Participants: Simon Albright, Fanouria Antoniou, Jean-Baptiste Bonnamy, GianPiero Di Giovanni, Jose Antonio Ferreira Somoza, Alessandro Floriduz, Eve Fortescue-Beck, Matthias Haase, Bettina Mikulec, Antony Newborough, Serge Pittet, Fabio Pozzi, Andrea Santamaria Garcia, Frank Schmidt, Jocelyn Tan.

Approval of minutes

The minutes of the LIU-PSB WG #222 meeting were approved.

Communications

LIU-PT Meeting

• The LIU event foreseen in the week of the 11^th of February 2018 will probably take place in the region of Annecy. M. Meddahi and G. Rumolo will soon work a first draft of the program.
• A new process has been put in place for the approval of the ECRs. The PLI meetings will no longer take place, but the follow up will be made directly by the configuration managers, who will also be in charge of seeking the approval from the LIU project leader or deputy.
• An updated version of the Master Schedule will be presented at the LS2 Days, which includes the two months of delay for the Linac4 beam tests (starting in September 2019 instead of July 2019). Several checks have to be done, especially for services like EN-CV. In fact, it seems that the chilled water will not be available and this is a concern for the power converters.
• The carry forward of the money not spent in 2018 will not be automatic. Please make sure that the EVM is updated, as well as the schedule.

LIU Beam Performance Meeting

• Presentation on the Linac4 current reliability run.
• LIU-PT meetings with dedicated equipment group:
  • Meeting with TE-VSC
  • Meeting with EN-CV

Transmission measurement of all the PSB machine (F. Schmidt)

• The damping resistors of the PSB have a resistance of 10 Ohms and their temperature will considerably increase (up to ~400°C) after the injectors energy upgrade.
• Several solutions were proposed, one of them consisting on doubling the value of the damping resistor. This became the baseline for LIU-PSB. This option needs to be studied carefully since the function of the damping resistors in the PSB is still unknown. They were installed in the machine in 1971 and the reports from that time have not been fully digitized yet.
• Studies involving measurements and simulations of the damping resistors were carried out, including four PSB dipoles connected in series and a focusing and a defocusing quadrupole. The simulations of the system were carried out by using a 4-pole model of the dipoles, where the vacuum chamber shielding effect is modelled by splitting the inductance into two parts and a small resistance is needed to shield the capacitance. The 4-pole model approximates a transmission line with an incoming forward wave and a reflected wave with a damping term alpha. 
• An example of impedance amplitude versus the frequency (measured and simulated) is showed for the case of the SPS.  A linear increase of the inductance with the frequency is observed. When the vacuum chamber is added the eddy currents become relevant.
• Transmission line measurements were done for the whole machine, which is challenging in the PSB. The modelling is not accurate and discrepancies appear at high frequencies (the damping resistors will damp frequencies above ~100 Hz).
• A plot of 1/alpha versus frequency is shown for simulated and measured values. It can be observed that at ~900 Hz the measured signal is reduced by 1/e compared to the simulation, which means that in reality there is more damping that the one predicted by the current model. Doubling the resistance in the simulations does not help fit the data.
• Next, the tune difference created by magnet ripples is presented. It is shown that the magnet ripple is smooth and that for a conservative voltage value the change in tune is between 10^-4 and 10^-3 at high frequencies for both the beginning and the end of the line for the current MPS. Only values approaching 10^-3 are considered dangerous since it might affect the beam stability at injection energy. Simulations with pyOrbit including this effect will be carried out in 2019.
• For the new POPS-B the potential dangerous frequencies are at 333 Hz and 2 kHz. A. Harle mentioned to F. Schmidt that he should be able to filter out the component at 333 Hz and that at 2 kHz the tune spread ripple is of the order of 10^-4 or below, so the POPS-B should be safer than the MPS.

Comments

• F. Schmidt commented that the tune ripple model is pessimistic since 28 V considers all the contributions, so it is probable that the change in tune is even below 10^-3.
• A. Newborough remarked that the issue with the tune ripple is only for the current power supply and not for POPS-B. Using the MPS is anyway a fall-back scenario in case of a disastrous event with the POPS-B.
• The ECR connected to the study, EDMS 1817987, will now seek approval at the IEFC

Next LIU-PSB meeting: 23^rd of October 2018 on the commissioning of the new wire scanner by Jose Luis Sirvent Blasco.