Accelerating Africa Experiment

• Project proposal - source
• Proposal video

Development

Date	Action
2015-08-20	Assembled goniometer in B4 office
2015-08-05	In contact with Ulrik Uggerhøj about goniometer at CERN
2015-07-10	Vidyo meeting with SimonHConnell and TimBrooks - discussed simulation results and planning
2015-07-01	Meeting with SergioBallestrero, MarkusJoos and TimBrooks - discussed status and plans moving forwards
2015-06-24	Vidyo meeting with SimonHConnell, MarkusJoos and TimBrooks - discussed experimental requirements
2015-06-16	Met with SergioBallestrero and SimonHConnell to discuss support for Team
2015-06-12	Contacted LauGatignon about magnet system Spoke to Jerome Alozy about rotation stage for crystal

Experimental design

• Current experimental layout:
  

• Proposed experimental layout:
  

Program

Preliminary task list:

• Empty run to calibrate detector,
• Team intends to work first with positrons, then electrons. Would electrons be better since they are a larger fraction of the Negative beam than positrons in the negative beam?
• Need identification of electrons/positrons.
• Need to extrapolate particles into the crystals to identify hit/no hit events. We rely on DWC0 & DWC1 to provide hit position on crystal. If we can construct a very small scintillator, we can trigger on events with a likely traversal of the crystal.
• Should measure angular distribution of incoming beam, gain using DWC0 & DWC1.
• Need to measure kinematics of the charged particles rejected by MNP17. Using the position of charged particles incident on DWC2, along with the initial trajectory in DWC0 & 1, we can derive particle momenta. Additionally, a LeadGlassCalorimeter block can independently measure the particle energy. With just the detectors in the beamline, we should be able to calibrate the tracking, energy and momentum mesurements by scanning the BeamLine energy with the Magnet off and then on.
• Need to assess backgrounds before installing crystals into the beam. How much synchrotron radiation can we expect and can we measure it?
• Need to position crystals in beam. How do we survey their positions? Can we measure their shape using the detector? Should we optimise their position?
• Measure photon energy spectra in events with a charged particle traversing the crystal. Check the photon + charged particle recovers the incident energy spectrum.
• Repeat measurement with the crystal in different orientations. Find point of maximum photon energy output.

Beam

An analysis has been done on DWC data from two runs in 2014, with beams focused on DWC0 and DWC2, resp. Events with three hits had tracks constructed using least squares fitting (Root, Minuit2). Below is shown some 2D graphs containing 100 tracks, the first ones with the beam focusing on DWC0, the second on DWC2. A beam spot size of about 4 cm * 4 cm is observed. It should be noted that the distributions are for events triggered by SC0 which means that the FULL beam profile is not shown. Actually, measurements of counts in the scintillator (SC2) from last year( see table 4.1 in the TR) show that there is a* large beam halo*, more than 20cm*20cm, most likely of muons. This should be taken into account by the Leo4G experiment.
Plots with high statistics showing the track distributions in X and Y for all three DWCs are seen in the attachments, for the run focusing on DWC0. As well as plots of the angular distributions in X and Y which show that the mean of the angles is around 5 mrad. By calculating the distance between fitted and measured points, the resolution is estimated to be about 1.5 mm.
As mentioned above, the experiment will use electrons and positrons that oscillate in the crystal to produce gamma rays. In the BL4S 2014 technical Report, measurements are shown of the rate of electrons in a beam of 4 GeV/c, see table 4.3. A rate of about .95 kHz was observed. Assuming a beam profile of 4cm*4cm, this implies about 60 Hz per 1cm*1cm. For the diamond (4*4 mm**2) this means about 10 Hz of electrons. For the Si-Ge crystal, about 20 Hz. The electron contents of the beam is strongly momentum dependent as shown in fig 2.2 of the TR.
The code developed is a monitoring program that can read events online or from a file:
~public/BL4S_DAQ/DataFlow/ROSMonitor/src/DWCTracking.cc (give the repository path ...) This program can be used to analyse the DWC data and provide a "burst" event display.

The rate of electrons/positrons can also be estimated from the T9 documentation. The figure on beam rates( Lau's presentation slide 13 or the office above Tim's desk ..) shows that the maximum rate of electrons at 4 GeV/c (with the collimators wide open) is about 10000 per burst. With a beam profile of 4*4 cm**2 that implies about 100 on 4*4 mm**2 per burst or 50 per second. This is a little higher than the estimate above probably because the collimators were not wide open last year(to be checked).

Particle Identification

The fixed Cerenkov counters allow to identify electrons and positrons. In principle, one Cerenkov counter is sufficient to identify the light particles. Operating the Cerenkovs with air at 1 atm is probably OK, see tables referenced in the TR 2014.
The analogue signals as well is the discriminated signals should be recorded in a QDC and TDC.

Crystals

Likely to have one diamond crystal and one Silicon-Germanium crystal. Si-Ge crystals may be made much larger.

The estimated sizes are 4 x 4 mm for diamond and about 4 x 10 mm for Si-Ge. The intent is to produce a 600nm pitch C-C(B) undulator with at least four periods radiating between 0.06 - 1.12 GeV.

Element Six have confirmed they will manufacture an undulator to the above specification. Two other manufactures will produce undulators also.

Spectrometry

The MagneticField from the MNP17 magnet is over . This should deflect a particle by . Over , that corresponds to a displacement of . This needs to be optimised to reject beam particles entering the calorimetry.

Henric has the MNP17 magnet booked for the BL4S beam-time, and the SHIP emulsion test prior to it. The positioning of the magnet is not critical for the SHIP test, so we may decide its location.

The DelayWireChambers have a linear acceptance of 80mm. Using MNP17 at full field, 0.5GeV particles would be deflected by 99mm, 30cm behind the magnet. 10 GeV particles would be deflected by 98mm 11 meters behind MNP17.

Calorimetry

Will use LeadGlassCalorimeter blocks the reject arm, after the spectrometry tracking. The front surfaces of the blocks are . This may also be suitable for the Photon calorimeter. It may be possible to add an external (shaping) amplifier to increase the energy range.

Need to investigate BGO Photon calorimeter from Aarhus group. Need sizing, power supply and readout requirements. The working range should cover 0.06 - 1.12 GeV.

Trigger

Since the Crystal's acceptance will be small, require small trigger scintillators, or halo counter as a veto. Jorgen is skeptical of halo counters due to inefficiencies of the Scintillators. A single small trigger scintillator may be better for this role - need to investigate possibility of small scintillator blocks.

Counters

Scintillator plates needed for trigger input. Possible backstop counter to tag muons?

Team contact

Team Twiki

• http://physics.uj.ac.za/wiki/CBL4S/Main/HomePage

Projects

• Calibration of LeadGlassCalorimeter using cosmic Muons or some beam time if we can get some.

Contacts

• TimBrooks
• Colleen Henning - St John's College Science HOD
• SergioBallestrero link. Atlas sysadmin and employed by Univ. Johannesburg.
• SimonHConnell (mentioned in the proposal) is his supervisor.
• ChristopherLee link. Atlas sysadmin and employed by Univ. Johannesburg
• Ulrik Uggerhøj - Aarhus contact for Goniometer

Open issues

Action	Priority	Due
Integration of Goniometer readback with DAQ chain Need information from Ulrik about goniometer model	1	2015-08-19
Understand requirements of Photon calorimeter Team in Arhus has a BGO calorimeter	1	2015-08-19
Production of trigger scintillator Checking active dimensions	3

Closed issues

Description	By	Status
Simulation of crystal interaction	Simon	Have some data in attached PDF
We will need a magnet	Tim, Lau, Henric	We have use of the MNP17 magnet we can decide on location
Sergio pointed out that the crystals have to be carefully aligned with respect to the beam. Therefore we need a suitable mechanical support	Markus, Simon	UJ will provide Labview controlled goniometer
The team proposes to test the crystal with both positrons and electrons	Tim	Estimate if T9 provides enough of the particles at the right energy and if inefficiencies in the particle identification could be a problem
The team proposes different materials that could be used for growing the crystal. Do we have a preference?	Tim, Sergio	Simon states the team will likely have one Diamond undulator and one Si-Ge
Sergio mentioned that synchrotron radiation may cause a background that masks the x-rays from the crystal	Tim, Sergio	discuss this further
What impact does the beam environment have pre- and post-crystal? Would a vacuum tube be feasible?	Tim	Looking at NA43/59 documentation

Resources

• Experimental investigation of the Landau-Pomeranchuk-Migdal effect in low-$Z$ targets Ulrik I. Uggerhøj et al - Description of BGO usage.
• Crystal Undulators as a New Type of Gamma-Ray Source Ulrik I. Uggerhøj
• The interaction of relativistic particles with strong crystalline fields Ulrik I. Uggerhøj
• The influence of anharmonic potentials in calculations of planar channeling radiation from GeV positrons J.A. Ellison, E. Uggerhøj, J.F. Bak
• Radiation from multi-GeV electrons and positrons in periodically bent silicon crystal Victor G. Bezchastnov, Andrei V. Korol, Andrey V. Solovyov.

-- TimBrooks - 2015-06-03

• 2_9GeV.pdf: Dechanneling length simulation