Asynchronous Beam Dump Studies

C.Bracco, B.Goddard

Worst-case for 1 bunch with TCDQ position OK

Initial distribution: one bunch of 32’000 particles centered at 7.5 mm on TCDQ

Beam 2 tracked from TCDQ to TCTs in IP5, that is the most critical region for losses in case of asynchronous beam dump.

p+ Absorbed at: * TCTH* TCSG

* TCDQ

Worst-case: particles absorbed at collimators

626 seeds for scattering routine ~ 11E6 p+

Collimators set at the physical aperture (in mm) defined during beam based alignment

p+ Absorbed at: * TCTV

All the particles reaching the TCTH and TCTV have been scattered by the TCSG or grazed by the TCDQ (< 1%) no primary protons

TCTHTCTH TCSG TCSGTCDQ

TCTV

TCTV

Density of Particles at the TCTH Density [p/sigma]

x [sigma]

y [sigma]

Den

sity

[p/s

igm

a]

y [sig

ma]

x [sigma]

Den

sity

[p/s

igm

a]

• All losses come from p+ scattered through TCSG which fill acceptance with scattered primaries

• Total p+ on TCTH is 0.3% of single bunch (8% impacting TCSG in this simulation) or 3.3108 p+

• Peak p+ density is about 0.016% of single bunch (equivalent to 2.5106 p+ with nominal ex,y)

• Consistent with expectations - full bunch on TCSG would be attenuated by 10, and have 180 emittance increase

CollimatorsCold Magnets

Warm Magnets

TCDQ +TCSG

TCTH+TCTV

Loss Map for Beam 2, 3.5 TeV, 2m b* in IP5 From SixTrack simulations:

120

Local cleaning inefficiency: = h

# particles lost in Ds

Ds × Totabs

Ds = 10 cm @ magnetsDs = 1 m @ collimators (jaw length)Totabs = 8’463’489

Collimator N [p+] % Totabs

TCDQ 7’639’643 90

TCSG 697’298 8

TCTH 22’186 0.3

TCTV 875 0.01

Statistical error = 1/√N max = 0.03

Beam2

Only primary protons losses.

1 bunch case

Nominal bunch (1.1E11 p+):3.3E8 p+ on TCT(3e-3 ratio)

3.5 TeV, 2m b*, 2mm (=1σ) offset

IR6 saturatedIR7 15Gy/sTCTH.4R5.B2 0.6 Gy/s 2E7 p+

Leakage from TCDQ ~2E-2 from BLMs (but saturated).

Measured ~4e9 p+ with abort gap monitor (AGM) at moment of dump

Using abort gap population and, according to our assumptions, the leakage from TCDQ is ~2E-3

BSRA

Possible worst-case scenarios...

• During setup with beam at 3.5 TeV:o Single bunch hitting metal collimator

o Requires asynchronous dump/kicker pretrigger, PLUS ‘unlucky’ timing, PLUS collimator at correct phase to be exposed

o Any way for single bunch to hit triplet aperture??o Seems unlikely (TCDQ/TCSG should protect TCT, and this is inside triplet)o Should check carefully through details of setup procedure and see what asynch dump would give at each

stage

• During normal operation:o Multiple bunches hitting metal collimatoro Requires another ‘non standard’ error somewhere (orbit at TCDQ, or TCDQ/TCT position, ...)o Studied by T.Kramer in PhD thesis o Detailed results obtained for different TCDQ retractions (same as orbit error)

Impacts on metal collimators from asynch dump

'TCSG.6R7.B1'

'TCSG.D4L7.B1'

0,0E+00

2,0E+11

4,0E+11

6,0E+11

8,0E+11

1,0E+12

1,2E+12

1,4E+12

1,6E+12

8 8,5 9 9,5 10 10,5 11 11,5 12 12,5 13 13,5 14 14,5 15

# o

f lo

sses

TCDQ setting in sigma

'TCTH.4L2.B1'

'TCTH.4L1.B1'

'TCSG.D4L7.B1'

'TCSG.B5R7.B1'

'TCSG.A6L7.B1'

'TCSG.A4L7.B1'

'TCSG.6R7.B1'

'TCP.C6L7.B1'

'TCLA.C6R7.B1'

'TCLA.A7R7.B1'

7 TeV prefire dump case with0.5 m * and all LHC errors.

Work needed to give FLUKA input...

• Define machine parameters for study (b*, optical errors, orbit, setup errors, ...)o Already some issues here – make many runs with many different machines, to find average and worst case, or take

a typical case (but what is ‘typical’?)

• Choose failure case to give more ‘realistic’ input for FLUKA

o For setup, need to choose “worst” time in procedure to have asynch dumpo Check with tracking the impact parameters and distribution

o For operational scenarios, more difficult o Need some assumption on the “concurrent” failure at time of asynch dump – orbit, setup errors, ...o Not to forget the “multiple pre-trigger” cases which are still possible until 2013

o Also need not to forget the basic case with the transmission of particles through 1 stage cleaningo Should not have damage during “normal” asynch dump at 0.55 m b*

Conclusions

Asynchronous beam dump simulations for a single bunch at 3.5 TeV (2m b* in point 5) have been performed with SixTrack for beam 2 – all movable elements at nominal positions

Simulations show that losses at the TCT come from particles scattered at the TCSG (less than 1% from particles grazing the TCDQ), no losses of primary protons are observed

Simulations allow to visualize the distribution of particles absorbed at the TCT: peak density is equivalent of 0.016% of full bunch with nominal emittance

An asynchronous beam dump, performed for the same case (3.5 TeV, 2m b* in point 5), and losses (from PM) have been analyzed.

Measurements agreed well with simulations

For worst-case situations, need to carefully choose conditions AND methodology easier for setup scenarios beam experience for the operational scenarios? detailed input from both LBDS and COLL teams needed – then simple 1 turn tracking