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B. J. Holzer et al.
fast (around 99% speed of light) hollow optical fibres were applied successfully
for analog and wideband signal transmission across the ring at COSY (FZ-Jülich,
Germany) [133].
Front end amplifiers showed slow but steady progress and these days we can
easily get an uncooled 1–2 GHz or 2–4 GHz device with a noise temperature of
30 K.
Examples of remarkable recent progress in the field of microwave stochastic
cooling are
• bunched beam stochastic cooling at RHIC and Fermilab [134–137],
• the impressive improvements of the performance and the interplay of all stochastic cooling and stacking systems at Fermilab together with elaborate beam
handling methods such as “slip stacking” [135, 136].
It should be noted that there have been unsuccessful attempts to get bunched
beam stochastic cooling operational in large machines despite the fact that one of
the first evidence on stochastic cooling at all, in ICE [137] already worked with a
bunched beam. However the bunch length was very large. Attempts which failed
were in the frame of the SPS p-pbar program at CERN [124] and later (around
1990) also in the Tevatron [138, 139]. Bunched beam cooling is of course hampered
by the higher particle density in the bunch. In fact in Eq. (6.74) the number N for
the coasting beam has to be replaced by N b /B f = N b ·1.4·2πR/l b (with R radius and
l b length of bunch) for a rough estimate [137, 140]. In addition to those expected
effects the direct (coherent) bunch signal (proportional to N at low frequencies)
tends to mask the very weak Schottky signals required for cooling [137, 140]. This
is one of the reasons to place the cooling bands towards high frequencies. In addition
a subtle but important difficulty is related to the presence of unexpected and rather
strong coherent signals in the bunched beam spectrum which lead to saturation of
the front end amplifiers via intermodulation [139, 140]. A theoretical treatment of
these persisting “turbulence islands” in the bunch was given by Blaskiewiecz [141].
Just in the recent years this problem became mastered at BNL (gold ions) [135]
and also in the Fermilab recycler [140]. However, bunched beam stochastic cooling
has always been working reasonably well in small machine like the CERN AC
[107], LEAR [142], Fermilab de-buncher and accumulator [143] and others since
the relative intensity of those coherent signals was less violent compared to large
machines. However for the small machines there was little interest in bunched beam
stochastic cooling.
New applications of stochastic cooling may include:
• fast cooling and stacking of low intensity radioactive ion beams with cooling
times of 100 ms or less as discussed for RIKEN [109] and under construction at
GSI [110],
• fast optical stochastic cooling [144–146] (e.g. of intense muon beams but also
for bunched beam cooling in large rings) for which a bandwidth of 10 12 –10 13 Hz
and a new pick-up, kicker and amplifier technology, and new lattice designs have
been contemplated.
B. J. Holzer et al.
fast (around 99% speed of light) hollow optical fibres were applied successfully
for analog and wideband signal transmission across the ring at COSY (FZ-Jülich,
Germany) [133].
Front end amplifiers showed slow but steady progress and these days we can
easily get an uncooled 1–2 GHz or 2–4 GHz device with a noise temperature of
30 K.
Examples of remarkable recent progress in the field of microwave stochastic
cooling are
• bunched beam stochastic cooling at RHIC and Fermilab [134–137],
• the impressive improvements of the performance and the interplay of all stochastic cooling and stacking systems at Fermilab together with elaborate beam
handling methods such as “slip stacking” [135, 136].
It should be noted that there have been unsuccessful attempts to get bunched
beam stochastic cooling operational in large machines despite the fact that one of
the first evidence on stochastic cooling at all, in ICE [137] already worked with a
bunched beam. However the bunch length was very large. Attempts which failed
were in the frame of the SPS p-pbar program at CERN [124] and later (around
1990) also in the Tevatron [138, 139]. Bunched beam cooling is of course hampered
by the higher particle density in the bunch. In fact in Eq. (6.74) the number N for
the coasting beam has to be replaced by N b /B f = N b ·1.4·2πR/l b (with R radius and
l b length of bunch) for a rough estimate [137, 140]. In addition to those expected
effects the direct (coherent) bunch signal (proportional to N at low frequencies)
tends to mask the very weak Schottky signals required for cooling [137, 140]. This
is one of the reasons to place the cooling bands towards high frequencies. In addition
a subtle but important difficulty is related to the presence of unexpected and rather
strong coherent signals in the bunched beam spectrum which lead to saturation of
the front end amplifiers via intermodulation [139, 140]. A theoretical treatment of
these persisting “turbulence islands” in the bunch was given by Blaskiewiecz [141].
Just in the recent years this problem became mastered at BNL (gold ions) [135]
and also in the Fermilab recycler [140]. However, bunched beam stochastic cooling
has always been working reasonably well in small machine like the CERN AC
[107], LEAR [142], Fermilab de-buncher and accumulator [143] and others since
the relative intensity of those coherent signals was less violent compared to large
machines. However for the small machines there was little interest in bunched beam
stochastic cooling.
New applications of stochastic cooling may include:
• fast cooling and stacking of low intensity radioactive ion beams with cooling
times of 100 ms or less as discussed for RIKEN [109] and under construction at
GSI [110],
• fast optical stochastic cooling [144–146] (e.g. of intense muon beams but also
for bunched beam cooling in large rings) for which a bandwidth of 10 12 –10 13 Hz
and a new pick-up, kicker and amplifier technology, and new lattice designs have
been contemplated.