Technology, Components, Subsystems

Beam Diagnostocs, Instrumentation

Paper	Title	Page
MO203	Non-Interfering Beam Diagnostic Developments	13
	A. Peters, P. Forck GSI, Darmstadt
	New high power proton and heavy ion linac projects are a big challenge for beam diagnostic developments. Due to the high inherent beam power mostly all destructive measurement techniques are not applicable. Thus a lot of beam diagnostic developments are under way from enhancements of well-known systems like beam position pick-ups or current transformers to new designs for profile or bunch length measurements using e.g. the interaction of the high power beams with the residual gas in the linacs. The latest progress in this field will be reviewed with descriptions of some remarkable solutions.
	Transparencies
TU302	Future Developments in Electron Linac Diagnostics	280
	M.C. Ross SLAC/NLC, Menlo Park, California
	The next generation of electron linacs will fill two different roles: ultra-low emittance, very high power accelerators for linear colliders and ultra-short bunch, high stability accelerators for SASE X-ray production. In either case, precision control based on non-invasive, reliable, beam instrumentation will be required. For the linear collider, low emittance transport is an important concern for both warm and superconducting linacs. Instrumentation will be used to control and diagnostics will be used to validate emittance preserving strategies, such as beam based alignment and dispersion - free steering. Tests at the KEK ATF and the SLAC FFTB have demonstrated the required performance for beam position and beam size monitors. Linacs intended for FEL's will require precision bunch length diagnostics because of expected non-linear micro-bunching processes. A wide variety of devices are now in development at FEL prototypes, including TTF2 at DESY and SPPS at SLAC. We present a review of the new diagnostic systems.
	Transparencies
TUP61	Beam Analysis Using the IPNS Linac ESEM	405
	J.C. Dooling, F. R. Brumwell, L. Donley, G.E. McMichael, V. F. Stipp ANL, Argonne, Illinois
	The Energy Spread and Energy Monitor (ESEM) is an on-line, non-intrusive diagnostic used to characterize the output beam from the 200 MHz, 50 MeV linac. The energy spread is determined from a 3-size, longitudinal emittance measurement and energy is derived from TOF analysis. Presently, a single particle distribution is used to yield energy and energy-spread results. Effort is on-going to allow for more realistic distributions to be included. Signals are detected on terminated 50 Ω, stripline BPMs. Each BPM is constructed with four striplines: top, bottom, left and right. Until recently, the ESEM signals were taken solely from bottom striplines in four separate BPM locations in the transport line between the linac and synchrotron. We have begun to use the top stripline data to examine, in more detail, beam position and attempt to measure beam size. The electrostatic coupling between the stripline and the beam depends on the capacitance, which in turn is inversely related to the beam-stripline separation. The electrostatic portion of fluctuations in beam motion will be nonlinear, possibly allowing one to infer beam size.
TUP63	The First Results of Bunch Shape Measurements in SNS Linac	408
	A. Feschenko, A. Gaidash, Yu. Kisselev, L.V. Kravchuk, A. Liyu, A. Menshov, A.N. Mirzojan RAS/INR, Moscow S. Assadi, W. Blokland, S. Henderson, E.P. Tanke ORNL/SNS, Oak Ridge, Tennessee D.-O. Jeon ORNL, Oak Ridge
	Three Bunch Shape Monitors with transverse scanning of low energy secondary electrons for the SNS Linac have been developed and fabricated. The peculiarity of the detectors is using of energy separation of the electrons. The separation enables to minimize influence of detached electrons originated from dissociation of H-minus ions in the detector wire target. The first detector was used at the exit of the first DTL tank during its commissioning. The results of Bunch Shape measurements are presented and discussed. These results were used to verify beam quality, to set parameters of the accelerating field, to estimate a longitudinal beam halo and to restore a longitudinal beam emittance.
	Transparencies
TUP64	Bunch Length Measurements at LEBRA	411
	K. Yokoyama KEK, Ibaraki K. Hayakawa, Y. Hayakawa, K. Nakao, I. Sato, T. Tanaka LEBRA, Funabashi
	The bunch length of the electron beam from the FEL linac at LEBRA (Laboratory for Electron Beam Research and Application) was estimated from the phase ellipse coefficient which is deduced from the dependence of the beam spread on the accelerating phase. The bunch length of FWHM was estimated approximately 0.33 mm from the results of the experiments. Besides, the pulse length of the FEL lights around the wavelength of 1.5 μm was measured by means of the autocorrelation. The pulse length was less than 0.06 mm according to the number of interfacial waves. These results indicate that the pulse length of the FEL lights isn’t equivalent to the electron bunch length.
TUP65	RF Tuning Schemes for J-PARC DTL and SDTL	414
	M. Ikegami KEK, Ibaraki Y. Kondo, A. Ueno JAERI, Ibaraki-ken
	J-PARC linac consists of a 3 MeV RFQ linac, a 50 MeV DTL (Drift Tube Linac), a 190 MeV SDTL (Separate-type DTL), and a 400 MeV ACS (Annular-Coupled Structure) linac. In high-current proton linacs, precise tuning of RF amplitude and phase is indispensable to reduce uncontrolled beam loss and beam-quality deterioration. Especially, accurate RF tuning is essential for J-PARC linac, because requirement for the momentum spread is extremely severe to enable effective injection to the succeeding RCS (Rapid Cycling Synchrotron). In this paper, planned tuning schemes for the DTL and SDTL are presented together with the beam diagnostic layout for the tuning.
TUP66	An Alternate Scheme for J-PARC SDTL Tuning	417
	M. Ikegami KEK, Ibaraki Y. Kondo, A. Ueno JAERI, Ibaraki-ken
	J-PARC linac consists of a 3 MeV RFQ linac, a 50 MeV DTL (Drift Tube Linac), a 190 MeV SDTL (Separate-type DTL), and a 400 MeV ACS (Annular-Coupled Structure) linac. As presented in a separate paper, we plan to perform phase-scan with precise TOF (Time Of Flight) beam-energy measurement in RF tuning of SDTL tanks. As a back-up method, we are considering to prepare an RF tuning scheme with rough TOF measurement for SDTL. In this paper, the principle of this scheme is presented, and its advantages and disadvantages are discussed based on a systematic particle simulation.
TUP67	Beam-Based Alignment Measurements of the LANSCE Linac	420
	R.C. McCrady, L. Rybarcyk LANL, Los Alamos, New Mexico
	We have made measurements of the alignment of the LANSCE Drift Tube linac (DTL) and Side Coupled linac (SCL) using beam position measurements and analyzing them with linear models. In the DTL, we varied the injection steering, measured the beam position after each DTL tank, and analyzed the data with a linear model using R-matrices that were computed by the Trace-3D computer program. The analysis model allowed for tank-to-tank misalignments. The measurements were made similarly in the SCL, where the analysis model allowed for misalignments of each quadrupole doublet lens. We present here the analysis techniques, the resulting alignment measurements and comparisons to measurements made with optical instruments.
TUP68	The LANSCE Low Momentum Beam Monitor	423
	R. Merl LANL, Los Alamos, New Mexico F. R. Gallegos, C. Pillai, S. Schaller, F. E. Shelley, A. I. Steck LANL/LANSCE, Los Alamos, New Mexico B. J. Sanchez ORNL/SNS, Oak Ridge, Tennessee
	A diagnostic has been developed at the Los Alamos Neutron Science Center (LANSCE) for the purpose of identifying low momentum beam tails in the linear accelerator. These tails must be eliminated in order to maintain the transverse and longitudinal beam size. Instead of the currently used phosphor camera system, this instrument consists of a Multi Wire Proportional Chamber (MWPC) front end coupled to an EPICS compliant VME-based electronics package. Low momentum tails are detected with a resolution of 5 mm in the MWPC at a high dispersion point near a bending magnet. While phosphor is typically not sensitive in the nano amp range, the MWPC is sensitive down to about a pico amp. The electronics package processes the signals from each of the MWPC wires to generate an array of beam currents at each of the lower energies. The electronics has an analog front end with a high-speed analog to digital converter for each wire. Data from multiple wires are processed with an embedded digital signal processor and results placed in a set of VME registers. An EPICS application assembles the data from these VME registers into a display of beam current vs. beam energy (momentum) in the LANSCE control room.
TUP69	Precision Alignments of Stripline BPMs with Quadrupole Magnets for TTF2	426
	G. Priebe, D. Nölle, M. Wendt, M. Werner DESY, Hamburg
	We report on our alignment setup to calibrate beam position monitors (BPM) with respect to the magnetic axis of the quadrupole magnets used in the warm sections of the TESLA Test Facility (TTF2). The Stripline BPM's are fixed inside the quadrupole magnets. A streched wire measurement was used to calibrate the electrical axis of the BPM wrt. to the magnetic axis of the quadrupole.
TUP70	Systematic Calibration of Beam Position Monitor in the High Intensity Proton Accelerator (J-PARC) LINAC	429
	S. Sato, K. Hasegawa, F. Hiroki, J. Kishiro, Y. Kondo, M. Tanaka, T. Tomisawa, A. Ueno, H. Yoshikawa JAERI, Ibaraki-ken Z. Igarashi, M. Ikegami, N. Kamikubota, S. Lee, K. Nigorikawa, T. Toyama KEK, Ibaraki
	In J-PARC, a MW class of proton accelerator is under construction. Improperly- tuned beam would critically result in unacceptable (>0.1%) energy loss. Systematic strategy of fine calibrations of the beam position monitor (BPM) detectors, is therefore required. First, Off-beam-line calibrations of BPMs are taken, with a dedicatedly- designed bench, which has a beam-simulating electric wire carrying 324 MHz. And then discrepancies are calibrated for each BPM between reconstructed electrical center of pick-up plates and measured mechanical center, before the installation of BPM on the beam line. Secondly, after BPMs are installed on the beam line, real beam is used for systematic calibrations (Beam Based Calibration (BBC)). The discrepancies are calibrated between electromagnetic center of Q-magnets and reconstructed beam position. In KEK we have the first stage of J-Parc LINAC with Ion source, RFQ, DTL, Q- and steering-magnets, and lots of BPMs. Implementation of BBC is going with SAD-language, which can also be used for beam steering and beam trajectory simulations, e.g. TRACE-3D. In this presentation, such strategic BPM calibration system will be intensively described.
TUP71	Highly Sensitive Measurements of the Dark Current of Superconducting Cavities for TESLA Using a SQUID Based Cryogenic Current Comparator	432
	W. Vodel, R. Neubert, S. Nietzsche FSU, Jena K. Knaack, M. Wendt, K. Wittenburg DESY, Hamburg A. Peters GSI, Darmstadt
	This contribution presents a Cryogenic Current Comparator (CCC) as an excellent tool for detecting dark currents generated, e.g. by superconducting cavities for the upcoming TESLA project (X-FEL) at DESY. To achieve the maximum possible energy the gradient of the superconducting RF cavities should be pushed close to the physical limit of 50 MV/m. The undesired field emission of electrons (so-called dark current) of the superconducting RF cavities at strong fields may limit the maximum gradient. The absolute measurement of the dark current in correlation with the gradient will give a proper value to compare and classify the cavities. The main component of the CCC is a highly sensitive LTS-DC SQUID system which is able to measure extremely low magnetic fields, e.g. caused by the dark current. For this reason the input coil of the SQUID is connected across a special designed toroidal niobium pick-up coil for the passing electron beam. A noise limited current resolution of nearly 2 pA/√(Hz) with a measurement bandwidth of up to 70 kHz was achieved in the laboratory. Design issues of the CCC and the application in the CHECHIA cavity test stand at DESY as well as experimental results will be discussed.
TUP72	TTF II Beam Monitors for Beam Position, Bunch Charge and Phase Measurements	435
	M. Wendt, D. Nölle DESY, Hamburg
	An overview of the basic beam instrumentation with regard to elecromagnetic beam monitors for the TESLA Test Facility phase II (TTF II) is given. Emphasis is put on beam position monitor (BPM) and toroid transformer systems for beam orbit and bunch charge observations. Furthermore broadband monitors, i.e. wall current and bunch phase monitors, are briefly presented.
TUP73	Beam Instrumentation Using BPM System of the SPring-8 Linac	438
	K. Yanagida, T. Asaka, H. Dewa, H. Hanaki, T. Kobayashi, A. Mizuno, S. Suzuki, T.  Taniuchi, H. Tomizawa JASRI-SPring-8, Hyogo
	A beam position monitor (BPM) system of the SPring-8 linac has been operated since 2002. The following upgrade programs have been carried out during this period: The BPMs were installed in the linac's dispersive sections. A synchronized accumulation of beam position data into the database system started. A feedback control of steering magnets for beam position stabilization has been under development. In this conference the authors report a performance of the BPM system, and discuss its usefulness for beam diagnostics, machine diagnostics and beam stabilization.
TUP74	The Beam Diagnostics System in the J-PARC LINAC	441
	S. Lee, Z. Igarashi, T. Toyama KEK, Ibaraki H. Akikawa JAERI/LINAC, Ibaraki-ken F. Hiroki, J. Kishiro, S. Sato, M. Tanaka, T. Tomisawa JAERI, Ibaraki-ken H. Yoshikawa JAERI/FEL, Ibaraki-ken
	Large amount of beam monitors will be installed in J-PARC linac. Electrostatic computations are used to adjust the BPM cross-section parameters to obtain 50 Ω transmission lines. BPMs are designed to control the offset between quadrupole magnet and BPM electrical centers less than 0.1mm. We present a procedure of beam based calibration/alignment (BBC/BBA) method to confirm the displacement of linac BPMs. The fast current transformer (FCT) has response of relative bunch phase <1%. To measure the beam energy at every accelerator tank and injection point of 3 GeV RCS, phase difference of FCT pairs are used, and 10-4 order energy resolutions can be expected. The loss monitor system (BLM) is composed of scintillator and Ar-CH4/CO2 gas filled proportional counter. To prevent the activation and heat load by intense beam loss, fast time response of loss signals is required. Profile measurements can also be used to determine the beam emittance of a matched beam in a periodic focusing lattice. The thin sensing wire scanner (WS) has been designed to obtain a current density distribution of the beam. This paper describes the instruments and R&D result of beam monitors in J-PARC linac.