Generation and acceleration of high intensity beams in the SLC injector Page: 2 of 3
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TABLE 1
Sector 1 Quads
QA
QB
QCH
QL
QW
Maximum / gsU (kG)
14.5
29.0
22.0
5.8
15.0
It If («u)
10.2
20.4
64
38.1
24.8
Aperture Radius (cm)
1.5
1.5
1.4
11.1
8.0
Maximum Current (Amps)
8
s
12
50
50
Cooling Mechanism
Air
Air
Air
fhO
JJjO
Total # in Injector
9
1
4
3
79
Figure 3 shows the horiiontal and vertical beam sires
throughout the Injector. The beam is deflected toward the
damping ring at the 120 m point and this It also where the
damped beam is re-injected. The beam sites are shown for
both the high omittance input electron beam and the low emit-
tance extracted beam.
P'l
EiDOtlion/
Reirijfrtlxin
r,,1 Po*n»
n L.
5 5
1 I
]
I--— j—
0 50
I00 (50
S (ml
200
Fig. 3. Horicontal and vertical beam sim throughout the in-
jector shown with the extracted, damped beam sice in the Fol-
lowing 100m of accelerator. The quadrupoie magnet locations
are also shown.
PERFORMANCE
The general performance of the injector was much im-
proved due to the increased focneing. Some pulse to pulse
energy fluctuation waa observed and traced to fluctuations in
the gun trigger timing. Gun timing jitter must be kept less
than Of < 1$ pi to keep energy jitter at the end of the injec-
tor < .1% . Development efforts are underway to limit and
monitor this. Present operation has < 30 pa.
Intensity, emit tance and energy spread measurements were
made at several places In the injector. Intensity is monitored
using both the faradiy cup at the 50 MeV point and a set
of e recently installed resonant toroids. Then devices res-
onate at 50 kHx when shock excited by the beam puke end
can monitor the beam intensity with 1% accuracy. Because of
the slow response time these toroids cannot be used to deter-
mine the intensity of each bunch of the pair. This can be done,
with lower resolution (1056), using the beam position monitor
(BPM) striplinea Installed throughout the injector.
The specified intensity of 5 x 10'° particle* in a single bunch
was reached and surpassed without difficulty. Peak bunch in-
tensities up to 7.6 X 10w were observed at the end of the injec-
tor. Bunch pain with Intensity up to 1.1 x 10u were observed.
Figure 4 summarises the amittesice measurements made at
the end of the Injector at different Intensities. The measure-
ment technique4 used a fine-grained fluorescent screen and e
video camera along with a transient digitiser. Slices of the im-
age art fit to a gauisinn In order to extract the width. Each Ct
is performed on date from a single pulse. At intensities above
3 x 19,0e“ eome dhitortton and movement of the beam spot is
seen due to Wakefield effects. Thu* with the image slice pro-
cessing technique, e broad distribution of wldlha Is seen. This
is reflected in the error hem for these points in Fig. 4. '
]? €0
>•> I (iOl0evpuitel
Fig- 4. Horizontal and vertical omittance data at the end
of the SLC injector for different beam currents. The points
at 10,,e'/pulse represent the superimposed emittance oT the
bunch pair.
The sweep speed of the camera si wotl as the decay time of
the phosphor preclude separate measurements of the emittance
of each pulse when both are preseot. The data shown at a beam
intensity of 10ne" represents the superimposed emittance of
the pulse pair.
Because the first bunch extracts 20 MeV/1010e_, so-called
beam loading of the RF fundamental, the power input to the
DLWG most rise in the interval between pulses to make the
menu energy of each bunch equal. This is conveniently accom-
plished with the SLED RF. IT the first pulse Is placed 100 ns
before the time of maximum energy, the second pulse, 62 ns
later, will have equal energy. Each bunch has a mean energy
which ia 2.556 below the peak (unloaded) energy.
The minimum energy spread ia achieved when the bunch
is short enough to occupy only 20“ of the S-band RF yet long
enough to prevent rapid blow up due to space charge forces.
The bunch length b set early in the injector, since it does not
change once the beam becomes relativisitlc. In order to moni-
tor this, a quarts radiator which products pubes of Cerenkov
light can be inserted at the 50 MeV point. These tight pulses
retain the longitudinal intensity structure of the beam and are
viewed by a streak camera. The ayatem resolution is 2 ps.
We observe a minimum energy spread of 1.456 at 5 x 10KV
with a bunch length of 3 mm. The combined energy spread of
the hunch pair was 256 at the full intensity of 1011 e~, within the
energy acceptance of the damping ring complex. It is broader
than the one bunch spectrum, not because of any separation
of the mean energy of each bunch, but because the second
bunch his n larger energy spread. This Is due in part to the
way the second bunch Is tuned. Since the phase of the 16th
sub-harmonic buncheta cannot be changed In the time between
2
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Ross, M. C.; Browne, M. J.; Clendenin, J. E.; Jobe, R. K.; Seeman, J. T.; Sheppard, J. C. et al. Generation and acceleration of high intensity beams in the SLC injector, article, April 1, 1985; California. (https://digital.library.unt.edu/ark:/67531/metadc1089319/m1/2/: accessed July 16, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.