10 Million Million Volts or bust…

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Nov 15, 2013 (3 years and 6 months ago)

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10 Million
Million

Volts

or Bust…

Tim
Koeth

April 29, 2008

Inspiration and Determination:

A Historical Path to Higher Energies

The history of accelerator physics has
been one of adventure, bravado, and
sometimes shear luck. Some say
accelerator physics is just a discipline of
engineering, but in fact advancement in
the field has always been from the finger
tips of physicists, well mostly…


Accelerator physics has been a staircase
evolution:
Inspiration

followed by
determination
over and over again.




I am going to give a brief over view of the
past 80 years.


In 1929 the motto was “10 Million Volts or
Bust”; in 2008 it is 10 Million
Million

Volts
or bust.

A Livingston Plot

Fermilab

LHC

“Start the Ball Rolling”

1927: Lord Rutherford requested a “copious supply” of
projectiles more energetic than natural alpha and beta
particles. At the opening of
their High
Tension Laboratory,
Rutherford went on to reiterate the goal:



What we require is an apparatus to give us
a potential of the order of 10 million volts
which can be safely accommodated in a
reasonably sized room and operated by a
few kilowatts of power. We require too an
exhausted tube capable of withstanding this
voltage… I see no reason why such a
requirement cannot be made practical.
1

MANY FAILED ATTEMPTS

1928: Curt Urban, Arno
Brasch
, and Fritz Lange successfully achieved 15 MV by harnessing
lightning in the Italian Alps
!
2













The two who
survived

the experiment went on to design an accelerator tube capable
of withstanding that voltage.

Just one example:

Cockcroft & Walton’s Voltage Multiplier:

Cockcroft

Walton

Rutherford

The multiplier worked, but is generally limited to 750kV. A C
-
W stack begins the
Fermilab

chain of accelerators

C&W 1951 Nobel Prize

Attributed with being the first to artificially disintegrate nuclei.



Wideroe

Linac

1929: Rolf
Wideroe


R.
Wideroe

proposed an accelerator by
using an alternating voltage across
several accelerating “gaps
.”


It was not without a myriad of problems


-

Focusing of
the beam


-

Vacuum leaks


-

Oscillating high
voltages


-

Length


-

Imagination



His professor refused any further work because
it was “sure to fail.”



Never the
less, thankfully
Wideroe

still published his
idea in
Archiv

fur
Electrotechnic



Wideroe

in the 1960’s having
the last laugh…

Linear Accelerators

SLAC


Stanford California

2 miles long

50
GeV

The proposed International Linear Collider

33 km long

Wideroe

won the Wilson Accelerator
Prize in 1992

Inspiration: Ernest
Orlando
Lawrence


In April 1929, UC Berkley’s youngest Physics professor
happened across
Archiv fur Electrotechnic
.



Not able to read German he just looked at the diagrams
and pictures of the journal.








Immediately after seeing Wideroe’s schematic,
Ernest fully comprehended it’s implications.

1939 Nobel Prize

1929: The Cyclotron

r
mV
r
F
2

qVB
F
B

qB
mV
r

“R cancels R !”

r
V
f




2
m
qB
f

2

Lawrence quickly jotted down:

and equated with

and solved for r:

and substituted V in terms of

The Cyclotron Frequency

Determination: The Grad Student

M. Stanley Livingston


M. Stanley Livingston (GS)

Ernest Lawrence

High Voltage DEE

Dummy DEE

The First Operational Cyclotron

Determination: Weak
Focusing

Intentionally introduce radial B
-
field
component at the cost of an vertical gradient: to be coined weak focusing.

-

Although the cyclotron worked, the beam intensity was very weak. Lawrence


-

Lawrence: wire grids and iron shims


Livingston removed the grids while Lawrence was out of town


beam intensity shot up.


Livingston took this remarkable finding to Lawrence. To which Lawrence responded:
“It’s obvious what happening…”


Seemed
to be No
Limit With Focusing …

Lawrence believed the
only limit on energy was the size of the
magnet.

-

27
-
inch ( 5MeV ) cyclotron
-

construction

-

60
-
inch (16
MeV
) cyclotron
-

design

-

184
-
inch (100
MeV

) cyclotron
-

fantasy


Hans
Bethe
disagreed !


practical only to 20
MeV

for protons.





Characteristically, Ernest
Lawrence was not
dissuaded &
proceeded full
steam…
“there is always more than one way to skin a cat.”


EOL

m
qB
f

2

Weak focusing could only go so far..

The greater the energy, the larger the radius, but the gap (AKA aperture) had to
correspondingly grow to produce the needed gradient. Thus the magnets were getting
impractically large.

For a sense of scale: I am sitting in the magnetic gap of
Enrico

Fermi’s
Cyclotron shortly before it was dismantled.

We have to pause for World War II…

In Parallel:
Robert J. Van de Graff

1931
-
4

Van

de

Graff

(VDG)

achieved

1
.
5

MV

in

1931
,

by

charge

exchange

onto

metal

spheres
.

The

“Van

de

Graff”

worked,

but

progress

towards

higher

voltages

was

slow




He

went

on

to

propose

two

20

foot

spheres

on

20

foot

towers

capable

of

10

MeV
.


The

resulting

awesome

VDG

installation

at

MIT

stood

43

feet

about

the

ground

and

the

spheres

were

15

feet

in

diameter
.


It

promised

10

MV,

but

was

not

realized

until

after

WWII
.



Simple

construction
:

many

labs

could

easily

obtain

a

VDG


VDG

generators

are

still

used

today


-

they

can

provide

very

mono
-
energetic

beam


-

only

m
Amps

of

beam

current



-

the

biggest

are

limited

to

about

25
MeV

Inspiration: Phase Stability beats Relativity


Edwin McMillan of UC Berkley, and the Russian V.I.
Veksler

independently discovered Phase stability in
1945.


Simply stated the principle of Phase Stability is:

-
The synchronous particle arrives at each successive accelerating gap at the same phase, incurring the same incremental
acceleration.

-

Slow traveling ions arrive at the next gap “late” & receive more push

-
Fast traveling ions arrive at the next gap “early” & receive less push

Thus,

a

“band” of ions continuously oscillate about and follow the phase of “stability” during acceleration.


The

stability was robust enough to allow adiabatic changes in the accelerating frequency: enabling the oscillating voltage to cha
ng
e with the
relativistic mass increase.





The cat was skinned !


McMillan proposed the synchrotron in a letter to Phys Rev in 1945 & won the Nobel Prize in 1951 (for chemistry)

Post WWII: Return to circular accelerators:

The Synchrotron:

-
Constant radius:

-

Inject a low energy beam and accelerate up

-

Ramp B
-
field & modulate accelerating frequency

-

Extract and send beam to target

-

repeat

-

Beam has pulsed structure as a result

Berkeley
Bevatron

Brobeck
, Lawrence, McMillan, and
Cooksey sitting in the large
aperture of the
Bevatron

10,000 turns: Still need transverse focusing


Grad Student Bob Wilson was fired several times by Lawrence, the final time it was for leaving a 2x4 in
the vacuum chamber of the
Bevatron
.

Inspiration: The Era of Strong Focusing

-
1953: E. D. Courant and H. S. Snyder of
BNL discovered that
rotating

one of their
weak focusing
cosmotron magnets would
create a strong focus
in one plane.

-
Further investigation showed that
periodically alternating the “weak focusing”
gradient magnets had net focusing effect
that was much stronger. Hence, the
magnet’s aperture could be greatly
reduced.

Analogous to series of converging and
diverging lenses to produce a net focusing
effect.

(Courant won the Wilson Accelerator Prize in 1987)

A
S
light
E
mbarrassment …

During a 1953 visit to the US, shortly after
Courant, Livingston & Snyder published their
results in Phys. Rev., the Greek owner of an
elevator repair company, Nicholas
Christofilos
,
read their article at a Brooklyn library.

Christofilos

marched out to BNL, and pointed
out to them that he not only
sent this idea to
them in a 1950

letter,
but that
he held a US
patent on the principle
.

Christofilos

was immediately offered a
position at BNL !

Ultimately a settlement was made for the
rights to strong focusing.

Nicholas
Christofilos

Strong Focusing & Synchrotrons

-
strong focusing + synchrotrons realized the goal of “unlimited” size


thus
unlimited achievable energy.

Many accelerators types have benefitted from strong focusing, but since the 1950’s
the synchrotron has been at the energy frontier being the workhorse HEP
community.

The first operational strong focusing synchrotron was Cornell’s 1.2
GeV
. The
machine, already under construction under Bob Wilson, was retrofitted with
poletips

to be a strong focusing machine.


400
GeV

synchrotron dipole
magnet. (Quads not shown)

400
MeV

synchrocyclotron

Fermilab
: Inspiration and Determination

Robert R. Wilson

In just a few years (1968 to 1972) Bob Wilson directed
the construction of the “National Accelerator Lab” (now
known as
Fermilab
) to accelerate protons to 400
GeV
.

Rutgers participated in
Fermilabs

first experiment:

-
Tom Devlin

-
Felix
Sannes

-
Richard Plano



Fermilab

~ 1972

Inspiration: Colliders

P. Panofsky (SLAC)

G. I.
Budker

(Novosibirsk)

2
E
E
col

For a low energy proton, hitting
stationary proton, the available
collision energy is:

Relativity complicates issues
even more, when E >> M then
the available collision energy is:

2
2
2
E
E
Mc
E
col



Collider Benefit:

Two particles of equal mass
traveling head on, after
collision, has a total combined
KE of zero, thus the entire
energy of both particles is
available as collision energy.



The challenge:

Luminosity….

I am omitting a deep history

-
Princeton/Stanford double ring

-
VEP I, II, III, IV (Novosibirsk)

-
SPEAR (SLAC) & DORIS (DESY)

-

ISR C. Rubbia & Van de
meer

-
SPbarPS

(CERN)

-
SLC(SLAC) & LEP (CERN)


Always a friendly competition !


As the remainder go towards the
KE of the system after collision.

Fermilab
: Inspiration and Determination

In the 1980’s Rich Orr, Helen Edwards, Richard Lundy, Alvin
Tollestrup

directed the
Tevatron

effort: a supplement to the 400
GeV

synchrotron with a superconducting
synchrotron to reach 1
TeV
.

Present day
Fermilab

site

Installation of the
Tevatron

below the
existing Main Ring accelerator

RU is a CDF collaborator

anti
-
proton ring anti
-
proton source

Main Injector

The
Tevatron

has been at the energy
frontier for over 25 years !

The LHC at CERN: 7
TeV

(14
TeV
col
)

-

US participation

-

27 km circumference (old LEP tunnel)

-

~ 100m below surface

-

crosses Swiss/French border

-

First beam expected in 2009

-

360 MJ stored energy in the beam

-

RU is a CMS collaborator

SPS: sister to
Fermilab’s

main ring

Best Light Sources Around:


A
ccelerators serve many disciplines

(e.g. condensed matter, Biology, Astrophysics)



1
st

Generation: “parasitic” synchrotron light


2
nd

Gen: dedicated low
emittance

synchrotrons: NSLS at BNL


3
rd

Gen: 2
nd

Gen with Insertion devices


4
th

Gen: FEL’s, XFEL: very short time structure for high times
resolution

Challenges of the present:


Push for higher energy


Cost reduction


RF superconductivity


Superconducting magnets


Energy recovery


Size constraint


Higher accelerating gradients


Stronger magnets


Material limitation


High
Tc

Superconducting materials


Intensity


The A0
Photoinjector

at
Fermilab

is an example of an Advanced Accelerator R&D facility.

Interesting programs

-

Plasma Wakefield acceleration

-

Laser induced acceleration

-

Dielectric acceleration

-

Energy recovery

-

Muon

colliders

-

Int’l Linear collider

-

FEL/ERL (light sources)

-

etc…

Students, I ask: What’s Next ?


Accelerator physics has been a history of innovation followed
determination. We find ourselves as were in 1927, as we now
need a source of inspiration to develop higher gradients in
order to make the next generation of accelerators feasible.

In 80 years from now, will we be able to quote from 2008:



“What we require is an apparatus to give us a potential of the
order of
10 million
million

million

volts which can be safely
accommodated in a reasonably sized building and operated by
a few megawatts of power… I see no reason why such a
requirement cannot be made practical.”