terrahertz radiation source
DESCRIPTION
LINAC CAVITY 1. LINAC CAVITY 2. PROGRESS ON THE COMMISSIONING OF ALICE, THE ENERGY RECOVERY LINAC-BASED LIGHT SOURCE AT DARESBURY LABORATORY. - PowerPoint PPT PresentationTRANSCRIPT
PROGRESS ON THE COMMISSIONING OF ALICE, THE ENERGY RECOVERY LINAC-BASED LIGHT SOURCE AT
DARESBURY LABORATORYC.Beard, S.Buckley, P.Corlett, D.Dunning, P.Goudket, S.Hill, F.Jackson, S.Jamison, J.Jones, L.Jones, P.McIntosh, J.McKenzie, K.Middleman, B.Militsyn, A.Moss, B.Muratori, J.Orrett, P.Phillips, Y.Saveliev, D.Scott, B.Shepherd, S.Smith, M.Surman, N.Thompson, A.Wheelhouse, P.Williams (STFC Daresbury Laboratory), D.Holder, P.Weightman (Liverpool Univ.), K.Harada (KEK)
Parameter Specification Present Value
Units
Beam Energy – Gun 350 230 keV
Beam Energy – Booster 8 4.8 MeV
Beam Energy – Linac 35 21 MeV
Bunch Charge 80 20-100 pC
Train Length 100 100 s
Train Repetition Rate 20 20 Hz
QE (in the gun) ~1 4.0 %
QE (in the laboratory) >10 %
RF-laser timing jitter <1000 650 fs
LATEST STATUS
Extensive work on SC linac cavities conditioning will allow ALICE to operate at higher beam energy of 25-27 MeV in an energy recovery mode and up to ~30 MeV in non-energy recovery mode.
Full energy recovery achieved up to 20pC and partial energy recovery achieved up to 40 pC
TERRAHERTZ RADIATION SOURCE
PHOTO-CATHODE PERFORMANCE BEAM LOADING
FUTURE DEVELOPMENTS IN 2009 INCLUDE
ENERGY RECOVERY ACHIEVED
Main linac RF power demand signals: without (left) and with (right) energy recovery
Full energy recovery has been established at 21MeV beam energy and several bunch charges up to 20pC. Higher bunch charges were not attempted because of the beam loading effects in the injector SC booster cavities
LINAC CAVITY 1
LINAC CAVITY 2
0
0.5
1
1.5
2
2.5
3
3.5
0 2 4 6 8 10
TH
z si
gnal
am
plit
ude,
V
Bunch charge, pC
ALICE provides a THz source with coherent enhancement due to sub-picosecond bunch length. The final dipole in the compression chicane is the source of THz radiation
Images on YAG screen after booster at various SOL-01. The FE after the booster becomes acceptable at SOL-01 setting above ~3.3A.
A field emitter was found at the centre of cathode, its effect can be mitigated by first solenoid next to gun. This field emitter is likely to be responsible for a hole in the quantum efficiency map of the cathode, which disappears after the cathode re-caesiation
FE SOL-01 =2.6A FE SOL-01 =3.3A 20 pC beam SOL-01 =3.3A
EMITTANCE MEASUREMENTS
0
5
10
15
20
25
0 10 20 30 40 50 60 70 80
Em
ittan
ce n
orm
alis
ed,
m
Bunch charge, pC
Only a limited number of emittance measurements were made in the injector beamline using slit scans. No attempts were made to minimise the emittance for each bunch charge. This and the existence of the field emission current probably accounts for significantly larger emittance values compared to that expected from the ASTRA model (~3mm at 80pC).
Faraday cup traces showing energy droop
-1.8
-1.6
-1.4
-1.2
-1
-0.8
-0.6
-0.4
-0.2
0
0.2
-5.0E-05 0.0E+00 5.0E-05 1.0E-04 1.5E-04 2.0E-04
time [s]
INJ
-FC
UP
-01
sig
na
l [V
]
DIP-01 = 2.76A
DIP-01 = 2.81A
DIP-01 = 2.91A
Faraday cup traces - energy droop gone
-1.8
-1.6
-1.4
-1.2
-1
-0.8
-0.6
-0.4
-0.2
0
0.2
-5.00E-05 0.00E+00 5.00E-05 1.00E-04 1.50E-04 2.00E-04
time [s]
INJ
-FC
UP
-01
sig
na
l [V
]
DIP-01 = 2.76A
DIP-01 = 2.81A
DIP-01 = 2.91A
Faraday cup traces with the energy droop (left) and after RF tweaking was done (namely, increasing “Grad Loop Gain” on BC1) to alleviate the problem. 20pC; 4.8MeV.
Beam loading in the booster was visible on the LLRF signals at train lengths of a few tens of microseconds and above 10pC. The effect is an energy droop of a few percent over the bunch train.
Beam loading was observed on the Faraday cup in a dispersive section of the injector. The Faraday cup current is not constant due to beam loading.
Typical signal from THz detector (bolometer) Quadratic dependence of the THz signal amplitude on the bunch charge.
A linear dependence on THz detector signal on the bunch train length was observed at constant bunch charge, and a clear quadratic dependence on bunch charge was observed at constant train length
PHOTO-GUN COMMISSIONING
0
50
100
150
200
250
300
0 1 2 3 4 5 6
U, kV (1)U, kV (2)
GU
N V
OLT
AG
E,
kV
Shift #
Gun HV conditioning progress (Period 5: September & October 2008)
Gun HV conditioning voltage as a function of the number of shifts
150
200
250
300
350
400
450
500
0 5 10 15 20
HV gun conditioningPeriod 4
30/10 - 07/11/2007
Vol
tage
re
ach
ed,
kV
Shift Number
The gun operating voltage of 350kV was initially used for gun commissioning but there were several failures of the high voltage insulating ceramic joint. It was necessary to install a more robust but smaller inner diameter ceramic that reduced the maximum gun operating voltage to ~230kV
Compton Backscattering X-ray source with photon energy of 15-30keV. The CBS source is powered by a terawatt IR femtosecond laser that can also be used as a stand-alone light source for a variety of experiments.
A programme of THz studies is planned including the first experiments at the Tissue Culture Facility to determine the safe limits of human exposure to THz radiation
Towards the end of 2009 experiments with EMMA, the first non-scaling FFAG, will commence and continue throughout 2010. www.astec.ac.uk
The latest observations (August 2009) of the THz intensity at the bunch charge of up to 40pC indicate that the THz pulse energy can reach several
tens of mJ.
LATEST NEWS
Tweaking the LLRF system and manipulating the external quality factors of the booster cavities allowed the operation of the machine at ~40pC bunch charge and up to 100ms train lengths
An oscillator type IR-FEL will be commissioned later in 2009. The undulator (originally from JLAB) will have variable gap, allowing FEL tuning in the range 4-12 MeV for beam energies in the range 24-35 MeV.
The FEL will be used to test energy recovery with a disrupted beam and provide FEL output for experiments. The facility could also be used as a test bed for now FEL concepts.
IR-FEL CBS X-ray Source THz Studies FFAG
See WEPC39 for further details