A systems study of an RF power source for a 1 TeV next linear collider based upon the relativistic-klystron two-beam accelerator Page: 2 of 15
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1. The induction linac technology is not as mature as existing rf-klystron
2. The TBA beam dynamics, particularly BBU, is difficult.
3. Induction linacs are perceived to be very expensive.
The objective and the approach undertaken in the present study were motivated by
In regards to the cost issue, past cost estimates were based on the technology
of ETAII (6) and ATA (7), which are applications requiring short pulse (50-70 ns)
high repetition rate, (kHz) high current (-10 kA). We have attempted in this
study to design an induction linac specifically for the RK-TBA.
In regards to the beam dynamics issues, we offer in this design conceptual
solutions for longitudinal beam stability as well as BBU control for both the low
frequency component, associated with induction gaps, and the high frequency
component, associated with rf extraction cavities. These concepts are supported
by detailed simulations.
Finally, in regards to the technology maturity issue, we note that significant
advances in induction linac technology have already been made and are being
made in intense electron beam (6,7) and heavy ion fusion (8) programs. What is
required is technology development specifically tailored to linear collider power
With these general considerations in mind, we propose a new version of the
RK-TBA. A systems study (9), including physics and engineering designs, as
well as "bottom-up" costing, has been conducted for a point design example with
the RK-TBA as a power source for a 1 TeV center-of-mass Next Linear Collider
1.2 The Key Ideas
To address the critical TBA issues quantitatively is the subject matter of this
report. A few key ideas underlie the whole design and are summarized below:
1. 'Betatron node scheme' for high frequency BBU control -- The most severe
BBU instability is associated with the dipole mode (HEM 11 mode) in the rf
cavities. Strong suppression of this mode is achieved by introducing a 'betatron
node scheme' in which adjacent rf extraction cavities are placed exactly one
betatron period apart. This scheme minimizes beam centroid displacement which
excites the dipole mode, and alters the nature of the instability from exponential to
a slow secular growth.
2. Landau damping for low frequency BBU suppression -- Quite apart from
the high frequency dipole mode associated with the rf cavities, there is a low
frequency (a few GHz) dipole mode associated with the induction reacceleration
gaps. This BBU instability is ameliorated by Landau damping due to a large
energy spread inherent in the rf buckets of the bunched drive beam. Combining
this feature with dipole mode suppression measures in the induction gap design,
the calculated low frequency BBU growth is minimal.
3. Inductively detuned cavities for longitudinal beam stability -- To maintain
tight rf bunches over long distances with multiple extraction cavities, the rf output
structures are inductively detuned. While the concept of inductive detuning is not
new, the theoretical framework has to be developed and implemented in
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Yu, S.; Goffeney, N. & Deadrick, F. A systems study of an RF power source for a 1 TeV next linear collider based upon the relativistic-klystron two-beam accelerator, article, November 1, 1994; California. (digital.library.unt.edu/ark:/67531/metadc669531/m1/2/: accessed December 12, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.