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Longitudinal Bunch Shape Monitor

Longitudinal Bunch Shape Monitor. U. Raich. Detector developped in Russia. Detector mainly developped by Institute for Nuclear Research (INR) Moscow A. Feschenko and collaborators INR is willing to build detectors for us Methods and Instrumentation for Bunch Shape Measurements

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Longitudinal Bunch Shape Monitor

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  1. Longitudinal Bunch Shape Monitor U. Raich Linac-4 instrumentation day May 2007

  2. Detector developped in Russia • Detector mainly developped by Institute for Nuclear Research (INR) Moscow A. Feschenko and collaborators INR is willing to build detectors for us Methods and Instrumentation for Bunch Shape Measurements A.V. Feschenko INR Moscow, proceedings of PAC Chicago 2001 Linac-4 instrumentation day May 2007

  3. The principle • Coherent transformation of longitudinal bunch structure into a transverse distribution of secondary electrons • Consists of • A wire in which secondary electrons are created • An electric field to accelerate the electrons • Deflecting plates with a deflecting field synchronous with the accelerator RF • An electron detector Linac-4 instrumentation day May 2007

  4. The principle (2) Secondary electrons created in the wire Only the electrons created by particles in the primary beam with a fixed phase are measured The deflection corresponds to a phase sweep Typical phase resolution: 1° at several 100 MHz Linac-4 instrumentation day May 2007

  5. Time resolution 350 MHz accelerating frequency => 3ns cycle time Micro bunches are much smaller Typical phase resolution is 1° => Time resolution of some tens of ps Linac-4 instrumentation day May 2007

  6. Different types of detectors • BLVD: Bunch Length and Velocity Detector • The wire can be displaced longitudinally • Displacement by one full RF period (bunch shape will be the same as the one before displacement • Measure wire displacement Linac-4 instrumentation day May 2007

  7. 3D-BSM Wire moves horizontally A slit moves vertically For each point in transverse phase space the longitudinal distribution can be measured Linac-4 instrumentation day May 2007

  8. Detector use Bunch shapes for different RF amplitudes Bunch shape with a tank on a wrong phase Linac-4 instrumentation day May 2007

  9. Longitudinal Emittance Modify particle energy by changing the accelerating amplitude Measure the bunch size for each energy Knowing the optics, calculate back to the last accelerating element Linac-4 instrumentation day May 2007

  10. Detached electrons (H- beams) Detached electrons can be seen in the bunch spectrum This is a problem if longitudinal beam halo is to be measured The problem can be solved by analyzing the electron energy Linac-4 instrumentation day May 2007

  11. Similar detector developed at GSI No wire The secondary electronics are created in the rest gas (non intercepting) Electrons accelerated in an electric field Source region is restricted by a slit Linac-4 instrumentation day May 2007

  12. Experience at CERN • BLVD at Linac-3 (Bunch Length and Velocity Detector) • 3-BSM at Linac-2 • Were used intensively for beam studies with good results • INR crew has left • CERN linkman in retirement • System was not integrated into the Linac control system Result: The detectors are currently not in use Linac-4 instrumentation day May 2007

  13. Problems to be solved • Thermal resistance of the wire (same problem as any intercepting device) • RF deflector must be adapted to the accelerator’s RF frequency • The wire works like a stripper and the detached electrons may disturb the measurements Linac-4 instrumentation day May 2007

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