Lab G measurements Yagmur Torun Center for Accelerator and Particle Physics Illinois Institute of Technology MUCOOL Collaboration Meeting - LBNL - October 23, 2002 ˘

INTRODUCTION ● We have been working on characterizing the radiation field around high gradient RF cavities for cavity diagnostics, guidance on MUCOOL instrumentation and MICE detector backgrounds ● ANL, FNAL, IIT, LBNL, Mississippi, UIUC, CERN, Imperial College ● A. Bross, L. Ducas, D. Errede, S. Geer, P. Gruber, D. Kaplan, D. Li, H. Li, E. McKigney, A. Moretti, J. Norem, M. Popovic, Z. Qian, A. Rowe, R. Rimmer, N. Solomey, D. Summers, V. Wu, M. Zisman,... ● Mostly at Lab-G facility in Fermilab using 12MW klystron (linac spare) ● Steep dependence of electron dark current and X-ray output on cavity gradient (and the phase of the moon, etc.) ● No detector can work/survive over the entire range of flux, had to (ab)use many different detectors ● Measured output from two 805MHz cavities: FNAL 6-cell (June-Dec. 01), LBNL pillbox (Feb. 02-now)

Lab-G Cave

BEAM TRANSFORMERS ● Simple, robust but weak signal (0.1-1 mA/A) ● Scary results (700mA at peak field for 6-cell), not measurable for the pillbox ● Approximate electron spectrum with rangestack or small magnet ● Doesn't help with low energy e+thick windows (pillbox) ● Doesn't work with magnetic field

RANGESTACK WITH BEAM TRANSFORMER

BEAM TRANSFORMER

SCINTILLATOR+PMT ● Simple, relatively robust ● Relevant to MICE ● Limited rate, saturates quickly with dark current ● Also suitable for rangestack ● No magnetic field ● Used thin (1mm) scintillator block for rate, thick (5cm) block for rate and approximate spectrum

SCINTILLATOR+PMT

SCINTILLATING FIBERS ● Tried MUSCAT prototype fiber detector with MICE collaborators (E. McKigney, P. Gruber), Nov. 01 ● 1mm x 10cm x 2 planes ● Rate data with different thicknesses of plastic shielding and magnetic field ● Phototube in fringe field, messy calibration ● Also in the beam, fried expensive MAPMT ● But obtained some idea about rates

SCINTILLATING FIBER ● Added long clear fiber lightguide and new PMT to MUSCAT prototype (Dec. 01) to put tube out of the magnetic field and dark current ● Low yield due to loss in lightguide, couldnot see singles ● Did rangestack study with clear results, rate shoots up to saturation whenever dark current electrons acquire enough energy to pass through shield ● No magnetic field (ran out of He by the time I replaced broken PMT/base and debugged the system) ● Need lower attenuation clear fiber and high QE detector for good signal

NEW SCINTILLATING FIBER DETECTOR (A. BROSS) ● 8 x 0.835mm x 30cm scintillating fiber (read out one) ● 6m clear fiber ● Hybrid (APD) PMT (Hamamatsu R ) and preamp ● Lost one PMT ● Noise pickup problems with preamp ● Working well after replacing PMT and shielding preamp

Ge crystal (P. Gruber)

DATA ACQUISITION ● Need to measure RF amplitude accurately pulse by pulse for reproducible measurements ● I am tired of squinting to see signals on the scope and writing down data on paper by hand ● Existing RF controls already put data on the network through IRM system ● Would be nice to save everything together

DATA ACQUISITION

● Cheap no-frills PC to running plain Linux ● Comedi (LBNL package for Linux based DAQ) for DAS card driver, received support from maintainer (F. M. Hess, UIUC) ● CAMAC equipment from Fermilab pool ● GPIB scope and CAMAC for fast signals ● IRM sample/hold and PCI-DAS for slow signals

6-cell cavity window interior

SEM picture of 6-cell cavity interior

Polaroid vs photographic paper

STATUS AND PLANS ● New fiber detector working for rate measurements ● Thick scintillator+fiber guide being built for spectrum measurement in magnetic field ● Ge crystal based system tested for spectrum measurement ● Auxiliary DAQ system is ready to automate and speed up measurements ● Some understanding of field emission based on Lab-G experience, low field behavior not well understood yet