ATS-Note-2012-052 MD

2012-06-26

john.jowett@cern.ch

p-Pb Feasibility Test and Modifications of LHC Sequence and Interlocking

R. Alemany, P. Baudrenghien, D. Jacquet, J.M. Jowett, M. Lamont, D. Manglunki, S.

Redaelli, Mariusz Sapinski, M. Schaumann, D. Valuch, R. Versteegen, J. Wenninger

Keywords: p-Pb, heavy-ion, beam-beam, RF-synchronisation, moving parasitic encounters, emittance growth,

Summary

The first part of the feasibility test of p-Pb operation of the LHC successfully demonstrated

the possibility of injecting Pb bunches in the presence of many proton bunches without

apparent harmful effects from moving long-range beam-beam encounters. Two bunches in

each beam were accelerated to top energy where the RF frequencies of the two rings could be

locked together. Finally an RF-rephasing operation to move the collision points some 9 km,

back to their proper places succeeded on the first attempt.

This note also provides documentation of the many changes made to the LHC operational

sequence and interlocking in order to implement this completely new mode of collider

operation.

1. Introduction

The MD was a feasibility test in preparation for a potential p-Pb run in 2012. It first aimed at

testing injection of a proton beam in Beam 1 (B1) and a Pb beam in Beam 2 (B2) with separated RF

frequencies in each ring. The second main goal was to test the ramp with unlocked frequencies, the

synchronization at flat top and the RF-rephasing procedure, which is necessary to get stationary

collisions between the two beams at the IPs. Different revolution frequencies due to unequal charge over

mass ratio provoke moving parasitic encounters at injection energy and during the ramp. As we expect a

reduction of the beam lifetime mainly due to emittance blow up arising from this new phenomenon, the

beam parameters have to be studied, and more specifically those of the Pb beam in the presence of the

proton beam (which has the larger charge). Consequently the MD also aimed at recording data during

the successive stages of the feasibility test.

The MD started at 07:00 on 31 October 2011 and ended precisely on time at 23:00 the same day.

This report presents the steps we went through during the MD, and a preliminary analysis of the

data. It is organized in three sections, as follows:

I. Injection with different RF frequencies in the two rings,

II. Pb beam emittance evolution at 450GeV in the presence of the proton beam,

III. Ramp, synchronization and RF-cogging with two bunches in each beam.

Then, Section 5 onwards summarises the main changes to the operational sequence implemented for this

mode of operation.

2. Injection with different RF frequencies in the two rings

- 2 -

It took a few hours to have the first Pb beam of the year as B2 circulating in the machine. Initially

there were synchronisation problems between SPS and LHC and later we had to decrease the single

bunch intensity to permit injection (it was three times the nominal). This beam was captured with 6 MV

RF-voltage (1st fill). It was dumped as well as a second fill, and then 4 Pb-bunches were re-injected (3rd

fill). The transverse damper was ON for the last bunch. The horizontal BGI monitors were recording

data continuously, and wirescans were made frequently in order to monitor the evolution of the beam

size and emittance. Finally, the mean bunch length was monitored. Its evolution is shown Fig. 1 for the

3rd fill, in the absence of protons.

Figure 1 : Bunch lengthening of Pb beam before injecting protons in Ring 1.

A proton pilot bunch was injected in B1 and was dumped while trying to inject a batch of 72

bunches. A second attempt was successful, and 1+12+72+72+72+72 proton bunches were injected

while 2nd fill of Pb beam remained stored. The spacing was 100 ns (specially prepared by the injectors),

and the intensity was approximately 10 % of the nominal proton bunch value. Some errors in the filling

pattern induced filling of wrong buckets and a decrease of the intensity per bunch. This prevented us

from injecting up to 588 bunches as foreseen. In view of the limited time available, we decided not to

start again to correct this but rather to press on with the attempt at a ramp. We already had the very

significant result that some Pb bunches could be stored in the presence of 304 proton bunches.

The evolution of the normalized emittance of B2 according to the wirescans is given Fig. 2. Colors

correspond to different bunches. “in” and “out” refer to the two successive measurements made by the

wirescanners. Switching on the transverse damper was beneficial for the fourth bunch which has smaller

initial emittance. As usual, there are a few outlying points where, typically, the data quality did not

allow a good fit to a Gaussian profile.

- 3 -

Figure 2 : Horizontal (top) and vertical (bottom) normalized emittance growth of B2 bunches during the

2nd and 3rd fills.

The decision was then made to keep the 304 protons bunches in, to dump B2 and to re-inject two

fresh Pb bunches in order to monitor their emittance evolution. These were kept about 20 minutes.

3. Pb beam emittance evolution at 450GeV in the presence of the proton beam

Figure 3 : Horizontal (left) and vertical (right) normalized emittance of B2 at injection energy

(4th fill) in the presence of circulating proton beam B1 (304 bunches).

Fig.3 shows the horizontal and vertical B2 emittances during 4th fill, in the presence of the

circulating proton beam. Injection emittance is less than nominal, and the nominal horizontal value is

reached after about 25 minutes. The effect in the vertical plane is small. Wire-scan values have been

averaged to be compared to BGI data, as plotted Fig. 4.

b1,b2,b3,b4 = bunches of B2

2nd fill 3rd fill

0

2

4

6

8

10

12

14

12:00 12:43 13:26 14:09 14:52 15:36 16:19 17:02 17:45 18:28 19:12

b1-in

b1-out

b2-in

b2-out

b3-in

b3-out

b4-in

b4-out

γεx(Pb)

time

0

2

4

6

8

10

12

14

12:00 12:43 13:26 14:09 14:52 15:36 16:19 17:02 17:45 18:28 19:12

b1-in

b1-out

b2-in

b2-out

b3-in

b3-out

b4-in

b4-out

γεy(Pb)

time

Injections of proton batches: 1b+12b+72b+72b+72b+72b

1st injection of protons (pilot)

Dump of B1

Dampers ON

0

0.5

1

1.5

2

2.5

19:33 19:40 19:48 19:55 20:02 20:09

b1-in

b1-out

b2-in

b2-out

γεx(Pb)

time

0

0.5

1

1.5

2

2.5

19:33 19:40 19:48 19:55 20:02 20:09

b1-in

b1-out

b2-in

b2-out

time

γεy(Pb)

0

0.5

1

1.5

2

2.5

19:33 19:40 19:48 19:55 20:02 20:09

b1-in

b1-out

b2-in

b2-out

γεx(Pb)

time

0

0.5

1

1.5

2

2.5

19:33 19:40 19:48 19:55 20:02 20:09

b1-in

b1-out

b2-in

b2-out

time

γεy(Pb)

- 4 -

Figure 4 : Mean horizontal normalized emittance as measured by the BGI (left), and by the wire

scanners (right) during 4th fill. The left axis of the BGI plot corresponds to the geometrical emittance

normalized to the proton relativistic gamma.

Initial measurements for horizontal emittance are consistent, but growth rates are different

depending on the instrumentation. Intra beam scattering is still to be calculated to be compared to these

data in order to extract the effect of the parasitic moving encounters. In this first fill with Pb beams, the

RF voltage at injection was low (6 MV) and the growth rates were quite high. Later in the regular Pb-

Pb operation, the voltage was increased to 8 MV and the emittance growth was checked. Nevertheless

the data shows no discernible increase in emittance growth of the Pb beam when the proton bunches are

injected.

B1 and B2 were dumped after these measurements, and the ramp was tested with 2 bunches in

each beam.

4. The first Ramp of the LHC with hybrid beams and RF-cogging

For the 5th fill, two proton bunches (1.3×1010

particles per bunch) were re-injected in Ring 1,

then two Pb bunches in Ring 2 (9.76×107 nuclei per bunch). As can be seen on Fig. 5, the beams were

ramped to 3.5 Z TeV with separated RF frequencies successfully with very little loss of intensity.

Figure 5 : Evolution of B1 and B2 RF frequencies and intensities during the first ramp.

1.44

1.36

1.28

1.2

1.12

1.04

0.96

0.88

<γεx(Pb)>

= 0.016 μm/min

* γ(p)/γ(Pb)

BGI with rough calibration (Mariusz Gracjan Sapinski)

0.88

0.96

1.04

1.12

1.2

1.28

1.36

1.44

1.52

1.6

1.68

1.76

19:33 19:40 19:48 19:55 20:02 20:09

slope = 0.025 μm/min

<γεx(Pb)>

Wire Scanner

- 5 -

At top energy, B1   400.789715 MHzRFf and B2   400.789639 MHzRFf . Locking

RF frequencies together imposes offsets of the central trajectories. We chose to get approximately the

mean RF frequency, implying that the momentum offset would be ~ ±3×10-4

, depending on the beam

(see Fig.6, the orbit measurement from the BPMs for B2). The Pb beam being the slower, the central

orbit is displaced to the inside of the ring. To carry out this operation, orbit feedback and radial loop

had to be switched off.

Figure 6 : BPM measurements of B2 after the RF synchronisation at top energy, showing the offset

closed orbit induced by the revolution frequency modification.

Figure 7 : Evolution of B2 lifetime during frequency shifts of the `cogging` operation. Small

shifts are visible on the green frequency curve.

The final frequency was (B1) (B2) 400.789685 MHzRF RFf f . After locking the two RF systems

together, we used the ATLAS BPTX monitor for the re-phasing. The initial shift between buckets 1 of

each beam was 19 μs, corresponding to a shift of the interaction point by some 9 km. Total time for the

- 6 -

cogging operation was about 30 min. The shifts in frequency can be seen on Fig.7. They did not exceed

10Hz. One can see on this plot that lifetime does not seem to be correlated to these shifts.

Fig. 8 is the final picture given by ATLAS (T. Pauly) showing B1 and B2 signals in the detector. Beams

indeed meet at IP1.

Figure 8 : ATLAS oscilloscope screenshot after the `cogging`, showing the signals

superimposition at IP1.

Bunch length (Fig.9) and transverse sizes of both beams (Fig.10) were recorded during the ramp,

during the RF synchronisation and during the “cogging” phase. Unfortunately no wire scans are

available during the ramp.

Figure 9 : B1 and B2 bunch length evolution during 5th fill, before and during the ramp, happening

between 21:40 and 21:50.

BGI data showed a substantial increase of the horizontal emittance during the ramp, leading to

much higher values at flat top than those given by the wire scans. However, slopes became similar again

once 3.5 Z TeV was reached. The problem can very likely be linked to the magnetic field of the BGI,

which became insufficient when the beam energy rose. This would make the radius of curvature of the

detected electrons larger. Detection would then be less precise, resulting in overestimated beam sizes.

This hypothesis is still to be confirmed. In any case, we note that the BGI was still in a testing phase

and not fully operational at the time.

- 7 -

Fig. 10 also shows the clear improvement of lifetime during the ramp. The lifetime of the Pb beam at

all stages was typical at all stages, showing no indication of being affected by the presence of the proton

beam. The relatively low lifetime at injection is attributed to IBS debunching.

Figure 10 : The top plots show the mean horizontal normalized emittance as measured by the BGI (left),

and by the wire scanner (right) during 5th fill. Wire scanner data start from the end of the ramp. The plot

at the bottom shows the lifetime from the FBCT during a 10 minute period corresponding to the ramp.

5. Machine Protection and Interlocking of proton-nucleus operation

At injection energy the only “noticeable” difference between protons and ions is the RF frequency

due to the different mass and charge. This difference is of the order of 5.3 kHz at injection energy

assuming identical magnetic settings. If the RF frequencies are wrongly set up at injection, an attempt to

inject a proton beam from the SPS into a ring setup for lead ions in the LHC, or vice versa, could

happen. In the following the possible implications are evaluated and an interlock proposed to protect the

machine.

In these circumstances, the RF frequency would be off by 5.3 kHz for the incoming beam from

the SPS, leading to an energy error of ±1.3% at extraction. This is still within the SPS aperture (but not

easy with large intensity). However it is not clear if the re-phasing SPS-LHC would work or if the beam

would even survive in the SPS (it is at the limit of the aperture, effects of non-linear chromaticity, etc).

Nevertheless the possibility of a successful extraction from the SPS cannot be excluded.

If the beam does leave the SPS, it will certainly be lost in the transfer lines (TI2/TI8) because of

the limited relative momentum error, of the order of ±0.4%, that can be accepted by the available

aperture of the lines.

Although the beam will never enter the LHC, the transfer lines must be protected.

2.8

2.4

2

1.6

1.2

0.8

γεx(Pb)

slope : 0.004 μm/min

0.8

1.2

1.6

2

2.4

2.8

3.2

21:50 22:04 22:19 22:33 22:48 23:02 23:16 23:31

slope : 0.005 μm/min

γεx(Pb)

time

- 8 -

In order to implement a reliable machine protection against misconfiguration of the LHC rings or

particle type injection errors, the information available in the SPS and LHC has been appropriately

combined into a Software Interlock (SIS) at the LHC. Among the available signals are:

the LHC RF frequency difference;

the SPS RF frequency at extraction – unfortunately no fast measurement available;

the SPS Radial position (centered) – arc BPMs;

the SPS RF low-level controls settings (timings, delays ….);

the SPS Momentum of the beams at injection (26 GeV for protons and 17 GeV

(proton equivalent setting) for Pb);

The following combination is operational in the LHC SIS and has been successfully

tested during 2011:

Proton conditions – applied for each ring

LHC: RF frequency within 1kHz of proton reference.

Monitoring at 0.2 Hz, accuracy ~ 20 Hz.

LHC : particle type in CPTY telegram = proton.

SPS: user name LHCx or LHCFASTx (x = 1,2,3,4…).

SPS: injection line TT10 settings consistent with 26 GeV:

Current interlock on 2 dipole and 2 main quadrupole strings.

Pb conditions – applied for each ring

LHC : RF frequency within 1kHz of Pb reference.

Monitoring at 0.2 Hz, accuracy ~ 20 Hz.

LHC : particle type in CPTY telegram = Pb

SPS : user name LHCIONx (x = 1,2,3,4…).

SPS : injection line TT10 settings consistent with 17 GeV:

Current interlock on 2 dipole and 2 main quadrupole strings.

The SIS will allow injection into a given ring if the settings are consistent with ions or

with protons. On top of being an efficient machine protection mechanism, it is flexible – it

needs no a priori knowledge of which ring is used for which species. It will also work to avoid

injecting ions during p-p runs (and vice-versa). An interlock at the level of the SPS extraction

BIS complements this software interlock. The extraction interlock effectively ensures that the

RF frequency is correct and that the beam is centred.

- 9 -

The TT10 injection is used in preference to the SPS main dipole current (also a

good candidate) because of technical issues with the current readout. This may change in the

near future when FGC SW is deployed in the LHC.

6. Nominal proton-nucleus operational sequence description

The name of the sequence is PROTON-NUCLEUS NOMINAL SEQUENCE. It is

composed of the following sub-sequences:

1. PA: PREPARE LHC FOR INJECTION (ALL BUT PCS)

2. PA: INJECTION PROBE BEAM

3. PA: INJECTION PHYSICS BEAM

4. PA: PREPARE RAMP

5. PA: RAMP

6. PA: RAMP DOWN

For the moment the sequence does not include the squeeze and the declaration of the

stable beams procedure since it has not been commissioned yet. This part will have to be

included during the setup for the 2012 p-Pb run.

In the following the various sub-sequences are explained emphasizing the particularities

relevant for the proton-nucleus collisions operational mode.

It should be pointed out that this sequence is fully based on the proton-proton and ion-ion

nominal sequences, therefore, if something changes there, the proton-nucleus nominal sequence

will have to be changed as well. In other words, this sequence needs continuous follow-up.

6.1 PA: PREPARE LHC FOR INJECTION (ALL BUT PCS) 6.1.1 Operational mode definition

Within the first tasks performed by this sub-sequence, the following tasks are called to set

the accelerator mode, the particle type and to check the right hyper-cycle is active:

1. Set accelerator mode = PROTON-NUCLEUS PHYSICS [1]

2. Set particle type RING 1 = PROTON

3. Set particle type RING 2 = PB82

4. Check hypercycle 3.5TEV_10APS_PPB_1M active

As can be deduced from tasks 2 and 3, this sequence prepares the accelerator for protons

circulating in RING 1 and lead ions in RING 2; therefore, if the beam are inverted (so-called

Pb-p operation), then those tasks will have to be changed to:

2. Set particle type RING 1 = PB82

3. Set particle type RING 2 = PROTON

- 10 -

Other nuclei, such as Argon (Z=18, A=40), Deuteron (Z=1, A=2) and Xenon (Z=54,

A=209) [1], could be defined. But for the moment only Pb (Z=82, A=208) injection is foreseen

into LHC.

The hypercycle name is explicitly defined in the task configuration. Therefore, if the

hypercycle name changes, the task will have to be updated.

6.1.2 RF frequency programs

A very important sub-sequence concerns the configuration of the RF systems for the

frequency programs. They have to be “UNLOCKED” all the time since the frequency of each

ring is different according to the charge-to-mass ratio of the particles injected. The frequencies

are “LOCKED” only when the cogging of both rings at top energy is performed. The sub-

sequence that performs the unlocking of the beams is called UNLOCK B1&B2 FREQUENCY

PROGRAMS.

6.1.3 Beam Position Monitors (BPM) Calibration

This task is called BPM ASYMMETRIC CALIBRATION and belongs to the sub-

sequence PREPARE MCS, BLM, BIS, BI FOR INJECTION BI CHECKS BEFORE

INJECTION. It is an interactive task, so the user has to select whether a different calibration

per ring, or the same one, should be performed. It allows different bunch spacings to be used

for each ring if necessary. For the 100 ns beams one has to select 125 ns bunch spacing. For the

single bunches or the 200 ns trains, it is recommended to select the single bunch calibration.

6.1.4 RF initial configuration 6.1.4.1 RF synchro injection settings

Within the sub-sequence PA: SEND RF FROM PHYSICS TO INJECTION there is a

sub-sequence called CHECK/LOAD RF SYNCHRO INJ SETTINGS. It contains a task called

LOAD RF SYNCHRO INJ SETTINGS that has to be performed before the SPS-LHC

synchronization takes place because when loading the RF SYNCHRO INJ settings the property

InjPulseDelay#Ring1/2Bt might be changed and after this action the RF synchro crate has to be

reset (Figure 1). The reset of the RF synchro crate takes place within the sub-sequence PA:

RESYNCHRONIZE RF BEAM CONTROL SPS CONNECTED that it is executed afterwards.

Figure 1: The sub-sequence CHECK/LOAD RF SYNCHRO INJ SETTINGS loads all these

values into the equipment. The InjPulseDelay#Ring1/2Bt adjusts the RF PREPULSE to

- 11 -

synchronize the beam injection with the MKI pulsing; the Offset#bucketOffsetRing1/2

adjust the RF bucket with respect to the abort gap.

6.1.4.2 Mass to charge ratio

A new system for the RF called RF UTILS B1/B2 (Figure 2) has been created with the

parameters that depend on the particle type. It should be stressed that the particle type is not

taken from the telegram or LSA DB but hard coded in the injection beam process; therefore it

depends on which particle type is circulating in each ring. This might not be a very safe

solution for the long term and a dynamic configuration should be envisaged. In the sequence

we have to execute the task LOAD MQ_RATIO ON RF VTU that will take the settings as

seen in the figure above and load them in the class ALLVTU, device ALLVTUFCCGB1/2,

property MqRatio, m/q = 2.517439 for Pb and m/q = 1 for proton.

Figure 2: A new system for the RF called RF UTILS B1/B2 has been created to configure the

charge to mass ratio that depends on the particle type being circulated.

6.1.4.3 PA: RF-LBDS FREQUENCY LOCK CHECK and PA: RESYNCHRONIZE RF BEAM CONTROL SPS CONNECTED sub-sequences

Those sub-sequences are a copy of the ones executed in the proton and ion nominal

sequences with the exception that the RF frequency programs are never locked.

Figure 3 shows the main sub-sequences of the PA: PREPARE LHC FOR

INJECTION (ALL BUT PCS) sub-sequence.

- 12 -

Figure 3: PA: PREPARE LHC FOR INJECTION (ALL BUT PCS) sub-sequence.

6.2 PA: INJECTION PROBE BEAM 6.2.1 Important re-checks This sub-sequence is the same as for p-p and Pb-Pb nominal sequences, except for the

three extra tasks aiming to recheck the following important points (Figure 4):

1. Check RF frequency programs are unlinked

2. Check that the RF proton frequency is at injection

3. Check that the RF ion frequency is at injection

Task 2 and 3 depends on which particle type is running in each ring. The way is currently set

up assumes that protons run in RING 1 and ions in RING 2. If this configuration changes, the

tasks will have to be updated.

- 13 -

Figure 4: PA: INJECTION PROBE BEAM.

6.3 PA: INJECTION PHYSICS BEAM This sub-sequence is the same as for p-p and Pb-Pb nominal sequences, except for the

BPM sensitivity configuration (Figure 5).

6.3.1 Beam Position Monitors (BPM) Sensitivity Configuration

The Lead nucleus beam has a different (generally lower) bunch intensity than the

proton beam. It happens to be of the order of the probe beam and therefore the sensitivity of

the BPMs in the ring where the Pb are injected has to be configured to HIGH SENSITIVITY.

On the contrary the proton beam can have a wide range of bunch intensities from probe to

high intensity (nominal LHC or more). Depending on the proton bunch intensity, the BPM

calibration task will have to be executed with different options.

Currently the sub-sequence PA: INJECTION PHYSICS BEAM, foresees high

intensity protons in B1 and Pb in B2. This is why the ring 1 is configured for high intensity

beam and ring 2 for pilot like beam. If low intensity beam in both rings is foreseen, i.e. 10%

of nominal intensity for protons in RING 1, then the sub-sequence PA: CONFIGURE

EQUIPMENT FOR NOMINAL doesn’t need to be executed.

Step2:SUB-SEQ:PA:INJECTIONPROBEBEAM

- 14 -

Figure 5: PA: INJECTION PHYSICS BEAM.

6.4 PA: PREPARE RAMP This sub-sequence is the same as for p-p and Pb-Pb nominal sequences, except for the

two extra tasks that check for each ring the RF watchdog and that the RF frequency programs

are still uncoupled; if this is not the case the ramp cannot be pursued and the sequence will

have to be started from the beginning since it is crucial that both frequency programs are

uncoupled and properly configured for each particle type. Another difference with respect to

the proton or nominal ion sequences is that the sub-sequence PA: PREPARE FEEDBACKS

FOR THE RAMP doesn’t switch on the RADIAL LOOP (for the moment the decision is

not to ramp with radial loop to avoid the residual frequency difference between both beams at

the end of the ramp due to RT trims) (Figure 6).

Step3:SUB-SEQ:PA:INJECTIONPHYSICSBEAM

- 15 -

Figure 6: PA: PREPARE RAMP.

6.5 PA: RAMP

This sub-sequence (Figure 7) is the same as for p-p and Pb-Pb nominal sequences, except for an

extra sub-sequence called PA: SWITCH RADIAL LOOP OFF to switch off the radial loop the

ramp was performed with the radial loop on. This sub-sequence has to be executed before

starting the RF rephrasing of both rings.

6.5.1 RF rephasing

Once the beams are at flat top, there is still a residual RF offset of ~ 70 Hz, therefore

the RF frequency of both beams have to PLEP until a common frequency at 10 Hz/s. For the

moment there is no sequencer task that allows us to PLEP or TRIM the RF frequencies at a

given linear rate. The way around consists in using the RF FGC Controller application (Figure

8). One has to open two of them and select one of the beams in each, as shown in Figure 8.

Then one sets the Final value 789685 and the linear rate 10 Hz/s (the TRIM controller

would always trim at 40 Hz/s and it cannot be changed by the user). Once this is configured,

we have to click on the pl.. button in both applications at the same time!.

This procedure remains too manual and error prone, so it is recommended for

implementation in a sequencer task.

Step4:SUB-SEQ:PA:PREPARERAMP

- 16 -

Figure 7: pA: RAMP.

Step5:SUB-SEQ:PA:RAMP

- 17 -

Figure 8: RF FGC Control application (left); evolution of the RF frequencies for both beams

along the injection, ramp and flat top (right).

7. Injection schemas prepared for 2011

Table 1 collects the most important information describing the injection schemas

prepared for the MDs and feasibility test of 2011. They are all persistently storage in the LSA

database under the category PROTON_IONS. The following pictures show the different

injection schemas as they appear in the LHC Injection Scheme editor.

Name Collisions/Exp B1, B2 or both Total num bunches

pPb_2b_1_1_1_1bpi2inj 1 B1&B2 2x2 (+1 pilot)

100ns_594b_1small_0_0_0_72bpi_pPb

0 B1 594x0 (+1 pilot)

Single_p6bPb6b_4_4_4_1bpi6inj

4 B1&B2 6x6

P100nsA200ns54p24A_16_16_16_p18A8bpi3inj

16 B1&B2 54x24 (B1 is 100 ns and B2

is 200 ns bunch spacing)

2x2onecoll/EXP

- 18 -

8. Conclusion

The MD dedicated to the feasibility test of a p-Pb run in 2012 was very successful. Injection of

the two different species at two different RF frequencies could be done without major difficulties, no

apparent enhancement of the emittance growth or losses of the Pb beam due to moving long-range

beam-beam encounters with >300 proton bunches in the other beam. Then the ramp, synchronization

and re-phasing of two beams of low intensity, made of two bunches each, was managed. We had some

594x40coll/EXP

6x64coll/EXP

54x2416coll/EXP

- 19 -

controls and operational issues through the different stages of the tests, but these will be worked out to

avoid losing time in the future.

Because of the unfortunate cancellation of the second part of this MD, we did not test injection of

many bunches in both beams at the same time, nor the ramp with many bunches.

References [1] R. Alemany, M. Lamont, S. Page; “LHC MODES”, EDMS DOC 865811.