A journey to CTA northern site

On the Canary island of La Palma (Spain), Cédric Champion, from APC Electronics, backed up remotely by Michael Punch (physicist at APC), are participating in the integration campaign of the prototype Large-Sized Telescope (LST) with the Cherenkov Telescope Array Observatory (CTAO) Array Control and Data Acquisition System (ACADA).
The LST has been in commissioning as a single Imaging Cherenkov Telescope for Gamma-ray astrophysics since 2018, with some science results already being produced.  But this integration step is crucial to allow the LSTs (of which there will be four on the Northern CTAO site) to be controlled centrally and integrated together with the Medium-Sized Telescopes (MSTs) of which there will be at least nine, to work smoothly as a stereoscopic array of IACTs, to be more powerful by up to an order of magnitude than the current four H.E.S.S. telescopes in Namibia in which the APC has a leading role.
For these LSTs, and also for the MSTs which will be installed at La Palma which will use the NectarCAM cameras, the APC provides the crucial time-stamping boards based on CERN White Rabbit technology, which allow the individual telescope triggers to be dated to the nearest nanosecond so that ACADA's SoftWare Array Trigger (SWAT) can then determine the stereoscopic coincidences for which the camera data will be written to disk.
The interaction of the APC's time-stamping with the CTAO-ACADA's SWAT is just one of the points being tested in this ACADA-LST integration campaign, which involves also computer scientists from CPPM, Marseilles, together with scientists and engineers from LST (mostly Japan, Germany, Spain, Italy, and France, among others) and from ACADA (from the CTAO project office with in-kind contributions from Germany, Italy, France, Switzerland, Spain, and Poland, all of which were represented in this integration campaign).
Some details:
* LSTs, 23m diameter dish, camera with 1855 0.1-degree photomultiplier pixels for a 4.3 degree Field-of-View
* MSTs, 11.5m diameter dish, camera with 1855 0.17-degree photomultiplier pixels for a 7.7 degree Field-of-View
"A journey to CTAO northern site" by Cedric Champion:
“After a 6-hour flight, I landed at La Palma airport ahead of schedule - a good sign? After an hour and a half's drive climbing over 2000 metres we arrived at the Roque de los Muchachos Observatory, where the CTAO Northern site is located. The first things you see when you arrive are the two MAGIC telescopes and the huge LST-1, which are breathtaking! Then, looking out over the landscape, you can see telescope domes all over the mountain, as well as construction sites for the next three LSTs – impressive. We started work just after lunch for a night shift. We then had long working days as we had to prepare the night’s tests during the day, but everything went well. So we're confident about the future of CTAO-North, with the construction of three new LSTs and nine MSTs. It was good to see that our electronics board, which is essential for the telescopes, worked well in a real-life situation. It was a pleasant and efficient working session, and also an opportunity to meet colleagues I'd only met virtually, and to work on-site with colleagues I already knew from CPPM or IFAE.”
APC CTA hardware team members:
Cédric Champion
Stéphane Colonges
Ronan Oger
Michael Punch
with support from:
Lydie Pavili-Baladine (admin)
Bernard Courty, Pierre Prat (computing, electronics)
The details on the full H.E.S.S.-CTA group at APC can be found on the APC website link.
1st LST on the North site of CTAO in La Palma
(© Cédric Champion @APC/CNRS)
Cedric Champion’s reflection in one of the mirrors, taking the photo
Where is Cedric?
(© Cédric Champion @APC/CNRS)
Commissioning container
(© Cédric Champion @APC/CNRS)
View above the clouds from the North site of CTAO in La Palma
(© Cédric Champion @APC/CNRS)
Sunset above the clouds from the North site of CTAO in La Palma
(© Cédric Champion @APC/CNRS)
Celebratory Sunday lunch (off-mountain) after a successful night’s work by the on-site team
Where is Cedric?
(© Dirk Hoffmann @CPPM/CNRS)
  • CTA
  • CTAO
  • LST
  • gamma ray


  • Astrophysique à Haute Energie

Objet de la publication: 

Faits marquants projets