New AD Production Beam
in the PSB
Until now, four h=1 bunches were ejected toward the
PS in a single batch.
New proposal (F. Pedersen): provide 5 bunches; either
in a single or a double batch PS filling scheme.
Aim: fill all the 5 available AD buckets instead of just 4
to increase the amount of delivered antiprotons.
APC 25/4/08
Alfred Blas
AB-RF-FB
1
New AD Production Beam
in the PSB
• The production of 5 bunches in 2 PSB batches will not be discussed
in this presentation as it doesn’t really affect the PSB operation.
Note that the first batch in the PS, waiting for the second might
experience a transverse blow-up due to space charge effects. This
dilution would have a negative effect on the antiprotons production
on the AD target that has not been quantified.
• The production of 5 bunches in 1 PSB batch having 3 rings with a
single bunch on h=1 and 1 ring with 2 bunches on h=2 will be
discussed.
APC 25/4/08
Alfred Blas
AB-RF-FB
2
New AD Production Beam
in the PSB
•
3 rings on h=1 and 1 ring on h=2 with the double intensity; all bunches should be
identical but transversally, the multi-turn injection induces more emittance when the
number of turns (intensity) is increased (normalized 2σ values: 55 μm instead of 30 μm
in H and 50 μm instead of 20 μm in V; wire scanner measurements). This aspect and its
impact on the final antiprotons production should be quantified (not done in this
presentation)
•
Up to the flat-top all rings are operated the same way
•
At the flat-top only one ring would undergo a splitting process from 1 to 2 bunches (=>
C02 voltage drop, C04 voltage increase, C16 blow-up, End dual harmonic loop, Start C04
phase loop, End C02 phase loop)
•
For the synchronization, a dedicated rf switch should provide the h2 reference to the
h=2 ring.
•
For this operation 4 new timing pulses and 1 rf switching unit need to be supplied
APC 25/4/08
Alfred Blas
AB-RF-FB
3
Present AD beam
PSB extraction h=1
Tbunch = 215ns
Blow-up active
Trev = 572 ns
5 turns injected
8 kV / h = 1
1 kV h=2 @180o
400.1010 p/bunch emittance = 1.72 eV.s
APC 25/4/08
Alfred Blas
AB-RF-FB
4
Present AD beam
Blow-up cavity
APC 25/4/08
Alfred Blas
AB-RF-FB
5
Present AD beam
Synchronization phases
APC 25/4/08
Alfred Blas
AB-RF-FB
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Present AD beam
Transfer line
APC 25/4/08
Alfred Blas
AB-RF-FB
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Present AD beam
Transfer line
For a proper filling of the h=8 buckets in the PS
and for letting enough room for the recombination kicker rise time in between bunches,
The bunch length should be limited to 191 ns (1-99 % rise time)
BTKFA10 and BTKFA20 rise time
(2-98)% = 88 ns
(1-99)% = 95 ns
APC 25/4/08
Alfred Blas
AB-RF-FB
8
Present CNGS h=2 beam
Vh2 = 8 kV
750.1010 p
Trf = 286 ns
Vh1 = 0.5 kV
Tbunch = 183 ns
375.1010 p/bunch Emittance = 1.61 eV.s
APC 25/4/08
Alfred Blas
AB-RF-FB
9
Present CNGS h=2 beam
APC 25/4/08
Alfred Blas
AB-RF-FB
10
How to create a h=2 matched beam?
First the blow-up should be such as to make each 2 bunches emittance equal to the h=1
bunch emittance. Compared to the present CNGS beam, the blow-up should be increase
to obtain 7% more emittance.
Second, the h=2 voltage should be set (Vh2 = 6.8 kV when Vh1 = 8 kV) so that all h=1 and
h=2 bunches have the same length.
Beam
Emittance
per bunch
Bunch length h / V
Bucket area
AD
1.72 eV.s
216 ns (198 ns
calculated)
1 / 8 kV
7.27 eV.s
Present CNGS
1.61 eV.s
183 ns (179 ns
calculated)
2 / 8 kV
2.56 eV.s
CNGS
(extrapolated)
1.72 eV.s
198ns
calculated
2 / 6.8 kV
2.36 eV.s
APC 25/4/08
Alfred Blas
AB-RF-FB
11
Other possibility for the h=2 beam creation:
Debunching and Recapture
This operation would require the acceleration of a high intensity h=1 beam, with a strong
blow-up (some more than for the CNGS beam) to obtain a total 3.4 eV.s beam emittance.
This blow-up should be operated after the maximum Bdot (205 ms before the flat-top) to
avoid losses due to bucket overfilling.
On the flat top, the beam should be debunched and re-captured on h=2 up to the voltage
of 6.8 kV. The beam should then be synchronized. All this should occur within the 40 ms
of the flat-top.
Using:
t db 
2   Bunch 
p
4  f rf  
p
for the debunching time constant (yellow book)
One gets: tdb = 62 μs (quite small; to be checked)
This gives us plenty of time for a proper adiabatic debunching and recapture
Instabilities in the transverse plane with debunched beam to be checked!
APC 25/4/08
Alfred Blas
AB-RF-FB
12
PS h=10 scenario
Filling h=10 instead of h=8 buckets in the PS has the following impact:
The bunch spacing in the transfer line becomes 229 ns (h=10 rf period) instead of 286 ns. Considering the kicker rise
time of 95 ns, this leaves only 134 ns for the bunch length
With h=1 at 8 kV and a bunch length of 134 ns, the beam emittance equals 0.75 eV.s instead of 1.72 eV.s in the h=8
scenario. This value is lower than the present 0.9 eV.s of the injected Linac beam.
As presently the bunch length is 216 ns on the AD beam when the calculated limit is 191 ns, there seem to be a margin
that would allow to create h=1 bunches without blow-up as the intensity is limited (4. 1012 p)
Concerning the h=2 pair of bunches, there might be a lot of difficulties to achieve a bunch splitting at high intensity
with such a little emittance. A stable splitting requires a well filled bucket, which can be obtained by lowering the rf
voltages at the price of being faced to cavity parasitic beam loading effects. Note that there are no operational high
intensity beam created without blow-up (robustness issues).
Note that there should be a remaining h=1 voltage on the splitted beam to insure the required bunch spacing which is
smaller than the rf h=2 period. The longitudinal matching issue with such a bucket should be considered.
If the splitting cannot be achieved, the debunching-rebunching operation can be envisaged with the question marks
invoked above and also the difficulty of having to add a h=1 phase locked voltage to create the proper bunch spacing.
The synchronization would occurs on the h=1 component of the splitted beam. This has never been tried, but a-priori
should not be a problem.
APC 25/4/08
Alfred Blas
AB-RF-FB
13
Conclusion
The required investment in the PSB to provide 5 bunches to the PS on h=8 and in a single
batch should be low.
The hardware changes require 3 man-day work and 0 CHF
The setting-up time, from the operation point of view, should be limited (copy of AD for 3
rings and slightly modified CNGS settings for the remaining ring)
Beam debunching and recapture on h=2 might be an alternative solution to the splitting
although there are some question marks about the degrouping time and the transverse
stability.
Feeding the PS on h=10 present more operational uncertainties related to rf gymnastics
with a low emittance beam. These aspects need more study before this operation type
can be proposed.
The AD target efficiency goes down with increased transverse emittances and the higher
the intensity in one ring, the higher the transverse emittance due to the multi-turn
injection process. This aspect has not been checked yet.
Thanks to M. Chanel, T. Eriksson, A. Findlay, S. Hancock for sharing their knowledge
APC 25/4/08
Alfred Blas
AB-RF-FB
14
Annex: slide from M. Chanel
eps[2s,pimmmrad]
Emittances and beam density versus number of particles in the PSB
25
60
eh[2s]
density[1010/mmmra
d]
30
ev[2s]
50
N/sqrt(epsh.epsv)
20
40
15
30
10
20
5
10
N[1010]
0
0
0
100
200
300
400
500
600
700
800
900
1000
For the AD beam (total 1.6 1013 on target), the PSB should accelerate 450 1010/ring. To add one bunch more
on target, one PSB ring should accelerate 900 1010at least. The beam density increases from 38 to 50
1010/mm.mrad(+32%)and the emittances from (eh,ev)=(16,7.5) to (24,14) mm.mrad. If all the particles are
on target, it will increase the production by 8% for a 20% increase of beam intensity!
APC 25/4/08
Alfred Blas
AB-RF-FB
15