cngs primary beam results

CNGS Primary Beam Results

1

J. Wenninger

Beam Intensity

2

The SPS beam intensity per extraction reached ~ 21013 p about one month after the startup.

The intensity remained stable until end of October when it had to be reduced due to RF problems.

The number of extractions was 995’000 almost reached 1 million !

Total intensity on T40 : 1.78x 1019 p

Presently the intensity is limited by: Losses in the PS SPS RF (no margin).

Typical transmission of the CNGS beam through the SPS cycle ~ 92%.

Injection losses ~ 6%.

Error : rms spread

& Co

3

Beam Emittance

4

The beam profiles were usually ‘Gaussian’. There were no large tails.

But the beams were sometimes slightly unstable at high energy in the horizontal plane.

Horizontal profile WS 51995 = 14 nm, * = 6 m

Vertical profile WS 51995 = 14 nm, * = 6 m

Intensity 4x1013 p

Interlocks & Incidents

5

The extraction interlock in LSS4 was modified in 2008 to accommodate the simultaneous operation of LHC and CNGS beams. This included the energy information (400 or 450 GeV) to apply the appropriate interlock logic.

The extraction interlock system ran fault-free and no incident or malfunctioning was observed. The performance was similar to 2007, with a few % of the extractions inhibited due to false interlocks.

A serious incident occurred however on June 27th at 17:03 due to a freezing of the SPS timing system. As a consequence a high intensity CNGS beam of 31013 p was not extracted (extraction interlock correctly inhibited the extraction), but also not dumped at the end of the cycle ! The beam was lost in dipole MBB.12530 as it was decelerated. The dipole was damaged (very large vacuum leak – to atmospheric pressure !) and had to be exchanged. Following that incident a number of measures were put in place to avoid a repetition of such an incident.

Interlocks & Incidents

6

Beam impact in MBB.12530

Incident Ring Beam Loss

7

Ring Beam Loss Pattern

-0.01

0

0.01

0.02

0.03

0.04

0.05

0.06

1 21 41 61 81 101 121 141 161 181 201

BLM No.

Loss

(G

ray)

In the ring the beam loss was distributed over a large area, but only one monitor exceeded the threshold (lowest ~ 40 mGray).

Incident Beam Loss

8

LSS1 Beam Losses

0

0.05

0.1

0.15

0.2

0.25B

LM

.117

40.M

KD

H1

BL

M.1

1771

BL

M.1

1809

.QF

A

BL

M.1

1831

.MD

HD

BL

M.1

1836

BL

M.1

1852

.MS

I

BL

M.1

1872

BL

M.1

1904

.MD

VA

BL

M.1

1933

.MK

P1

BL

M.1

1954

.MK

P4

BL

M.1

1998

BLM

Loss (Gray)

The largest losses were observed in LSS1 reduction of the thresholds.

Red : incident cycle.Blue : normal cycle.

Note the large peak are losses from the beam dumped in the TIDV.

LSS1 Interlock Thresholds

9

Following the incident the LSS1 interlock thresholds were reduced on all USERs since those BLMs were closest to triggering a bump before the beam could damage the magnet.

SPS Extraction

10

Interlock reference 30.4 mmInterlock tolerance ± 2 mm

Before extraction the SPS beam is bumped out by ~ 31 mm to approach the magnetic septum.

SPS beam position stability before extraction at 400 GeV is excellent :

~ 0.25 mm over a run.

Only ONE small (~ mm) re-adjustment of the extraction point over 5 months (on September 22nd).

Error : rms spread

Extraction Bump

11

Setting 31.1 mm.Non-closure 0.4 mm ~ 1%.

Extraction Losses

12

Interlock threshold 50 mGray

To minimize activation of the extraction channel and radiation levels in ECA4, the beam gap must be as clean as possible.

The gap is kept clean using the injection kicker (cleaning during the second injection).

In 2008 the losses on the absorber protecting the septum (TPSG) were 3 times lower than in 2007, below 5 mGray for a large fraction of the run.

5 mGray corresponds to ~ 5109 p lost on the septa, i.e. 0.025% of the extracted batch intensity.

The integrated loss on the septa in 2008 is 3940 Gray or 41015 p (0.02% of the total intensity on T40).

247 extractions (0.024%) triggered a beam dump by the BLMs (above threshold).

The largest losses (~220 mGray) were recorded in 2 extractions during a period with extraction kicker control problems (evening of August 14nd).

Error : rms spread

TT40-TT41 Trajectory

13

The largest excursions of the reference trajectory just exceed 2 mm, well below the tolerance of 4 mm.

The beam position is interlocked to ±4 mm in the most the line, except for the last 4 monitors where the tolerances are reduced to ±2 mm and ±0.5 mm (last 2 monitors).

The total trajectory drift over the 2008 run is ~ 1 mm rms in each plane.

TT40-TT41 Trajectory

14

For most position monitors the rms position change over the entire run was only 0.1-0.2 mm. For some monitors the spread is larger, but it is due to :

fluctuations of the momentum error for the H plane. This affect BPMs at places of large dispersion.

A trajectory re-steering ~ middle of the run for the V.

Error : rms spread

Reference Trajectory

15

Horizontal and vertical reference trajectory with corrector settings.

BPM Interlock Settings

16

The TT40 BPMs had to be removed from the interlock logic because the LHC beams triggered false interlocks (settings are made non-PPM).

Interlocks

17

A certain number of fake interlocks were observed, mostly due to measurement errors.

All readings of the last 3 BPMs are shown here : one notices a tail of strange readings on BPG.41444 that were a source of fake interlocks (not present on the other monitors).

BPM Readings

18

BPG.4117 was a source of frequent fake interlocks, and was disabled for interlocking for a large fraction of the run : large tail of large position measurements.

BPG.4110 shows: Large(r) H spread due to large

dispersion & momentum offset fluctuations.

Large(r) V spread due to re-steering.

Target Beam Position

19

The position stability of the extracted beam was excellent, ~ 50 microns over the

entire run.

No active position feedback is necessary, 1-2 small steerings / week are sufficient !

Beam position on the last BPM in front of the target

H Extr 1

H Extr 2

V Extr 1

V Extr 2

Target Beam Position

20

The beam position on target for extraction 1 and 2 are strongly correlated.

The time evolution of the beam position indicates that the horizontal spread increased in the periods with the highest beam intensities.

Error : rms spread

Transfer Line Losses

21

The transfer of the beam to the target is extremely clean and losses are rare – losses are concentrated in the extraction channel (septum).

Losses exceeded the thresholds in only 2 periods:

July 18th 18:00-19:00 : 8 extractions (always the first). Problem with a screen moving back and forth through the extraction channel.

August 14th 22:00-23:00 : 2 extractions (always the second) during a period of control problem with the extraction kicker. For those 2 extractions the losses on the septa also reached their record of 220 mGray.

Red line is the interlock threshold

TT41TT40

22

Exceptional Loss Event : Example 1

Blue : Event dataGreen : Reference/normal extractionRed : BLM interlock thresholds

Afternoon of 6th August 2008

>> Typical event with vertically unstable beam

The beam is extracted and the extraction loss pattern large losses towards the end of the septum

1. Trajectory is normal.

2. Extraction losses are strongly enhanced around Mon. no. 5-8.

3. Some loss visible in TT41.

4. Note : no interlock in this case !

TT41

TT40Extraction Chan.

23


Evening of 6th September 2008

>> Typical event with too many particles in the beam gap

The beam is extracted and a significant loss occurs on the extraction septum (and its protection device TPSG).


2. Extraction losses ~20 larger than normal, >> LSS4 BLM interlock!

3. No losses in TT41.


24


Evening of 23rd July 2008

>> BTVE screen (41831) in the extraction channel moves back and forth in an uncontrolled way.

The beam is extracted and a significant loss occurs on the first BLMs due to the presence of the screen.


2. Extraction losses larger than normal, >> LSS4 BLM interlock!

3. Losses in TT40 also exceed threshold,

>> TT40 BLM interlock!



25

Evening of 14th August 2008 : 2 events

>> Problems with MKE control

The beam is extracted asynchronously and with significant kick error

1. Very large trajectory excursions of close to 15 mm >> BPM interlock!

2. Extraction losses almost 100 larger than normal,

>> LSS4 & TT40 BLM interlock!

3. Only half of the beam intensity measured on target.

4. The beam position on target for extraction 1 and 2 are strongly correlated.


LSS4 Radiation Levels

26

The remnant radiation measurements clearly show the loss peak in the extraction channel : ~400 Sv/h some 30 hours after the run for ~ 41015 lost protons.

A small secondary peak is visible around cell 422 where the some debris are lost at the entrance of the arc.Courtesy N. Conan SC/RP

TT41 Radiation

27

In TT41 the remnant radiation levels are very low (6 weeks after beam stop).

A few peaks to <= 1 Sv/h.

TT41 Radiation

28

The few peaks correspond to :

Locations of large hor. dispersion >> off-momentum particles loss there.

Vertical aperture limits (2nd, 4th, 6th peak on the plot).

Muon Monitors

29

The position stability of the muon beam in the second pit is ~ 3 cm rms.

The muon beam position is correlated to the beam position on T40. It can be steered easily by a parallel displacement of the primary beam on T40.

H Extr 1

H Extr 2

V Extr 1

V Extr 2

Muon Monitors

30

The muon beam positions for extraction 1 and 2 are strongly correlated – this is expected since the beam positions on target are also correlated !

Dipole Magnets

31

During interleaved CNGS-LHC operation, it cannot be excluded that the dipole converter is not switched (has happened).

o CNGS Inom : 4090 A

o TI8 Inom : 5250 A

In such an event the CNGS magnets are pushed beyond their 450 GeV (4950 A) setting >> far into saturation.

According to D. Smekens, this is ‘OK’ but should be avoided.

Courtesy D. Smekens

Dipole Magnets : test with beam

32

When the main bends converter pulses into TT41 with the LHC 450 GeV settings of TI8, the magnetic field during the CNGS transfer is increased by 0.2 permill.

Trajectory change during CNGS transfer following a pulse to TI8 450 GeV settings. Characteristic dispersion trajectory. The effect on target is uncritical.

MBG Switch for LHC

33

MBG / RBI.410010 reference is clamped to 0 during the LHC beam transfer. Automatic when reference below 1% of Imax.

LHC transfer

MKP Reference 2008

34

Second kick length also 11.5 and delay 72.7The second kick is advanced and lengthened in order to clean the beam gap.

CNGS Beam Structure

35

CNGS Beam Structure : CT & MTE

36

MTE Beam Extractions

37

No particular problems with extraction of the MTE beam once it is positioned correctly (RF bucket) :

With the same MKE4 settings (delay) than for CT the extraction losses on the TPSG were:

~15 mGray for ~ 51012 p/extraction for MTE

5 mGray for a CT extraction of ~ 21013 p.

TT40/41 BPMs triggered correctly.

MKE4 Reference 2008

38

MKE4 erratics were observed a few times. It seems however that the triggering of the clipper switches after 800 s is very effective and no beam losses were observed during such events.

The only large losses due (mostly likely) due to the MKE4 were observed in the evening of August 14th (see prev. slides) during a control problem.

MKE4 Loss Scan

39

Delay (s) Length (s) TPSG Loss (mGray)

71.75 11.5 25

71.85 11.5 5-7

71.95 11.5 5 Nominal

72.05 11.45 5

72.15 11.4 5

72.25 11.4 8

72.35 11.35 8-10

72.45 11.35 8-10

72.55 11.3 15-20

Sensitivity measurement on MKE4 delay for first kick, October 15th.

MKE4 Heating

40

Cooling down of the MKE4 after heating up by high intensity LHC beams has a typical slope of ~20/8 hours.

The max. temperature for extraction in 70.

MKE4 Vacuum

41

Vacuum pressure rise associated to the MKE4 heating.

MKP Vacuum

42

Out-gasing of the TIDV dump leads to vacuum pressure rises in nearby MKP injection kicker. This is critical when the high intensity CNGS beam is dumped repeatedly.

SIS surveys the MKP vacuum and stops the beam before an MKP interlock is triggered.

Pressure reaches 10-7 in a ~5 minutes

cngs primary beam results

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