longitudinal bunch shape monitor
DESCRIPTION
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 - PowerPoint PPT PresentationTRANSCRIPT
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
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
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
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
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
3D-BSM
Wire moves horizontally
A slit moves vertically
For each point in transverse phase space the longitudinal distribution can be measured
Detector use
Bunch shapes for different RF amplitudes
Bunch shape with a tank on a wrong phase
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
Detached electrons (H- beams)
Detached electrons can be seen in the bunch spectrumThis is a problem if longitudinal beam halo is to be measured
The problem can be solved by analyzing the electron energy
Similar detector developed at GSI
No wireThe secondary electronics are createdin the rest gas (non intercepting)Electrons accelerated in an electric fieldSource region is restricted by a slit
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
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