Configuration with a FC is actually in stand-by. Most likely the comparison studies won't be ready for the review meeting.

The SC technology is not a show stopper. The DPA/year is a limitation for the present AMD with this aperture.

I briefly wanted to come back to you concerning the operating conditions for the FCCee positron source (since it was mentioned in the meeting today). As you know, it is important for us to know the cumulative number of electrons on the target in order to estimate the long-term radiation damage in the target and coils. One of the key ingredients is the time for filling the collider from scratch. So far we assumed for Z-operation, that it takes 1035 s to fill the collider -> his number was derived by Salim [1]. We assume that during these 1035 s, the source is running *constantly* with the nominal drive beam parameters (1.8E10 electrons, 200 Hz). However, I saw in the slides for Barbara Dalena today (slide 2 in [2]) that filling the collider from scratch in Z operation takes 284 s. Did the numbers change so much, or do I misunderstand something? It would be important to make a table with the latest numbers (also for WW, ZH, ttbar) since this has a significant impact on conclusions/shielding design. For all beam modes, we would need:

In Barbara D.'s slides, the values are for one species. To get the total filling times, you have to multiply by two. The filling times from scratch are 570 s using the SPS and about 500 s using the HE linac. The collider lifetime is 1085-1090 s, which means that the actual filling time meets this specification. We can meet this specs we need 2-bunch at 200 Hz with a charge of 5 nC for positrons and electrons. Based on the actual yield and capture of positrons in the DR, a drive beam with 1.8E10 electrons (2.88 nC) is a good assumption for your study considering a positron yield of about 2. Here Iryna can also comment. I cannot answer about the frequency of the top up injections but I will ask someone for this.

We had a dedicated meeting on this topic in March this year (https://indico.cern.ch/event/1133521/) where Salim presented the filling times for the two options, using the SPS or using the HE linac. Salim did not prepare a summary table, so the official table remains the one preset in September 2021 by Oide. However, the changes are small.

For now, those values still remains the reference for the pre-injector. In the next few days I will include this table in the excel file with the pre-injector specification parameters. Sometimes it is diffcult even for me to follow all the changes, but for the injector we will have to refer to that excel document on the collaborative workspace.

Last piece of information: Oide et al. are doing studies to insert a polarisation wiggler in the collider that drastically reduces the lifetime. In this scenario, we would have to completely rethink the injector. However, the project coordinators told me that for now these are work in progress studies and that for now the specification table is as mentioned above.

Thanks for your reply. Indeed, in the indico link from Salim [1] which you provided I see that the injection time is half (i.e., around 570 sec) compared to Salim's previous estimate (1035 s) [2], which he had presented in a WP3 meeting. Unfortunately, we had missed this update.
Since the e+ and e- injections into the collider are interleaved, I suppose the e+ source does not run at full power during the 570 sec injection time but only during the e+ injections? Salim had given a Linac duty factor of 80.4% in [2]: does this reflect the fraction of 570 sec the e+ source runs at full power or does this refer to something else?
And indeed, for Z mode we assumed a drive beam with *one* bunch (1.8E10 electrons), with a frequency of 200 Hz (i.e. 1.8E10 *200 electrons impacting on the target per second). Does this change for WW, ZH, ttbar, or will the electron drive bunch charge/frequency be the same as for Z?
I think it would be highly beneficial, if we could agree on a table, listing the electrons on target per day for each mode, i.e., Z, WW, ZH, ttbar (maybe assumg 2x filling from scratch per day, while the rest is top-up injection). This would be very important for us since the long-term radiation damage depends on the number of e- on target.

The main reason for the change in filling times was the change in the number of buckets to be filled. Fewer buckets with more charge. I don't know what Salim's duty cycle refers to but what I can say is that using the HE linac we will have a train of 4800 rf pulses with 2 bunches (in total 9600 bunches). The trains of positrons and electrons last 24 s with a distance between trains of about 1 second or more (see attachment).

The assumption of 1.8E10 electrons for the drive beam is an upper limit for us to keep until we have a more robust damping ring acceptance. Iryna can also comment this point.

The other modes of operation of the collider involve fewer buckets to be filled and less charge. This means that the timing for filling and the filling pattern will be different but the positron source will have to provide less charge. At this time, we have not yet addressed the question of the other modes of operation.