photocathode and anode.This tube is a linear structured version with 16 anodesmeasuring 0.8*16 mm with a 1mm pitch, and an anodepulse rise time of about 0.6 ns.A motorized rotation stage can rotate the MPTM from 0ºto 90º, so with the same monitor, this allows to takealternatively horizontal or vertical profiles. The set offilters, the gain of MPMT and the rotation stage areremotely controlled.Beam ObjectiveMultianode      PMT Motorizedrotation stage    0 - 90ºFiltersWindow OTR RadiatorFig. 2 shows the detector with the acquisition electronicssystem mounted on the same support.Figure 2: Fast Beam Profile Monitor3. READOUT ELECTRONICSA new wide band readout electronics has beendeveloped, in order to digitize and store simultaneously 16signals at a frequency up 50 MHz (Fig. 3).Very short cables connect the output of each anode of theMPMT to an amplifier (used to limit the anode current).This analog signal is digitized by an 8 bits flash ADCFigure 3: Bloc diagram of MPMT readout electronics.and the sampled values are stored in an internal memory of32 Kbytes.Two modes of operation have been foreseen: internalclock and bunch auto trigger to work correctly with thedifferent beam structures. In the internal clock mode, usedwith the continuous transfer of 5 PS turns, an external gatesynchronous to the injection resets the counter memoryand starts the acquisition process and an internal clock at40 MHz stores the profiles in the memory.The bunch auto trigger mode is used to analyse bunchedbeams; in this case the external gate is used to reset thecounter memory and to generate an “enable” for theacquisition process.A very fast low-level discriminator detects the presenceof an analog signal on the anodes, generated by one bunch,and starts one conversion for all channels. The buncheshave to be separated by at least 25ns.In both cases at the end of the injection, on request of theCPU installed in a surface building, the data are transferredto a VME interface over a serial RS 422 line.4. SOFTWARE DESCRIPTIONThe software system is based on a client-serverarchitecture.  The server is located in the front-end CPU, aPowerPC VME card (type: CES RIO-8062) running theLynxOS real time system. It has been developed in C andconsists in two threads. The first one acquiringcontinuously the profiles at predefined events (first protoninjection, second proton injection...), the second handlingthe communications with the outside world. On the clientside, a graphical user interface has been developed for ourHPUX workstations. It allows the user to configure theobserved events, to monitor the system settings (PMvoltage, acquisition plane...) and of course to retrieve,display (Fig. 4, 6) and store the acquisitions via the servercommunication thread.A M P .1A M P .1 6R A M  1 3 2 k * 8A D C  1 6  8  b itsP M T  M u lt ia no d eA n o de  1A n o de  1 6A D C  1 8  b i tsD I S C R IM I N A T O RC L O C K  4 0  M H zR A M  1 6 3 2 k * 8A D D R E S S  C O U N T E RR A M  3 2 k* 1 6  C L O C KC O U N T E RT IM IN GD A T A  1D A T A  16WWS CS CADDRESSC KC KWDATAB U N C H  A U T O  -T R I G G E RIN T E R N A L  C L O C KSTARTSTOPPRE-PULSER E S E TR E S E T1 2 nT =  X  nsA C Q U IS IT I O NO U T  A M P L IF IE R T H R E S H O L DX  =  >  25 n sB U N C H  A U T O  -T R IG G E R1 2 3 nT = 2 5n sA C Q U IS IT I O NO U T  A M P L IF IE RIN T E R N A L  C L O C KTHRESHOLDCPU    INTERFACEa m p  4a m p  8a m p  1 25. EXPERIMENTAL RESULTSProfile measurements have been done with ions: Fig. 4shows the horizontal profiles of the four batches, of 16bunches each, used in the injection of one SPS cycle.The system has shown the peculiar behaviour of the firstbunch of each batch, a phenomenon impossible to see withthe others profile monitors installed in the transfer line.Figure 4: Horizontal profiles of 4 batches of Pb ions of 16bunches each (from right to left).In order to correct this problem the timing of the CPSextraction kicker was changed; Fig. 5 shows that themonitor was able to follow the evolution of the position ofthe bunches. This test has revealed that the length of thekicker pulse was not long enough to perform a goodejection.Figure 5: Evolution of first ions batch during the timingtuning of the CPS extraction kicker.The relative intensity, the position and the beam sizesalong the spill of the beam delivered by 5 CPS turns inContinuous Transfer mode have been measured by meansof the processing of about 600 profiles acquired during theinjection (Fig. 6).The observation and the improvement of the transversecharacteristics of this proton beam are simplified.Figure 6: Evolution of: rms size, position and intensity of5 CPS turns injected in the SPS.6. CONCLUSIONSingle bunch to bunch measurements, by the Fast BeamProfile Monitor, have proven to be feasible. Somephenomena, which would pass undetected by SEM Grid orBTP monitor profile, have been highlighted.The OTR screen does not significantly blow-up thebeams injected into the SPS, and can be used as apermanent monitoring tool.This diagnostic tool has been extremely useful in theoptimisation of different parameters of the injection line.The small number of channels of the MPMT can be adisadvantage. A limitation appears when resolutions lessthan 1 mm are needed; a more sophisticated optical setupwould be required to overcome this limitation.ACKNOWLEDGEMENTSWe would like to thank J. Camas and M. Sillanoli whoperformed the mechanical and installation works, andJ. Koopman who provided the Step Control for the rotationstage and filters.REFERENCES[1] J. Camas et al: Screen versus Sem grids for single passmeasurements. Pro. of DIPAC 95 Travemunde,Germany 28-31 May 95.[2] J. Bosser et al: Optical Transition Radiation protonbeam profile monitor. NIM A238 (1985) 45-22.024681012141618202224261 3 5 7 9 11 13 15 1 3 5 7 9 11 13 15 1 3 5 7 9 11 13 15 1 3 5 7 9 11 13 15N. BunchH Pos. [mm], 2sigma H [mm],  Intensity [bit/20]

Beam profile measurements at 40 MHz in the PS to SPS transfer channel

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