Configurations for Special Runs / VdM in 2018
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Configurations for Special Runs / VdM in 2018 |
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The parameters on this page reflect the best current knowledge and will be regularly updated and changed accordingly. Please consider this when using these parameters for any estimate. In case of doubts do not hesitate to ask the LPC.
After TS1 up to and including the 90m run the AGK should be adjusted to 31271
Afterwards it will be reverted to the standard 32811 for this years physics production
The VdM programme is scheduled to start after the 3b validation fill after TS1. This will probably fall on the weekend of the 23/6/2018 24/6/2018. The programme consists of the following steps (no turn-around times taken into account here).
Maximum separation allowed by MPP: 2.5 nominal σ for each beam in one plane at a time. Separation in both planes at the same time are not allowed. The limits are given in terms of nominal emittance : εn=3.5µm. This means that the de-facto separation is larger since we in fact run with lower emittance (~2.3µm).
| Step | Duration | Experiments activities | Remarks | ||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 3b validation fill | 30min |
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30min Stable Beams for MPP with crossing angle and beta star anti leveling
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| Calibration transfer fill (150b) | 4.5h |
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Filling Scheme: Multi_525ns_140b_140_75_16_8bpi_19inj.csv Scheme optimised for few AGK changes No crossing angle or ß* anti-levelling |
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| 600b | 2.5h |
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Filling Scheme: 25ns_603b_590_524_542_48bpi_17inj |
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| 1200b | 8h |
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Filling Scheme: 25ns_1227b_1214_1054_1102_144bpi_14inj.csv |
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| 2460b | 8h |
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Filling Scheme: 25ns_2460b_2448_2052_2154_144bpi_19injv2.csv |
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| Scans IP2/8 |
8h45min |
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Filling Scheme: |
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| Scans IP1/5 |
15h45min |
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Filling Scheme: ATLAS 1 2 and 3 4 need to be in same fill CMS: 1 and 2 need to be in same fill |
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| Sandwich fill 2460b | 3h or more: adapted to start of 90m run |
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Filling Scheme: 25ns_2460b_2448_2052_2154_144bpi_19injv2.csv |
After this programme the 90m special run with be started.
| Items | Remarks |
|---|---|
| Filling Scheme | Multi_525ns_140b_140_75_16_8bpi_19inj.csv |
| Bunch Spacing | 525 ns (minimal) |
| Injections | up to 2 batches of 4 bunches |
| Emittance in Stable Beams | tolerable variations: 2µm to 3µm |
| Intensity in Stable Beams | 1.2x1011 ppb -- tolerable variations: 1.1x1011 ppb to 1.25x1011 ppb; |
| Brightness (bunch intensity / emittance) | < 0.5 x 1011 ppb / µm |
| Items | Remarks |
|---|---|
| Filling Scheme | Multi_70b_58_20_22_4bpi_19inj.csv |
| Bunch Spacing | 1000 ns (minimal) |
| Injections | up to 4 batches of 1 bunch ("traditional" VdM schemes) |
| Emittance in Stable Beams | 3µm for LHCb; >3µm for ALICE (second in scan programme) |
| Intensity in Stable Beams | 0.7x1011 - 0.9x1011 ppb in LHCb 0.4x1011 - 0.9x1011 ppb in ALICE (Alice is second in the scan programme) |
| Profiles | Preparation for VdM : Gaussian profiles which factorise the beam wrt H and V planes |
| IP 8 Dipole polarity | + / + |
| IP 8 external half crossing angle | 145 µrad; internal half crossing angle : -75 µrad --> effective half crossing angle at IP: 70 µrad which is ok for using the ZDC. |
| Injection Optics | With crossing angle to not have problems with LR interactions when beams are large at injection |
| IP2 polarities | + / + (Dipole and L3 magnet) |
| IP2 internal crossing angle | -75µrad |
| IP2 external crossing angle | 145 µrad |
| IP2 effective crossing angle | +70µrad |
| IP2 y - vertex shift | -1 mm |
| Items | Remarks |
|---|---|
| Filling Scheme | 525ns_140b_124_32_23_16bpi_11inj.csv |
| Bunch Spacing | 525 ns (minimal) |
| Injections | up to 4 batches of 4 bunches |
| Emittance in Stable Beams | 3µm -- tolerable variations: 2µm to 4µm; some spread O(20%-30%) is welcome |
| Intensity in Stable Beams | 0.85x1011 ppb -- tolerable variations: 0.70x1011 ppb to 0.95x1011 ppb; some spread O(20%-30%) is welcome |
| Profiles | Preparation for VdM : Gaussian profiles which factorise the beam wrt H and V planes |
| IP 8 Dipole polarity | + / + |
| IP 8 external half crossing angle | 145 µrad; internal half crossing angle : -75 µrad --> effective half crossing angle at IP: 70 µrad which is ok for using the ZDC. |
| Injection Optics | With crossing angle to not have problems with LR interactions when beams are large at injection |
| BGV measurements | Requested by CMS (to be followed up by LPC) |
The 90m run is scheduled for taking place after the VdM programme scheduled after TS1.
The squeeze for this fill will be very long (40m).
The 90m programe starts with the 100ns beam. This beam will be used until ATLAS has collected 0.5/pb at a pileup of 0.1 ... 0.15. This needs approx. 10 hours.
| Items | Remarks |
|---|---|
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Ramp - up |
At least 2 hours SB, expert check heat load |
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Ramp - up |
At least 2 hours SB, expert check heat load Fill 1 : 50ns_302b_300_70_63_72bpi_7inj.csv Fill 2 : 50ns_734b_732_284_398_144bpi_11inj.csv Fill 3 : 50ns_1452b_1450_21_1128_144bpi_11inj.csv (production scheme) The schemes use batches with 12 and 18 bunches. The 12b train is used as first train for steering and MPP. |
| Bunch spacing | 100ns and possibly 50ns |
| β* in IP1 | 90m |
| β* in IP5 | β*x=45m ; β*y=90m --> ßeff = 64m |
| εn | 1,2µm - 1.6µm (1.2µm is hoped for by the physics comunity. J. Wenninger remarked that there will be probably some blow-up in the ramp) |
| half crossing angle | 50μrad; to be seen if the crossing angle in IP1 can be increased if enough corrector strength available |
Most of the values below are assuming conservatively an emittance of 1.6µm
With the values below it is expected that we need to run 8.2 hours with 100ns with the full 100ns scheme before going to 50ns. (The 100ns ramp up will result in approximately 0.56pb for ATLAS)
| bs [ns] | n-colliding | I (ppb) | εn [µm] | half c-angle [µrad] | ßeff [m] | sep [µm] | µ | Lumi | Remark |
|---|---|---|---|---|---|---|---|---|---|
| 100 | 732 | 1.0x1011 | 1.2 | 50 | 64 | 0 | 0.57 | 5.92x1031 | emittance too low |
| 100 | 732 | 1.0x1011 | 1.6 | 60 | 64 | 0 | 0.43 | 4.44x1031 | 0.16 pb/h |
| 100 | 732 | 1.0x1011 | 1.6 | 60 | 90 | 310 | 0.15 | 1.55x1031 | 0.058 pb/h |
| 50 | 1450 | 0.8x1011 | 1.6 | 60 | 64 | 0 | 0.28 | 5.6x1031 | 0.20pb/h |
| 50 | 1450 | 0.8x1011 | 1.6 | 60 | 90 | 0 | 0.20 | 4.0x1031 | 0.14pb/h |
This special run is planned to have three components:
The programme foresees to use the collimation configuration tested successfully on Tuesday the 2nd of October. It was agreed that towards the beginning of the data taking programme (but during day time since experts need to be available) also one or two runs with the crystal collimation scheme should be taken. TOTEM considers this scheme even favourable since they observed a smaller (almost no) growth of the background rates with a very high Signal to Noise ratio. However ALFA observed that the background is distributed such that it is more difficult ot separate from the signal than in the "standard" collimations scheme and therefore does not want a significant fraction of data to be taken with crystal collimation. ALFA welcomes to take one fill with crystal collimation anyway.
TOTEM requests to take an integrated luminosity comparable to that taken in the 2.5km run in 2016: 380µb-1.
ALFA requests to take 106 elastic events. This should correspond to an integrated luminosity around 400µb-1.
Therefore the requests of both experiments are compatible with each other.
For the bunch intensities a trade off between luminosity per bunch and background conditions has to be found. The aim is to maximise the luminosity with clean background conditions. During the collimaition test it was found that when increasing the initial bunch intensity to close to 1e11 ppb the background conditions after the first scraping have been bad whereas after a second scraping they were excellent. However these two scraping processes cost 20% luminosity drop each, hence a 40% luminosity loss. It has therefore been decided to go for more moderate beam intensities and more bunches which should allow data taking after one scraping process.
It was further agreed that one should try to inject higher intensities (0.9e11-1e11) with the first 5 bunches and then scrape these bunches down until another 1 or 2 bunches can be injected. Then one more scraping would be performed. With the experience of the test this could lead to very clean conditions at reasonably high luminosity (up to 40% higher than the first data taking period with 5 bunches during the test)
It has been agreed that at the beginning of the data taking some experimentation with the beam parameters / scraping procedures might be performed. However it should be avoided to continuously change the requested intensities from the injectors and once a good configuration has been found, the physics data should be taken with that configuration until the requested luminosity is acquired.
| Items | Remarks |
|---|---|
| No bunches | 6 or 7 |
| Non colliding bunches | 2 fills with 1 non-colliding bunch to be taken towards the start and the end of the data taking period. |
| Intensity per bunch at injection | 0.9 - 1 x 1011 ppb (see remark above) |
| Initial Intensity when taking data (after scraping) | ~0.6 x 1011 ppb |
| Emittance | ~1.2µm |
| ß*eff TOTEM | 84m |
| ß*eff ALFA | 70m |
Two independent estimates have been performed based on observations during the test run. Using beam parameters and lumi calculator one can do the following (conservative) estimate:
Intensity per bunch: 0.55 x 1011 ppb
Average emittance: 1.2µm (taking into account some emittance growth during a fill. The initial emittance has been observered to be around 1µm)
Lumi per bunch at TOTEM (ß*=84m) : 1.3 x 1027
| collisions | lumi | T400µb [h] | Lumi drop and duty cyle (120min data / 30min filling) factor 0.65 [h] |
Lumi per hour [µb/h] | 70% availability [h] |
|---|---|---|---|---|---|
| 5 | 6.5 x 1027 s-1cm-2 | 17.1 | 26.3 | 15.2 | 37.6 |
| 6 | 7.7 x 1027 s-1cm-2 | 14.4 | 22.2 | 18.0 | 31.6 |
| 7 | 9.0 x 1027 s-1cm-2 | 12.3 | 18.9 | 21.1 | 27.0 |
From the rates seen in ALFA a similar esimtation can be performed: ALFA saw an elastic rate of the order of 9Hz in each arm resulting in a total of 18Hz elastic events. To reach 106 elastic events at 18Hz, 15.4 hours are needed. Considering the lumi drop and duty cycle (factor 0.65) and 70% availability this results in 33.8 hours which is compatible with the above estimates within the errors.
The VdM scan will be performed with injection optics but taking out the crossing angle bumps. The filling patteren with contain as many bunches as possible at 525ns bunch spacing. 2 non-colliding bunches will be injected.
LHCb is able to measure ghost charge.
| Item | Remarks |
|---|---|
| Filling scheme | Multi_525ns_152_150_0_0_8bpi_19inj.csv |
| Optics | Injection optics without crossing angle bumps |
| Crossing angle | 0 |
| ß* | 11m |
| Transverse emittance | 1.5µm - 2.5µm in the LHC at the start of the (Note: 1.8µm is the minimum emittance if the brightness limit and the intensity limits should be respected) |
| Intensity | 1.2e11 -- 1.4e11 ppb |
| Brightness | < 0.65 x 1011 ppb/µm (This is a hard criteria) |
| Others | Special VdM scraping treatment for gaussian shape and factorisation of beam profiles |
| Injections | 2 batches of 4x1b spaced by 525ns; batch spacing also 525ns |
The first VdM scan performed during the special run suffered from a very high ghost and satellite contribution. In addition a technical problem in LHCb prevented most of the data of the SMOG ssytem to be recorded to measure these contributions precisely. This will lead to a high systematic uncertainty for the luminosity. Therefore, if possible, a second try for this scan will be performed during the recovery of the Ion source problem after TS3. Changed parameters will be signalled in red.
The VdM scan will be performed with injection optics but taking out the crossing angle bumps. The filling patteren with contain as many bunches as possible at 525ns bunch spacing. 2 non-colliding bunches will be injected.
Again LHCb will kindly provide ghost charge measuremnts with their SMOG system.
| Item | Remarks |
|---|---|
| Filling scheme | Multi_525ns_152_150_0_0_8bpi_19inj.csv |
| Optics | Injection optics without crossing angle bumps |
| Crossing angle | 0 |
| ß* | 11m |
| Transverse emittance | 1.5µm - 2.5µm in the LHC at the start of the fill |
| Intensity | max 1.0e11 ppb |
| Brightness | < 0.65 x 1011 ppb/µm (This is a hard criteria) |
| Others | Special VdM scraping treatment for gaussian shape and factorisation of beam profiles |
| Injections | 2 batches of 4x1b spaced by 525ns; batch spacing also 525ns |
| RF cavity voltage | Increased to 12 MV (RF experts consider blow-up after injection) |
| Scan programme | Duration 2.5h to 3h; has to start immediately after the filling. |
| Abort Gap Cleaning | Active during the entire programme or at least between the various scans (to be discussed with ATLAS) |
This run has been requested by TOTEM in order to extend the acceptance in the higher t range. It is assumed that an equivalent luminosity of 400µb should be taken. Due to the optics having ß*=11m a factor of 7 in luminosity is expected wrt the low E high ß run. Hence the data could be taken in O(3h) assuming 100% availability.
It was decided that a 2 stage collimation system should be set up for this run. This will be done directly before the data will be taken.