1. Status of the InGrid detector for 2016
Christoph Krieger

2. The InGrid detector for 2016
Main features:
Ultrathin silicon nitride window
Drift cylinder with field cage
Readout module hosting 7 InGrids (central chip surrounded by 6 chips to veto partial tracks mimicking X-rays)
Decoupling of grid signal
Two veto scintillators (a small & a bigger one)

3. Ultrathin silicon nitride windows
First batch of silicon nitride windows made by Norcada:
14 mm aperture with 3x3 array of membranes
200 nm membranes plus 20 nm Aluminum
0.5 mm ribs with 200 µm thickness
5 windows delivered to Bonn end of last week
Also received 2 “rib devices“ of 500 µm thickness for reinforcing window structure
Testing at Bonn:
Will (re)setup improvised vacuum teststand used for samples end of last year
Glue windows onto new cathode plates & SLOWLY pump them
Foresee destructive pressure test for at least 1 or 2 windows as well as several pumping & venting cycles
Will glue “rib device” to 2 windows
Feedback to Norcada as soon as possible for second batch

4. Readout module hosting 7 InGrids
Central chip surrounded by 6 “veto” chips
Track fragments mimicking low energy X-ray events can be vetoed as rest of track is visible on “veto” chips
Should contribute most to the background reduction at low energies
Status of “The Magnificent Seven” readout module:
New electronic boards (intermediate board & chip carrier) have been received and are being assembled
Mechanic parts have been submitted to workshop (already 2 months ago, still waiting…)
Testing of electronic parts is starting right now
About 20 InGrids from batch IZM-7 are available for the 2016 InGrid detector

5. Drift cylinder with field cage
Outer chips are quite close to drift cylinder
Inhomogeneous electric field expected in this region
Equipped existing drift cylinder with simple field shaping structure to minimize distortions
Copper strips on Kapton with SMD resistor chain

6. Decoupling of grid signal & veto scintillators
Decoupling of induced grid signal is foreseen
Ortec preamplifier will be used as close to detector as possible
Signal will be sampled with an FADC
Signal shape will help to discriminate tracks perpendicular to chip surface mimicking ~ 8 keV photons
Small piggyback veto scintillator on backside of detector for same reason
Bigger veto scintillator on top of shielding to veto fluorescence X-ray photons induced by cosmic rays
Time between last veto signal and FADC trigger is recorded
Veto scintillators can only be used together with decoupling & sampling of grid signal
None of these is expected to significantly improve low energy background (depends on trigger threshold of FADC and noise)
Veto scintillators shall be read out with SiPM, currently some issues with electronics to read out SiPMs, still to be understood
Further tests on decoupling the grid signal start next week (has already worked before)

7. Readout system & software
New features have been implemented in readout firmware but need testing with hardware (only available now)
Readout of seven chips already working, may need a bit of timing adjustment for new hardware
Interplay of FADC trigger and readout of chip already implemented in firm- & software, already mostly tested
Operation of HV power supply now integrated in readout software, uses same bus as FADC readout, already mostly tested (need to check with long USB)
Reminder: frame-based, untriggered readout of chip
FADC trigger will close frame after short delay, else frame is closed after defined time, all frames are read out & recorded, timestamp of FADC trigger is recorded
Time between last veto scintillator signals and FADC trigger is recorded
Still a lot testing & debugging to do

8. Preparation of the infrastructure @ CAST
InGrid’s vacuum system remounted at the end of April and brought back to life
Afterwards last opportunity of laser alignment was used
IMPORTANT: chameleon installed ;)
Needle valve will have to be exchanged for operation with ultrathin windows (Pressure gradient ~< few mbar/min required)

9. Measuring InGrid’s position
After laser alignment InGrid’s position was remeasured by the geometers
Same measurement was done last November before dismounting
Position is calculated by measuring points on three circumferences & fitting circles to the points (stated precision is ~ 1 mm)
Old & new position agree with in few 100 µm in X and within 1 mm in Y & Z, taking into account measurement precision it seems to be fine
Alignment precision of ~ 0.5 mm expected from laser alignment (included in systematic uncertainties in chameleon analysis)

10. Installation end of July
Foreseen to start in week 30 (25.7)
Rough schedule: 25.7    Arriving at CERN with the equipment/detector 26.7    Installing the additional infrastructure for the detector & modify the vacuum system for really slow pumping    Setup the detector (not mounting it yet) and get it running & perform a dry run for the slow pumping (no thin window) & start pumping XRT    Debug the detector & keep pumping XRT      Mount the detector & last debugging of detector plus tests 3.8      Really slow pumping of InGrid vacuum with thin window in place 4.8      Pumping until desired pressures are reached 5.8      Mount shielding
If possible, shifting by one or two weeks would help with tight schedule and allow for a bit more testing at Bonn, should not affect start of the run… possible???

11. Status of XRT vacuum system
Currently there is no one responsible for operation & maintenance of XRT vacuum system
Bonn cannot do it, neither enough manpower nor enough money
Who will be responsible for operation & maintenance of the XRT vacuum system in 2016 and beyond?
In April sudden pressure rise in bellow region caused system to stop, reason unknown but maybe hinting at failing turbopump
Spare(s) for turbopumps available, but pump types no longer serviced by Leybold  if spares are used up, we are screwed

12. The InGrid detector beyond 2016
Just some ideas… (on request of Wolfgang)
Even thinner window: 100 nm silicon nitride
Maybe Timepix3-InGrids (datadriven readout, similultaneous measurement of time & charge, …)
Adopt design of current SRMM (copper body)
Depends on funding!

13. Conclusion, Outlook & Questions
Building the 2016 InGrid detector: thinner windows & more chips
Very tight schedule: still a lot of things to test & debug
Testing of first full-size ultrathin 200 nm windows will start this week
Installation foreseen for end of July
Maybe shift schedule by one or two weeks to gain time for more testing at Bonn??? (should not affect start of the run)
Who will be responsible for operation & maintenance of the XRT vacuum system in 2016 and beyond?
Who has to approve the operation of the XRT with the ultrathin windows before opening the XRT downstream gatevalve?