Barth, K

Benda, V

Borghi, S

Davenport, M

Dellille, B

Elias, N

Gonidec, A

Guillaume, D

Haug, F

Konstantin, Zioutas

Lindell, K G

Losasso, M

Martyn, Davenport

Niinikoski, T

Pirotte, O

Viargues, F

Zioutas, K

CERN Document Server

  14-Nov-06 Minutes of the Technical Design Review for the 3He system of the CAST experiment page1 out of 2 CERN-SPSC-2006-036         SPSC-M-750        Minutes of the Technical Design Review for the 3He system of the CAST experiment   Batiment 165   R-006 17 October 2006.  Committee: Francois Viargues CEA-SBT Grenoble, Didier Guillaume CEA-STB Grenoble, Vladislav Benda CERN AT-ACR, Allain Gonidec CERN PH-DT1, Marcello Losasso CERN PH-DT1, K G Lindell CERN-Safety Commission, Benoit Dellille  CERN-Safety Commission.  CAST team: Nuno Elias PH-DI, Tapio Niinikoski AT-ECR, Konstantin Zioutas PH-UGC, Martyn Davenport PH-DT1, Silvia Borghi PH-DT1.   Invited observers: Klaus Barth AT-ECR, Olivier Pirotte AT-ECR, Friedrich Haug AT-ECR  The bound version of the CAST 3He gas system TDR (CAST TDR1, CERN SPSC-2006-029 and SPSC-TDR-001) was distributed at the start of the meeting. M Davenport proposed himself as chairman of the meeting with the tasks of collating the shortlist of critical items from the reviewers and producing and circulating the minutes of the meeting. In addition, he would produce the first draft of the Review report and circulate it to the review committee for corrections and comments. The Review report will be submitted to the Chairman of the SPSC and the Steering Committee of CAST  The agenda was as follows:  • Introduction to CAST Phase II experiment [K Zioutas / Spokesman CAST] • Presentation of 3He gas system project [N Elias] • Safety Issues concerning the installation and operation of the new system [M Davenport ] • Open discussion between reviewers and CAST representatives • Closed Session for reviewers to make short list of critical items  The terms of reference of the reviewers were the following: • The primary aim is to verify all the technical aspects of the system and that they are consistent with the stated ‘Requirements and Functionalities’ of the system.  • For completeness, the reviewers are also welcome to comment on the cost estimates and timescales contained in the TDR.  Introduction to CAST Phase II experiment [K Zioutas / Spokesman CAST]  Professor K Zioutas summarised the history of the theoretical and experimental work on axions. The CAST experiment is to search for axions which are thermally produced in the solar core by the Primakoff effect and which then propagate to the earth where they can be converted into X-rays by the reverse Primakoff effect in a strong transverse magnetic field before being detected by very sensitive low-background X-ray detectors situated at each end of the magnet cryostat. He outlined the basic operation of the experimental apparatus and the results so far obtained with vacuum inside the cold bores of the magnet (a 10m LHC prototype). The magnet is computer-guided to follow the sun for ~ 100 minutes at sunrise and sunset each day. A signal for an axion would be a significant excess of X-ray events when tracking the sun compared to that expected from the intrinsic environmental background. No signal was seen in CAST during this phase (Phase I). With vacuum inside the cold bores, the coherence condition for the transformation of axion to photon in the transverse field of the magnet is only satisfied for axion rest masses < 0.02 eV/c2. In order to scan a much wider rest mass range, and approach the region favoured by theory, the coherence condition must again be satisfied.  An idea, originally put forward by K van Bibber, to introduce a gas into the cold bore to restore the coherence criterion can be used, but the criterion is only satisfied for a near-unique axion mass value. In order to scan a wide mass region (0.02 to 1 eV/c2), it is necessary to change each day the gas density inside the cold bores by a small and well defined step. The gas density reproducibility must be   14-Nov-06 Minutes of the Technical Design Review for the 3He system of the CAST experiment page2 out of 2 precise to between 10-3 and 10-4 – a very difficult criterion to achieve in practice. Hence the need to build a precision cryogenic gas system able to introduce precise quantities of gas into the cold bore.  He showed that since the start of the Phase II of CAST, a significant range of axion rest mass has already been covered using a provisional 4He gas system but indicated that the range was limited due to the saturated vapour pressure of 4He at 1.8K to approx 16 mbar (axion rest mass ~ 0.42 eV/c2).  He highlighted the need for the new gas system using 3He which would enable the CAST experiment to extend their measurements ultimately up to about 120 mbar (axion rest mass ~ 1.16 eV/c2).  Presentation of 3He gas system project [N Elias]  N Elias presented the project to build and operate the 3He gas system. He outlined the key requirements for the system and the practical constraints. The two key requirements being the precision with which the gas density must be set and the ability of the system to protect the cold X-ray windows in the event of a magnet quench whilst the full charge of gas is in the cold bore. The protection system is particularly important since about ten quenches per year are expected at CAST, mainly due to power cuts.  He then systematically worked his way through the elements of the system and described the procedures for the various operating modes of the system. The precision metering of the gas introduced into the magnet cold bores was described and the estimated precision of the density setting was presented. At the highest densities corresponding to 120 mbar at 1.8K, the density setting can be reproduced, starting at vacuum, to within one density step between settings. The largest contributions to the error on the density setting being the variation in ambient temperature and the number of times the metering volume must be filled and emptied into the cold bore to arrive at the density setting required. It will be necessary to temperature control ‘dead volumes’ and introduce a larger metering volume to improve the precision at the highest densities.  He then outlined the timetable and milestones of the installation of the system in the 1Q2007 and presented the cost estimates for the project.    Safety Issues concerning the installation and operation of the new system [M Davenport ]  M Davenport presented a preliminary outline of the main items which could involve personnel safety issues during the installation and operation of the 3He gas system. He was asked to make a Risk Assessment by the Safety Commission, who are willing to help by giving advice.  Open discussion between reviewers and CAST representatives  After the presentations there was a lengthy exchange of views and specific technical questions concerning various parts of the system. At the end of this session, there were no significant outstanding questions concerning the routine operation and feasibility of the 3He gas system design and its ability to satisfy the ‘Requirements and Functionalities’ of the 3He system.  There was however a general agreement that the response of the system in case of single and multiple point failures correlated with the rupture of a cold X-ray window required some more study since the loss of  3He was  possible.  There were also a safety concern linked to a possible over-pressurisation of the 3He pipe-work at each end of the magnet in case a large quantity of air had been cryo-pumped into the system from an undetected air leak, additional safety systems were discussed.   Closed Session for reviewers to make short list of critical items  The list of key points and observations were compiled and discussed.  A document named the ‘CAST 3He Review Committee’s Report’ will be produced and circulated to the committee for corrections. When corrected, this document will be sent to the CAST team and the Chairman of the SPSC and Steering Committee of CAST. The CAST team will be requested to send rapid feedback to the Review Committee on the points raised. If necessary, a follow-up meeting or an audio conference will be arranged to clear up any remaining points.  Martyn Davenport 13.11.06 

Minutes of the Technical Design Review of the 3-He system of the CAST experiment

Minutes of the Technical Design Review of the 3-He system of the CAST experiment

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