Barrier RF Stacking Weiren Chou and Dave Wildman Fermilab, U.S.A. October 20, 2004 Presentation at the Proton Driver Session ICFA-HB2004, Bensheim, Germany, Oct 18-22, 2004

W. Chou ICFA-HB2004 Workshop, October 20, Barrier RF Study Group Fermilab-KEK-Caltech collaboration: Fermilab - D. Wildman, J. Griffin, K.Y. Ng, J. MacLachlan, C. Bhat, W. Chou KEK - A. Takagi, Y. Mori Caltech - H. Zhang, D. Michael Acknowledgement: Helpful discussions with Takayama’s group

W. Chou ICFA-HB2004 Workshop, October 20, Outline  Motivation  Goals and methods  Simulations  Barrier rf system  Beam experiments  Summary

W. Chou ICFA-HB2004 Workshop, October 20, Collider Experiment Run2 Pbar target CDF D0

W. Chou ICFA-HB2004 Workshop, October 20, Neutrino Experiment NuMI

W. Chou ICFA-HB2004 Workshop, October 20, Booster – the Bottleneck  The new Main Injector can accept 25e12 protons per Booster cycle.  However, the old Booster can only deliver 5e12 particles per cycle. Webber’s data in October 2000Prebys/Lackey’s data in January 2004

W. Chou ICFA-HB2004 Workshop, October 20, Solution - Stacking  A solution is to stack two Booster bunches into one Main Injector RF bucket  This is possible because the Main Injector longitudinal acceptance (0.72 eV-s) is larger than the Booster beam emittance (0.13 eV-s)

W. Chou ICFA-HB2004 Workshop, October 20, Goals  Run2 – To increase protons per second (pps) on the pbar target by 100% Present: 5e12 every 2 sec Goal: 2 x 5e12 every 2 sec  NuMI – To increase pps on the NuMI target by 70% Baseline: 3e13 every 2 sec Goal: 2 x 3e13 every sec

W. Chou ICFA-HB2004 Workshop, October 20, Two Methods  Adiabatic stacking:  Beam injected on-axis  Adiabatically compress the beam by moving rf barrier  Fast stacking:  Beam injected off-axis  Using two barriers, one stationary, another moving  Continuous injection and stacking  First proposed by J. Griffin

W. Chou ICFA-HB2004 Workshop, October 20, Two Types of Barrier Stationary barrier Moving barrier +V -V +V -V

W. Chou ICFA-HB2004 Workshop, October 20, Adiabatic Stacking Simulation (K-Y. Ng)Measurement

W. Chou ICFA-HB2004 Workshop, October 20, Fast Stacking Simulation: 2-Batch (courtesy K.Y. Ng)

W. Chou ICFA-HB2004 Workshop, October 20, Batch Stacking (cont…)

W. Chou ICFA-HB2004 Workshop, October 20, Fast Stacking Simulation: 12-Batch (courtesy K.Y. Ng)

W. Chou ICFA-HB2004 Workshop, October 20, Batch Stacking (cont…)

W. Chou ICFA-HB2004 Workshop, October 20, Batch Stacking (cont…)

W. Chou ICFA-HB2004 Workshop, October 20, Batch Stacking (cont…)

W. Chou ICFA-HB2004 Workshop, October 20, Batch Stacking (cont…)

W. Chou ICFA-HB2004 Workshop, October 20, Batch Stacking (cont…)

W. Chou ICFA-HB2004 Workshop, October 20, Batch Stacking (cont…)

W. Chou ICFA-HB2004 Workshop, October 20, Barrier RF System  Design goal:  6 kV wideband RF system  Two main components:  Cavity: made of Finemet cores (Hitachi, Japan)  Modulator: made of high voltage fast switches (Behlke, Germany)

W. Chou ICFA-HB2004 Workshop, October 20, Specifications Fast Switch (Behlke)  HTS GSM  Peak voltage2  16kV  Peak current60 A  Pulse width300 ns  Pulse spacing  s  Repetition rate100 kHz  Burst length400 ms  Burst rep rate0.5 Hz Finemet Core (Hitachi)  FT3M  OD500 mm  ID139.8 mm  thickness25 mm  Inductance56  H (per core)  Resistance190  (per core)

W. Chou ICFA-HB2004 Workshop, October 20, Barrier RF System (cont…) Finemet coreHigh voltage fast switch

W. Chou ICFA-HB2004 Workshop, October 20, Finemet vs. Ferrite (4M2)

W. Chou ICFA-HB2004 Workshop, October 20, Barrier RF System (cont…) ModulatorCavity

W. Chou ICFA-HB2004 Workshop, October 20, Full-Bridge Push-Pull Bipolar Circuit in the tunnelupstairs 9:1 1:9

W. Chou ICFA-HB2004 Workshop, October 20, Bench Test trigger current primary voltage gap voltage Before tuning After tuning 6 kV

W. Chou ICFA-HB2004 Workshop, October 20, Beam Experiment in the Main Injector capture debunch squeeze rebunch acceleration Beam intensity RF voltage

W. Chou ICFA-HB2004 Workshop, October 20, Beam Experiment (cont…) SqueezingSqueezed Moving barrier Beam squeezing 6 kV

W. Chou ICFA-HB2004 Workshop, October 20, Mountain View Stacking offStacking on t 1.6  s 3.2  s

W. Chou ICFA-HB2004 Workshop, October 20, More Mountain Views

W. Chou ICFA-HB2004 Workshop, October 20, GeV squeezing High Beam Intensity after Stacking

W. Chou ICFA-HB2004 Workshop, October 20, MHz RF voltage Beam intensity (10e12) Try Even Higher Beam Intensity

W. Chou ICFA-HB2004 Workshop, October 20, Emittance Simulation  ESME (2 x 5e12, final bunch after recapture, courtesy J. MacLachlan) Bucket size = 0.30 eV-sBucket size = 0.35 eV-s

W. Chou ICFA-HB2004 Workshop, October 20, Stationary bucket, beam intensity = 5.23e12, emittance = 0.13 eV-s Emittance Measurement – Injected Bunch

W. Chou ICFA-HB2004 Workshop, October 20, Low intensity Emittance Measurement – Stacked Bunch High intensity Medium intensity

W. Chou ICFA-HB2004 Workshop, October 20, Bunch width = 10 ns moving area factor = 0.45 Stationary bucket area = 1.6 eV-s bunch emittance = 0.72 eV-s Emittance Measurement – Accelerated Bunch

W. Chou ICFA-HB2004 Workshop, October 20, Summary  A barrier RF system has been built and installed in the Main Injector  It has successfully stacked two Booster batches into one and reached 8.3e12 at 120 GeV, ~ 60% increase in beam intensity  There is large emittance dilution during stacking  Causing losses at the beginning of acceleration  Making bunch too long for pbar production  But not a problem for NuMI  A second system is under construction and will be used for fast stacking experiment

Questions?