1
Beam Loss Monitors
By Kay Wittenburg, Deutsches Elektronen Synchrotron DESY, Hamburg, Germany
You do not need a BLM System as long as you have a perfect machine without any problems. However, you probably do not have such a nice machine, therefore you better install one. Discussing Wire Scanner heat load:
- 3. Wire heat load
According to Bethe-Blochs formula, a fraction of energy dE/dx of high energy particles crossing the wire is deposit in the wire. Each beam particle which crosses the wire deposits energy inside the wire. The energy loss is defined by dE/dx (minimum ionization loss) and is taken to be that for a minimum ionizing particle. In this case the temperature increase of the wire can be calculated by: where N is the number of particles hitting the wire during one scan, d' is the thickness of a quadratic wire with the same area as a round one and G [g] is the mass of the part of the wire interacting with the beam. The mass G is defined by the beam dimension in the direction of the wire (perpendicular to the measuring direction):
] [ 1 ' /
0C
G c N d dx dE C T
p m
⋅ ⋅ ⋅ ⋅ ⋅ =
unknown
] [ 2 1 /
0C
c v f n dx dE C T
v p bunch bunch h
α σ ⋅ ⋅ ⋅ ⋅ ⋅ ⋅ ⋅ =
Therefore, the temperature increase of the wire after one scan becomes:
] [ 2 1 /
0C
c v f n dx dE C T
v p bunch bunch h
α σ ⋅ ⋅ ⋅ ⋅ ⋅ ⋅ ⋅ =
Parameter table
Where h, denotes the horizontal (h) scanning direction. The cooling factor 'α' is described in the next
- section. Note that the temperature does not depend on the wire diameter and that it depends on
the beam dimension perpendicular to the measuring direction. The temperature increase is inverse proportional to the scanning speed, therefore a faster scanner has a correspondingly smaller temperature increase.
] [ 1 ' /
0C
G c N d dx dE C T
p m
⋅ ⋅ ⋅ ⋅ ⋅ =
[ ]
g d volume wire G Mass
v
ρ σ ρ ⋅ ⋅ ⋅ = ⋅ =
2
' 2 ) ( '
bunch rev
n NB v f d N ⋅ ⋅ ⋅ =
] [ ' 2 1 ) ( ' ' /
2
C d c n NB v f d d dx dE C T
v p bunch rev m h
α ρ σ ⋅ ⋅ ⋅ ⋅ ⋅ ⋅ ⋅ ⋅ ⋅ ⋅ ⋅ ⋅ =
In MeV/cm
bunch rev m
f NB f and g cm MeV dx dE dx dE with = ⋅ ⎥ ⎦ ⎤ ⎢ ⎣ ⎡ ⋅ =
2
/ / ρ
- D. Möhl, Sources of emittance growth (also P. Bryant;
CAS, Beam transfer lines):
β π ε δ ⋅ Θ ⋅ =
2
2 1
rms
Unit of phase space emittance Averaging over all Betatron-phases
β π ε δ ⋅ Θ ⋅ =
2
4 1
rms
- M. Giovannozzi (CAS 2005)
x rms
β ε δ
σ
⋅ Θ ⋅ =
2
2 1
- D. Möhl, Sources of emittance
growth, 2007: mrad mm
rms
π β δ π ε δ
2 2 2
10 1 . 5 2
−
⋅ = ⋅ Ψ ⋅ Θ ⋅ =
Literature from π 2
Emittance growth due to a wire scan:
Beam Loss Monitors
By Kay Wittenburg, Deutsches Elektronen Synchrotron DESY, Hamburg, Germany
You do not need a BLM System as long as you have a perfect machine without any problems. However, you probably do not have such a nice machine, therefore you better install one.
Contents Loss Classes Common aspects for a sufficient Beam Loss Monitor Systems (Lets try to design a BLM system for a superconducting accelerator) Examples for irregular losses Examples for regular losses used for beam diagnostic
Beam loss monitor systems are designed for measuring beam losses around an accelerator or storage ring. A detailed understanding of the loss mechanism, together with an appropriate design of the BLM-System and an appropriate location of the monitors enable a wide field of very useful beam diagnostics and machine protection possibilities.