Electron Spectrometer: Status July 14 Simon Jolly, Lawrence Deacon 1 st July 2014

Spectrometer Tasks 1.Separate the spectrometer response and the readout response. 2.Do all calculations in steps and show the results for each step 3.Provide the individual contributions to the spectrometer resolution as a function of detected energy coming from: –transverse emittance (zero dispersion). –dispersion (point source). 4.For the 2 injection scenarios (on axis & side injection), calculate the number of visible photons generated for a fixed magnetic field: –as a function of position along the scintillator screen. –as a function of energy. 5.Track the vertical beam size through the spectrometer to determine the vacuum pipe size. 6.Look at the influence of other effects that can limit the measurements e.g. the fringe fields of the magnet, correlation between energy and emittance or size, etc. 7.Make a full comparison between having the scintillator inside and outside the vacuum, studying for example: –What is the maximum radiation length allowed in case the electron beam passes through a window. –If viewports of adequate size be found for the scintillator in vacuum case. 8.Automate the generation of the results so that the expected energy spectra in the experiment can be systematically generated from various phase space distributions. 9.Specify the minimum needed vacuum level. 01/07/14Spectrometer Status July 142

1. Separate the spectrometer response and the readout response Recorded are: –electrons entering the scintillator screen –visible photons emitted from the scintillator screen –visible photons entering camera lens The spectrometer response and readout response are therefore separated. Results for a typical on-axis spectrum were presented at the April collaboration meeting by L. Deacon (0850 on 11th April): – ntribution/24/material/slides/0.pdf 01/07/14Spectrometer Status July 143

Input Energy Input: witness electron bunch file consisting of 12,688 electrons injected in a length 120 mm +/- a few mm behind the laser pulse. Repeated this file to fire a total of x10 7 ~ 6% of the number predicted by plasma wakefield simulations (30% injection eficiency - > “final N e = 3·108” — Alexey's Talk) 01/07/14Spectrometer Status July 144

Measured Energy: Electrons at Screen The positions of the primary electrons were recorded at the screen. These positions were then used to reconstruct the energy spectrum. The energies are binned with the bin widths of the camera pixels (variable width bins). 01/07/14Spectrometer Status July 145

Measured Energy: Electrons at Screen The two histograms plotted on the same axes. However, the electrons will not be detected directly: –Phosphor screen. –Camera. We simulate the photon production in the screen and count photons in the camera lens. 01/07/14Spectrometer Status July 146

Measured Energy: Photons at Camera Lens Sampling plane placed 4 m away from the screen. Position at the screen of optical photons within the lens diameter (50 mm) recorded. Total of 2.29x10 5 photons in lens acceptance. Energy reconstructed from these positions (perfect image assumed). Rescaled using conversion factor (photons per electron at screen) to plot the e - spectrum (magenta on plot). 01/07/14Spectrometer Status July 147

2. Do all calculations in steps and show the results of each step For pre-camera steps see task 1. For post camera steps, we are checking our camera model with reference to all camera sub systems (photocathode, micro-channel plate [MCP], fibre coupling, phosphor screen and CCD chip) in order to include the camera noise and point spread function. MCP and Fibre Optic Plate have 6 micron channels, so no 1:1 matching with CCD (35 micron pixels) but resolution not reduced by MCP. 01/07/14Spectrometer Status July 148

3. Individual contributions to the spectrometer resolution from: emittance, dispersion The simulation and analysis chain is set up. A summer student will scan the different variables. This will be carried out for uniform magnetic field before moving on to MBPS field map. Not clear what emittance means for such large energy spreads, so will try and set resolution limits for electron position/angle as a function of energy (unless anyone has a better idea…). 01/07/14Spectrometer Status July 149

4. Number of visible photons generated for a fixed magnetic field We have been working to verify/tune the simulation of the screen photon output in comparison with experimental data. Presented at IPAC Left: photons per input electron — our simulation vs. experiment. 01/07/14Spectrometer Status July 1410

4. Number of visible photons generated for a fixed magnetic field Left: angular distribution — our simulation vs experiment for various screen thicknesses. Next we will plot photon output as a function of screen beam energy/position for a fixed magnetic field. 01/07/14Spectrometer Status July 1411

5. Track the beam to determine the vacuum pipe beam size Lately we have been concentrating on looking at the electron beam vacuum window. We still have to track the beam through the vacuum chamber and determine the best vacuum chamber vertical size. 01/07/14Spectrometer Status July 1412

6. Look at other effects e.g. fringe fields, correlation between energy and emittance or size etc. We have set up the fringe fields in the simulation based on measurements from the 1960’s but have not run the simulation yet. We will look at these effects soon. Summer student will help. 01/07/14Spectrometer Status July 1413

7. Make a full comparison between having a scintillator inside or outside the vacuum We assume a carbon fibre window. The FWHM of the position distribution of photons emitted from the screen vs. window thickness is plotted for the beam at: –45 degrees to the screen (worst case). –90 degrees to the screen. –for various beam energies. Also the efficiency (number of photons per incident electron) is plotted. 01/07/14Spectrometer Status July 1414

15 MeV Beam at 45° to Screen Blue line shows required FWHM res. of screen (assuming we need 50% of camera res., and camera resolution = 35 microns). Update: camera res. measured as ~25 microns (measured by Andor). 01/07/14Spectrometer Status July 1415

15 MeV Beam at 45° to Screen Efficiency = photons emitted per electron. 01/07/14Spectrometer Status July 1416

15 MeV Beam at 90° to Screen 01/07/14Spectrometer Status July 1417

100 MeV Beam at 90° to Screen 01/07/14Spectrometer Status July 1418

200 MeV Beam at 90° to Screen 01/07/14Spectrometer Status July 1419

500 MeV Beam at 90° to Screen 01/07/14Spectrometer Status July 1420

1 GeV Beam at 90° to Screen 01/07/14Spectrometer Status July 1421

8. Automate the generation of results for different input beams Simulation and analysis chain is set up. Procedure: –Edit input file to select the choses input beam file. –Run a script to submit jobs to the batch farm/ run locally on desktop. –Run another script to plot the results and produce output. 01/07/14Spectrometer Status July 1422

9. Specify the minimum needed vacuum level Simulations were carried out to measure the effect of photon/beam gas scattering on screen output — preliminary results presented at Collaboration Meeting Dec To be run with updated simulation including updated vacuum chamber, electron beam window, screen etc. 01/07/14Spectrometer Status July 1423

9. Specify the minimum needed vacuum level 01/07/14Spectrometer Status July 1424 From Dec 2013:

Information Needed Status of BI Fellow. Latest CAD models… 01/07/14Spectrometer Status July 1425