Minutes from REX meeting 2005-09-23

Present: Mats Lindroos (chair), Karsten Riisager, Didier Voulot, Pierre Delahaye, Romain Savreux, Nicolas David, Han Broere, Luis Fraile, Richard Scrivens and Fredrik Wenander

General

* The beryllium run (isotopes 12 and 11) went very well. A summary is attached to these minutes.

* The krypton run (isotopes 88 and 92) went well. A summary is attached to these minutes.

* Xenon 138, 140 and 142 have been delivered to the experiment. A summary will come with the next minutes. The transmission from HRS to the trap dropped from 100% to 50% without any apparent reason. The high efficiency could not be regained.

* Romain was not accepted as a CERN PhD student. The REX group therefore urges him to apply for future upcoming jobs as REX operator or similar as he has become an important cog in the REX machinery.

* Fredrik will update the spending figures for 2005 together with Didier and Mats next week.

* David Porret will be asked to come over and start implementing the last vacuum elements into the Simatics PLC next week.

* It was decided that an extra run for REX will be scheduled. Between Thursday evening 26/10 and 1/11 9Li should be delivered to the second beam line. Didier and Hans Broere are however away so we are hoping for a well behaved linac.

* Didier will be away from 29/10 to 2/11.

* Mats presented a status report of the ISOLDE and REX-ISOLDE control system at the AB/CO review meeting. He underlined the necessity of having a coordinator for all control system activities at CERN. ISOLDE has all the technical requirements for a functioning CS.

TRAP and EBIS

* The main control computer for the REXTRAP CS has now been running uninterrupted for three weeks.

* Bugs in the scanning interface for the REXTRAP CS will be corrected for next week.

* Sylvestre Catin will come next week and install extra memory for some of CS computers.

* Nicolas David would like to measure the capacitance of the excitation electrodes in the trap during next week.

* A test confirmed that the injection efficiency into the EBIS is maximal at an electron beam current of 190 mA and decreases for higher currents even if the injection optics is retuned. This is undesirable as heavier charge bred ions will require a higher electron beam current. Dedicated tests with higher currents have to be carried out after the Zn run.

* For the next Li or Be run we could imagine injecting He gas into the EBIS to make use of the ion-ion cooling effect. This would however need some testing before.

LINAC

* The 9-gap amplifier is now operational and Xe is presently accelerated to 2.85 MeV/u. The operation frequency is 5 Hz but could be increased. The amplifier can deliver 90-93 kW. However, the amplifier still trips occasionally. The tuning controller was faulty and causing instabilities. It has been replaced by a temporary one.

* Before the Li run at 50 Hz the 9-gap cavity has to be slowly conditioned for this higher power a week or more in advance.

* 100 Hz operation can not be performed before a new transformer is installed in 7-gap 3 amplifier.

* As higher power levels can now be reached in the 9-gap (in principle 100kW / 0.1duty cycle) the Safety Commission should monitor the x-ray along the linac and if necessary install warning signals.

* It was difficult to obtain a nice beam spot at the Miniball PPAC when using the 9-gap. The question of a proper functioning of the PPAC was raised. Test with stable beams next week are foreseen.

* The general application window for the current (visual basic) control application of the Linac beam optics needs modifications. New elements should be added and the readback feature implemented for the program to be useful. Didier will speak to Nikolai about these issues (keeping in mind a new application will be available next year).

Minutes taken by Fredrik Wenander