General discussion
Integration of the e+ elements
Laszlo Liszkay
•
•
•
•
BGT1
Positron line
Buffer gas trap (BGT)
Multi-ring trap (MRT)
Reaction chamber
BGT2
BGT
BGT3
MRT1
MRT2
Bunc
her
Field
exit
Lenses
Targ
et
Present status of the different parts
• BGT: being tested
• MRT: magnet awaiting commissioning, electrodes to be
installed
• Buncher/lenses assembled, to be tested
• Target: under construction
Differences between the Saclay and CERN installation
• No MRT in Saclay
• Buncher directly after BGT
• Higher frequency (1 Hz?)
• Different pulse energy/intensity at buncher
• Different magnetic field at magnetic field exit
• At CERN, no access to the beam during operation
• All beam diagnostics with remote control
Can we use the MRT trap at first in a shoot-through
configuration, without trapping, in the first
measurements? (in order to perform measurements
before the trap works) Or just in a simplified
configuration (rectangular potential well, switches)?
• Can we use the MRT trap at first in a flat-field
configuration, without trapping, in the first
measurements? (in order to perform measurements
before the trap works)
• Or just in a simplified configuration (rectangular
potential well, switches)?
Diagnostics
cross
DN100
straight tube +
solenoid
Do we need
a pump
here?
DN100
bellows + coils
Integration of the positron source and the buffer gas trap
• Beamline: to be completed
• bellows + coils
• tube with solenoid
• cross + pump if needed (decision?)
• Other interactions:
• Information from linac (frequency, trigger, on/off)
• Pressure values & position of the gate valve
Who?
• Purchase/manufacture vacuum parts (DN100CF tube,
bellows) - length depends on other choices
• Wind coils
• Prepare support (NORCAN or similar)
When?
• Before the installation of the buffer gas trap
Do we need one more pump here?
Missing:
DN100 bellows
DN100CF valve
Integration of the buffer gas trap with MRT
• Connection with bellows (available) if no extra pump is needed
(decision)
• DN100CF gate valve (check if available)
• Trigger: ejection from BGT
• Other information exchange: pressure, position of the valve
• To do: calculate magnetic field (put together existing models)
Who?
• Has to be done together with the assembly/testing of MRT
When?
• Parts can be found:ordered immediately
• Possibility: new chamber to replace the old RIKEN one
• With better magnetic properties if possible
• With large enough tube for pumping
DN100 cross
for pumping
(which pump?)
+ buncher
• cross (available or – better new DN160) + coils (available)
+ power supply (use reserve +
buy new)
• Or totally new chamber/cross
(time + manpower)
Integration of the MRT trap with the target chamber
• Cross + coils (exist in DN100CF)
• Pump: which type?
• Cryo: best but very expensive (>20k€)
• Ion getter: distortion of the magnetic field
• Turbomolecular: pressure limit too low(?)
• Trigger:
• Injection trigger from BGT
• Ejection trigger from ELENA (+ delay+gate/veto)
• Other information: vacuum pressure, valve position
NaI/CsI
Diagnostics
MCP
CsI
(~4 targets)
MCP +
scint.
MCP (atoms)
MCP (ions)
Tracker (anti~)
Faraday cup (p)
MCP
CsI/NaI
Faraday cup (e+)
PbWO
Beam diagnostics
• Detection of the annihilation radiation
• CsI+diode: at the moment, problems with direct 511 keV
calibration (noise); no time information
• NaI + PM: more robust signal but sensitive to magn. field; no
time information
• Plastic + PM: difficult to calibrate, sensitive to magn. field;
good time information
• PbWO: difficult to calibrate, sensitive to magn. field, good
time information; works well with high intensity
• Beam shape detection
• MCP (double) + phosphor screen + camera
time information is possible
• Faraday cup for direct charge detection
• Must capture secondary electrons
• Only at higher pulse intensity (?>1M e+?)
• Can be used to verify calibration of scintillation detectors
Calibration of the detectors
• Calibrate one or two NaI (or perhaps CsI) detectors by
• Measurement of the 511 keV gamma line
• Determination of the mean signal amplitude per positron (G4
simulation, verified by measurement)
• Calibrate the other detector with the help of the calibrated ones
Data acquisition:
• At the moment, we have only destructive beam diagnostics devices
• Only one can be used at a time, so several detector can use the
same data acquisition device if needed (by using a signal switch)
• The only continuously operating data sources of the positron line
will be the gamma detectors in the reaction chamber
• We should check if a non-destructive diagnostics device (toroidal
current monitor?) is possible when the MRT trap works
Different parts
• Beam diagnostics at the beam exit from the bunker: oscilloscope at
the moment, can be switched to PXI card+amplifier if we have
enough money
• BGT – PXI card, working (archiving to EPICS?)
• BGT – MCP + camera, working (manual, manual archiving)
• Reaction chamber: oscilloscope (scintillator detectors + MCP signal)
• Reaction chamber: MCP+camera (to be ordered, same as MRT)
Timing signals:
• BGT works with internal timing + gives trigger signal to MRT
• MRT ejection is triggered by ELENA (ns jitter)
• Laser triggered by ELENA (+ pre-trigger)
• Atom/ion detection is triggered by ELENA (10ns jitter is OK)