Laser Geiger cell (update) UCL Laser Geiger cell (update) Robert L. Flack March 2008 Cell review meeting, MSSL

Cell review meeting, MSSL Introduction Investigated the drift speed of the electrons to the anode after ionisation in a 3cm and 5cm diameter cell. The 3cm diameter cell was constructed with the help of the University of Manchester. The 5cm cell was constructed at UCL (thanks to Brian and Derek). A nitrogen laser, λ = 337nm, is used to simulate the ionisation of the gas by a charged particle (double photon capture by impurities from the pump oil in the gas). March 2008 Cell review meeting, MSSL

Schematic of the test cell March 2008 Cell review meeting, MSSL

Cell review meeting, MSSL tf t0 ← 45μs → tf March 2008 Cell review meeting, MSSL

DAQ (Thanks to Gianfranco Sciacca) Use a Camac TDC. Event triggered by PMT. Anode pulse stops the event, if it appears within a pre-specified time window of 340ns. If outside of the window it is assumed to be a cosmic. March 2008 Cell review meeting, MSSL

Investigation of the drift speed of electrons to the anode after ionisation March 2008 Cell review meeting, MSSL

Laser 4 mm under the anode Interpretation of the distribution is that it is due to the geometry of the laser beam. The peak is due to the increase density of photons at the focal region. Peak ~150nS The tail is due to the less dense region of the laser beam. Drift speed ~ 1mm/37.5nS Time nS March 2008 Cell review meeting, MSSL

Ionisation times v Vertical distance March 2008 Cell review meeting, MSSL

Combined drift times and speeds 3cm in green 5cm in red March 2008 Cell review meeting, MSSL

Cell review meeting, MSSL Efficiency The strategy is as follows. The ionisation process, double photon capture, is the same in the 3 and 5cm cell. Hence an estimate for the relative efficiency can be found for this process. The absolute efficiency for the totally different process, ionisation of the He gas by a charged particle, in a 3cm cell is known from NEMO3. Assuming the efficiency for both processes scale identically then an estimate of the efficiency for the 5cm cell can be calculated. Specifically the number of ionisations per mm. March 2008 Cell review meeting, MSSL

Observation inline with the anode Tail is constant across the cell March 2008 Cell review meeting, MSSL

Relative efficiency @ 2mm Using data 2mm from the anode: 3cm; 958 events in 13.6mm = 71/mm 5cm; 1198 events in 13.6mm = 88/mm The time taken to take the data is 4 times faster for the 3cm cell. Rel eff = 4 x 71/88 = 3.2 March 2008 Cell review meeting, MSSL

Relative efficiency @ 8mm Using data 8mm from the anode: 3cm; 1900 events in 17.8mm = 107/mm 5cm; 2083 events in 17.8mm = 117/mm The time taken to take the data is 2 times faster for the 3cm cell. Rel eff = 2 x 107/117 = 1.8 March 2008 Cell review meeting, MSSL

Cell review meeting, MSSL Conclusion The 5cm cell appears to work satisfactorily. The distribution of speeds in the 3 and 5cm cells are consistent with NEMO3 out to 23mm radius. The relative efficiency is 3.2 at 2mm and 1.8 at 8mm. March 2008 Cell review meeting, MSSL

Cell review meeting, MSSL Backup slides March 2008 Cell review meeting, MSSL

Test cell at Manchester March 2008 Cell review meeting, MSSL

Cell review meeting, MSSL Cathode ring + wires March 2008 Cell review meeting, MSSL

Cell review meeting, MSSL Test cell at UCL March 2008 Cell review meeting, MSSL

Cell review meeting, MSSL Stage for laser UV-Laser Diverging lens Convex lens CCD camera March 2008 Cell review meeting, MSSL

Cell review meeting, MSSL Diverging lens Converging lens Pulse rate = 20 Hz Pulse width = 3ns Power = 5 mW Laser light Focal point Pinhole March 2008 Cell review meeting, MSSL

Cell review meeting, MSSL A typical profile of the laser beam. Fitted with a 2D polynomial March 2008 Cell review meeting, MSSL